Lithium-ion secondary battery and preparation method therefor, electric device, and use

Abstract

A lithium-ion secondary battery and a preparation method therefor, an electric device, and the use. The lithium-ion secondary battery comprises a negative electrode sheet and an electrolyte. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector. The negative electrode active material layer comprises an electronegative coating active material, and the electronegative coating active material comprises a coating layer. The coating layer comprises doped carbon, the doped carbon comprises a carbon matrix and an electronegative doping element, and the carbon matrix comprises one or more of soft carbon and hard carbon. The Pauling electronegative scales of the electronegative doping element and carbon are respectively marked as χ1 and χC, and the absolute difference between χ1 and χC is 0.03-0.49. The negative electrode active material layer comprises a first negative electrode active layer and can further comprise a second negative electrode active layer located between the negative electrode current collector and the first negative electrode active layer.

Description

Lithium-ion secondary batteries, their preparation methods, electrical devices and applications

[0001] Related applications

[0002] This application claims priority to Chinese patent application filed on January 17, 2025, with application number CN2025100804523, entitled "Lithium-ion secondary battery and preparation method thereof, power device and application thereof", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of lithium-ion secondary battery technology, and further to a lithium-ion secondary battery and its preparation method, power supply device and application. Background Technology

[0004] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0005] With the technological advancements in lithium-ion rechargeable batteries, they are increasingly being used in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. They are also widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants. The demand for fast-charging performance in lithium-ion rechargeable batteries is also increasing. Summary of the Invention

[0006] According to various embodiments and examples of this application, this application provides a lithium-ion secondary battery, a method for its preparation, an electrical device thereof, and its application. This lithium-ion secondary battery exhibits significantly improved fast-charging performance.

[0007] In a first aspect of this application, a lithium-ion secondary battery is provided.

[0008] In some embodiments, a lithium-ion secondary battery is provided, which includes a negative electrode sheet and an electrolyte; the negative electrode sheet includes a negative current collector and a negative active material layer located on at least one side of the negative current collector, the negative active material layer including a first negative active layer;

[0009] The first negative electrode active layer includes a first negative electrode active material, which includes an electronegatively coated active material. The electronegatively coated active material includes a negative electrode active body and a coating layer located on at least a portion of the surface of the negative electrode active body. The coating layer includes doped carbon, which includes a carbon matrix and an electronegatively dopant element. The carbon matrix includes one or more of soft carbon and hard carbon. The Pauling electronegativity scale of the electronegatively dopant element is denoted as χ1, and the Pauling electronegativity scale of carbon element is denoted as χ. C Then χ1 and χ CThe absolute value of the difference is between 0.03 and 0.49, which means that 0.03 ≤ |χ1-χ C |≤0.49.

[0010] In this lithium-ion secondary battery, an electronegative coating active material is disposed in the negative electrode active material layer of the negative electrode sheet. The coating layer contains doped carbon including electronegative dopant elements. The carbon matrix in the doped carbon may include one or more of soft carbon and hard carbon. On the one hand, the introduced electronegative dopant elements have special Pauling electronegativity scaling characteristics, which limit the Pauling electronegativity scaling difference between the electronegative dopant elements and the carbon elements of the carbon matrix to the aforementioned |χ1-χ C Within a certain range, the electronegative dopant elements create unique polarization characteristics between the electronegative dopant and the carbon matrix, thereby enhancing the polarization characteristics of the negative electrode active material surface, strengthening the adsorption of foreign atoms, and weakening the binding force between the negative electrode active material and solvated lithium ions. This reduces the contact angle between the negative electrode active material surface and the electrolyte, improving its wettability and accelerating the rate of lithium ion insertion into the negative electrode active material. Furthermore, both soft and hard carbon in the carbon matrix have a high degree of disorder, which is conducive to lithium ion entry. The disordered stacking of carbon layers in soft carbon allows for relatively rapid lithium ion transport, while hard carbon provides abundant lithium insertion sites and rapid transport channels. This promotes faster and more abundant lithium ion insertion into the negative electrode active material. In addition, the introduction of electronegative dopant elements also facilitates the formation of inorganic components in the solid electrolyte interphase (SEI) film, which can improve the lithium conductivity of the SEI film and reduce the interfacial impedance. Based on the aforementioned multiple effects, this is beneficial to improving battery kinetics and enhancing the battery's fast-charging capability.

[0011] In some embodiments, the electronegative doping element includes nitrogen, and the electronegative doping element in the doped carbon includes at least one of pyridine nitrogen type and pyrrole nitrogen type.

[0012] By controlling the doping form of electronegative doping elements in doped carbon, including at least one of pyridine nitrogen and pyrrole nitrogen, and leveraging the higher reactivity of the doped N atoms in pyridine nitrogen and pyrrole nitrogen, it is beneficial to improve the adsorption of foreign atoms in the first negative electrode active material, reduce lithium-ion mass transfer resistance, and enhance the wettability of the electrolyte to the first negative electrode active layer, thereby improving the wettability to the second negative electrode active layer and ultimately improving the fast-charging performance of the battery. Furthermore, it also helps to reduce the difficulty of the doping process.

[0013] In some embodiments, the negative electrode active material layer further includes a second negative electrode active layer, which is located between the negative electrode current collector and the first negative electrode active layer.

[0014] In this lithium-ion secondary battery, a first negative electrode active layer and a second negative electrode active layer are disposed in the negative electrode active material layer of the negative electrode sheet (the direction away from the surface of the negative electrode current collector is considered as the upper layer, and the direction towards the surface of the negative electrode current collector is considered as the lower layer). Further, an electronegative coating active material is disposed in the first negative electrode active layer, wherein the coating layer contains doped carbon including electronegative dopant elements. The carbon matrix in the doped carbon may include one or more of soft carbon and hard carbon. On the one hand, the introduced electronegative dopant elements have special Pauling electronegativity scaling characteristics, by limiting the Pauling electronegativity scaling difference between the electronegative dopant elements and the carbon elements of the carbon matrix within the aforementioned |χ1-χ... C Within a certain range, the electronegative dopant elements form unique polarization characteristics with the carbon matrix, thereby enhancing the polarization characteristics of the negative electrode active material surface, strengthening the adsorption of foreign atoms by the negative electrode active material, and weakening the binding force between the negative electrode active material and solvated lithium ions. This reduces the contact angle between the surface of the first negative electrode active material and the electrolyte, improving its wettability and accelerating the rate of lithium ion insertion into the first negative electrode active material. Furthermore, both soft and hard carbon in the carbon matrix have a high degree of disorder, which facilitates lithium ion entry. The disordered stacking of carbon layers in soft carbon allows lithium ions to... Ions can be transported relatively quickly within the material, and hard carbon provides abundant lithium intercalation sites and fast transport channels, which facilitates faster and more frequent insertion of lithium ions into the first negative electrode active material. Furthermore, the introduction of electronegative doping elements is beneficial for the formation of inorganic components in the solid electrolyte interphase (SEI) film, which can improve the lithium conductivity of the SEI film and reduce the interfacial impedance. Additionally, the improved wettability of the electrolyte in the first negative electrode active layer is beneficial for improving the wettability of the electrolyte in the second negative electrode active layer. Based on the aforementioned multiple effects, this is conducive to improving battery kinetics and enhancing the battery's fast charging capability.

[0015] In some implementations, χ1 and χ C The difference between them, expressed in absolute value, is 0.04 to 0.49, that is, 0.04 ≤ |χ1-χ C |≤0.49.

[0016] By controlling the difference between the electronegativity dopant element and the Pauling electronegativity scale of carbon within the aforementioned range, and by controlling the Pauling electronegativity scale of the electronegativity dopant element within a more suitable range, on the one hand, it is beneficial to reduce the contact angle between the surface of the negative electrode active material and the electrolyte, and to improve the wettability of the electrolyte to the first negative electrode active material. On the other hand, by controlling the difference in electron-withdrawing ability between the electronegativity dopant element and carbon atoms within a more suitable range, it is beneficial to form a stable covalent bond between the electronegativity dopant element and carbon atoms.

[0017] In some embodiments, the electronegative dopant element is covalently bonded to the carbon matrix;

[0018] Optionally, at least a portion of the electronegative dopant elements are covalently bonded to two or three carbon atoms simultaneously;

[0019] Optionally, 80% to 100% of the electronegative dopant elements are simultaneously covalently bonded to 2 or 3 carbon atoms;

[0020] Optionally, any one atom of the electronegative dopant element is covalently bonded to two or three carbon atoms simultaneously.

[0021] By covalently doping electronegative dopants into a carbon matrix, the stability of electronegative dopants in the coating layer can be improved, which is beneficial to improving the stability of electrolyte wettability and thus improving battery cycle stability.

[0022] In some embodiments, the electronegative doping element in the doped carbon includes one or more of N, P, and S.

[0023] In some embodiments, the doped carbon satisfies one or more of the following characteristics:

[0024] (ta1) The electronegative doping element includes a bridged N atom, wherein the bridged N atom is covalently bonded to at least one carbon atom;

[0025] (ta2) The electronegative doping element includes a bridged S atom, which is covalently bonded to at least one carbon atom;

[0026] (ta3) The electronegative doping element includes bridging P atoms, and at least a portion of the bridging P atoms have any covalent sites independently covalently bonded in a COP or CSP manner; optionally, 80% to 100% of the bridging P atoms have any covalent sites independently covalently bonded in a COP or CSP manner.

[0027] (ta4) Among the electronegative doping elements of the doped carbon, the doping amount of N is higher than that of S.

[0028] Optionally, among the electronegative doping elements of the doped carbon, the doping amount of N is higher than that of P, and the doping amount of N is higher than that of S.

[0029] The surface polarization induced by sulfur (S) doping is lower than that induced by nitrogen (N). Introducing S doping is more difficult than N doping. However, it is possible to control the N doping level to be higher than the S doping level.

[0030] Phosphorus (P) does not readily bond with carbon (C), so it is usually necessary to introduce at least one of oxygen (O) and sulfur (S) to form a COP or CSP bond.

[0031] In some embodiments, the electronegative coated active material satisfies one or more of the following characteristics:

[0032] (tb1) The average thickness of the coating layer is 1nm to 500nm, optionally 100nm to 500nm, and further optionally 100nm to 200nm;

[0033] (tb2) The thickness of at least one of the coating layers is 1 nm to 1000 nm, optionally 100 nm to 1000 nm, and further optionally 100 nm to 200 nm;

[0034] (tb3) The electronegative doping element in the doped carbon has a mass percentage of 0.1% to 0.6%, optionally 0.2% to 0.6%, and more preferably 0.2% to 0.4%;

[0035] (tb4) The electronegative dopant element in the coating layer has a mass percentage of 0.1% to 0.6%, optionally 0.2% to 0.6%, and more preferably 0.2% to 0.4%;

[0036] (tb5) The coating layer has a mass percentage of 0.2% to 5% in the electronegative coating active material, and can be optionally 0.5% to 3%;

[0037] (tb6) The average thickness of the coating layer is related to the D of the first negative electrode active material. v The ratio of 50 is 0.5% to 12.5%, and can be selected as 1% to 10%;

[0038] (tb7) The mass percentage of the doped carbon in the coating layer is 80% to 100%, and optionally 90% to 100%;

[0039] (tb8) The sum of the mass percentages of soft carbon and hard carbon in the carbon matrix is ​​80% to 100%, optionally 90% to 100%; optionally, the mass percentage of soft carbon in the carbon matrix is ​​80% to 100%, further optionally 90% to 100%, or the mass percentage of hard carbon in the carbon matrix is ​​80% to 100%, further optionally 90% to 100%;

[0040] (tb9) The carbon matrix is ​​soft carbon.

[0041] By comparing the average thickness of the coating layer, the local thickness of the coating layer, the mass percentage of electronegative dopant elements in the doped carbon, the mass percentage of electronegative dopant elements in the coating layer, and the average thickness of the coating layer with the D of the first negative electrode active material... v Controlling one or more of the following parameters within the aforementioned ranges—the ratio of 50, the mass percentage of doped carbon in the coating layer, and the sum of the mass percentages of soft carbon and hard carbon in the carbon matrix—is beneficial for controlling the content of electronegative dopant elements within a suitable range. This is beneficial for improving the fast-charging performance of the battery based on the aforementioned multiple effects, and also for reducing the probability of electronegative dopant elements participating in side reactions, which is conducive to achieving good battery cycle performance. However, it is not limited to the aforementioned theories.

[0042] In some embodiments, the electronegative coating active material accounts for 20% to 100% of the first negative electrode active material, and can be optionally 40% to 100%. By controlling the proportion of the electronegative coating active material in the first negative electrode active material within the aforementioned range, it is beneficial to better improve battery dynamics based on the multiple functions of the electronegative coating active material and enhance the battery's fast charging capability.

[0043] In some embodiments, the electronegative coating active material accounts for 20% to 80% of the first negative electrode active material, and is further optionally 40% to 80%. By controlling the proportion of the electronegative coating active material in the first negative electrode active material within the aforementioned range, it is beneficial to improve the fast charging capability of the battery and also to balance manufacturing costs.

[0044] In some embodiments, the electronegatively coated active material includes electronegatively coated secondary particles, wherein the negative electrode active body in the electronegatively coated secondary particles is a secondary particle.

[0045] Introducing electronegative coated secondary particles into the first negative electrode active material helps to increase the surface roughness of the active particles in the electronegative coated active material, thereby increasing the sites for lithium ion adsorption. This, in turn, helps to improve the wettability of the electrolyte, further improving the wettability of the electrolyte to the first negative electrode active layer, and also further improving the wettability to the second negative electrode active layer, thus better improving the fast charging performance of the battery.

[0046] In some embodiments, the electronegatively coated secondary particles constitute 20% to 100% of the first negative electrode active material, optionally 40% to 100%. By controlling the proportion of electronegatively coated secondary particles in the first negative electrode active material within the aforementioned range, it is beneficial to better improve the fast-charging performance of the battery.

[0047] In some embodiments, the electronegatively coated secondary particles account for 20% to 80% of the first negative electrode active material, and can be optionally 40% to 80%. By controlling the proportion of electronegatively coated secondary particles in the first negative electrode active material within the aforementioned range, it is beneficial to improve the fast charging performance of the battery and also to balance manufacturing costs.

[0048] In some embodiments, the negative electrode active body in the electronegatively coated active material includes one or more of carbon-based and silicon-based active materials.

[0049] Non-limitingly, the negative electrode active body in the electronegatively coated active material may include one or more of carbon-based and silicon-based active materials, in which case the first negative electrode active material includes one or more of carbon-based and silicon-based materials. The electronegatively coated active material may include electronegatively coated secondary particles. When the negative electrode active body includes a carbon-based active material, it is beneficial to give the first negative electrode active material better conductivity, which is beneficial to reducing internal resistance and providing better fast charging capability. When the negative electrode active body includes a silicon-based active material, it is beneficial to utilize the high specific capacity of silicon-based active materials to increase the amount of lithium intercalation per unit time, which is beneficial to improving fast charging speed, and also beneficial to improving energy density.

[0050] In some embodiments, the first negative electrode active material satisfies one or more of the following characteristics:

[0051] (tc1) The carbon-based active material includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon;

[0052] (tc2) The first negative electrode active material includes a carbon-based material, wherein the mass percentage of the carbon-based material in the first negative electrode active material is 20% to 100%, optionally 20% to 80%, and further optionally 40% to 80%.

[0053] By controlling the mass ratio of carbon-based materials in the first negative electrode active material within the aforementioned range, it is beneficial to better control the volume expansion of the negative electrode during fast charging, improve the structural stability of the first negative electrode active material during charge-discharge cycles, and also take into account the energy density of the negative electrode and the battery.

[0054] In some embodiments, the lithium-ion secondary battery satisfies one or more of the following characteristics:

[0055] (td1) The negative electrode active body in the electronegative coated active material includes graphite;

[0056] (td2) The electronegatively coated active material includes electronegatively coated secondary particulate graphite, wherein the negative electrode active body in the electronegatively coated secondary particulate graphite is secondary particulate graphite, and the electronegatively coated secondary particulate graphite accounts for 20% to 100% of the first negative electrode active material, optionally 40% to 100%, and further optionally 40% to 80%.

[0057] (td3) D of the first negative electrode active material v 50 is 8μm to 16μm, and can be selected as 10μm to 14μm;

[0058] (td4) The porosity of the first negative electrode active layer is 22% to 32%, and can be selected as 26% to 30%;

[0059] (td5) At at least one temperature condition from 20°C to 35°C, the ionic conductivity of the electrolyte is 13 mS / cm to 18 mS / cm; optionally, at 25°C, the ionic conductivity of the electrolyte is 13 mS / cm to 18 mS / cm.

[0060] The fast-charging performance of a lithium-ion secondary battery can be improved by making it satisfy one or more of the characteristics (td1), (td2), (td3), (td4), and (td5).

[0061] Introducing graphite into the negative electrode active body of the electronegatively coated active material can improve the conductivity of the electronegatively coated active material, reduce internal resistance, and provide better fast charging capability.

[0062] Introducing electronegatively coated secondary graphite particles into electronegatively coated active materials can help to combine the advantages of both electronegatively coated secondary particles and graphite bulk.

[0063] By using a negative electrode active material D v Controlling the concentration of 50% within the aforementioned range helps to better control the degree of particle accumulation in the first negative electrode active layer, better control the porosity between particles, provide better lithium-ion transport channels, and better improve battery dynamics and fast charging performance.

[0064] By controlling the porosity of the first negative electrode active layer within the aforementioned range, it is beneficial to provide better lithium-ion transport channels, allowing the first negative electrode active material in the first negative electrode active layer to be better wetted by the electrolyte. This enables the electronegative dopant elements in the electronegatively coated active material to better adsorb foreign atoms, better combine solvated lithium ions, and better promote lithium-ion intercalation into the first negative electrode active material. When the porosity of the second negative electrode active layer is controlled within the aforementioned range, the improvement effect of electronegative dopant elements on battery fast-charging performance is more significant. By controlling the ionic conductivity of the electrolyte within the aforementioned range, it is beneficial to promote rapid lithium-ion transport and better improve battery kinetics and fast-charging performance.

[0065] In some embodiments, the negative electrode active material layer further includes a second negative electrode active layer, which is located between the negative electrode current collector and the first negative electrode active layer;

[0066] The lithium-ion secondary battery satisfies one or more of the following characteristics:

[0067] (t1) The porosity of the first negative electrode active layer is higher than that of the second negative electrode active layer;

[0068] (t2) The ratio of the difference in compaction density between the second negative electrode active layer and the first negative electrode active layer to the compaction density of the negative electrode sheet is denoted as R. PΔ R PΔ The range is 0 to 2, and can be selected as 0 to 0.834. Further optionally, 0 <R PΔ ≤0.834;

[0069] (t3) The charging rate of the first negative electrode active layer is higher than that of the second negative electrode active layer; optionally, the charging rate of the first negative electrode active layer is higher than that of the second negative electrode active layer.

[0070] By controlling the porosity of the first negative electrode active layer to be higher than that of the second negative electrode active layer, it is beneficial to balance the fast charging performance and energy density of the battery. The high porosity of the first negative electrode active layer can be used to promote the rapid transport of lithium ions, while the low porosity of the second negative electrode active layer can be used to improve the energy density of the negative electrode.

[0071] The ratio of the difference in compaction density between the second negative electrode active layer and the first negative electrode active layer to the compaction density of the negative electrode sheet (R) is used to measure the density difference between the second negative electrode active layer and the first negative electrode active layer. PΔ Controlling the density within the aforementioned range helps to provide a better lithium-ion transport channel for the particle stacking degree of the first negative electrode active layer, thereby improving battery dynamics and fast charging performance. In addition, the second negative electrode active layer can be used to provide a higher energy density, which helps to balance battery fast charging performance and energy density.

[0072] By controlling the charging rate of the first negative electrode active layer to be higher than that of the second negative electrode active layer, it is beneficial to promote the faster insertion of lithium ions into the first negative electrode active layer, thereby improving the fast-charging performance of the battery.

[0073] In some embodiments, the negative electrode active material layer further includes a second negative electrode active layer, which is located between the negative electrode current collector and the first negative electrode active layer; the second negative electrode active layer includes a second negative electrode active material, and the negative electrode sheet satisfies one or more of the following characteristics:

[0074] (te1) D of the second negative electrode active material v 50 is 10μm to 20μm, and can be selected as 13μm to 17μm;

[0075] (te2) D of the second negative electrode active material v 50 is higher than the D of the first negative electrode active material v 50;

[0076] (te3) The compaction density of the second negative electrode active layer is higher than that of the first negative electrode active layer;

[0077] (te4) The compaction density of the powder in the second negative electrode active layer is higher than that in the first negative electrode active layer.

[0078] By enabling lithium-ion secondary batteries to meet one or more of the characteristics (te1), (te2), (te3), and (te4), it is beneficial to enable lithium-ion secondary batteries to have improved fast-charging performance while also meeting energy density requirements.

[0079] By using the D of the second negative electrode active material v Keeping 50 within the aforementioned range is beneficial for achieving a higher compaction density in the second negative electrode active layer, which in turn helps to improve the energy density.

[0080] By controlling the D of the second negative electrode active material v 50 higher than the D of the first negative electrode active material v 50 is beneficial for achieving a higher compaction density in the second negative electrode active layer, which in turn helps to improve the energy density.

[0081] By adjusting the compaction density of the second negative electrode active layer in a lithium-ion secondary battery to be higher than that of the first negative electrode active layer, it is beneficial to improve the energy density of the lithium-ion secondary battery.

[0082] By controlling the powder compaction density of the second negative electrode active layer in the lithium-ion secondary battery to be higher than that of the first negative electrode active layer, it is beneficial to impart a higher compaction density to the second negative electrode active layer during the cold pressing process of the electrode sheet, so that the second negative electrode active layer in the lithium-ion secondary battery has a higher compaction density.

[0083] In some embodiments, the negative electrode active material layer further includes a second negative electrode active layer, the second negative electrode active layer being located between the negative electrode current collector and the first negative electrode active layer; the negative electrode sheet satisfies one or more of the following characteristics:

[0084] (tf1) On one side of the negative electrode current collector, the ratio of the areal density of the first negative electrode active layer to the areal density of the second negative electrode active layer is 2:8 to 6:4, and optionally 4:6 to 5:5.

[0085] (tf2) Taking the negative electrode current collector as a single side, the ratio of the thickness of the first negative electrode active layer to the sum of the thicknesses of the first negative electrode active layer and the second negative electrode active layer is denoted as F. H Satisfying 20% ​​≤ F H ≤65%, optionally, 40% ≤F H ≤60%;

[0086] (tf3) The thickness of the first negative electrode active layer is 10 μm to 50 μm, and optionally 20 μm to 40 μm, depending on the single side of the negative electrode current collector.

[0087] By controlling the ratio of the areal density of the second negative electrode active layer to the areal density of the first negative electrode active layer within the aforementioned range, it is beneficial to better balance the battery's fast charging performance and energy density.

[0088] By controlling the thickness of the first negative electrode active layer to satisfy one or more of the above features (tf2) and (tf3), it is beneficial to better leverage the role of electronegative doping elements in the coating layer in improving the fast charging performance of the battery while also taking into account the energy density of the battery.

[0089] In some embodiments, the areal density of the negative electrode sheet is 5 mg / cm³, calculated on one side of the negative electrode current collector. 2 ~15mg / cm 2 .

[0090] By controlling the areal density of the negative electrode sheet within the aforementioned range, it is beneficial to balance the battery's fast charging performance and energy density.

[0091] In some embodiments, the lithium-ion secondary battery further includes a positive electrode sheet, the positive electrode sheet includes a positive active layer, the positive active layer includes a positive active material, and the positive active material includes one or more of lithium phosphate active materials and lithium composite metal oxide active materials.

[0092] Introducing lithium phosphate-containing active materials into the positive electrode active material can improve the structural stability of the positive electrode active material during charge-discharge cycles and extend the cycle life of the battery.

[0093] Introducing lithium-composite metal oxide active materials into the positive electrode active material is beneficial to improving the energy density of the positive electrode and the battery.

[0094] In some embodiments, the positive electrode active material includes a lithium phosphate-based active material, and the positive electrode active material satisfies one or more of the following characteristics:

[0095] (tg1) The mass percentage of the lithium phosphate-containing active material in the positive electrode active layer is greater than or equal to 80%, and can be selected as 80% to 97%;

[0096] (tg2) The lithium-containing phosphate active materials include one or more of lithium iron phosphate, lithium iron phosphate and carbon composite materials, lithium manganese phosphate, lithium manganese phosphate and carbon composite materials, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composite materials.

[0097] (tg3) The lithium phosphate active material includes a lithium phosphate active body and a carbon coating layer located on at least a portion of the surface of the lithium phosphate active body, wherein the carbon coating layer includes one or more of soft carbon, hard carbon and amorphous carbon.

[0098] By controlling the mass ratio of lithium phosphate active materials in the positive electrode active layer within the aforementioned range, it is beneficial to extend the cycle life of the battery.

[0099] The types of lithium phosphate active materials can be flexibly selected to meet different application needs.

[0100] By setting one or more carbon coating layers, including soft carbon, hard carbon, and amorphous carbon, on the surface of lithium phosphate active materials, the conductivity of the material can be improved. This is beneficial for improving the electrical contact network within the positive electrode, providing a fast and stable channel for electron transport within the positive electrode, thereby improving the rate performance and fast charging capability of the battery.

[0101] In a second aspect of this application, a method for preparing a lithium-ion secondary battery is provided, which can be used to prepare the lithium-ion secondary battery of the first aspect of this application.

[0102] In some embodiments, a method for preparing a lithium-ion secondary battery is provided, which includes preparing a negative electrode sheet;

[0103] The preparation of the negative electrode sheet includes the following steps:

[0104] A negative electrode active material layer is disposed on at least one side of the negative electrode current collector; wherein, the negative electrode active material layer includes a first negative electrode active layer, the first negative electrode active layer includes a first negative electrode active material, the first negative electrode active material includes an electronegatively coated active material, the electronegatively coated active material includes a negative electrode active body and a coating layer located on at least a portion of the surface of the negative electrode active body; the coating layer includes doped carbon, the doped carbon includes a carbon matrix and an electronegatively dopant element, the carbon matrix includes one or more of soft carbon and hard carbon, the Pauling electronegativity scale of the electronegatively dopant element is denoted as χ1, and the Pauling electronegativity scale of carbon element is denoted as χ. C Then χ1 and χ C The absolute value of the difference between them satisfies 0.03 ≤ |χ1-χ C |≤0.49.

[0105] In the prepared lithium-ion secondary battery, an electronegative coating active material is set in the negative electrode active material layer of the negative electrode sheet. As described above, the electronegative doping elements and carbon matrix in the coating layer can promote the faster and more extensive embedding of lithium ions into the negative electrode active material through synergistic effect, which is beneficial to improving battery dynamics and enhancing the fast charging capability of the battery.

[0106] In some embodiments, a method for preparing a lithium-ion secondary battery is provided, which includes preparing a negative electrode sheet;

[0107] The preparation of the negative electrode sheet includes the following steps:

[0108] A second negative electrode active layer and a first negative electrode active layer are sequentially disposed on at least one side of the negative electrode current collector; wherein, the first negative electrode active layer includes a first negative electrode active material, the first negative electrode active material includes an electronegative coated active material, and the definition of the electronegative coated active material is as described above.

[0109] In the prepared lithium-ion secondary battery, a first negative electrode active layer and a second negative electrode active layer are disposed in the negative electrode active material layer of the negative electrode sheet. An electronegative coating active material is disposed in the first negative electrode active layer. As described above, the electronegative doping elements and carbon matrix in the coating layer can promote the faster and more extensive embedding of lithium ions into the first negative electrode active material through synergistic effect. It is also beneficial to improve the wettability of the electrolyte in the second negative electrode active layer based on the improvement of the electrolyte wettability of the first negative electrode active layer. Based on the aforementioned multiple effects, it is beneficial to improve battery dynamics and enhance the fast charging capability of the battery.

[0110] In some embodiments, the carbon matrix in the doped carbon includes soft carbon, and the electronegative coated active material is prepared by an in-situ coating method;

[0111] Optionally, the electronegative coated active material is prepared by a method comprising the following steps:

[0112] In the presence of a doped precursor, the negative electrode active body and the soft carbon precursor are mixed and subjected to doping heat treatment and soft carbonization heat treatment, so that the soft carbon precursor and the doped precursor together form a doped soft carbon coating on at least a portion of the surface of the negative electrode active body; wherein, the doped precursor includes the electronegative doping element.

[0113] In some embodiments, the method for preparing the electronegative coated active material satisfies one or more of the following characteristics:

[0114] (th1) The doped precursor includes an N-containing precursor, which includes one or more of urea and ammonia;

[0115] (th2) The doped precursor includes an S-containing precursor, which includes one or more of sulfur and sulfur vapor;

[0116] (th3) The doped precursor includes a P-containing precursor, which includes one or more of red phosphorus and phosphorus vapor;

[0117] (th4) The doping heat treatment includes N doping treatment, and the conditions for carrying out the N doping treatment include: heating rate of 2℃ / min~10℃ / min, holding temperature of 400℃~800℃, and holding time of 1h~6h.

[0118] (th5) The doping heat treatment includes S doping treatment, and the conditions for carrying out the S doping treatment include: heating rate of 2℃ / min~10℃ / min, holding temperature of 200℃~600℃, and holding time of 1h~6h.

[0119] (th6) The doping heat treatment includes P doping treatment. The steps of performing the heat treatment include: performing one or both of O doping treatment and S doping treatment, followed by P doping treatment. The conditions for performing the P doping treatment include: a heating rate of 2℃ / min to 10℃ / min, a holding temperature of 200℃ to 600℃, and a holding time of 1h to 6h. The conditions for performing the O doping treatment include: heating at a heating rate of 2℃ / min to 10℃ / min in an air atmosphere, holding at a nitrogen atmosphere and at 400℃ to 800℃, and holding for 1h to 6h.

[0120] (th7) In the steps of performing doping heat treatment and performing soft carbonization heat treatment, the soft carbon precursor includes pitch;

[0121] (th8) The conditions for carrying out the soft carbonization heat treatment include: heat treatment in an inert gas atmosphere and at 700℃~1300℃.

[0122] In some embodiments, the carbon matrix in the doped carbon includes hard carbon, and the electronegative coated active material is prepared by an in-situ coating method;

[0123] Optionally, the electronegative coated active material is prepared by a method comprising the following steps:

[0124] At least a portion of the surface of the negative electrode active body is coated with hard carbon, a doping source including an electronegative doping element is introduced, and the electronegative doping element is introduced into the hard carbon by gas displacement method to form a doped hard carbon coating at least a portion of the surface of the negative electrode active body.

[0125] Optionally, the gas replacement method may employ one of ammonia, sulfur vapor, and phosphorus vapor.

[0126] In a fourth aspect of this application, an electrical device is provided, comprising at least one of the lithium-ion secondary batteries described in the first aspect of this application and lithium-ion secondary batteries prepared by the preparation method of the lithium-ion secondary batteries described in the second aspect of this application.

[0127] In a fifth aspect of this application, the application of the lithium-ion secondary battery described in the first aspect of this application in supplying and / or storing electrical energy is provided;

[0128] The application includes the process of charging the lithium-ion secondary battery at a rate of 2C or higher;

[0129] Optionally, the application includes the process of charging the lithium-ion secondary battery at at least one rate from 2C to 6C.

[0130] Optionally, the application includes the process of charging the lithium-ion secondary battery at at least one rate of 2C to 4C or 4C to 6C.

[0131] Optionally, the maximum charging rate of the lithium-ion secondary battery is greater than or equal to 2C, and can be selected as 2C to 6C, or further selected as 2C to 4C or 4C to 6C.

[0132] The lithium-ion secondary battery provided in the first aspect of this application can provide high rate performance and good fast charging capability.

[0133] Details of one or more embodiments or examples of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0134] To better describe and illustrate the embodiments, examples, or models provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments, examples, or models, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0135] Figure 1 is a schematic diagram of a battery cell according to an embodiment of this application.

[0136] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1.

[0137] Figure 3 is a schematic diagram of a battery device according to an embodiment of this application.

[0138] Figure 4 is a schematic diagram of a battery pack according to one embodiment of this application.

[0139] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4.

[0140] Figure 6 is a schematic diagram of an electrical device using a lithium-ion secondary battery as a power source according to an embodiment of this application.

[0141] Explanation of reference numerals in the attached drawings: 1, battery pack; 2, upper casing; 3, lower casing; 4, battery assembly; 5, individual battery cell; 51, housing; 52, electrode assembly; 53, cover plate; 6, electrical device. Detailed Implementation

[0142] The following describes in detail, with appropriate reference to the accompanying drawings, some embodiments and examples of the lithium-ion secondary battery of this application, its preparation method, power supply device, and application. However, some unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0143] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be included or excluded independently and can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when describing a parameter as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 for that parameter. For instance, when describing a parameter as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0144] In this application, unless otherwise specified, "about" means within a reasonable range above and below the stated number, and the range of fluctuation may vary depending on the type and value of the stated number. For example, a range of ±10%, ±5%, ±2%, ±1%, etc., may be allowed. For example, taking "about 20°C" and its approximation as ±1°C, approximate values ​​such as 19°C, 19.5°C, etc., within the approximation range indicated by "about 20°C" should also be included in the range indicated by "about 20°C".

[0145] In this application, the terms "multiple," "various," "multiple items," "several," etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more (greater than or equal to) two. It can be understood that when "any number of" items are involved, it refers to any suitable combination of multiple items, that is, a combination of "any number of" items in a manner that does not conflict and enables the implementation of this application.

[0146] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0147] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0148] In this application, open-ended technical features or solutions described using terms such as "containing," "comprising," or "including" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if 'a' includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both features or solutions where "a consists of a1, a2, and a3" or "a is selected from a1, a2, and a3," and features or solutions where "a includes not only a1, a2, and a3, but also other members."

[0149] In this application, unless otherwise specified, M (e.g., m1) means that m1 is a non-limiting example of M, and it is understood that M is not limited to m1.

[0150] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it is selected from either "with" or "without." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "option" is independent. Unless otherwise specified, the descriptions such as "optionally include" and "optionally contain" in this application, taking "optionally include" as an example, mean "may include or not include."

[0151] In this application, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. Any and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "M and / or N" represents the group consisting of M, N, and "a combination of M and N". "Containing M and / or N" can mean "containing M, containing N, and containing both M and N", or "containing M, containing N, or containing both M and N", and can be appropriately understood according to the context.

[0152] In this document, the word "suitable" in "suitable combination" or "suitable method" refers to the technical solution that can implement this application.

[0153] In this document, terms such as "preferred," "better," "more effective," "gooder," and "superior" are merely descriptions of more effective implementation methods or embodiments and should be understood not to limit the scope of protection of this application. If multiple "preferred" terms appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "preferred" term shall be independent.

[0154] In this application, terms such as "further," "even more," "especially," "for example," "as," and "example" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0155] In this application, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0156] In this application, unless otherwise expressly specified and limited, the term "connection" and other such terms should be interpreted broadly, for example, as a fixed connection, a detachable connection, or an integral part. Those skilled in the art will understand the appropriate meaning of the above terms in this application based on the context.

[0157] In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can indicate a horizontal positional relationship, or it can simply indicate the existence of an attachment relationship without specifying a horizontal positional relationship.

[0158] In this application, the term "room temperature" generally refers to 4℃ to 35℃, and may refer to 20℃ ± 5℃. In some embodiments or examples of this application, room temperature refers to 20℃ to 30℃.

[0159] In this application, when a unit is specified for a data range, if it is only followed by the right endpoint, it indicates that the units for the left and right endpoints are the same. For example, 3~5μm or 3-5μm both mean that the units for the left endpoint "3" and the right endpoint "5" are both μm (micrometers), and have the same meaning as 3μm~5μm. Furthermore, similar descriptions of other parameters such as temperature and size are interpreted in the same way.

[0160] In this application, "greater than or equal to" and "≥" have the same meaning and can be used interchangeably; "less than or equal to" and "≤" have the same meaning and can be used interchangeably; "greater than" can be equivalently represented as ">", and "less than" can be equivalently represented as "<". In this application, unless otherwise specified, "greater than or equal to" and "≥" can be considered as providing two additional solutions: "greater than" and "equal to". In this application, unless otherwise specified, "less than or equal to" and "≤" can be considered as providing two additional solutions: "less than" and "equal to".

[0161] In this application, the exemplary descriptions such as "in some implementations (or embodiments)" and "in one implementation (or embodiment)" may cover, but are not limited to, the following meanings: these solutions can be combined with other solutions in a suitable manner to form new technical solutions.

[0162] Unless otherwise stated, the improvements described in this application are not intended to be limited to any theoretical constraints.

[0163] In this application, when two or more test methods are provided for a certain parameter, all test results of at least one test method that are within the described range are included in the protection scope of this application.

[0164] Currently, the demand for fast charging performance of lithium-ion rechargeable batteries is increasing, requiring lithium ions to be transported quickly within the negative electrode. However, in traditional lithium-ion rechargeable batteries, the portion of the negative electrode far from its surface is not ideally wetted by the electrolyte, which affects the further improvement of the battery's fast charging performance.

[0165] According to various embodiments and examples of this application, this application provides a lithium-ion secondary battery, its preparation method, power application device, and application. The lithium-ion secondary battery includes a negative electrode and an electrolyte. The negative electrode includes a negative active material layer, which includes an electronegative coated active material. This lithium-ion secondary battery exhibits significantly improved fast-charging performance.

[0166] It is understandable that the negative electrode active material in the negative electrode active material layer includes electronegative coated active materials.

[0167] In some embodiments, a lithium-ion secondary battery includes a negative electrode and an electrolyte; the negative electrode includes a negative current collector and a negative active material layer located on at least one side of the negative current collector; the negative active material layer includes an electronegative coated active material, which includes a coating layer; the coating layer includes doped carbon, which includes a carbon matrix and an electronegative dopant element, wherein the carbon matrix includes one or more of soft carbon and hard carbon, and the Pauling electronegativity scales of the electronegative dopant element and carbon element are denoted as χ1 and χ, respectively. C Satisfying 0.03≤|χ1-χ C |≤0.49. The negative electrode active material layer includes a first negative electrode active layer, and may also include a second negative electrode active layer located between the negative electrode current collector and the first negative electrode active layer. This lithium-ion secondary battery has significantly improved fast-charging performance.

[0168] It is understandable that the first negative electrode active layer includes an electronegatively coated active material.

[0169] In some embodiments, the negative electrode active material layer includes a first negative electrode active layer, the first negative electrode active layer includes a first negative electrode active material, and the first negative electrode active material includes an electronegatively coated active material.

[0170] In some embodiments, the electronegative coated active material includes a negative electrode active body and a coating layer located on at least a portion of the surface of the negative electrode active body. The coating layer includes doped carbon, which includes a carbon matrix and an electronegative dopant element. The carbon matrix includes one or more of soft carbon and hard carbon.

[0171] In this application, unless otherwise specified, the term "lithium-ion secondary battery" refers to a secondary battery in which the active ions include lithium ions, and "lithium-ion battery cell" refers to a battery cell in which the active ions include lithium ions. Typically, a lithium-ion secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0172] In this application, unless otherwise specified, "electrode active material layer" includes at least one of the positive active material layer of the positive electrode sheet and the negative active material layer of the negative electrode sheet. Depending on the specific circumstances, the electrode active material layer may refer to either the positive active material layer or the negative active material layer. In this application, "positive active material layer" may also be referred to as "positive active layer" and "negative active material layer" may also be referred to as "negative active layer".

[0173] In this application, the term "negative electrode sheet" includes a negative electrode active material layer, which includes a negative electrode active material. The term "negative electrode active material" refers to a material used in a negative electrode sheet that is capable of reversibly inserting and de-inserting active ions.

[0174] In this application, unless otherwise specified, "negative electrode sheet" includes a negative electrode current collector. A "negative electrode current collector" refers to a structure responsible for collecting and conducting electrons at the negative electrode. In the negative electrode sheet, the negative electrode active layer is located on at least one side of the negative electrode current collector, and may be located on one or both sides of the negative electrode current collector.

[0175] In this application, the term "positive electrode sheet" includes a positive electrode active material layer, which includes a positive electrode active material. The term "positive electrode active material" refers to a material used in a positive electrode sheet that is capable of reversibly extracting and inserting active ions.

[0176] In this application, unless otherwise specified, "positive electrode sheet" includes a positive current collector. A "positive current collector" refers to a structure responsible for collecting and conducting electrons at the positive electrode. In the positive electrode sheet, the positive active layer is located on at least one side of the positive current collector, and may be located on one or both sides of the positive current collector.

[0177] In this application, unless otherwise specified, "separation membrane" and "diaphragm" have the same meaning and can be used interchangeably.

[0178] In a first aspect of this application, a lithium-ion secondary battery is provided.

[0179] In some embodiments, a lithium-ion secondary battery is provided, which includes a negative electrode sheet and an electrolyte; the negative electrode sheet includes a negative current collector and a negative active material layer located on at least one side of the negative current collector, the negative active material layer including a first negative active layer;

[0180] The first negative electrode active layer includes a first negative electrode active material, the first negative electrode active material includes an electronegative coating active material, the electronegative coating active material includes a negative electrode active body (which may be referred to as the first active body) and a coating layer located on at least a portion of the surface of the negative electrode active body.

[0181] The coating layer includes doped carbon, which comprises a carbon matrix and an electronegative dopant element. The carbon matrix may include one or more types of soft carbon and hard carbon. The Pauling electronegativity scale of the electronegative dopant element is denoted as χ1, and the Pauling electronegativity scale of carbon element is denoted as χ. C Then χ1 and χ C The absolute value of the difference is between 0.03 and 0.49, which means that 0.03 ≤ |χ1-χ C |≤0.49.

[0182] In some embodiments, the negative electrode active material layer further includes a second negative electrode active layer, which is located between the negative electrode current collector and the first negative electrode active layer; in this case, a lithium-ion secondary battery is provided, which includes a negative electrode sheet and an electrolyte; the negative electrode sheet includes a negative electrode current collector and a second negative electrode active layer and a first negative electrode active layer sequentially disposed on at least one side of the negative electrode current collector.

[0183] In this application, the "negative electrode active material layer" in the negative electrode sheet may include one or more negative electrode active layers, that is, the negative electrode active material layer may be a single-layer structure or a multi-layer structure. Unless otherwise specified, the negative electrode active material layer includes at least a first negative electrode active layer. In some embodiments, the negative electrode active material layer is a single-layer structure, including only one negative electrode active layer. In this case, the negative electrode active material layer is the first negative electrode active layer.

[0184] In this application, unless otherwise specified, "electronegative coated active material" falls under the category of negative electrode active material, which includes a negative electrode active body and a coating layer located on at least a portion of the surface of the negative electrode active body; the "negative electrode active body" may be referred to as "first active body" and has the ability to reversibly insert and extract active ions; the coating layer includes doped carbon.

[0185] In this application, unless otherwise specified, "doped carbon" includes a carbon matrix and an electronegative dopant element. Typically, in electronegative coated active materials, the carbon matrix of the doped carbon in the coating layer is a different material from the negative electrode active body. In some embodiments, the carbon matrix may include one or more of soft carbon and hard carbon. Doped carbon with a soft carbon matrix can be referred to as "doped soft carbon," and it is understood that doped soft carbon includes soft carbon and an electronegative dopant element; doped carbon with a hard carbon matrix can be referred to as "doped hard carbon," and it is understood that doped hard carbon includes hard carbon and an electronegative dopant element. Doped carbon may include one or more of doped soft carbon and doped hard carbon.

[0186] In this application, "soft carbon" and "hard carbon" have the well-known meanings in the art. Soft carbon can be graphitized through further high-temperature treatment, while hard carbon is difficult to graphitize even with further high-temperature treatment. The disordered stacking of carbon layers in soft carbon allows for relatively rapid lithium-ion transport. Hard carbon has a disordered internal crystal arrangement and numerous pores, providing abundant lithium intercalation sites and rapid transport channels.

[0187] Unless otherwise stated in this application, |χ1-χ C The pair of "|" in the equation indicates an absolute value, which is a positive number. |χ1-χ C | refers to "χ1 and χ C The absolute value of the difference between them. Those skilled in the art will understand that the Pauling electronegativity scale (χ²) of carbon... C() is a numerically determined parameter. By limiting |χ1-χ C The value or range of | defines the degree of electronegativity difference between the electronegative dopant and carbon, which is essentially equivalent to defining the value or range of the Pauling electronegativity scale (χ1) of the electronegative dopant.

[0188] In this application, unless otherwise stated, the "Pauling electronegativity scale" has a well-known meaning in the art. It is a parameter proposed by the American chemist Linus Pauling, used to reflect the ability of atoms of a certain class of elements to attract electrons, and can be used to characterize the electronegativity of elements. A larger Pauling electronegativity scale indicates a stronger ability of the corresponding atom to attract electrons, and thus a stronger electronegativity. The Pauling electronegativity scale for each element can be found in chemical handbooks or known literature. In the Pauling electronegativity scale, the electronegativity of fluorine is defined as 4.0, which is the highest electronegativity among all elements. Furthermore, by way of example, the Pauling electronegativity scales for carbon (C), nitrogen (N), sulfur (S), and phosphorus (P) are 2.55, 3.04, 2.58, and 2.19, respectively.

[0189] Those skilled in the art generally understand that the difference in the Pauling electronegativity scale (χ value) between two different elements reflects the degree of difference in their ability to attract electrons, and thus reflects the degree of polarization when the two elements bond. For doped carbon in the coating layer, since the doped matrix is ​​carbon (corresponding to the carbon matrix), the χ value of carbon (χ... C Based on ), it can be obtained through |χ1-χ C The value or range of | determines the types of electronegative doping elements that can form a specific degree of polarization with carbon.

[0190] In some embodiments of lithium-ion secondary batteries, an electronegative coating active material is disposed in the negative electrode active material layer of the negative electrode sheet. This coating layer contains doped carbon including an electronegative dopant element. The carbon matrix in the doped carbon may include one or more of soft carbon and hard carbon. On one hand, the introduced electronegative dopant element possesses a specific Pauling electronegativity scaling characteristic, by limiting the Pauling electronegativity scaling difference between the electronegative dopant element and the carbon element of the carbon matrix to the aforementioned |χ1-χ... CWithin a certain range, the electronegative dopant elements create unique polarization characteristics between the electronegative dopant and the carbon matrix, thereby enhancing the polarization characteristics of the negative electrode active material surface, strengthening the adsorption of foreign atoms, and weakening the binding force between the negative electrode active material and solvated lithium ions. This reduces the contact angle between the negative electrode active material surface and the electrolyte, improving its wettability and accelerating the rate of lithium ion insertion into the negative electrode active material. Furthermore, both soft and hard carbon in the carbon matrix have a high degree of disorder, which is conducive to lithium ion entry. The disordered stacking of carbon layers in soft carbon allows for relatively rapid lithium ion transport, while hard carbon provides abundant lithium insertion sites and rapid transport channels. This promotes faster and more abundant lithium ion insertion into the negative electrode active material. In addition, the introduction of electronegative dopant elements also facilitates the formation of inorganic components in the solid electrolyte interphase (SEI) film, which can improve the lithium conductivity of the SEI film and reduce the interfacial impedance. Based on the aforementioned multiple effects, this is beneficial to improving battery kinetics and enhancing the battery's fast-charging capability.

[0191] In some embodiments of lithium-ion secondary batteries, a first negative electrode active layer and a second negative electrode active layer (with the direction away from the surface of the negative electrode current collector defined as "upper" and the direction towards the surface of the negative electrode current collector defined as "lower") are disposed in the negative electrode active material layer of the negative electrode electrode sheet. Further, an electronegative coating active material is disposed in the first negative electrode active layer, wherein the coating layer contains doped carbon including an electronegative dopant element. The carbon matrix in the doped carbon may include one or more of soft carbon and hard carbon. On one hand, the introduced electronegative dopant element has a special Pauling electronegativity scaling characteristic, by limiting the Pauling electronegativity scaling difference between the electronegative dopant element and the carbon element of the carbon matrix to the aforementioned |χ1-χ... CWithin a certain range, the electronegative dopant elements form unique polarization characteristics with the carbon matrix, thereby enhancing the polarization characteristics of the negative electrode active material surface, strengthening the adsorption of foreign atoms by the negative electrode active material, and weakening the binding force between the negative electrode active material and solvated lithium ions. This reduces the contact angle between the surface of the first negative electrode active material and the electrolyte, improving its wettability and accelerating the rate of lithium ion insertion into the first negative electrode active material. Furthermore, both soft and hard carbon in the carbon matrix have a high degree of disorder, which facilitates lithium ion entry. The disordered stacking of carbon layers in soft carbon allows lithium ions to... Ions can be transported relatively quickly within the material, and hard carbon provides abundant lithium intercalation sites and fast transport channels, which facilitates faster and more frequent insertion of lithium ions into the first negative electrode active material. Furthermore, the introduction of electronegative doping elements is beneficial for the formation of inorganic components in the solid electrolyte interphase (SEI) film, which can improve the lithium conductivity of the SEI film and reduce the interfacial impedance. Additionally, the improved wettability of the electrolyte in the first negative electrode active layer is beneficial for improving the wettability of the electrolyte in the second negative electrode active layer. Based on the aforementioned multiple effects, this is conducive to improving battery kinetics and enhancing the battery's fast charging capability.

[0192] In this application, unless otherwise specified, in the thickness direction of the negative electrode sheet, for the negative electrode active material layer, the direction closer to the surface of the negative electrode sheet is referred to as "upper", and the direction farther away from the surface of the negative electrode sheet is referred to as "lower". Taking a negative electrode sheet including a negative electrode current collector as an example, the direction farther away from the surface of the negative electrode current collector is referred to as upper, and the direction toward the surface of the negative electrode current collector is referred to as lower.

[0193] In this application, the cross-section of the negative electrode sheet can be observed for microscopic morphology to examine the microscopic morphology of each negative electrode active layer in the negative electrode active material layer and the boundaries between different negative electrode active layers, thereby determining the thickness of different negative electrode active layers. "Cross-section of the negative electrode sheet" refers to a section perpendicular to the thickness of the negative electrode sheet. Furthermore, the cross-section of the negative electrode sheet can be observed for microscopic morphology and combined with compositional analysis (such as energy dispersive spectroscopy (EDS)) to identify elemental types, thus confirming the composition of different negative electrode active layers in the negative electrode active material layer. Non-limitingly, the cross-section of the negative electrode sheet can be obtained using instruments or equipment including but not limited to focused electron beam (FIB) microscopes (non-limiting examples such as the FEI Scios 2HiVac device), ion cross-section polishers (non-limiting examples such as the IB-09010CP argon ion cross-section polisher and IB-19500CP ion cross-section polisher from JEOL Corporation of Japan), or by plasma quenching. Microscopic morphology observation methods can employ instruments or equipment including but not limited to scanning electron microscopy (SEM) technology. In particular, high-resolution field emission scanning electron microscopes can be used. Examples of non-limiting SEM instruments include the Sigma 300 scanning electron microscope and the Apreo 2SEM field emission scanning electron microscope from ZEISS GmbH, Germany.

[0194] Those skilled in the art can identify the components in the negative electrode active material layer, the first negative electrode active layer, and the second negative electrode active layer using one or more of the following detection methods known in the art, including but not limited to: Fourier transform infrared (FT-IR) spectroscopy, ultraviolet spectroscopy, and proton nuclear magnetic resonance (NMR) spectroscopy. 1 Methods include 1H NMR, gel permeation chromatography (GPC), high performance liquid chromatography (HPLC), mass spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, single crystal X-ray diffraction (SCXRD), inductively coupled plasma optical emission spectrometry (ICP), and energy dispersive spectroscopy (EDS). The sample preparation and testing methods for these methods are known to those skilled in the art, and the test parameters can be appropriately adjusted according to the structure of the material or substance and the characteristics of the sample.

[0195] As a non-limiting example, EDS can be used to distinguish between carbon and silicon, and thus between carbon-based and silicon-based materials. Similarly, EDS can be used to detect the type and content of conductive agents, but is not limited to these applications.

[0196] Using natural graphite and artificial graphite as non-limiting examples, the negative electrode active materials can be distinguished by the appearance and morphology of the particles. Further X-ray diffraction (XRD) analysis can be performed. In the XRD pattern, if the characteristic peak near 2θ26.5° is very sharp and has a high intensity, it is natural graphite; if the characteristic peak near 2θ26.5° is relatively broad and has a weak intensity, it is artificial graphite.

[0197] Taking graphite and soft carbon as examples of negative electrode active materials, Raman spectroscopy can be used to distinguish between them. More specifically, the characteristic peak information of carbon components in the spectrum (such as the intensity ratio of the D peak to the G peak, I...) can be used. D / G The analysis focused on soft carbon. Both the D and G peaks are Raman characteristic peaks of carbon atom crystals. The D peak represents defects in the carbon atom crystal; the more defects, the greater the intensity of the D peak. The intensity of the D peak reflects the content of amorphous (randomly stacked) regions. The G peak represents the in-plane stretching vibrations of sp2 hybridized carbon atoms; the intensity of the G peak reflects the content of graphitized (layered structure) regions. As the degree of disorder in carbon atoms increases, the intensity ratio of the D peak to the G peak also increases. The Raman spectra can also be compared. D / G Standard Raman spectrum of graphite I D / G The difference between the two peaks can be used to determine whether the material being tested contains soft carbon. Similarly, the difference in intensity between the D and G peaks in the Raman spectrum can be used to distinguish between graphite and hard carbon. Likewise, the difference in intensity between the D and G peaks in the Raman spectrum can be used to distinguish between natural graphite and synthetic graphite.

[0198] In this application, unless otherwise specified, the constituent materials of the negative electrode active material layer are referred to as negative electrode material, the constituent materials of the first negative electrode active layer are referred to as first negative electrode material, and the constituent materials of the second negative electrode active layer are referred to as second negative electrode material. The first negative electrode material includes the first negative electrode active material, and the second negative electrode material includes the second negative electrode active material. The terms "first" and "second" in "first negative electrode material," "second negative electrode material," "first negative electrode active material," and "second negative electrode active material" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0199] The test sample for the first negative electrode active material can be obtained by the following method to determine whether it includes electronegative coated active material: Disassemble the battery cell to obtain the negative electrode sheet, and soak and clean it with a solvent (such as dimethyl carbonate (DMC)) to remove residual electrolyte; scrape powder from the first negative electrode active layer of the negative electrode sheet to obtain the first negative electrode material; for example, a certain amount of powder sample can be scraped from near the surface of the negative electrode sheet, or a sample with a thickness of 10 μm can be scraped. Further, the obtained first negative electrode material can be thoroughly soaked in a solvent (such as N-methylpyrrolidone (NMP)) to dissolve organic components such as binders and thickeners. Ultrasonic dispersion can be optionally used to promote dissolution. After washing and filtration, the collected solid phase is used as the test powder for the first negative electrode active material. It should be noted that a small amount of conductive agent in the test sample may have a relatively small impact on the test results. Similarly, a certain amount of powder sample can be scraped from the negative electrode active material layer near the negative electrode current collector to obtain the second negative electrode active material (e.g., a sample amount of 10 μm thickness), and then further processed in a similar manner to obtain the test sample of the second negative electrode active sample.

[0200] The following methods can be used to detect and analyze the coating structure of electronegative coated active materials: After the powder is cut into sections using FIB (Focused Ion Beam), the cross-sectional morphology of the particles is observed under TEM (Transmission Electron Microscopy). A clear boundary can be observed at the coating interface. Based on the TEM image, the thickness and average thickness of the coating layer can be calculated. Furthermore, by combining one or more of the following methods, such as energy dispersive spectroscopy (EDS), Raman spectroscopy, and X-ray diffraction (XRD), the types of materials in the coating layer and the negative electrode active body can be identified respectively.

[0201] The elemental composition and composition of the coating layer in electronegative coated active materials can be analyzed using or with reference to the methods described above. As a non-limiting example, the detection of electronegative dopant elements can be performed using methods including, but not limited to, X-ray photoelectron spectroscopy (XPS). A method can be used whereby the negative electrode active material sample is converted into an aerosol, introduced into a high-temperature plasma, and the type and content of electronegative dopant elements are quantitatively analyzed using the characteristic spectra generated after element ionization. Non-limiting examples of electronegative dopant elements include nitrogen (N), phosphorus (P), and sulfur (S).

[0202] In some implementations, χ1 and χ C The difference between them, expressed in absolute value, is 0.03 to 0.49 (i.e., 0.03 ≤ |χ1 - χ2|). C |≤0.49), optionally, χ1 and χ C The difference between them, expressed in absolute value, is 0.04 to 0.49 (i.e., 0.04 ≤ |χ1 - χ2) C |≤0.49). Without limitation, χ1 and χC The difference between them is expressed in absolute value (i.e., |χ1-χ) C |) can also be any of the following values ​​or a range consisting of any two of the following values: 0.03, 0.04, 0.05, 0.06, 0.08, 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, 0.2, 0.22, 0.23, 0.24, 0.25, 0.26, 0.28, 0.3, 0.32, 0.34, 0.35, 0.36, 0.38, 0.4, 0.42, 0.44, 0.45, 0.46, 0.48, 0.49, etc.

[0203] By controlling the difference between the electronegativity dopant element and the Pauling electronegativity scale of carbon within the aforementioned range, and by controlling the Pauling electronegativity scale of the electronegativity dopant element within a more suitable range, on the one hand, it is beneficial to reduce the contact angle between the surface of the negative electrode active material and the electrolyte, and to improve the wettability of the electrolyte to the first negative electrode active material. On the other hand, by controlling the difference in electron-withdrawing ability between the electronegativity dopant element and carbon atoms within a more suitable range, it is beneficial to form a stable covalent bond between the electronegativity dopant element and carbon atoms.

[0204] In some embodiments, the electronegative dopant element is covalently bonded to the carbon matrix. Unless otherwise stated, "the electronegative dopant element is covalently bonded to the carbon matrix" means that the electronegative dopant element is covalently bonded to the carbon framework of the carbon matrix.

[0205] In some of these embodiments, at least a portion of the electronegative dopant elements are covalently bonded to multiple (e.g., 2 or 3) carbon atoms simultaneously.

[0206] Optionally, the carbon matrix can be one or more of soft carbon and hard carbon. In some embodiments, the electronegative dopant element is covalently bonded to the soft carbon. In some embodiments, the electronegative dopant element is covalently bonded to the hard carbon.

[0207] In some implementations, the carbon matrix is ​​soft carbon.

[0208] In other embodiments, the carbon matrix is ​​hard carbon.

[0209] In some embodiments, 80% to 100% of the electronegative dopant elements are simultaneously covalently bonded to multiple (e.g., 2 or 3) carbon atoms. Non-limitingly, the percentage of electronegative dopant elements "simultaneously covalently bonded to 2 or 3 carbon atoms" in the total number of electronegative dopant elements in the electronegatively coated active material can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, 99%, 100%, etc.

[0210] By covalently doping electronegative dopants into a carbon matrix, the stability of electronegative dopants in the coating layer can be improved, which is beneficial to improving the stability of electrolyte wettability and thus improving battery cycle stability.

[0211] In some implementations, the electronegative doping element in the doped carbon may include one or more of N, P, and S.

[0212] N, P, and S all have electronegativity differences relative to C atoms, and all can bond with C atoms.

[0213] Nitrogen (N) atoms have a greater electronegativity difference than carbon atoms, making them more likely to bond with carbon atoms. However, this also results in more defects due to the adsorption of foreign atoms. Taking the bonding of N with a carbon matrix as an example, three bonding modes are possible, but not limited to: pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen. Among these, pyridine nitrogen and pyrrole nitrogen exhibit higher reactivity, which is beneficial for improving the adsorption of foreign atoms by the first negative electrode active material, reducing lithium-ion mass transfer resistance, and enhancing the wettability of the electrolyte to the first negative electrode active layer, thereby improving the wettability to the second negative electrode active layer and ultimately enhancing the battery's fast-charging performance.

[0214] In this application, the “foreign atoms” that the electronegative dopant can adsorb refer to atoms from outside the negative electrode active material, which can typically include atoms from the electrolyte, such as electrolyte anions from the electrolyte.

[0215] The surface polarization induced by sulfur (S) doping is lower than that induced by nitrogen (N). Introducing S doping is more difficult than N doping. However, it is possible to control the N doping level to be higher than the S doping level.

[0216] Phosphorus (P) does not readily bond with carbon (C), so it is usually necessary to introduce at least one of oxygen (O) and sulfur (S) to form a COP or CSP bond.

[0217] In some implementations, the electronegative doping element of the doped carbon is N at a higher doping level than P.

[0218] In some embodiments, among the electronegative doping elements of the doped carbon, the doping amount of N is higher than that of P, and the doping amount of N is also higher than that of S.

[0219] In this application, unless otherwise specified, the “doping amount” of electronegative dopant in doped carbon refers to the mass percentage of electronegative dopant in doped carbon.

[0220] In some implementations, the doped carbon satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0221] (ta1) Electronegative doping elements include bridged N atoms, which are covalently bonded to at least one carbon atom;

[0222] (ta2) Electronegative doping elements include bridged S atoms, which are covalently bonded to at least one carbon atom;

[0223] (ta3) The electronegative doping element includes bridged P atoms, and at least a portion of the bridged P atoms have any covalent site independently covalently bonded in a COP or CSP manner; optionally, 80% to 100% of the bridged P atoms have any covalent site independently covalently bonded in a COP or CSP manner.

[0224] (ta4) Among the electronegative doping elements of doped carbon, the doping amount of N is higher than that of S.

[0225] Optionally, among the electronegative doping elements of doped carbon, the doping amount of N is higher than that of P, and the doping amount of N is higher than that of S.

[0226] In this application, unless otherwise stated, a “bridging atom” refers to an atom that is covalently bonded to at least two adjacent atoms, such that the bridging atom exhibits a divalent or higher valence state in terms of covalent bond valence.

[0227] In some embodiments, in the doped carbon, the electronegative dopant element includes a bridging N atom, which is covalently bonded to at least one carbon atom.

[0228] In some embodiments, in the doped carbon, the electronegative dopant element includes a bridging S atom, which is covalently bonded to at least one carbon atom.

[0229] In some embodiments, in the doped carbon, the electronegative dopant element includes bridging P atoms, and at least a portion of the bridging P atoms have any covalent site independently covalently bonded in a COP or CSP manner. In some embodiments, 80% to 100% of the bridging P atoms have any covalent site independently covalently bonded in a COP or CSP manner. Non-limitingly, the percentage of "bridging P atoms with any covalent site independently covalently bonded in a COP or CSP manner" in the "bridging P atoms in the electronegative coated active material" can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, 99%, 100%, etc.

[0230] In some embodiments, the electronegative doping element includes nitrogen, and the electronegative doping form of the doped carbon includes at least one of pyridine nitrogen type and pyrrole nitrogen type.

[0231] By controlling the doping form of electronegative doping elements in doped carbon, including at least one of pyridine nitrogen and pyrrole nitrogen, and leveraging the higher reactivity of the doped N atoms in pyridine nitrogen and pyrrole nitrogen, it is beneficial to improve the adsorption of foreign atoms in the first negative electrode active material, reduce lithium-ion mass transfer resistance, and enhance the wettability of the electrolyte to the first negative electrode active layer, thereby improving the wettability to the second negative electrode active layer and ultimately improving the fast-charging performance of the battery. Furthermore, it also helps to reduce the difficulty of the doping process.

[0232] In some embodiments, the electronegatively coated active material satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0233] (tb1) The average thickness of the coating layer is 1nm to 500nm, optionally 100nm to 500nm, and further optionally 100nm to 200nm;

[0234] (tb2) The thickness of at least a portion of the coating layer is 1 nm to 1000 nm, optionally 100 nm to 1000 nm, and further optionally 100 nm to 200 nm;

[0235] (tb3) The mass percentage of electronegative dopant elements in doped carbon is 0.1% to 0.6%, optionally 0.2% to 0.6%, and further optionally 0.2% to 0.4%;

[0236] (tb4) The mass percentage of electronegative dopant elements in the coating layer is 0.1% to 0.6%, optionally 0.2% to 0.6%, and further optionally 0.2% to 0.4%;

[0237] (tb5) The mass percentage of the coating layer in the electronegative coating active material is 0.2% to 5%, and can be selected as 0.5% to 3%;

[0238] (tb6) The average thickness of the coating layer and the D of the first negative electrode active material v The ratio of 50 is 0.5% to 12.5%, and can be selected as 1% to 10%;

[0239] (tb7) The mass percentage of doped carbon in the coating layer is 80% to 100%, and can be selected as 90% to 100%;

[0240] (tb8) The sum of the mass percentages of soft carbon and hard carbon in the carbon matrix is ​​80% to 100%, optionally 90% to 100%; optionally, the mass percentage of soft carbon in the carbon matrix is ​​80% to 100%, further optionally 90% to 100%, or the mass percentage of hard carbon in the carbon matrix is ​​80% to 100%, further optionally 90% to 100%;

[0241] (tb9) The carbon matrix is ​​soft carbon.

[0242] Non-limitingly, the average thickness of the coating layer in the electronegative coated active material can be 1 nm to 500 nm, preferably 100 nm to 500 nm, further preferably 100 nm to 200 nm, and can also be any of the following thicknesses or a range selected from any two of the following thicknesses: 5 nm, 10 nm, 20 nm, 40 nm, 50 nm, 60 nm, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm, 150 nm, 160 nm, 180 nm, 200 nm, 250 nm, 300 nm, 400 nm, 500 nm, etc.

[0243] In a non-limiting manner, in the electronegative coated active material, the thickness of at least a portion of the coating layer can be 1 nm to 1000 nm, optionally 100 nm to 1000 nm, further optionally 100 nm to 200 nm, and can also be any of the following thicknesses or a range selected from any two of the following thicknesses: 5 nm, 10 nm, 20 nm, 40 nm, 50 nm, 60 nm, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm, 150 nm, 160 nm, 180 nm, 200 nm, 250 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, etc.

[0244] Non-limitingly, in the electronegative coated active material, the mass percentage of the electronegative dopant element in the doped carbon can be 0.1% to 0.6%, optionally 0.2% to 0.6%, further optionally 0.2% to 0.4%, and can also be any of the following percentages or a range selected from any two of the following percentages: 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, etc.

[0245] Non-limitingly, in the electronegative coated active material, the mass percentage of electronegative dopant elements in the coating layer can be 0.1% to 0.6%, optionally 0.2% to 0.6%, further optionally 0.2% to 0.4%, and can also be any of the following percentages or a range selected from any two of the following percentages: 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, etc.

[0246] Non-limitingly, the mass percentage of the coating layer in the electronegative coated active material can be 0.2% to 5%, optionally 0.5% to 3%, or any of the following percentages or a range selected from any two of the following percentages: 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.25%, 1.5%, 1.6%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0247] Non-limiting, the average thickness of the coating layer in the electronegatively coated active material is related to the D of the first negative electrode active material. v The ratio of 50 can be 0.5% to 12.5%, can be selected from 1% to 10%, can be further selected from 2% to 8%, and can also be any of the following percentages or a range composed of any two of the following percentages: 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.25%, 1.5%, 1.6%, 1.8%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 12.5%, etc.

[0248] Non-limitingly, the mass percentage of doped carbon in the coating layer can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 94%, 95%, 96%, 98%, 100%, etc.

[0249] Non-limitingly, the sum of the mass percentages of soft carbon and hard carbon in the carbon matrix can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 94%, 95%, 96%, 98%, 100%, etc.

[0250] In some embodiments, the mass percentage of soft carbon in the carbon matrix can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 94%, 95%, 96%, 98%, 100%, etc.

[0251] In other embodiments, the mass percentage of hard carbon in the carbon matrix can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 94%, 95%, 96%, 98%, 100%, etc.

[0252] Non-limitingly, the sum of the mass percentages of doped soft carbon and doped hard carbon in the doped carbon or coating layer can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 94%, 95%, 96%, 98%, 100%, etc.

[0253] In some embodiments, the mass percentage of doped soft carbon in the doped carbon or coating layer can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 94%, 95%, 96%, 98%, 100%, etc.

[0254] In other embodiments, the mass percentage of doped hard carbon in the doped carbon or coating layer can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 94%, 95%, 96%, 98%, 100%, etc.

[0255] By comparing the average thickness of the coating layer, the local thickness of the coating layer, the mass percentage of electronegative dopant elements in the doped carbon, the mass percentage of electronegative dopant elements in the coating layer, and the average thickness of the coating layer with the D of the first negative electrode active material... v Controlling one or more of the following parameters within the aforementioned ranges—the ratio of 50, the mass percentage of doped carbon in the coating layer, the sum of the mass percentages of soft carbon and hard carbon in the carbon matrix, and the mass percentages of doped soft carbon and doped hard carbon in the doped carbon or coating layer, the mass percentage of doped soft carbon in the doped carbon or coating layer, and the mass percentage of doped hard carbon in the doped carbon or coating layer—is beneficial for controlling the content of electronegative dopants within a suitable range. This is beneficial for improving the fast-charging performance of the battery based on the aforementioned multiple effects, and also for reducing the probability of electronegative dopants participating in side reactions, thus contributing to good battery cycle performance. However, this approach is not limited to the aforementioned theories.

[0256] In some embodiments, the electronegative coated active material accounts for 20% to 100% of the first negative electrode active material, optionally 40% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, etc. By controlling the proportion of the electronegative coated active material in the first negative electrode active material within the aforementioned range, it is beneficial to better improve battery dynamics based on the multiple functions of the electronegative coated active material and enhance the battery's fast-charging capability.

[0257] Electronegative coated active materials can be identified by combining detection and analysis methods such as scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS), and then the proportion of electronegative coated active materials in the first negative electrode active material can be statistically obtained.

[0258] In some embodiments, the electronegative coating active material accounts for 20% to 80% of the first negative electrode active material, and is further optionally 40% to 80%. It can also be any of the following percentages or a range selected from any two of the following percentages: 20%, 30%, 40%, 50%, 60%, 70%, 80%, etc. By controlling the proportion of the electronegative coating active material in the first negative electrode active material within the aforementioned range, it is beneficial to improve the battery's fast-charging capability while also taking into account manufacturing costs.

[0259] In some embodiments, the first negative electrode active material includes secondary particles; further, the first negative electrode active material may optionally include non-agglomerated primary particles. In some embodiments, the amount of secondary particles in the first negative electrode active material is greater than or equal to 20%, optionally 30% to 80%, further optionally 30% to 60%, and may also be any of the following percentages or a range selected from any two of the following percentages: 20%, 30%, 40%, 50%, 60%, 70%, 80%, etc.

[0260] Introducing secondary particles into the first negative electrode active material helps to increase the surface roughness of the active particles in the first negative electrode active material, thereby increasing the sites for lithium ion adsorption. This, in turn, helps to improve the wettability of the electrolyte, further improving the wettability of the electrolyte to the first negative electrode active layer, and also improving the wettability to the second negative electrode active layer, thus better improving the fast charging performance of the battery.

[0261] In this application, unless otherwise specified, "primary particles" in electrode active materials refer to the basic particle unit in the electrode active materials. It is understood that primary particles exist in electrode active materials. Taking the negative electrode as an example, in the negative electrode active material, primary particles can exist in a non-agglomerated state or can form aggregates. Non-agglomerated primary particles can be called "non-agglomerated primary particles," and aggregates of primary particles can be called "secondary particles." For those skilled in the art, non-agglomerated primary particles and secondary particles can be identified based on the particle morphology image of the electrode active material. Taking the negative electrode active material as an example, the particle morphology image of the electrode active material can be obtained using the testing results of a scanning electron microscope (e.g., ZEISS Sigma 300), and the sample to be tested can be obtained by laying the electrode active material and adhering it to conductive adhesive.

[0262] In some embodiments, the electronegatively coated active material includes electronegatively coated secondary particles, wherein the negative electrode active body in the electronegatively coated secondary particles is a secondary particle.

[0263] In this application, "electronegatively coated secondary particles" refers to an electronegatively coated active material in which the negative electrode active body is a secondary particle. It is understood that electronegatively coated secondary particles include a negative electrode active body and a coating layer located on at least a portion of the surface of the negative electrode active body, and the negative electrode active body is a secondary particle. The definition of the coating layer can be found in the section on coating layers in electronegatively coated active materials. Electronegatively coated secondary particles also fall under the category of secondary particles.

[0264] Introducing electronegative coated secondary particles into the first negative electrode active material helps to increase the surface roughness of the active particles in the electronegative coated active material, thereby increasing the sites for lithium ion adsorption. This, in turn, helps to improve the wettability of the electrolyte, further improving the wettability of the electrolyte to the first negative electrode active layer, and also further improving the wettability to the second negative electrode active layer, thus better improving the fast charging performance of the battery.

[0265] Non-limitingly, the proportion of electronegatively coated secondary particles in the first negative electrode active material can be greater than or equal to 20%, optionally 20% to 100%, optionally 40% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, etc. By controlling the proportion of electronegatively coated secondary particles in the first negative electrode active material within the aforementioned range, it is beneficial to better improve the fast-charging performance of the battery.

[0266] In some embodiments, the proportion of electronegatively coated secondary particles in the first negative electrode active material can be 20% to 80%, optionally 40% to 80%, or any of the following percentages or a range selected from any two of the following percentages: 20%, 30%, 40%, 50%, 60%, 70%, 80%, etc. By controlling the proportion of electronegatively coated secondary particles in the first negative electrode active material within the aforementioned range, it is beneficial to improve the fast-charging performance of the battery and also to balance manufacturing costs.

[0267] In some embodiments, the negative electrode active body in the electronegatively coated active material includes one or more of carbon-based and silicon-based active materials.

[0268] It is understandable that the negative electrode active body includes electronegatively coated active materials of carbon-based active substances, which belong to carbon-based materials, and the negative electrode active body includes electronegatively coated active materials of silicon-based active substances, which belong to silicon-based materials.

[0269] Without limitation, carbon-based active materials may include one or more of artificial graphite, natural graphite, soft carbon, and hard carbon.

[0270] Without limitation, carbon-based active materials may include graphite, and further, graphite may include one or more of artificial graphite and natural graphite.

[0271] Without limitation, silicon-based active materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0272] In some embodiments, the negative electrode active material comprises a carbon-based active substance. Further, the negative electrode active material comprises one or more of graphite, soft carbon, and hard carbon, and may further comprise one or more of artificial graphite, natural graphite, soft carbon, and hard carbon. Optionally, the electronegatively coated active material comprises electronegatively coated secondary particles.

[0273] Non-limitingly, the negative electrode active body in the electronegatively coated active material may include one or more of carbon-based and silicon-based active materials, in which case the first negative electrode active material includes one or more of carbon-based and silicon-based materials. The electronegatively coated active material may include electronegatively coated secondary particles. When the negative electrode active body includes a carbon-based active material, it is beneficial to give the first negative electrode active material better conductivity, which is beneficial to reducing internal resistance and providing better fast charging capability. When the negative electrode active body includes a silicon-based active material, it is beneficial to utilize the high specific capacity of silicon-based active materials to increase the amount of lithium intercalation per unit time, which is beneficial to improving fast charging speed, and also beneficial to improving energy density.

[0274] In some embodiments, the first negative electrode active material includes one or more of carbon-based and silicon-based materials.

[0275] In some embodiments, the first negative electrode active material includes a carbon-based material. Non-limitingly, the carbon-based material may constitute 20% to 100% of the mass of the first negative electrode active material, optionally 20% to 80%, further optionally 40% to 80%, or any of the following percentages or a range selected from any two of the following percentages: 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, etc.

[0276] By controlling the mass ratio of carbon-based materials in the first negative electrode active material within the aforementioned range, it is beneficial to better control the volume expansion of the negative electrode during fast charging, improve the structural stability of the first negative electrode active material during charge-discharge cycles, and also take into account the energy density of the negative electrode and the battery.

[0277] In some embodiments, the negative electrode active body in the electronegatively coated active material includes graphite, and further, the graphite may include one or more of artificial graphite and natural graphite.

[0278] In some embodiments, the negative electrode active body in the electronegatively coated active material includes graphite and soft carbon. Further, the graphite may include artificial graphite, in which case the negative electrode active body includes artificial graphite and soft carbon. Non-limitingly, the mass percentage of soft carbon relative to graphite can be 1% to 10%, optionally 1% to 5%, or any of the following percentages or a range selected from any two of the following percentages: 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, etc.

[0279] In some embodiments, the negative electrode active body in the electronegatively coated active material includes graphite and hard carbon. Further, the graphite may include artificial graphite, in which case the negative electrode active body includes artificial graphite and hard carbon. Non-limitingly, the mass percentage of hard carbon relative to graphite can be 1% to 10%, optionally 1% to 5%, or any of the following percentages or a range selected from any two of the following percentages: 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, etc.

[0280] In some embodiments, the negative electrode active body includes an electronegatively coated active material of graphite in the first negative electrode active material, which may account for 20% to 100% by mass, optionally 20% to 80%, further optionally 40% to 80%, or any of the following percentages or a range selected from any two of the following percentages: 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, etc.

[0281] In some embodiments, the negative electrode active body includes an electronegatively coated active material of soft carbon in the first negative electrode active material at a mass ratio of 0% to 10%, preferably 1% to 10%, further preferably 1% to 5%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, etc.

[0282] In some embodiments, the negative electrode active body includes an electronegatively coated active material of hard carbon in the first negative electrode active material at a mass ratio of 0% to 10%, preferably 1% to 10%, further preferably 1% to 5%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, etc.

[0283] In some implementations, the lithium-ion secondary battery satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0284] (td1) The negative electrode active body in the electronegative coated active material includes graphite;

[0285] (td2) The electronegatively coated active material includes electronegatively coated secondary particulate graphite, the negative electrode active body in the electronegatively coated secondary particulate graphite includes secondary particulate graphite, and the electronegatively coated secondary particulate graphite accounts for 20% to 100% of the first negative electrode active material, optionally 40% to 100%, and further optionally 40% to 80%.

[0286] (td3) D of the first negative electrode active material v 50 is 8μm to 16μm, and can be selected as 10μm to 14μm;

[0287] (td4) The porosity of the first negative electrode active layer is 22% to 32%, and can be selected as 26% to 30%;

[0288] (td5) The ionic conductivity of the electrolyte is 13 mS / cm to 18 mS / cm at at least one temperature condition from 20°C to 35°C; optionally, the ionic conductivity of the electrolyte is 13 mS / cm to 18 mS / cm at 25°C.

[0289] The fast-charging performance of a lithium-ion secondary battery can be improved by making it satisfy one or more of the characteristics (td1), (td2), (td3), (td4), and (td5).

[0290] In some embodiments, the negative electrode active body in the electronegatively coated active material includes graphite. In this case, the electronegatively coated active material includes electronegatively coated graphite. In some embodiments, the negative electrode active body in the electronegatively coated active material is graphite, i.e., the graphite body.

[0291] In this application, the “graphite body” is composed of graphite.

[0292] In this application, an electronegatively coated active material whose negative electrode active body is graphite can be referred to as "electronegatively coated graphite"; electronegatively coated graphite includes graphite and a coating layer located on at least a portion of the graphite surface. The definition of the coating layer in electronegatively coated graphite can be found in the section on coating layers in electronegatively coated active materials.

[0293] Non-limitingly, the proportion of electronegatively coated graphite in the first negative electrode active material can be 20% to 100%, optionally 40% to 100%, further optionally 40% to 80%, and can also be any of the following percentages or a range selected from any two of the following percentages: 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, etc.

[0294] Introducing graphite into the negative electrode active body of the electronegatively coated active material can improve the conductivity of the electronegatively coated active material, reduce internal resistance, and provide better fast charging capability.

[0295] In some embodiments, the electronegatively coated active material comprises electronegatively coated secondary particulate graphite. In this case, the negative electrode active body in the electronegatively coated active material comprises secondary particulate graphite. In some embodiments, the electronegatively coated active material is electronegatively coated secondary particulate graphite.

[0296] In this application, "secondary graphite" refers to an aggregate of primary graphite, and "primary graphite" is the basic graphite grain unit.

[0297] In this application, the electronegatively coated active material whose negative electrode active body is secondary particle graphite can be referred to as "electronegatively coated secondary particle graphite"; electronegatively coated secondary particle graphite includes secondary particle graphite and a coating layer located on at least a portion of the surface of the secondary particle graphite. The definition of the coating layer in electronegatively coated secondary particle graphite can be found in the section on coating layers in electronegatively coated active materials.

[0298] Non-limitingly, the proportion of electronegatively coated secondary particulate graphite in the first negative electrode active material can be 20% to 100%, optionally 40% to 100%, further optionally 40% to 80%, and can also be any of the following percentages or a range selected from any two of the following percentages: 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, etc.

[0299] Introducing electronegatively coated secondary graphite particles into electronegatively coated active materials can help to combine the advantages of both electronegatively coated secondary particles and graphite bulk.

[0300] Non-limiting, the first negative electrode active material may include soft carbon-coated secondary particulate graphite material (in this case, the electronegative coating active material includes soft carbon-coated secondary particulate graphite material); the soft carbon-coated secondary particulate graphite material includes secondary particulate graphite and a coating layer located on at least a portion of the surface of the secondary particulate graphite, the coating layer including doped soft carbon. Doped soft carbon is doped carbon with a soft carbon matrix. Non-limiting, the proportion of soft carbon-coated secondary particulate graphite material in the first negative electrode active material may be 20% to 100%, optionally 40% to 100%, further optionally 40% to 80%, and may also be any of the following percentages or a range selected from any two of the following percentages: 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, etc.

[0301] Non-limiting, the first negative electrode active material may include hard carbon-coated secondary particulate graphite material (in this case, the electronegative coating active material includes hard carbon-coated secondary particulate graphite material); the hard carbon-coated secondary particulate graphite material includes secondary particulate graphite and a coating layer located on at least a portion of the surface of the secondary particulate graphite, the coating layer including doped hard carbon. Doped hard carbon is doped carbon with a hard carbon matrix. Non-limiting, the proportion of hard carbon-coated secondary particulate graphite material in the first negative electrode active material may be 20% to 100%, optionally 40% to 100%, further optionally 40% to 80%, and may also be any of the following percentages or a range selected from any two of the following percentages: 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, etc.

[0302] In some embodiments, the D of the first negative electrode active material v 50 is 8μm to 16μm, can be selected from 10μm to 14μm, and can also be any of the following values ​​or a range composed of any two of the following values: 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, etc.

[0303] Unless otherwise stated in this application, D v 50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50% in the material. This parameter indicates that the particle size of 50% of the material's volume is less than or equal to D. v 50, and particles accounting for 50% of the material volume have a particle size greater than D. v 50. Those skilled in the art will understand D v The meaning of 50 can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd. (UK) or the LS-909 laser particle size analyzer (Omega). The standard procedure for determining the material's D value can be referenced in GB / T19077-2016 / ISO 13320:2009. v 50 is tested. The detailed test procedure includes: taking an appropriate amount of the sample to be tested, adding solvent (the solvent can be deionized water, and the sample concentration can be controlled at 8%~12% opacity), sonicating for 5 minutes (53KHz / 120W) to fully disperse the sample, and then measuring the sample according to GB / T19077-2016 / ISO 13320:2009 standard. After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. Under the irradiation of the laser beam, the particle size distribution characteristics can be obtained by receiving and measuring the energy distribution of the scattered light. Based on the test data, a particle size volume distribution map is plotted, and D is obtained from the distribution map. v50. To avoid agglomeration during the drying process affecting particle size testing, a dispersion test was performed on the washed and moistened sample. The D values ​​of the first and second negative electrode active materials were... v All 50 can be tested using the methods described above.

[0304] By using a negative electrode active material D v Controlling the concentration of 50% within the aforementioned range helps to better control the degree of particle accumulation in the first negative electrode active layer, better control the porosity between particles, provide better lithium-ion transport channels, and better improve battery dynamics and fast charging performance.

[0305] In some embodiments, the porosity of the negative electrode active material layer is 20% to 32%, optionally 22% to 32%, further optionally 26% to 30%, and may also be any of the following percentages or a range selected from any two of the following percentages: 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 32%, etc.

[0306] By controlling the porosity of the negative electrode active material layer within the aforementioned range, it is beneficial to provide a better lithium-ion transport channel, allowing the negative electrode active material to be better wetted by the electrolyte, thereby better leveraging the role of the electronegative dopant elements in the electronegative coating active material in adsorbing foreign atoms, and better promoting the embedding of lithium ions into the negative electrode active material.

[0307] In some embodiments, the porosity of the first negative electrode active layer in the negative electrode sheet of the lithium-ion secondary battery or in the negative electrode sheet obtained after cold pressing is 22% to 32%, optionally 26% to 30%, and may also be any of the following percentages or a range selected from any two of the following percentages: 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 32%, etc.

[0308] In this application, "porosity" refers to the percentage of pore volume to total volume in a material, and can be expressed as a percentage. The "porosity" of the second negative electrode active layer refers to the percentage of pore volume in the second negative electrode active layer relative to the total volume of the second negative electrode active layer. The "porosity" of the first negative electrode active layer refers to the percentage of pore volume in the first negative electrode active layer relative to the total volume of the first negative electrode active layer. The "porosity" of the negative electrode active material layer of the negative electrode sheet refers to the percentage of pore volume in the negative electrode active material layer relative to the total volume of the negative electrode active material layer, and can also be denoted as "porosity of the negative electrode sheet".

[0309] By controlling the porosity of the first negative electrode active layer within the aforementioned range, it is beneficial to provide better lithium-ion transport channels, allowing the first negative electrode active material in the first negative electrode active layer to be better wetted by the electrolyte. This enables the electronegative doping elements in the electronegative coating active material to better adsorb foreign atoms, better combine with solvated lithium ions, and better promote lithium-ion insertion into the first negative electrode active material. When the porosity of the second negative electrode active layer is controlled within the aforementioned range, the improvement effect of the electronegative doping elements on the battery's fast-charging performance is even more significant.

[0310] In this application, the porosity (δ) of the negative electrode active material layer N The porosity (δ) of the negative electrode active material layer can be determined using instruments and methods known in the art. For example, GB / T 24586-2009 can be referenced for measurement using the gas displacement method. The porosity (δ) of the negative electrode active material layer can be calculated using the following formula. N ):

[0311] Porosity δ N =(V N2 -V N1 ) / V N2 ×100%, where V N2 =S N ×D N ×n.

[0312] The test sample consists of n negative electrode discs; S N The area of ​​the negative electrode active material layer in a single negative electrode disc, in cm². 2 ;D N The thickness of the negative electrode active material layer in a single negative electrode disc, in cm; V N1 The true volume of the test sample, in cm 3 V N2 The apparent volume of the test sample, in cm³. 3 .

[0313] Pretreatment: The negative electrode sheets are punched. In a drying room, ≥20 discs with good appearance and no powder shedding from the edges are selected using tweezers and placed into a sample cup. The test sample consists of n negative electrode disc discs. Record the number of discs n and calculate the apparent volume V of the test sample. N2 .

[0314] True volume V N1 Test: The sample cup containing the test sample is placed in a true density analyzer. The test system is sealed, and helium gas is introduced according to the procedure. By detecting the gas pressure in the sample chamber and expansion chamber, and then calculating the true volume according to Bohr's law (PV = nRT), the porosity of the test sample is obtained, which can be recorded as the porosity (δ) of the negative electrode active material layer. N ).

[0315] The above method can be used to test not only the negative electrode sheet removed after disassembling the battery cell, but also the negative electrode sheet obtained after cold pressing.

[0316] For example, the porosity (δ) of the entire negative electrode active material layer can also be obtained by testing separately. N ) and the porosity (δ2) of the second negative electrode active layer, when δ N When the porosity is greater than δ², it can be considered that "the porosity of the first negative electrode active material layer is higher than that of the second negative electrode active layer". Furthermore, the total thickness D of the negative electrode active material layer can also be considered. N And the thickness D2 of the second negative electrode active layer, the thickness D1 of the first negative electrode active layer, and then according to formula D N ×δ N =D1×δ1+D2×δ2, the porosity (δ1) of the first negative electrode active layer is calculated.

[0317] For example, the porosity (δ2) of the second negative electrode active layer can be obtained by testing using the following method:

[0318] (1) Obtain a test sample including at least a portion of the second negative electrode active layer and excluding the first negative electrode active layer: Disassemble the battery cell, take the negative electrode sheet, and use a micrometer to measure the electrode sheet thickness L; take another negative electrode sheet, wipe off the negative electrode active material layer on both sides of the remaining empty current collector foil, and measure the thickness L0. The total thickness of the negative electrode active material layer on both sides of the negative electrode current collector is L-L0; scrape off the negative electrode active material layer on one surface of the negative electrode sheet to expose the negative electrode current collector surface, and scrape off the negative electrode material on the other surface until the electrode sheet thickness is L1 = L0 + Δd. Collect the powder of the Δd thickness portion of the negative electrode active material layer below the L1 thickness. The thickness of the second negative electrode active layer can be determined in advance based on the observation results of the electrode sheet cross-sectional morphology, thereby controlling that when the thickness is L1, the first negative electrode active layer has been completely removed, and the remaining negative electrode active material layer corresponds to part or all of the second negative electrode active layer. For example, Δd can be exemplarily 15μm, 20μm, etc. The sample to be tested retains only the second negative electrode active layer on one side of the negative electrode current collector.

[0319] (2) The porosity (δ2) of the second negative electrode active layer is obtained by testing the porosity of the sample to be tested by referring to the method for testing the porosity of the negative electrode sheet, and is recorded as the porosity of the second negative electrode active layer.

[0320] For example, the porosity of the negative electrode active material layer in the negative electrode sheet can also be tested using the following method, and the porosity of the first negative electrode active layer and the second negative electrode active layer can also be tested and / or compared: Disassemble the battery cell and remove the negative electrode sheet; punch the negative electrode sheet into small discs, and use the nanoscale spatial dynamic resolution and layer-by-layer cutting technique of FIB-SEM (Focused Electron Beam Electron Microscopy-Scanning Electron Microscopy) to reconstruct the three-dimensional structure of the sample; use energy dispersive spectroscopy (EDS) to analyze the distribution and proportion of each element, and use software to quantitatively analyze the porosity of the first negative electrode active layer, the second negative electrode active layer, and the overall negative electrode active material layer. The FEI Scios 2HiVac instrument can be used for testing.

[0321] In some embodiments, at at least one temperature condition from 20°C to 35°C, the ionic conductivity of the electrolyte can be from 13 mS / cm to 18 mS / cm, or it can be any of the following values ​​or a range selected from any two of the following values: 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm, etc. The test temperature can be 25°C. Non-limitingly, at 25°C, the ionic conductivity of the electrolyte can be from 13 mS / cm to 18 mS / cm, or it can be any of the following values ​​or a range selected from any two of the following values: 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm, etc.

[0322] In this application, unless otherwise specified, the term "ionic conductivity" of the electrolyte has a well-known meaning in the art and can be tested and analyzed using existing methods in the field. Ionic conductivity can be obtained using a conductivity meter, such as the DDSJ-318 conductivity meter. The method described in HG-T 4067-2015 can be used for testing. The test temperature can be 25±0.1℃. Non-limitingly, a method including the following steps can be used for testing:

[0323] Pretreatment: Take the standard liquid and keep it at a constant temperature of 25℃ (deviation ±0.1℃), and take the test liquid and keep it at a constant temperature of the test temperature (deviation ±0.1℃);

[0324] Test: The instrument was calibrated using two standard solutions at 25℃. After calibration and cleaning the electrode, the test sample electrode was vertically placed into the liquid to be tested. Click "Start Test" and record the test results after the data stabilized for more than 10 seconds.

[0325] By controlling the ionic conductivity of the electrolyte within the aforementioned range, it is beneficial to promote the rapid transport of lithium ions, which in turn helps to improve battery dynamics and fast-charging performance.

[0326] The ionic conductivity of the electrolyte in some embodiments can be found in the context of this application. Electrolytes with high conductivity can be obtained by selecting solvents with low viscosity characteristics, but are not limited thereto.

[0327] In a non-limiting sense, the electrolyte includes non-aqueous solvents, which include low-viscosity solvents. Low-viscosity solvents may include one or more of ethyl acetate, methyl acetate, dimethyl carbonate, ethyl methyl carbonate, etc., and solvents whose viscosity at 25°C is less than or equal to that of at least one of the aforementioned reagents.

[0328] Unless otherwise specified in this application, the viscosity of solvents or electrolytes can be tested using conventional methods in the art, and can be determined using instruments and methods known in the art. For example, it can be measured according to the national standard GB / T10247-2008 "Methods for Viscosity Measurement", and can be performed based on the rotational viscometer in Appendix D of the national standard GB / T10247-2008. Non-limitingly, the viscosity of solvents or electrolytes can be tested by placing a certain mass of the sample to be tested in a sample container and using a Brookfield DV2TLV rotational viscometer.

[0329] In some embodiments, the first negative electrode active material is electronegatively coated secondary particles, in which case the negative electrode active body of the first negative electrode active material is secondary particles; in some other embodiments, the negative electrode active body of the first negative electrode active material is graphite, that is, the negative electrode active body of the first negative electrode active material is secondary particle graphite, in which case the first negative electrode active material is electronegatively coated secondary particle graphite, which is both electronegatively coated graphite and electronegatively coated secondary particles. The structure and composition of the coating layer can be found in the context of this application.

[0330] In some embodiments, the first negative electrode active material is electronegatively coated graphite, in which case the negative electrode active body of the first negative electrode active material is graphite; in some embodiments, the negative electrode active body of the first negative electrode active material is secondary particulate graphite; further, the negative electrode active body of the first negative electrode active material is artificial graphite and is secondary particulate graphite. The structure and composition of the coating layer can be found in the context of this application.

[0331] In some embodiments, the coating layer is doped soft carbon, and the carbon matrix is ​​soft carbon; in some other embodiments, the doped soft carbon includes the electronegative dopant element N. The doping method can be found in the context of this application.

[0332] In some embodiments, the negative electrode active body of the first negative electrode active material is secondary particulate graphite; in some embodiments, the D of the first negative electrode active material... v 50 can be referred to in the context of this application, for example, 12 μm.

[0333] In some embodiments, the negative electrode active material layer further includes a second negative electrode active layer, which is located between the negative electrode current collector and the first negative electrode active layer; in some embodiments, the second negative electrode active material is secondary particulate graphite, and more specifically, the D of the second negative electrode active material... v 50 can be referred to in the context of this application, for example, 15 μm.

[0334] In some embodiments, the D of the first negative electrode active material v 50 is 8μm~16μm (optional 10μm~14μm), the D of the second negative electrode active material v 50 is 10μm to 20μm (optionally 13μm to 17μm), and further reference can be made to the context of this application; in some embodiments, the D of the second negative electrode active material v 50 higher than the D of the first negative electrode active material v 50.

[0335] In some embodiments, the negative electrode active material layer further includes a second negative electrode active layer, which is located between the negative electrode current collector and the first negative electrode active layer.

[0336] Furthermore, lithium-ion secondary batteries satisfy one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0337] (t1) The porosity of the first negative electrode active layer is higher than that of the second negative electrode active layer;

[0338] (t2) The ratio of the difference in compaction density between the second negative electrode active layer and the first negative electrode active layer to the compaction density of the negative electrode sheet is denoted as R. PΔ R PΔ The range is 0 to 2, and can be selected as 0 to 0.834. Further optionally, 0 <R PΔ ≤0.834;

[0339] (t3) The charging rate of the first negative electrode active layer is higher than that of the second negative electrode active layer; optionally, the charging rate of the first negative electrode active layer is higher than that of the second negative electrode active layer.

[0340] In some embodiments, the porosity of the first negative electrode active layer is higher than that of the second negative electrode active layer.

[0341] By controlling the porosity of the first negative electrode active layer to be higher than that of the second negative electrode active layer, it is beneficial to balance the fast charging performance and energy density of the battery. The high porosity of the first negative electrode active layer can be used to promote the rapid transport of lithium ions, while the low porosity of the second negative electrode active layer can be used to improve the energy density of the negative electrode.

[0342] In this application, in a lithium-ion secondary battery, the ratio of the difference in compaction density between the second negative electrode active layer and the first negative electrode active layer to the compaction density of the negative electrode sheet can be denoted as R. PΔ .

[0343] In some implementations, R PΔ The range is 0 to 2, and can be selected as 0 to 0.834. Further optionally, 0 <R PΔ ≤0.834, and can also be any of the following values ​​or a range selected from any two of the following values: 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.1, 0.11, 0.12, 0.125, 0.13, 0.133, 0.134, 0.135, 0.14, 0.1 45, 0.15, 0.155, 0.16, 0.17, 0.175, 0.18, 0.19, 0.2, 0.21, 0.22, 0.225, 0.23, 0.235, 0.24, 0.245, 0.25, 0.26, 0.265, 0.266, 0.27, 0.275, 0.28, 0.285, 0.286, 0.29, 0.3, 0.33, 0.34 1 / 3, 0.35, 0.36, 0.38, 0.4, 0.417, 0.42, 0.45, 0.48, 0.49, 0.5, 0.55, 0.6, 0.61, 0.62, 0.625, 0.66, 2 / 3, 0.67, 0.672, 0.673, 0.674, 0.675, 0.68, 0.7, 0.72, 0.74, 0.75, 0.76, 0.78, 0 0.80, 0.82, 0.83, 0.833, 5 / 6, 0.834, 0.85, 0.86, 0.87, 0.88, 0.90, 0.95, 1, 1.05, 1.08, 1.09, 1.1, 1.12, 1.15, 1.2, 1.3, 1.4, 1.5, 1.6, 5 / 3, 1.67, 1.8, 1.9, 1.95, 1.96, 1.98, 1.99, 2, etc.

[0344] In some implementations, R PΔ Greater than 0.

[0345] Without limitation, R PΔIt can also be selected from any of the following ranges: 0 <R PΔ ≤2, 0 <R PΔ ≤1.67, 0 <R PΔ ≤5 / 3、0 <R PΔ ≤1.2、0 <R PΔ ≤1.1、0 <R PΔ ≤1, 0 <R PΔ ≤0.834, 0 <R PΔ ≤5 / 6、0 <R PΔ ≤0.625, 0 <R PΔ ≤0.42, 0~1.67, 0 to 5 / 3, 0~1.2, 0~1.1, 0~1, 0 to 5 / 6, 0~0.625, 0~0.42, etc.

[0346] The ratio of the difference in compaction density between the second negative electrode active layer and the first negative electrode active layer to the compaction density of the negative electrode sheet (R) is used to measure the density difference between the second negative electrode active layer and the first negative electrode active layer. PΔ Controlling the density within the aforementioned range helps to provide a better lithium-ion transport channel for the particle stacking degree of the first negative electrode active layer, thereby improving battery dynamics and fast charging performance. In addition, the second negative electrode active layer can be used to provide a higher energy density, which helps to balance battery fast charging performance and energy density.

[0347] Compared to the negative electrode sheet obtained after cold pressing, the volume of the negative electrode sheet in a lithium-ion secondary battery will have a certain rebound, resulting in a lower compaction density of the negative electrode sheet in a lithium-ion secondary battery compared to the negative electrode sheet obtained after cold pressing.

[0348] In this application, the ratio of the difference in compaction density between the second negative electrode active layer and the first negative electrode active layer to the compaction density of the negative electrode sheet obtained after cold pressing can be denoted as R. PΔ0 R PΔ0 With R PΔ The test values ​​are similar. When the volume expansion rates of the first and second negative electrode active layers are equal, R PΔ0 With R PΔ The values ​​are theoretically equal.

[0349] In this application, unless otherwise stated, "negative electrode sheet obtained after cold pressing" refers to the state of the negative electrode sheet obtained after cold pressing immediately after the cold pressing is completed. It can be considered that in this state, no or almost no rebound of the electrode sheet volume has occurred.

[0350] In some embodiments, the compaction density of the first negative electrode active layer in the negative electrode sheet obtained after cold pressing is 1.40 g / cm³. 3 ~1.60g / cm 3 The compaction density of the second negative electrode active layer is 1.65 g / cm³.3 ~1.90g / cm 3 .

[0351] In some embodiments, in a lithium-ion secondary battery, the difference between the compaction density of the second negative electrode active layer and the compaction density of the first negative electrode active layer (which can be denoted as P) Δ ) is 0g / cm 3 ~0.5g / cm 3 0g / cm can be selected 3 ~0.48g / cm 3 Further options include 0.04 g / cm³. 3 ~0.48g / cm 3 It can also be any of the following values ​​or a range consisting of any two of the following values: 0 g / cm³ 3 0.01g / cm 3 0.02g / cm 3 0.04g / cm 3 0.05g / cm 3 0.06g / cm 3 0.08g / cm 3 0.1g / cm 3 0.12g / cm 3 0.15g / cm 3 0.16g / cm 3 0.18g / cm 3 0.2g / cm 3 0.22g / cm 3 0.24g / cm 3 0.25g / cm 3 0.3g / cm 3 0.35g / cm 3 0.4g / cm 3 0.45g / cm 3 0.48g / cm 3 0.5g / cm 3 wait.

[0352] In some embodiments, the rate of charge of the first negative electrode active layer is higher than that of the second negative electrode active layer; alternatively, the rate of charge of the first negative electrode active layer is higher than that of the second negative electrode active layer.

[0353] In this application, the "rate" of the first negative electrode active layer and the second negative electrode active layer is a parameter reflecting the charging and discharging capability, and the "charging rate" is a parameter reflecting the charging capability. The higher the charging rate, the better the fast charging performance.

[0354] The first and second active layer electrodes can be prepared using the following method: Based on a negative electrode obtained through cold pressing or dismantling a battery cell, the first negative electrode material is extracted from the first negative electrode active layer, and the second negative electrode material is extracted from the second negative electrode active layer. These are then resuspended in deionized water to form uniform slurries, denoted as the first resuspension slurry and the second resuspension slurry, respectively. The second resuspension slurry is coated onto one side of the copper foil of the negative electrode current collector, dried, and cold-pressed to obtain the second active layer electrode. Conversely, the first resuspension slurry is coated onto one side of the copper foil of the negative electrode current collector, dried, and cold-pressed to obtain the first active layer electrode. The difference between the first and second resuspension slurries lies only in the difference between the first and second negative electrode materials; the coating weight, drying, and cold-pressing parameters are the same. The first and second active layer electrodes can be combined with lithium-ion cells to form coin cells, and rate testing can be performed. If the coin charge ratio of the electrode prepared with the first active layer is higher than that prepared with the second active layer, then it is considered that "the coin charge ratio of the first negative electrode active layer is higher than that of the second negative electrode active layer". Existing methods in the art for testing coin charge ratios can be used for this test.

[0355] Unless otherwise specified in this application, the rate capability or charging rate of the first negative electrode active layer and the second negative electrode active layer can be compared using the following method:

[0356] The first negative electrode active material, conductive agent conductive carbon black (Super P), stabilizer sodium carboxymethyl cellulose, and binder styrene-butadiene rubber (SBR) are dispersed in deionized water at a certain mass ratio (such as 97.3:0.7:1.2:0.8) to form the first slurry.

[0357] The second negative electrode active material, conductive agent conductive carbon black (Super P), stabilizer sodium carboxymethyl cellulose and binder SBR are dispersed in deionized water at a certain mass ratio (such as 96.4:1.0:1.2:1.4) to form a second slurry.

[0358] The first and second slurries are respectively coated onto one side of the copper foil current collector and dried in an oven for later use.

[0359] A lithium metal plate is used as the counter electrode; a polypropylene (PP) membrane is used as the separator; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a mixed solvent, and then lithium hexafluorophosphate (LiPF6) is dissolved in the above mixed solvent to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0360] All components were assembled into a CR2430 button cell in an argon-protected glove box. "CR" represents the international IEC designation for coin-type lithium manganese batteries, with a diameter of 24 mm and a thickness of 30 mm. After resting for 12 hours, the resulting button cell was discharged at a constant current of 0.05C to 0.005V, and then discharged again at a constant current of 10μA to 0.005V. After resting for 5 minutes, the resulting button cell was charged at a constant current of 0.1C to 2V, and then rested for 5 minutes; the charging capacity C0 was recorded. The battery was placed at a constant temperature of 25℃ for 2 hours, and charge-discharge tests were performed at rates of 1C0, 2C0, 3C0, 4C0, and 5C0 to determine the capacity retention rate. Under the same cycling conditions and number of cycles, a higher capacity retention rate indicates better rate performance, and the "rate" can be considered higher.

[0361] Furthermore, under the same charging conditions, charging to the same SOC (e.g., 80% SOC, with a cutoff current of 0.01C) at the same rate, the shorter the time taken, the better the charging rate performance, and the higher the "charging rate" can be considered.

[0362] By controlling the charging rate of the first negative electrode active layer to be higher than that of the second negative electrode active layer, it is beneficial to promote the faster insertion of lithium ions into the first negative electrode active layer, thereby improving the fast-charging performance of the battery.

[0363] In some embodiments, in the negative electrode sheet of a lithium-ion secondary battery or in the negative electrode sheet obtained after cold pressing, the negative electrode active material layer further includes a second negative electrode active layer, which is located between the negative electrode current collector and the first negative electrode active layer; the second negative electrode active layer includes a second negative electrode active material, and the negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0364] (te1) D of the second negative electrode active material v 50 is 10μm to 20μm, and can be selected as 13μm to 17μm;

[0365] (te2) D of the second negative electrode active material v 50 higher than the D of the first negative electrode active material v 50;

[0366] (te3) The compaction density of the second negative electrode active layer is higher than that of the first negative electrode active layer;

[0367] (te4) The compaction density of the powder in the second negative electrode active layer is higher than that in the first negative electrode active layer.

[0368] By enabling lithium-ion secondary batteries to meet one or more of the characteristics (te1), (te2), (te3), and (te4), it is beneficial to enable lithium-ion secondary batteries to have improved fast-charging performance while also meeting energy density requirements.

[0369] In some embodiments, the D of the second negative electrode active material v 50 represents 10μm to 20μm, can be selected from 13μm to 17μm, and can also be any of the following values ​​or a range composed of any two of the following values: 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, etc.

[0370] By using the D of the second negative electrode active material v Keeping 50 within the aforementioned range is beneficial for achieving a higher compaction density in the second negative electrode active layer, which in turn helps to improve the energy density.

[0371] In some embodiments, the D of the second negative electrode active material v 50 higher than the D of the first negative electrode active material v 50.

[0372] By controlling the D of the second negative electrode active material v 50 higher than the D of the first negative electrode active material v 50 is beneficial for achieving a higher compaction density in the second negative electrode active layer, which in turn helps to improve the energy density.

[0373] In some embodiments, the compaction density of the negative electrode sheet in the lithium-ion secondary battery is greater than or equal to 1.40 g / cm³. 3 The option is 1.40 g / cm³. 3 ~1.75g / cm 3 A further option is 1.50 g / cm³. 3 ~1.75g / cm 3 It can also be any of the following compaction densities or a range selected from any two of the following compaction densities: 1.40 g / cm³ 3 1.45g / cm 3 1.50g / cm 3 1.55g / cm 3 1.60g / cm 3 1.65g / cm 3 1.70g / cm 3 1.75g / cm 3 wait.

[0374] In this application, unless otherwise specified, the “compacted density” of the negative electrode sheet refers to the ratio of the mass to the volume of the negative electrode active material layer in the negative electrode sheet.

[0375] Non-limitingly, the compaction density of the negative electrode sheet in a lithium-ion secondary battery can be tested using the following method: disassemble the battery to obtain the negative electrode sheet, and punch the obtained negative electrode sheet into a piece with an area S0 (e.g., 1540.25 mm²). 2 The small circular disc is used to measure its mass M. B and thickness L B Take another negative electrode sheet from a different region, wipe off the surface negative electrode active material layer, and cut the remaining negative electrode current collector foil (which can be referred to as empty negative electrode current collector foil) into small circular pieces with an area of ​​S0. Weigh the mass M0 and thickness L0 of the empty negative electrode current collector foil. Then, the compaction density PD of the negative electrode sheet is... B =(M B -M0) / [S0×(L B Test multiple small discs (e.g., at least 10, or even at least 20) and take the average.

[0376] By controlling the compaction density of the negative electrode sheet in the lithium-ion secondary battery within the aforementioned range, the liquid phase impedance occupies a higher proportion of the impedance inside the negative electrode sheet. Quaternary ammonium salt compounds improve the liquid phase impedance by guiding lithium ions in the electrolyte. Therefore, controlling the compaction density of the negative electrode sheet within the aforementioned range is beneficial to better leveraging the role of quaternary ammonium salt compounds in improving the fast charging performance of the battery.

[0377] In some embodiments, the compaction density of the second negative electrode active layer is higher than that of the first negative electrode active layer.

[0378] In this application, unless otherwise specified, the "compacted density" of the second negative electrode active layer refers to the ratio of the mass to the volume of the second negative electrode active layer, and the "compacted density" of the first negative electrode active layer refers to the ratio of the mass to the volume of the first negative electrode active layer.

[0379] For example, the compaction density of the second negative electrode active layer in the negative electrode sheet of a lithium-ion secondary battery can be tested using the following method: disassemble the battery to obtain the negative electrode sheet, wipe off part of the negative electrode active material layer to obtain an electrode sample including at least a portion of the second negative electrode active layer but excluding the first negative electrode active layer, and punch it into an area S0 (e.g., 1540.25 mm²). 2 Small circular pieces of material are used. The mass M2 and thickness L2 of the electrode sample are measured respectively. The mass M0 and thickness L0 of the empty negative electrode current collector foil with the same area S0 are measured. Then the compaction density PD2 of the electrode sample is (M2-M0) / [S0×(L2-L0)], which can be used as the compaction density of the second negative electrode active layer.

[0380] When the compaction density PD of the negative electrode sheet B The compaction density PD2 of the second negative electrode active layer is lower than that of the first negative electrode active layer, so it can be considered that "the compaction density of the second negative electrode active layer is higher than that of the first negative electrode active layer".

[0381] By adjusting the compaction density of the second negative electrode active layer in a lithium-ion secondary battery to be higher than that of the first negative electrode active layer, it is beneficial to improve the energy density of the lithium-ion secondary battery.

[0382] In some embodiments, the powder compaction density of the second negative electrode active layer is higher than that of the first negative electrode active layer.

[0383] In this application, unless otherwise specified, the “powder compaction density” of the second negative electrode active layer refers to the powder compaction density of the powder material constituting the second negative electrode active layer, and the “powder compaction density” of the first negative electrode active layer refers to the powder compaction density of the powder material constituting the first negative electrode active layer.

[0384] In this application, "powder compaction density" has a well-known meaning in the art, referring to the ratio of mass to volume of a powder material after compaction under a certain pressure. The "powder compaction density" of the negative electrode material can be determined using instruments and methods known in the art. For example, it can be determined using an electronic pressure testing machine (e.g., UTM7305) according to standard GB / T24533-2009. An exemplary test method is as follows: Weigh out a mass M (e.g., 1g) of the material to be tested, and add a bottom area A (e.g., 1.327cm²). 2 In a mold, pressure is applied to a certain pressure P0 (e.g., 3-5 tons (3T-5T), such as 3T, 4T, 5T), and held for a certain time (e.g., 5T for 30s). Then, the pressure is released, and the pressure is maintained for a period of time (e.g., 10s). The compacted density of the negative electrode material powder under pressure P0 is then recorded and calculated. The aforementioned method can be used to compare or obtain the first negative electrode material powder in the first negative electrode active layer and the second negative electrode material powder in the second negative electrode active layer.

[0385] By controlling the powder compaction density of the second negative electrode active layer in the lithium-ion secondary battery to be higher than that of the first negative electrode active layer, it is beneficial to impart a higher compaction density to the second negative electrode active layer during the cold pressing process of the electrode sheet, so that the second negative electrode active layer in the lithium-ion secondary battery has a higher compaction density.

[0386] In some embodiments, the negative electrode active material layer further includes a second negative electrode active layer, which is located between the negative electrode current collector and the first negative electrode active layer; the negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0387] (tf1) On one side of the negative electrode current collector, the ratio of the areal density of the first negative electrode active layer to the areal density of the second negative electrode active layer is 2:8 to 6:4, and can be selected as 4:6 to 5:5.

[0388] (tf2) Taking the negative electrode current collector as a single side, the ratio of the thickness of the first negative electrode active layer to the sum of the thicknesses of the first and second negative electrode active layers is denoted as F. H Satisfying 20% ​​≤ F H ≤65%, optionally, 40% ≤F H ≤60%;

[0389] (tf3) The thickness of the first negative electrode active layer is 10 μm to 50 μm, and can be selected as 20 μm to 40 μm, depending on the single side of the negative electrode current collector.

[0390] In some embodiments, the ratio of the areal density of the second negative electrode active layer to the areal density of the first negative electrode active layer, measured on one side of the negative electrode current collector, is 2:8 to 6:4, optionally 4:6 to 5:5, or any of the following ratios or a range selected from any two of the following ratios: 2:8 (corresponding to 1:4, also corresponding to 0.25), 0.3, 1:3, 0.4, 0.45, 0.5, 0.55, 0.6, 2:3 (corresponding to 4:6), 0.67, 0.7, 0.75, 0.8, 0.75, 0.9, 0.95, 1, 1.05, 1.1, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5 (corresponding to 6:4), etc.

[0391] In this application, unless otherwise specified, "the areal density of the second negative electrode active layer, measured on one side of the negative electrode current collector," refers to the ratio of the mass of the second negative electrode active layer on one side of the negative electrode current collector to the area of ​​the second negative electrode active layer on that side. "The areal density of the first negative electrode active layer," refers to the ratio of the mass of the first negative electrode active layer on one side of the negative electrode current collector to the area of ​​the first negative electrode active layer on that side. The corresponding "area" is equal to the projected area of ​​each of the second and first negative electrode active layers along the electrode thickness direction. Numerically, measured on one side of the negative electrode current collector, the areal density of the second negative electrode active layer is equal to the product of the compacted density of the second negative electrode active layer and the thickness of the second negative electrode active layer. Mass and area data can be obtained by referring to the test method for the compacted density of the second negative electrode active layer. Numerically, measured on one side of the negative electrode current collector, the areal density of the first negative electrode active layer is equal to the product of the compacted density of the first negative electrode active layer and the thickness of the second negative electrode active layer. Mass and area data can be obtained by referring to the test method for the compacted density of the first negative electrode active layer.

[0392] By controlling the ratio of the areal density of the second negative electrode active layer to the areal density of the first negative electrode active layer within the aforementioned range, it is beneficial to better balance the battery's fast charging performance and energy density.

[0393] In this application, the "ratio of the thickness of the first negative electrode active layer to the sum of the thicknesses of the first negative electrode active layer and the second negative electrode active layer" is denoted as F. H .

[0394] In some implementations, 20% ≤ F is calculated on one side of the negative electrode current collector. H ≤65%, optionally, 40% ≤F H ≤60%. Without limitation, F H It can also be any of the following percentages or a range consisting of any two of the following percentages: 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, etc.

[0395] In some embodiments, in the negative electrode sheet of a lithium-ion secondary battery or in the negative electrode sheet obtained after cold pressing, the thickness of the first negative electrode active layer, measured on one side of the negative electrode current collector, can be 10 μm to 50 μm, optionally 20 μm to 40 μm, or any of the following values ​​or a range selected from any two of the following values: 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, etc.

[0396] By controlling the thickness of the first negative electrode active layer to satisfy one or more of the aforementioned characteristics (tf2) and (tf3), it is beneficial to better leverage the effect of electronegative doping elements in the coating layer on improving the battery's fast-charging performance while also considering the battery's energy density. As a non-limiting theory, controlling the thickness of the first negative electrode active layer to satisfy one or more of the aforementioned characteristics (tf2) and (tf3) can better leverage the effect of electronegative doping elements in the coating layer on improving electrolyte wettability, thereby improving the wettability of the electrolyte to the first negative electrode active layer, and consequently improving the wettability to the second negative electrode active layer, thus further enhancing the battery's fast-charging performance.

[0397] In some embodiments, the areal density of the negative electrode sheet is 5 mg / cm³, calculated on one side of the negative electrode current collector. 2 ~15mg / cm 2 It can also be any of the following values ​​or a range consisting of any two of the following values: 5 mg / cm³ 2 6mg / cm 2 7mg / cm 2 8mg / cm 2 9mg / cm 2 10mg / cm 2 11mg / cm 2 12mg / cm 2 13mg / cm2 14mg / cm 2 15mg / cm 2 wait.

[0398] In this application, unless otherwise specified, "the areal density of the negative electrode sheet, measured on one side of the negative electrode current collector," is equal to the ratio of the mass of the negative electrode active material layer on one side of the negative electrode current collector to the area of ​​the negative electrode active material layer. The corresponding "area" is equal to the orthogonal projected area of ​​the negative electrode active material layer along the thickness direction of the electrode sheet. Refer to the test method for the compaction density of the negative electrode sheet, based on (M... B -M0) / S0 is calculated.

[0399] By controlling the areal density of the negative electrode sheet within the aforementioned range, it is beneficial to balance the battery's fast charging performance and energy density.

[0400] In some embodiments, the lithium-ion secondary battery further includes a positive electrode sheet, which includes a positive active layer, and the positive active layer includes a positive active material, which includes one or more of lithium phosphate active materials and lithium composite metal oxide active materials.

[0401] In some embodiments, the positive electrode active material includes lithium phosphate-based active materials.

[0402] In this application, unless otherwise specified, lithium phosphate-containing active materials may include at least one of lithium phosphates and their modifications. Lithium phosphate-containing active materials may have an olivine structure. Unless otherwise specified, "lithium phosphate" refers to materials containing lithium, transition metal elements, and phosphate ions (PO4). 3- The positive electrode active material is olivine-structured lithium phosphate. Non-limiting examples of lithium phosphates may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites.

[0403] Introducing lithium phosphate-containing active materials into the positive electrode active material can improve the structural stability of the positive electrode active material during charge-discharge cycles and extend the cycle life of the battery.

[0404] In some embodiments, the positive electrode active material includes lithium-ion composite metal oxide active materials.

[0405] In this application, unless otherwise specified, lithium composite metal oxide active materials include at least one of lithium composite metal oxides and their modified forms. Unless otherwise specified, "lithium composite metal oxide" refers to a positive electrode active material comprising lithium, non-lithium metal elements, and oxygen. Typically, the non-lithium metal elements in lithium composite metal oxides include transition metal elements; therefore, lithium composite metal oxides can also be called "lithium transition metal oxides." Lithium composite metal oxide active materials can have crystal structures suitable for positive electrode active materials, such as layered structures and spinel structures. In some embodiments, the lithium composite metal oxide active material comprises a layered structure. In some embodiments, the lithium composite metal oxide active material has a layered structure.

[0406] Introducing lithium-composite metal oxide active materials into the positive electrode active material is beneficial to improving the energy density of the positive electrode and the battery.

[0407] In this application, unless otherwise specified, "a modified positive electrode active material" includes the positive electrode active material itself and the modifying element. Furthermore, the modifying element may exist as a dopant element, a coating element, or a combination of a dopant element and a coating element. Unless otherwise specified, "a modified positive electrode active material" still falls within the scope of positive electrode active materials.

[0408] In this application, unless otherwise specified, "doping element" in positive electrode active material refers to a modifying element doped into the positive electrode active material; unless otherwise specified, "coating element" in positive electrode active material refers to a positive electrode active material comprising a positive electrode active particle body and a coating layer located on at least a portion of the surface of the positive electrode active particle body, wherein the coating element is a modifying element located in the coating layer. As a non-limiting example, in positive electrode active material, "the modifying element exists in a combination of doping element and coating element" means that the positive electrode active material comprises a positive electrode active particle body and a coating layer located on at least a portion of the surface of the positive electrode active particle body, at least a portion of the modifying element is doped into the positive electrode active material body, and at least a portion of the modifying element is also contained in the coating layer. Both the doping modification method of introducing doping elements and the coating modification method of introducing coating elements can adopt or refer to existing modification methods in the art, including but not limited to the selection of element type, doping amount, and coating amount. In some embodiments, the positive electrode active particle body can be the positive electrode active material itself or its doped modified form. In some embodiments, the doping element may include one or more of Na, K, Ca, Ba, Sb, Ti, Zr, W, Sr, Nb, Mo, Si, Mg, B, Cr, Ta, etc. In some embodiments, the coating element may include one or more of Ti, Mg, Nb, C, etc.

[0409] In some embodiments, the positive electrode active material includes a lithium phosphate-based active material, which satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0410] (tg1) The mass percentage of lithium phosphate active material in the positive electrode active layer is greater than or equal to 80%, and can be selected as 80% to 97%;

[0411] (tg2) Lithium-containing phosphate active materials include one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0412] (tg3) Lithium phosphate active materials include a lithium phosphate active body and a carbon coating layer located on at least a portion of the surface of the lithium phosphate active body, wherein the carbon coating layer includes one or more of soft carbon, hard carbon and amorphous carbon.

[0413] In some embodiments, the mass percentage of lithium phosphate-containing active material in the positive electrode active layer can be greater than or equal to 80%, optionally 80% to 97%, and further optionally 95% to 97%. Non-limitingly, the mass percentage of lithium phosphate-containing active material in the positive electrode active layer can also be any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 93%, 94%, 95%, 95.2%, 95.4%, 95.5%, 96%, 96.5%, 96.6%, 96.8%, 96.9%, 97%, etc.

[0414] By controlling the mass ratio of lithium phosphate active materials in the positive electrode active layer within the aforementioned range, it is beneficial to extend the cycle life of the battery.

[0415] In some embodiments, the lithium phosphate-containing active material includes one or more of lithium iron phosphate (LFP), lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium iron phosphate include LiFePO4. Examples of lithium manganese phosphate include LiMnPO4.

[0416] The types of lithium phosphate active materials can be flexibly selected to meet different application needs.

[0417] In some embodiments, the lithium phosphate-based active material includes a lithium phosphate-based active body and a carbon coating layer located on at least a portion of the surface of the lithium phosphate-based active body. Optionally, the carbon coating layer includes one or more of soft carbon, hard carbon, and amorphous carbon.

[0418] The definitions of soft carbon and hard carbon can be found in the previous text.

[0419] In some embodiments, the carbon coating layer comprises soft carbon.

[0420] In some embodiments, the carbon coating layer comprises hard carbon.

[0421] In some embodiments, the carbon coating layer comprises amorphous carbon.

[0422] In this application, unless otherwise specified, "amorphous carbon" refers to transitional carbon materials with a very low degree of graphitization and crystallization, exhibiting an approximately amorphous morphology (or lacking a fixed shape and periodic structural regularity). In this application, "amorphous carbon" can also refer to the product of carbonization treatment of an organic carbon source. Similarly, amorphous carbon can be identified based on the intensity difference between the D and G peaks in the Raman spectrum.

[0423] By setting one or more carbon coating layers, including soft carbon, hard carbon, and amorphous carbon, on the surface of lithium phosphate active materials, the conductivity of the material can be improved. This is beneficial for improving the electrical contact network within the positive electrode, providing a fast and stable channel for electron transport within the positive electrode, thereby improving the rate performance and fast charging capability of the battery.

[0424] In some embodiments, the lithium phosphate active substrate includes at least one of lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate.

[0425] In some embodiments, the positive electrode active material includes a lithium iron phosphate (LFP)-based positive electrode active material. The "lithium iron phosphate-based positive electrode active material" at least includes a lithium iron phosphate body, and may further include a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate body. Optionally, the carbon coating layer in the lithium iron phosphate-based positive electrode active material may include one or more of soft carbon, hard carbon, and amorphous carbon. Non-limitingly, the lithium iron phosphate-based positive electrode active material may include carbon-coated lithium iron phosphate.

[0426] In some embodiments, the positive electrode active material includes carbon-coated lithium iron phosphate, which comprises a lithium iron phosphate body and a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate body. Further, the carbon coating layer may include one or more of soft carbon, hard carbon, and amorphous carbon. In this case, the positive electrode active material includes a lithium phosphate active material, which includes carbon-coated lithium iron phosphate.

[0427] Those skilled in the art can use conventional techniques to select and control the mass percentage of the carbon coating layer in lithium iron phosphate-based cathode active materials (examples of which include carbon-coated lithium iron phosphate) and the thickness or average thickness of the carbon coating layer. Non-limitingly, the mass percentage of the carbon coating layer in the lithium iron phosphate-based cathode active material (e.g., carbon-coated lithium iron phosphate) can be 0.2% to 2%, but is not limited thereto. Non-limitingly, in lithium iron phosphate-based cathode active materials, the average thickness of the carbon coating layer can be 10 nm to 20 nm, but is not limited thereto. Non-limitingly, in lithium iron phosphate-based cathode active materials, the thickness of the carbon coating layer in a certain region can be 10 nm to 20 nm, but is not limited thereto.

[0428] In some embodiments, the positive electrode active material includes soft carbon-coated lithium iron phosphate. Further, soft carbon-coated lithium iron phosphate includes a lithium iron phosphate body and soft carbon located on at least a portion of the surface of the lithium iron phosphate body.

[0429] The detection of positive electrode active material in the positive electrode active layer can be carried out by disassembling the battery after it is fully discharged, removing the positive electrode plate, scraping off the material of the positive electrode active layer, and using elemental analysis methods such as inductively coupled plasma (ICP) spectroscopy to test and analyze the types and proportions of elements, thereby confirming the elemental composition and chemical formula of the positive electrode active material.

[0430] In some embodiments, the positive electrode active material includes a positive electrode active body and a coating layer located on the positive electrode active body.

[0431] For cathode active materials that include a coating layer (e.g., a carbon coating layer), a cross-section can be obtained using FIB (Focused Ion Beam) and the particle cross-sectional morphology can be observed under TEM (Transmission Electron Microscopy). A clear boundary can be observed at the coating interface, and the thickness and average thickness of the coating layer can be calculated based on the TEM image. Further analysis using one or more methods such as energy-dispersive spectroscopy (EDS) and Raman spectroscopy can identify the types of substances in both the coating layer and the cathode active material.

[0432] The following are some other descriptions of the positive electrode sheet.

[0433] The positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer including a positive active material.

[0434] The definitions of the positive electrode sheet, positive electrode active layer, and positive electrode active material in some embodiments can be found in the context of this application.

[0435] Without limitation, the mass percentage of the positive electrode active material in the positive electrode active layer may be greater than or equal to 80%, and may further be greater than or equal to 90%.

[0436] As a non-limiting example, the positive current collector has two surfaces that are opposite to each other in its own thickness direction, and the positive active layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0437] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. In the positive electrode current collector, the composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. In the positive electrode current collector, the composite current collector may be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. Non-limitingly, in the positive electrode current collector, the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0438] The types of positive electrode active materials can be found above. Positive electrode active materials may also include other types of positive electrode active materials known in the art for use in lithium-ion secondary batteries. A single positive electrode active material may be used alone, or two or more may be used in combination.

[0439] As a non-limiting example, the positive electrode active material may include, but is not limited to, one or more of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modifications.

[0440] In some embodiments, the positive electrode active material comprises a lithium-containing phosphate with an olivine structure. Non-limiting examples of lithium-containing phosphates with an olivine structure include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium iron phosphate include LiFePO4. Examples of lithium manganese phosphate include LiMnPO4.

[0441] In some embodiments, the positive electrode active material includes a lithium transition metal oxide. Examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of lithium cobalt oxide may include LiCoO2; non-limiting examples of lithium nickel oxide may include LiNiO2; non-limiting examples of lithium manganese oxide may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxide may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.80 Co 0.15 Al 0.05 O2.

[0442] Understandably, lithium (Li) is intercalated and deintercalated during the charging and discharging process of a battery, and the Li content in the positive electrode varies depending on the state of discharge. In the exemplary description of the positive electrode active material in this application, unless otherwise specified, the Li content can be the initial state of the material or a non-initial state after charge-discharge cycles. When the positive electrode active material is applied to the positive electrode in a battery system, the Li content in the positive electrode active material at the positive electrode will usually change after charge-discharge cycles. The Li content can be measured in atomic molar content, but is not limited to this. Regarding "Li content is the initial state of the material," the initial state of the material refers to the state before it is formed into the positive electrode active layer. It is understood that new materials or substances obtained by appropriately modifying the listed positive electrode active materials are also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to an acceptable modification method for the positive electrode active material, and non-limiting examples include one or more of coating modification and doping modification.

[0443] In the exemplary description of the positive electrode active material in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the atomic molar content of oxygen, and the actual O content will fluctuate. The O content can be measured in atomic molar content, but is not limited to this.

[0444] In some embodiments, the positive electrode active layer optionally includes a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. Typically, the binder may constitute 0–10% by mass in the positive electrode active layer, more commonly 0–8%, and even more commonly 1%–5%, based on the total mass of the positive electrode active layer.

[0445] In some embodiments, the positive electrode active layer optionally includes a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Typically, the mass percentage of the conductive agent in the positive electrode active layer can be 0–10%, more further 0–8%, and even further 0–5%, based on the total mass of the positive electrode active layer.

[0446] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry. Further, the positive electrode slurry is coated onto at least one surface of the positive current collector, and after drying, cold pressing, and other processes, the positive electrode sheet is obtained. Cold pressing can be performed using a cold rolling mill. The solvent in the positive electrode slurry can be, but is not limited to, any of the solvents described in the foregoing embodiments, for example, it can include N-methylpyrrolidone (NMP), and more specifically, NMP. The surface of the positive current collector coated with the positive electrode slurry can be a single surface of the positive current collector or both surfaces of the positive current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s to 25000 mPa·s.

[0447] In some embodiments, the positive electrode active material includes a lithium phosphate-containing active material. Further, the mass percentage of the lithium phosphate-containing active material in the positive electrode active material can be greater than or equal to 50%, but is not limited thereto. When coating the positive electrode slurry, the coating areal density (based on dry weight, minus solvent) (based on the coating areal density of both sides) can also be (0.1–0.6) g / 1540.25 mm².2 However, this is not the only possibility. The compaction density of the positive electrode sheet can be 1.9 g / cm³. 3 ~2.7g / cm 3 .

[0448] In some embodiments, the positive electrode active material includes a lithium composite metal oxide active material. Further, the mass percentage of the lithium composite metal oxide active material in the positive electrode active material can be greater than or equal to 50%, but is not limited thereto. When coating the positive electrode slurry, the coating areal density (dry weight, minus solvent) can be 15 mg / cm³. 2 ~35mg / cm 2 The compaction density of the positive electrode sheet can be measured by the surface density of the coating on both sides, which is 3.0 g / cm³. 3 ~3.6g / cm 3 3.3g / cm³ is an option. 3 ~3.5g / cm 3 .

[0449] In this application, unless otherwise specified, the compaction density of the positive electrode sheet refers to the ratio of the mass of the positive electrode active layer to its volume.

[0450] The following are some other descriptions of the negative electrode plate.

[0451] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material. The negative electrode active material layer includes at least a first negative electrode active layer. The first negative electrode active layer includes a first negative electrode active material.

[0452] It is understandable that the negative electrode active material includes the first negative electrode active material.

[0453] In some embodiments, the negative electrode active material layer further includes a second negative electrode active layer, which is located between the first negative electrode active layer and the negative electrode current collector. The second negative electrode active layer includes a second negative electrode active material. The first and second negative electrode active materials may be the same or different, as can be seen from the context description. In this case, the negative electrode active material includes both the first and second negative electrode active materials.

[0454] In some embodiments, at least one side of the negative electrode active material layer includes a first negative electrode active layer and a second negative electrode active layer, with the second negative electrode active layer located between the first negative electrode active layer and the negative electrode current collector.

[0455] The definitions of negative electrode sheet, negative electrode active material layer, first negative electrode active layer and second negative electrode active layer, negative electrode active material, first negative electrode active material and second negative electrode active material in some embodiments can be found in the context of this application.

[0456] As a non-limiting example, the negative electrode sheet includes a negative current collector and a second negative active layer and a first negative active layer sequentially disposed on at least one side of the negative current collector.

[0457] Without limitation, the mass percentage of the negative electrode active material in the negative electrode active material layer may be greater than or equal to 80%, and may further be greater than or equal to 90%.

[0458] Without limitation, the mass percentage of the first negative electrode active material in the first negative electrode active layer may be greater than or equal to 80%, and may further be greater than or equal to 90%.

[0459] Without limitation, the mass percentage of the second negative electrode active material in the second negative electrode active layer may be greater than or equal to 80%, and more particularly greater than or equal to 90%.

[0460] As a non-limiting example, the negative electrode current collector has two surfaces that are opposite to each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0461] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. In the negative electrode current collector, the composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. In the negative electrode current collector, the composite current collector may be formed by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limitingly, in the negative electrode current collector, the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0462] In addition to the types of negative electrode active materials mentioned in the context and examples, the negative electrode active material in the negative electrode active material layer may also include other types of negative electrode active materials known in the art and suitable for lithium-ion secondary batteries. A single negative electrode active material may be used alone, or two or more may be used in combination. In some embodiments, the negative electrode active material also includes one or more of tin-based materials and lithium titanate. In the negative electrode active material layer, these negative electrode active materials may be used alone, or two or more may be used in combination. In the first negative electrode active layer and the second negative electrode active layer, each independently, these negative electrode active materials may be used alone, or two or more may be used in combination.

[0463] In addition, the first negative electrode active material may also be other types of negative electrode active materials known in the art for use in lithium-ion secondary batteries.

[0464] Non-limitingly, the second negative electrode active material can be other types of negative electrode active materials known in the art for use in lithium-ion secondary batteries. The second negative electrode active material may include one or more of carbon-based materials, silicon-based materials, tin-based materials, and lithium titanate. Carbon-based materials may include one or more of artificial graphite, natural graphite, soft carbon, and hard carbon. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. As a non-limiting example, the second negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. However, the second negative electrode active material is not limited to these materials or substances, and other conventional materials that can be used as battery negative electrode active materials may also be used. In the second negative electrode active layer, these negative electrode active materials may be used alone or in combination of two or more. In some embodiments, the second negative electrode active material includes one or more of carbon-based materials and silicon-based materials. In some embodiments, the second negative electrode active material comprises a carbon-based material. In some embodiments, the mass percentage of the carbon-based material in the second negative electrode active material can be 60% to 100%, 80% to 100%, further preferably 90% to 100%, and even more preferably 97% to 100%.

[0465] In some embodiments, the negative electrode active material layer may optionally include a binder.

[0466] In some embodiments, the first negative electrode active layer and the second negative electrode active layer may each optionally include a binder independently.

[0467] Non-limitingly, in the negative electrode sheet, the binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The types of binders in the first negative electrode active layer and the second negative electrode active layer may be the same or different.

[0468] Non-limitingly, the mass percentage of the binder in the negative electrode active material layer can be 0% to 20%, further can be 0% to 10%, even further can be 0% to 5%, even further can be 1% to 5%, and even further can be 1% to 3%.

[0469] Non-limiting, the mass percentage of the binder in the first negative electrode active layer can be 0% to 20%, further can be 0% to 10%, even further can be 0% to 5%, even further can be 1% to 5%, and even further can be 1% to 3%.

[0470] Non-limiting, the mass percentage of the binder in the second negative electrode active layer can be 0% to 20%, further can be 0% to 10%, even further can be 0% to 5%, even further can be 1% to 5%, and even more preferably 1% to 3%.

[0471] In some embodiments, the negative electrode active material layer may optionally include a conductive agent.

[0472] In some embodiments, the first negative electrode active layer and the second negative electrode active layer may each optionally include a conductive agent independently.

[0473] In a non-limiting sense, the conductive agent in the negative electrode may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The types of conductive agents in the first negative electrode active layer and the second negative electrode active layer may be the same or different.

[0474] Non-limitingly, the mass percentage of the conductive agent in the negative electrode active material layer can be 0% to 15%, more preferably 0% to 10%, and even more preferably 0% to 5%.

[0475] Non-limiting, the mass percentage of the conductive agent in the first negative electrode active layer can be 0% to 15%, more preferably 0% to 10%, and even more preferably 0% to 5%.

[0476] Non-limitingly, the mass percentage of the conductive agent in the second negative electrode active layer can be 0% to 15%, more preferably 0% to 10%, and even more preferably 0% to 5%.

[0477] In some embodiments, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). Non-limitingly, the mass percentage of these other additives in the negative electrode active material layer may be 0% to 15%, more preferably 0% to 10%, even more preferably 0% to 5%, even more preferably 0% to 3%, and even more preferably 0% to 2%.

[0478] In some embodiments, the first and second negative electrode active layers may each optionally and independently include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). Non-limitingly, the mass percentage of these other additives in the first or second negative electrode active layer may independently be 0% to 15%, more preferably 0% to 10%, even more preferably 0% to 5%, even more preferably 0% to 3%, and even more preferably 0% to 2%.

[0479] In some embodiments, a method comprising the following steps is used to prepare a negative electrode sheet, which can be used to prepare a negative electrode sheet in which the negative electrode active material layer has a single-layer structure:

[0480] S110: Preparation of negative electrode slurry. The components described above for preparing the negative electrode active material layer, such as the negative electrode active material, conductive agent, binder, and any other components, are dispersed in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry. It is understood that the negative electrode active material includes electronegatively coated active materials.

[0481] S120: Preparation of the negative electrode sheet. A negative electrode slurry is coated onto at least one surface of the negative electrode current collector. After drying and cold pressing, a negative electrode active material layer is formed, obtaining the negative electrode sheet. Cold pressing can be performed using a cold rolling mill. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 30wt%–70wt%, optionally 40wt%–60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s–10000mPa·s, optionally 3000mPa·s–10000mPa·s.

[0482] In some embodiments, a negative electrode sheet is prepared by a method including the following steps: S110' and S120'; this method can be used to prepare a negative electrode sheet in which the negative electrode active material layer includes a first negative electrode active layer and a second negative electrode active layer.

[0483] S110': Preparation of a first negative electrode slurry and a second negative electrode slurry. The components described above for preparing the first negative electrode active layer, such as a first negative electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (a non-limiting example of a solvent is deionized water) to form a first negative electrode slurry. The components described above for preparing the second negative electrode active layer, such as a second negative electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (a non-limiting example of a solvent is deionized water) to form a second negative electrode slurry.

[0484] S120': Preparation of the negative electrode sheet. A double-layer coating machine is used to coat a second negative electrode slurry and a first negative electrode slurry onto at least one surface of the negative electrode current collector. The second negative electrode slurry is coated first, followed by the first negative electrode slurry. After drying and cold pressing, a second negative electrode active layer and a first negative electrode active layer are formed accordingly. The second negative electrode active layer is located between the first negative electrode active layer and the negative electrode current collector. The non-solvent components of the first negative electrode slurry form the first negative electrode active layer, and the non-solvent components of the second negative electrode slurry form the second negative electrode active layer. Cold pressing can be performed using a cold rolling mill. The surfaces of the negative electrode current collector coated with the first and second negative electrode slurries can be a single surface or both surfaces of the negative electrode current collector. The solid content of the first and second negative electrode slurries can each be independently 30wt% to 70wt%, or independently selectable as 40wt% to 60wt%. The viscosity of the first negative electrode slurry and the second negative electrode slurry at room temperature can be independently adjusted to 2000 mPa·s to 10000 mPa·s, and can be independently selected to be 3000 mPa·s to 10000 mPa·s.

[0485] The coating density and compaction density of the negative electrode sheet can be found in the context of this application.

[0486] Compared to the negative electrode sheet obtained after cold pressing, the volume of the negative electrode sheet in a lithium-ion secondary battery will have a certain rebound, resulting in a lower compaction density of the negative electrode sheet in a lithium-ion secondary battery compared to the negative electrode sheet obtained after cold pressing.

[0487] The electrolyte is described below as an example.

[0488] The electrolyte serves to conduct ions between the positive and negative electrodes. A suitable electrolyte can be selected based on specific requirements.

[0489] Electrolytes consist of electrolyte salts and solvents. Solvents include non-aqueous solvents.

[0490] In some embodiments, the electrolyte is a non-aqueous electrolyte. A non-aqueous electrolyte may include an electrolyte salt and a solvent.

[0491] The concentration of electrolyte salts in the electrolyte solution is typically 0.5 mol / L to 5 mol / L.

[0492] In some embodiments, the electrolyte salt includes an electrolyte lithium salt.

[0493] In some embodiments, the solvent in the non-aqueous electrolyte may include ethylene carbonate (EC). ), propylene carbonate (PC, propylene carbonate) ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC). One or more of the following: fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0494] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0495] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), etc.

[0496] The following is an exemplary description of the separator membrane.

[0497] The definition of the isolation membrane in some implementations can be found in the context of this application.

[0498] This application does not impose any particular restrictions on the type of diaphragm; any well-known porous diaphragm with good chemical and mechanical stability can be selected.

[0499] In some embodiments, the diaphragm material may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The diaphragm may be a single-layer film or a multi-layer composite film, without particular limitation. When the diaphragm is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0500] In some embodiments, the thickness of the diaphragm is 4 μm to 40 μm, and optionally 7 μm to 20 μm.

[0501] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0502] In some embodiments, the lithium-ion secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0503] In some embodiments, the outer packaging of the lithium-ion secondary battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the lithium-ion secondary battery can also be a soft pack, such as a pouch. The soft pack can be made of plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0504] A lithium-ion secondary battery includes at least one battery cell. A lithium-ion secondary battery may include one or more battery cells.

[0505] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

[0506] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. The electrode assembly 52 is immersed in an electrolyte. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to actual needs.

[0507] The lithium-ion secondary battery can be a battery device 4 or a battery pack 1.

[0508] The battery device includes at least one battery cell. The number of battery cells in the battery device can be one or more, and those skilled in the art can select an appropriate number according to the application and capacity of the battery device.

[0509] Figure 3 shows a battery device 4 as an example. Referring to Figure 3, in the battery device 4, multiple battery cells 5 can be arranged sequentially along the length of the battery device 4. Of course, they can also be arranged in any other arbitrary way. Furthermore, the multiple battery cells 5 can be fixed in place by fasteners.

[0510] Optionally, the battery device 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0511] In some embodiments, the battery devices described above can also be assembled into a battery pack, and the number of battery devices contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0512] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery compartment and multiple battery devices 4 disposed within the battery compartment. The battery compartment includes an upper compartment 2 and a lower compartment 3, the upper compartment 2 covering the lower compartment 3 to form a closed space for accommodating the battery devices 4. The multiple battery devices 4 can be arranged in any manner within the battery compartment.

[0513] In another aspect of this application, a negative electrode sheet is provided, which may have the same features as the negative electrode sheet described in the first aspect of this application, or may be in the state after cold pressing and before immersion in electrolyte corresponding to the negative electrode sheet described in the first aspect of this application.

[0514] In some embodiments, a negative electrode sheet is provided, which includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector, the negative electrode active material layer including a first negative electrode active layer;

[0515] The first negative electrode active layer includes a first negative electrode active material, which includes an electronegatively coated active material. The electronegatively coated active material includes a negative electrode active body and a coating layer located on at least a portion of the surface of the negative electrode active body. The coating layer includes doped carbon, which includes a carbon matrix and an electronegatively dopant element. The carbon matrix includes one or more of soft carbon and hard carbon. The Pauling electronegativity scale of the electronegatively dopant element is denoted as χ1, and the Pauling electronegativity scale of carbon element is denoted as χ. C Then χ1 and χ C The absolute value of the difference between them satisfies 0.03 ≤ |χ1-χ C |≤0.49.

[0516] As mentioned earlier, by setting an electronegative coating active material in the negative electrode active material layer of the negative electrode sheet, the electronegative doping elements and carbon matrix in the coating layer can synergistically promote the faster and more extensive embedding of lithium ions into the negative electrode active material, improve the lithium conduction capability of the SEI film, reduce the interface impedance, and help improve the fast charging capability of the battery.

[0517] In some embodiments, the negative electrode active material layer further includes a second negative electrode active layer, which is located between the negative electrode current collector and the first negative electrode active layer. In this case, the negative electrode sheet includes a negative electrode current collector and a second negative electrode active layer and a first negative electrode active layer sequentially disposed on at least one side of the negative electrode current collector.

[0518] In some embodiments, a negative electrode sheet is provided, which includes a negative current collector and a second negative active layer and a first negative active layer sequentially disposed on at least one side of the negative current collector; the first negative active layer includes a first negative active material, and the first negative active material includes an electronegative coated active material.

[0519] For a definition of electronegative coated active materials, please refer to the first aspect of this application.

[0520] By setting a first negative electrode active layer on the upper layer and a second negative electrode active layer on the lower layer in the negative electrode sheet, and setting an electronegative coating active material in the first negative electrode active layer, as described above, the electronegative doping elements and carbon matrix in the coating layer can synergistically promote the faster and more extensive embedding of lithium ions into the first negative electrode active material, improve the lithium conductivity of the SEI film, reduce the interface impedance, and also improve the wettability of the electrolyte in the first negative electrode active layer. Based on the improvement of the electrolyte wettability of the first negative electrode active layer, the wettability of the electrolyte in the second negative electrode active layer can be further improved. Based on the multiple effects, it is beneficial to improve the fast charging capability of the battery.

[0521] In this application, the effect of the electronegative coating active material on the electrolyte wettability of the negative electrode active material layer or the first negative electrode active layer can be evaluated by the change in the liquid absorption rate. A higher liquid absorption rate indicates better electrolyte wettability. The following method can be used for testing and analysis: the negative electrode sheet to be tested is fixed on the sample stage, electrolyte is dropped onto the surface of the negative electrode sheet, and a stopwatch is used to time the process; the weight increase and time are recorded; the liquid absorption rate on the surface of the negative electrode sheet is calculated by the change in weight over time, which can be considered as the liquid absorption rate of the first negative electrode active layer. Non-limiting examples of electrolytes include the electrolyte formulation in Example 1. Electrolytes with the same composition as those used in lithium-ion secondary batteries can also be used to test the liquid absorption rate. Commercially available electrolytes such as electrolyte E30 can also be used. In some examples, the electrolyte composition consists of a solvent and 1 mol / L lithium hexafluorophosphate (LiPF6), with the solvent composition being ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1.

[0522] In some embodiments, the negative electrode is the negative electrode as defined in the first aspect of this application.

[0523] In a second aspect of this application, a method for preparing a lithium-ion secondary battery is provided, which can be used to prepare the lithium-ion secondary battery of the first aspect of this application.

[0524] In one embodiment, a method for preparing a lithium-ion secondary battery is provided, which includes preparing a negative electrode sheet.

[0525] In another aspect of this application, a method for preparing a negative electrode sheet is also provided.

[0526] In some embodiments, the preparation of the negative electrode sheet includes the following steps:

[0527] S100: A negative electrode active material layer is disposed on at least one side of the negative electrode current collector; wherein, the negative electrode active material layer includes a first negative electrode active layer, the first negative electrode active layer includes a first negative electrode active material, the first negative electrode active material includes an electronegatively coated active material, the electronegatively coated active material includes a negative electrode active body and a coating layer located on at least a portion of the surface of the negative electrode active body; the coating layer includes doped carbon, the doped carbon includes a carbon matrix and an electronegatively dopant element, the carbon matrix includes one or more of soft carbon and hard carbon, the Pauling electronegativity scale of the electronegatively dopant element is denoted as χ1, and the Pauling electronegativity scale of the carbon element is denoted as χ. C Then χ1 and χ C The absolute value of the difference between them satisfies 0.03 ≤ |χ1-χ C |≤0.49.

[0528] In the prepared lithium-ion secondary battery, an electronegative coating active material is set in the negative electrode active material layer of the negative electrode sheet. As described above, the electronegative doping elements and carbon matrix in the coating layer can promote the faster and more extensive embedding of lithium ions into the negative electrode active material through synergistic effect, which is beneficial to improving battery dynamics and enhancing the fast charging capability of the battery.

[0529] In some embodiments, a method for preparing a lithium-ion secondary battery is provided, which includes preparing a negative electrode sheet;

[0530] The preparation of the negative electrode sheet includes the following steps:

[0531] A second negative electrode active layer and a first negative electrode active layer are sequentially disposed on at least one side of the negative electrode current collector; wherein, the first negative electrode active layer includes a first negative electrode active material, the first negative electrode active material includes an electronegative coating active material, and the definition of the electronegative coating active material can be as described in the first aspect of this application.

[0532] In the prepared lithium-ion secondary battery, a first negative electrode active layer and a second negative electrode active layer are disposed in the negative electrode active material layer of the negative electrode sheet. An electronegative coating active material is disposed in the first negative electrode active layer. As described above, the electronegative doping elements and carbon matrix in the coating layer can promote the faster and more extensive embedding of lithium ions into the first negative electrode active material through synergistic effect. It is also beneficial to improve the wettability of the electrolyte in the second negative electrode active layer based on the improvement of the electrolyte wettability of the first negative electrode active layer. Based on the aforementioned multiple effects, it is beneficial to improve battery dynamics and enhance the fast charging capability of the battery.

[0533] In one embodiment, the preparation of the negative electrode sheet includes the following steps:

[0534] S100': A second negative electrode active layer and a first negative electrode active layer are sequentially disposed on at least one side of the negative electrode current collector; wherein, the first negative electrode active layer includes a first negative electrode active material, the first negative electrode active material includes an electronegative coating active material, the electronegative coating active material includes a negative electrode active body and a coating layer located on at least a portion of the surface of the negative electrode active body; the coating layer includes doped carbon, the doped carbon includes a carbon matrix and an electronegative dopant element, the carbon matrix includes one or more of soft carbon and hard carbon, the Pauling electronegativity scale of the electronegative dopant element is denoted as χ1, and the Pauling electronegativity scale of the carbon element is denoted as χ. C Then χ1 and χ C The absolute value of the difference is 0.03 ≤ |χ1-χ C |≤0.49, which means that 0.03≤|χ1-χ C |≤0.49.

[0535] In some embodiments, the electronegative coated active material is prepared by an in-situ coating method, that is, the carbon matrix of doped carbon in the coating layer is introduced in-situ by the coating method; non-limitingly, the precursor material of the carbon matrix can be mixed with the negative electrode active body and heat-treated to transform the precursor material into the carbon matrix in-situ on the surface of the negative electrode active body; optionally, while the precursor material is transformed into the carbon matrix in-situ, electronegative doping elements can also be introduced simultaneously, in which case both coating and electronegative doping are carried out in-situ.

[0536] When the carbon matrix is ​​soft carbon, the precursor material of the carbon matrix is ​​a soft carbon precursor. In this case, the soft carbon precursor (such as pitch) can soften at the heat treatment temperature to form a fluid. Therefore, solvents are not required when the negative electrode active body and the soft carbon precursor are coated in situ.

[0537] In some embodiments, an in-situ coating method is used to form a carbon matrix on at least a portion of the surface of the negative electrode active body. In some embodiments, an in-situ coating method is used to form doped carbon on at least a portion of the surface of the negative electrode active body, with the carbon matrix and electronegative dopant elements introduced simultaneously.

[0538] In some embodiments, the carbon matrix in the doped carbon includes soft carbon. In this case, the coating layer in the electronegative coating active material includes doped soft carbon, and the electronegative coating active material can be prepared by an in-situ coating method.

[0539] Optionally, the electronegative coated active material can be prepared by a method including the following steps:

[0540] S10: In the presence of a doped precursor, the negative electrode active body and a soft carbon precursor are mixed, and then subjected to doping heat treatment and soft carbonization heat treatment, so that the soft carbon precursor and the doped precursor together form a doped soft carbon coating on at least a portion of the surface of the negative electrode active body; wherein, the doped precursor includes an electronegative dopant element. A non-limiting example of a soft carbon precursor is asphalt.

[0541] In step S10, electronegative doping and in-situ coating are carried out simultaneously.

[0542] The mass percentage of electronegative dopant in the doped carbon and in the coating layer can be adjusted by controlling the amount of the doped precursor relative to the soft carbon precursor. In some embodiments, the mass percentage of the doped precursor relative to the soft carbon precursor is greater than or equal to 0.5%, and the resulting electronegatively coated active material satisfies one or both of the following characteristics: (i) the mass percentage of the electronegative dopant in the doped carbon is greater than or equal to 0.1%, and (ii) the mass percentage of the electronegative dopant in the coating layer is greater than or equal to 0.1%. The mass percentage of the electronegative dopant in the doped carbon and the mass percentage of the electronegative dopant in the coating layer can also be found in the first aspect of this application.

[0543] The doping conditions for introducing electronegative dopants can be adjusted appropriately according to the ease of introducing the dopant. For example, different holding temperatures can be selected, and one or both of the heating rate and holding time can be adjusted.

[0544] In some embodiments, in step S10, the doped precursor and the soft carbon precursor pitch are first mixed, and then the precursor mixture is used to coat the surface of the negative electrode active body (corresponding to the first active body). Doping heat treatment and soft carbonization heat treatment can be performed in the presence of the precursor mixture. A non-limiting example of the negative electrode active body is graphite. When the electronegative doping element includes P, one or both of O-doping and S-doping treatments can be performed before P doping. This method is beneficial for improving coating uniformity. It is understood that the doping heat treatment and soft carbonization heat treatment can be performed simultaneously. During the soft carbonization heat treatment, the electronegative doping element in the doped precursor can combine with carbon (C) to form a new chemical structure with high defects, effectively adsorbing foreign atoms, which can improve the wettability of the negative electrode sheet and the fast-charging capability of the battery.

[0545] In some embodiments, the doping precursor includes a nitrogen-containing precursor. Considerations for selecting the nitrogen-containing precursor may include compatibility with bitumen. The nitrogen-containing precursor may include one or more of urea and ammonia. Without limitation, the nitrogen-containing precursor may also include one or more other organic nitrogen compounds, such as amines, amides, nitro compounds, and nitrogen heterocyclic compounds. In some embodiments, the nitrogen-containing precursor may also include one or more of aliphatic amines, aromatic amines, polyamines, aliphatic amides, aromatic amides, nitrobenzene, nitrobenzene, pyridine, quinoline, and carbazole.

[0546] In some embodiments, the doped precursor includes a sulfur-containing precursor. The sulfur-containing precursor may include one or more of sulfur and sulfur vapor. Without limitation, the sulfur-containing precursor may also include one or more other sulfur-containing compounds, such as vulcanized petroleum resins, vulcanized rubbers, thiosulfates, thiols, and thioamidine.

[0547] In some embodiments, the doped precursor includes a phosphorus-containing precursor, which includes one or more of red phosphorus and phosphorus vapor. Without limitation, the phosphorus-containing precursor may also include one or more other phosphorus-containing compounds, such as phosphate esters, polyphosphate esters, phosphates, and phosphorus heterocyclic compounds.

[0548] In some embodiments, step S10, the doping heat treatment includes N doping treatment. The conditions for performing the N doping treatment include: a heating rate of 2℃ / min to 10℃ / min, a holding temperature of 400℃ to 800℃, and a holding time of 1h to 6h. In the N doping treatment step, the heating rate can be any one of 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min, or it can be selected from any two of the following ranges. In the N doping treatment step, the holding temperature can be 400℃ to 800℃, or it can be any one of the following temperatures or a range selected from any two of the following temperatures: 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, or 800℃. In the N-doping process, the holding time can be from 1 h to 6 h, or any of the following durations or a range selected from any two of the following durations: 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 6 h, etc.

[0549] By controlling appropriate process conditions, the presence of sulfur (S) and phosphorus (P) as elemental impurities can be reduced or avoided. This helps to suppress the probability of lithium intercalation reactions in elemental S and P, inhibits the anode electrode's volume expansion, reduces the risk of coating layer damage, and ultimately contributes to good long-term battery performance. By controlling the conditions for S and P doping to more suitable levels (e.g., slightly increasing the doping temperature during S doping, or introducing at least one of O and S before introducing P), the battery can achieve better long-term cycle performance. In some embodiments, during S doping, one or more of the following conditions may be introduced: reducing the heating rate, extending the holding time, and reducing the sulfur (S) vapor flow rate.

[0550] In some embodiments, step S10, the doping heat treatment includes S-doping treatment. The conditions for performing the S-doping treatment include: a heating rate of 2℃ / min to 10℃ / min, a holding temperature of 200℃ to 600℃, and a holding time of 1h to 6h. In the S-doping treatment step, the heating rate can be any one of 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min, or a range consisting of any two of the following rates. In the S-doping treatment step, the holding temperature can be 200℃ to 600℃, or any one of the following temperatures or a range consisting of any two of the following temperatures: 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, or 600℃. In the S doping process, the holding time can be from 1 h to 6 h, or any of the following durations or a range of any two of the following durations: 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 6 h, etc.

[0551] In some embodiments, in step S10, the doping heat treatment includes P doping treatment. The heat treatment steps include performing one or both of O doping treatment and S doping treatment followed by P doping treatment. The conditions for P doping treatment include: a heating rate of 2℃ / min to 10℃ / min, a holding temperature of 200℃ to 600℃, and a holding time of 1h to 6h. The conditions for O doping treatment include: heating at a heating rate of 2℃ / min to 10℃ / min in an air atmosphere, holding at 400℃ to 800℃ in a nitrogen atmosphere, and a holding time of 1h to 6h. In the P doping treatment step, the heating rate can be any one of 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min, or a range consisting of any two of the above rates, such as 2℃ / min to 10℃ / min, or 2℃ / min to 6℃ / min. Non-limitingly, in the P-doping step, the holding temperature can be from 200℃ to 600℃, or any one of the following temperatures or a range selected from any two of the following temperatures: 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, etc. Non-limitingly, in the P-doping step, the holding temperature can also be from 300℃ to 700℃, or any one of the following temperatures or a range selected from any two of the following temperatures: 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, etc. In the P-doping process, the holding time can be from 1 h to 6 h, or any of the following durations or a range of any two of the following durations: 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 6 h, etc.

[0552] In some embodiments, in step S10, the soft carbon precursor includes a liquid precursor in the steps of performing doping heat treatment and soft carbonization heat treatment.

[0553] In some embodiments, the conditions for performing the soft carbonization heat treatment include holding the treatment in an inert atmosphere at a temperature of 700°C to 1300°C. A non-limiting example of an inert atmosphere is a nitrogen atmosphere. Non-limitingly, the holding conditions can be any of the following temperatures or a range selected from any two of the following temperatures: 700°C, 800°C, 900°C, 1000°C, 1020°C, 1040°C, 1050°C, 1060°C, 1080°C, 1100°C, 1120°C, 1140°C, 1150°C, 1160°C, 1180°C, 1200°C, 1250°C, 1300°C, etc.

[0554] In some embodiments, the method for preparing the electronegatively coated active material satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0555] (th1) Doped precursors include N-containing precursors, which may include one or more of urea and ammonia;

[0556] (th2) Doped precursors include S-containing precursors, which may include one or more of sulfur and sulfur vapor;

[0557] (th3) Doped precursors include P-containing precursors, which include one or more of red phosphorus and phosphorus vapor;

[0558] (th4) Doping heat treatment includes N doping treatment. The conditions for N doping treatment are: heating rate of 2℃ / min~10℃ / min, holding temperature of 400℃~800℃, and holding time of 1h~6h.

[0559] (th5) Doping heat treatment includes S doping treatment. The conditions for S doping treatment are: heating rate of 2℃ / min~10℃ / min, holding temperature of 200℃~600℃, and holding time of 1h~6h.

[0560] (th6) The doping heat treatment includes P doping treatment. The steps of the heat treatment include: performing one or both of O doping treatment and S doping treatment, followed by P doping treatment. The conditions for P doping treatment include: heating rate of 2℃ / min to 10℃ / min, holding temperature of 200℃ to 600℃, and holding time of 1h to 6h. The conditions for O doping treatment include: heating at a heating rate of 2℃ / min to 10℃ / min in an air atmosphere, holding at 400℃ to 800℃ in a nitrogen atmosphere, and holding time of 1h to 6h. Further, the conditions for S doping treatment can be found in feature (th5), but are not limited thereto.

[0561] (th7) In the steps of performing doping heat treatment and performing soft carbonization heat treatment, the soft carbon precursor includes a liquid precursor.

[0562] (th8) The conditions for soft carbonization heat treatment include: heat treatment in an inert atmosphere and at 700℃~1300℃.

[0563] In some embodiments, the soft carbon precursor includes asphalt; furthermore, the temperature for soft carbonization treatment can be 1150°C, but is not limited to this, such as holding the treatment at 700°C to 1300°C, or holding the treatment at 1000°C to 1200°C, or any of the following temperatures or a range selected from any two of the following temperatures: 700°C, 800°C, 900°C, 1000°C, 1020°C, 1040°C, 1050°C, 1060°C, 1080°C, 1100°C, 1120°C, 1140°C, 1150°C, 1160°C, 1180°C, 1200°C, 1250°C, 1300°C, etc. By more rationally controlling the amount of asphalt used, it is beneficial to better maintain the fast ion ring effect of the asphalt, to improve the uniformity of the asphalt coating, and to form more carbon end faces, thereby making lithium intercalation more efficient. Through the aforementioned multiple effects, the fast charging capability of the battery can be improved.

[0564] Introducing asphalt into soft carbon precursors can bring one or more of the following advantages: (1) Abundant carbon source: It can be converted into carbon-based materials with high carbon content through high-temperature treatment, for example, it can be converted into soft carbon; (2) Controllable structure: Asphalt can form complex microporous and mesoporous structures during pyrolysis, which helps to improve the specific surface area and porosity of the carbon-based materials formed, thereby improving the electrochemical performance of lithium-ion batteries; (3) Cost-effectiveness: Asphalt is an industrial by-product with wide availability and relatively low price, resulting in relatively high cost-effectiveness; (4) Promotes graphite (5) Improved interface performance: Carbon-based materials derived from asphalt can improve the interface performance between soft carbon and electrolyte, reduce the occurrence of side reactions, and improve the cycle stability and safety of the battery; (6) Easy to modify: Asphalt can be chemically modified to introduce heteroatoms (such as N, P, S, etc.), which can further optimize the electrochemical performance of carbon-based materials.

[0565] At the battery level, the introduction of geonegative doping elements, such as N, P, and S, may have one or more of the following effects:

[0566] (1) Structural stability: The incorporation of N, P, and S elements may alter the interlayer spacing and structure of carbon-based materials. Controlling the appropriate doping amount helps to keep the interlayer spacing variation of carbon-based materials within a more suitable range, which is beneficial for improving the structural stability and cycle performance of batteries during lithium-ion insertion and extraction.

[0567] (2) Electrochemical performance: By controlling the probability of N, P, and S dopants reacting with the electrolyte, the formation of additional byproducts can be reduced or avoided. For example, the thickening of the SEI film (solid electrolyte interface film) and the increase in battery internal resistance can be suppressed, which is beneficial to achieving better battery kinetics and cycle stability. In addition, by controlling the dopant elements within a suitable content range, it is also beneficial to suppress or avoid the dopant elements participating in additional electrochemical reactions, reduce the probability of consuming active lithium ions, and achieve better battery capacity.

[0568] (3) Thermal stability: The introduction of N, P and S elements may affect the thermal stability of the battery. For example, by introducing S element and controlling it within a more appropriate range, it is beneficial to improve the stability of the battery at high temperatures and to better control the risk of thermal runaway of the battery.

[0569] (4) Capacity and actual energy density: By controlling the doping amount of N, P and S elements within a more suitable range, the doping of N, P and S elements can improve the conductivity of graphite and the lithium ion diffusion rate, thereby improving the battery capacity and actual energy density. At the same time, it can also reduce the risk of carbon-based material structure being damaged, and can improve the overall performance of the battery.

[0570] In some embodiments, during the N-doping and P-doping process, the heating rate is 2°C / min to 6°C / min, and the precursor containing N and P is mixed with pitch and negative electrode active body (such as graphite) at 1150°C, and the mixture is kept at this temperature for 9h to 12h.

[0571] In some embodiments, during the S doping process, the heating rate is 6°C / min to 10°C / min, and the S-containing precursor is mixed with pitch and negative electrode active material (such as graphite) at 1150°C, and the mixture is kept at this temperature for 9h to 12h.

[0572] In some embodiments, the coating layer in the electronegative coated active material includes doped soft carbon, in which case the carbon matrix in the coating layer includes soft carbon.

[0573] In some embodiments, the electronegative coating active material includes a negative electrode active body and doped soft carbon located on at least a portion of the surface of the negative electrode active body.

[0574] Non-limiting, the negative electrode active body in the electronegatively coated active material can be any suitable negative electrode active material, and further reference can be made to the first aspect of this application. In some embodiments, the negative electrode active body in the electronegatively coated active material includes a carbon-based active material, further comprising graphite, and even further comprising graphite.

[0575] In some embodiments, the negative electrode active body in the electronegatively coated active material includes graphite, and further, the graphite may include one or more of artificial graphite and natural graphite.

[0576] In some embodiments, the soft carbon precursor is pitch, and the doped precursor is one or more of sulfur, urea, and red phosphorus. Further, the doped precursor is one of sulfur, urea, and red phosphorus. Even further, the negative electrode active substrate is secondary particulate graphite.

[0577] In some embodiments, one or more of the following methods ① to ⑤ are used to perform electronegative doping coating on the negative electrode active body without a coating layer to introduce doped soft carbon including electronegative doping elements into the coating layer.

[0578] In some embodiments, an electronegatively coated negative electrode active material is prepared using a method comprising the following steps (which may be referred to as method ①):

[0579] Method ①: First, physically mix pitch and an electronegatively doped precursor to obtain a precursor mixture. Then, carbonize the precursor mixture with secondary particle graphite to form a coating layer including soft carbon on the surface of the secondary particle graphite. When introducing S doping, the heating rate can be reduced and the holding time extended. When introducing P, after introducing O / S (where O / S can represent one or both of O and S), O / S can be bonded to P to form one or both of COP and CSP bonds.

[0580] "Electrononegative doping precursor" is a precursor that provides electrononegative doping elements.

[0581] In some embodiments, an electronegatively coated active material is prepared using a method comprising the following steps (which may be referred to as method ②).

[0582] Method 2: Use urea as an N-containing precursor.

[0583] In some embodiments, an electronegatively coated active material is prepared using a method comprising the following steps (which may be referred to as method ③).

[0584] Method ③: Using sulfur as a sulfur-containing precursor, sulfur can be directly added to asphalt to form sulfurized asphalt.

[0585] In some embodiments, an electronegative coated active material is prepared using a method comprising the following steps (which may be referred to as method ④).

[0586] Method 4: Red phosphorus was used as a phosphorus-containing precursor.

[0587] In some embodiments, an electronegatively coated active material is prepared using a method comprising the following steps (which may be referred to as method ⑤).

[0588] Method ⑤: The doping heat treatment and soft carbonization heat treatment process includes the control of heating rate, holding temperature and holding time; in a protective atmosphere, the heating rate is 2℃ / min~10℃ / min, and the temperature is held at 700℃~1300℃ for 6h~12h to prepare an electronegative coated active material in which the carbon matrix in the coating layer includes soft carbon.

[0589] In some embodiments, one or two of the following methods (i) to (ii) are used to obtain a new electronegatively coated active material through elemental substitution, thereby changing the elemental composition of the coating layer. In this case, the choice of coating temperature can be independent of the asphalt.

[0590] In some embodiments, electronegative coated active materials are prepared using a method (which may be referred to as method (i)) including the following steps.

[0591] Method (i): N-doping and / or P-doping of the carbon matrix in the coating layer: In an NH3 atmosphere, the electronegative coated active material is heated at a rate of 2℃ / min to 10℃ / min and held at 400℃ to 800℃ for 1h to 6h to obtain a new electronegative coated active material, the coating layer of which includes the electronegative dopant element N. When performing P-doping, the ammonia atmosphere can be changed to a phosphorus vapor atmosphere.

[0592] In some embodiments, electronegative coated active materials are prepared using a method (which may be referred to as method (ii)) including the following steps.

[0593] Method (ii): S doping of the carbon matrix in the coating layer: The electronegative coating active material is mixed with asphalt and sulfur, and in an atmosphere of S vapor, the temperature is increased at a rate of 2℃ / min to 10℃ / min and held at 200℃ to 600℃ for 1h to 6h to obtain a new electronegative coating active material, the coating layer of which includes the electronegative doping element S.

[0594] It is understandable that electronegative coated active materials can be prepared using pitch as a soft carbon precursor, but are not limited to this.

[0595] In some embodiments, one or both of the following steps (a) and (b) are used to prepare the electronegative coated active material: introducing two electronegative doping elements, and when P doping is included, introducing them by grafting O or S (i.e., introducing O or S first to make subsequent P introduction easier).

[0596] In some embodiments, an electronegative coated active material is prepared using a method comprising the following steps: (a)

[0597] Method (a) S-doping (S-doping) of carbon matrix in coating layer: The negative electrode active matrix is ​​mixed with pitch and sulfur, and held at 200℃ to 600℃ for 1h to 6h in an atmosphere of S vapor at a heating rate of 2℃ / min to 10℃ / min to obtain S-doped product (a negative coating active material, in which the negative doping element in the doped carbon includes S).

[0598] Oxidation pretreatment (oxidation): The S-doped product is heated at a rate of 2℃ / min to 10℃ / min and held at 400℃ to 800℃ for 1h to 6h to obtain the O-doped product; the atmosphere during the heating process is air and the atmosphere during the holding process is nitrogen, which helps to reduce or prevent the weight loss of asphalt due to oxidation.

[0599] In some embodiments, the electronegative coated active material is prepared using a method (b) including the following steps:

[0600] Method (b) employs a stepwise P-doping method: the S and / or O doped products obtained by S-doping and / or oxidation are placed in a P vapor atmosphere and heated at a rate of 2℃ / min to 10℃ / min, and held at 200℃ to 600℃ for 1h to 6h.

[0601] In some embodiments, the carbon matrix in the doped carbon includes hard carbon. In this case, the coating layer in the electronegatively coated active material includes doped hard carbon. The electronegatively coated active material can be prepared by a method including the following steps (optionally, the electronegatively coated active material can be prepared by an in-situ coating method):

[0602] At least a portion of the surface of the negative electrode active body is coated with hard carbon. A doping source, including an electronegative dopant element, is introduced into the hard carbon to form a doped hard carbon coating at least a portion of the surface of the negative electrode active body. The electronegative dopant element can be introduced into the hard carbon using a gas displacement method.

[0603] In some embodiments, the coating of at least a portion of the surface of the negative electrode active body with hard carbon is achieved by in-situ coating.

[0604] In some embodiments, a hard carbon coating layer can be first formed on at least a portion of the surface of the negative electrode active body by an in-situ coating method, and then the hard carbon coating layer can be electronegatively doped; the hard carbon coating layer can be electronegatively doped by a gas displacement method.

[0605] In some embodiments, the electronegative coated active material can be prepared by an in-situ coating method, which includes at least the following steps: in-situ coating of at least a portion of the surface of the negative electrode active body with hard carbon.

[0606] Those skilled in the art can use existing methods to prepare at least a portion of the hard carbon coating on the surface of the negative electrode active body.

[0607] In some embodiments, the gas replacement method employs one of ammonia, sulfur vapor, and phosphorus vapor.

[0608] In some embodiments, a method including the following steps can be used to coat the surface of the negative electrode active body with hard carbon to prepare a hard carbon-coated negative electrode active material: mixing a hard carbon precursor with the negative electrode active body in a liquid phase (corresponding to an in-situ coating method), and stirring to disperse; solidifying the hard carbon precursor onto at least a portion of the surface of the negative electrode active body by heating and drying (optionally, the heating and drying method is drying at 100°C to 300°C), followed by carbonization treatment (optionally, carbonization treatment is performed at 700°C to 1300°C, further optionally, the carbonization treatment time is 1h to 6h; exemplaryly, the heating rate of the carbonization treatment can be 2°C / min to 10°C / min); during the carbonization process, the hard carbon precursor undergoes surface polymerization on the surface of the negative electrode active body to achieve hard carbon coating on at least a portion of the surface of the negative electrode active body, and the prepared hard carbon-coated negative electrode active material includes a negative electrode active body and a hard carbon coating layer located on at least a portion of the surface of the negative electrode active body. In some embodiments, the negative electrode active body can be a graphite body.

[0609] In some embodiments, in the step of liquid-phase mixing of the hard carbon precursor with the negative electrode active body, the hard carbon precursor is a liquid resin, dissolved without solvent or using a non-aqueous solvent.

[0610] In this application, "curing" in "curing hard carbon precursor on at least a portion of the surface of the negative electrode active body" refers to the process of transforming from a liquid phase to a solid phase.

[0611] In some embodiments, taking graphite (which can be referred to as the first negative electrode body) as the negative electrode active body, and taking the hard carbon coating of graphite as an example, the hard carbon coating of graphite can be carried out on the surface of the first negative electrode body by means of the following steps to prepare the hard carbon coated negative electrode active material: the hard carbon precursor and graphite are mixed in liquid phase and dispersed by stirring; the hard carbon precursor is dried at 100℃~300℃ to solidify the hard carbon precursor on the graphite surface, and then carbonized at 700℃~1300℃ for 1h~6h, the heating rate of the carbonization treatment can be 2℃ / min~10℃ / min; during the carbonization process, the hard carbon precursor undergoes surface polymerization on the graphite surface to achieve at least a portion of the hard carbon coating on the surface of the negative electrode active body, and the prepared hard carbon coated negative electrode active material includes a graphite body (the corresponding negative electrode active body is graphite) and a hard carbon coating layer located on at least a portion of the surface of the graphite body.

[0612] Hard carbon precursors containing a high content of electronegative doping elements can be selected. Non-limiting examples of hard carbon precursors may include one or more of polyimide, melamine, polyacrylonitrile (PAN), etc.

[0613] In some embodiments, electronegative doping elements can be introduced into the hard carbon in the coating layer using the following gas displacement method based on the hard carbon-coated negative electrode active material, but is not limited to these doping methods:

[0614] N-doping and / or S-doping, that is, N-doping and / or S-doping: the hard carbon-coated negative electrode active material is placed in an atmosphere of ammonia (NH3) or S vapor, and heated at a rate of 2℃ / min to 10℃ / min for 1h to 6h at 400℃ to 700℃.

[0615] Oxidation treatment: Hard carbon-coated negative electrode active material is heated at a rate of 2℃ / min to 10℃ / min and held at 400℃ to 700℃ for 1h to 6h; the atmosphere during the heating process is air and the atmosphere during the holding process is nitrogen, which helps to reduce or prevent the oxidation and weight loss of the coating layer.

[0616] P doping: The negative electrode active material is coated with S-oxidized or oxidized hard carbon and placed in a P vapor atmosphere. The temperature is increased at a rate of 2℃ / min to 10℃ / min and held at 400℃ to 700℃ for 1h to 6h.

[0617] In a third aspect of this application, an electrical device is provided, comprising at least one of the lithium-ion secondary battery described in the first aspect of this application, the aforementioned negative electrode sheet, and a lithium-ion secondary battery prepared by the method for preparing a lithium-ion secondary battery described in the second aspect of this application.

[0618] Electrical devices that include the aforementioned lithium-ion secondary batteries may have the advantages of the aforementioned lithium-ion secondary batteries, including but not limited to improved fast charging performance.

[0619] Electrical devices including the aforementioned negative electrode may have the advantages of the aforementioned negative electrode, including but not limited to improved fast charging performance.

[0620] In some embodiments, the electrical device includes a lithium-ion secondary battery according to any of the embodiments provided in this application.

[0621] Lithium-ion secondary batteries can be used as a power source for electrical devices or as an energy storage unit for electrical devices. Electrical devices can include, but are not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Mobile devices can include, for example, mobile phones and laptops; electric vehicles can include, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, electric motorcycles, power tools, etc., but are not limited to these. This type of electrical device can also be applied to military equipment, aerospace, and other fields, as well as to energy storage power systems such as hydroelectric, thermal, wind, and solar power plants.

[0622] As an electrical device, lithium-ion rechargeable batteries can be selected according to its usage requirements.

[0623] Figure 6 shows an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the lithium-ion secondary battery for this electrical device, a battery device or battery pack can be used.

[0624] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a lithium-ion rechargeable battery as their power source.

[0625] In a fourth aspect of this application, the application of the lithium-ion secondary battery described in the first aspect of this application in supplying and / or storing electrical energy is provided;

[0626] The application includes the process of charging a lithium-ion secondary battery at a rate of 2C or higher, that is, the lithium-ion secondary battery can provide a charging rate of 2C or higher.

[0627] In this application, unless otherwise specified, the term "rate" for a battery has a well-known meaning in the art, referring to the current required to charge or discharge a battery to its rated capacity within a specified time, expressed in C. Unless otherwise specified, "specified time" is 1 hour (h), 1C means completing charge / discharge in 1 hour, and 1 / 3C means completing charge / discharge in 3 hours. The battery rate reflects the battery's charging and discharging capabilities at different currents. A higher rate means the battery can charge and discharge quickly in a short time. The higher the rate, the better the fast-charging performance.

[0628] In this application, unless otherwise specified, for the charging rate, "1C" refers to the current required to fully charge the battery from zero charge to full charge or from full charge to complete discharge within one hour. For the charging rate, when charging from zero charge at a 1C rate, the battery will be fully charged in one hour.

[0629] In some embodiments, the application includes a process of charging a lithium-ion secondary battery at at least one rate from 2C to 6C, that is, the lithium-ion secondary battery is capable of providing a charging rate from 2C to 6C.

[0630] In some embodiments, the application includes a process of charging a lithium-ion secondary battery at at least one rate from 2C to 4C.

[0631] In some embodiments, the application includes a process of charging a lithium-ion secondary battery at at least one rate from 4C to 6C.

[0632] In a non-limiting manner, the lithium-ion secondary battery can be charged at any of the following rates, or at a rate greater than or equal to any of the following rates, or at a rate selected from any two of the following rates: 2C, 3C, 4C, 5C, 6C, etc.

[0633] In some implementations, lithium-ion secondary batteries can provide a charging rate of 2C or higher.

[0634] In some implementations, lithium-ion secondary batteries can provide charging rates of 2C to 6C.

[0635] In this application, "able to provide a charging rate Cx" means that the battery cell can be charged under the condition of charging rate Cx; for example, it can be charged to 97% SOC, but it is not limited to this SOC state.

[0636] In some embodiments, the maximum charging rate of the lithium-ion secondary battery can be greater than or equal to 2C, and can be selected as 2C to 6C, or further selected as 2C to 4C or 4C to 6C.

[0637] In some implementations, the maximum charging rate of the lithium-ion secondary battery can be greater than 2C (C max >2C), can be selected as greater than 2C and less than or equal to 6C (2 <C max ≤6C), further optionally greater than 2C and less than or equal to 4C (2 <C max ≤4C) or optionally greater than or equal to 4C and less than or equal to 6C (4C≤C) max ≤6C).

[0638] Without limitation, the maximum charging rate of the lithium-ion secondary battery may also be any of the following charging rates or a range selected from any two of the following charging rates: 2C, 3C, 4C, 5C, 6C, etc.

[0639] In this application, the "maximum charging rate (which can be denoted as C)" of the lithium-ion secondary battery is defined as... maxThe term "lithium plating" has a well-known meaning within the industry and can be obtained through testing using conventional methods within the field. For example, tests can be conducted at different charging rates to obtain a lithium plating window curve, and the critical charging rate at which lithium plating occurs can be used as the test value of the battery's maximum charging rate. Test parameters can be as follows: The battery under test is charged at a constant current to 3.8V at different rates (e.g., 1C, 2C, 2.5C, 3C, 3.5C, 4C, ...), then charged at a constant voltage until the current is ≤0.05C, left to stand for 5 minutes, and then charged at a constant current of 0.33C to 3.8V, left to stand for 5 minutes, and then disassembled to observe the lithium plating at the negative electrode. For example, a series of parallel samples can be prepared, starting from 1C and tested at 0.1C intervals until lithium plating appears at the negative electrode. To reduce the sample size, a larger interval can be selected first to determine the range of the maximum charging rate, and then a smaller interval can be selected to more accurately determine the maximum charging rate. The intervals can be 1C, 0.5C, 0.2C, and 0.1C, respectively.

[0640] The following describes some embodiments of this application. The described embodiments are only a part of the embodiments of this application, and not all of them. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application and its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0641] Unless otherwise specified in the examples, the procedures described above, or those described in the literature in this field, or those described in the product instructions, shall be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products, or products that can be synthesized using conventional methods from commercially available products.

[0642] In the specific embodiments described below, the measurement parameters involving raw material components may have slight deviations within the weighing accuracy range unless otherwise specified. Temperature and time parameters are subject to acceptable deviations due to instrument testing accuracy or operational precision.

[0643] In the following examples, room temperature refers to 20°C to 30°C.

[0644] In the following examples, unless otherwise specified, the parameters involved can be confirmed by referring to the test methods described above. For example, the percentage of secondary graphite particles in the first negative electrode active material, and the percentage of secondary graphite particles in the negative electrode active material, can be confirmed by SEM (such as the Sigma 300 scanning electron microscope from ZEISS, Germany) test results; the D of the first and second negative electrode active materials... v50 can be tested using a Malvern 2000 (MasterSizer 2000) laser particle size analyzer; for coating layers in electronegative coated active materials and carbon coating layers in lithium iron phosphate-based cathode active materials, a JEM-F200 transmission electron microscope combined with EDS (energy dispersive spectroscopy) can be used for testing and analysis; for the doping form of electronegative dopants in electronegative coated active materials, X-ray photoelectron spectroscopy (XPS, Thermo Scientific ESCALAB Xi+) can also be used for testing and analysis. Other examples include the compaction density of the negative electrode sheet, a comparison of the compaction densities of the first and second negative electrode active layers, a comparison of the areal densities of the first and second negative electrode active layers (based on one side of the negative electrode current collector), the porosity of the first and second negative electrode active layers, the porosity of the negative electrode active material layers, and the difference in compaction density (P) between the second and first negative electrode active layers. Δ and P Δ0 The ratio of the difference in compaction density between the second negative electrode active layer and the first negative electrode active layer to the compaction density of the negative electrode sheet (R) PΔ and R PΔ0 Examples include: rate comparison of the first and second negative electrode active layers, and charging rate comparison of the first and second negative electrode active layers. Another example involves the testing of the electrolyte's ionic conductivity, using a DDSJ-318 conductivity meter, following the testing method in HG-T 4067-2015.

[0645] I. A method for preparing electronegative coated active materials for use as first anode active materials.

[0646] The negative electrode active substrate used for coating is artificial graphite and includes secondary particulate graphite. The secondary particulate graphite accounts for 20% to 100% of the raw material of the negative electrode active substrate (optionally 40% to 100%, further optionally 40% to 80%). v 50 is 8μm to 16μm (optionally 10μm to 14μm). The negative electrode active body corresponds to the negative electrode active body in the electronegatively coated active material. The obtained electronegatively coated active material includes electronegatively coated secondary particle graphite, and correspondingly, the proportion of electronegatively coated secondary particle graphite in the first negative electrode active material is 20% to 100% (optionally 40% to 100%, further optionally 40% to 80%).

[0647] (a) The carbon matrix in the coating layer is soft carbon.

[0648] Electronegative coated active materials are prepared using one or more of methods ①~⑤, (i) and (ii), (a) and (b), wherein the "electronegative doping precursor" is a precursor that provides the electronegative doping element. Electronegative coated active materials are prepared using pitch as a soft carbon precursor. Doping heat treatment can be performed first, followed by soft carbonization heat treatment, or the doping heat treatment and soft carbonization heat treatment can be performed simultaneously. The heating rate for soft carbonization heat treatment is 2℃ / min~10℃ / min, the holding temperature is 700℃~1300℃, and the holding time is 1h~6h.

[0649] Method ① First, asphalt and an electronegatively doped precursor are physically mixed to obtain a precursor mixture. The precursor mixture is then carbonized with the negative electrode active substrate to form a coating layer including soft carbon on the surface of the negative electrode active substrate. When S doping is introduced, the heating rate can be reduced and the holding time extended. When P is introduced, O / S (where O / S can represent one or both of O and S) can be introduced first, and then O / S can be bonded to P to form one or both of COP and CSP bonds.

[0650] Method ② uses urea as an N-containing precursor.

[0651] Method ③ uses sulfur as a sulfur-containing precursor. Sulfur can be directly added to asphalt to form sulfurized asphalt.

[0652] Method ④ uses red phosphorus as a phosphorus-containing precursor.

[0653] Method ⑤ involves controlling the heating rate, holding temperature, and holding time during the doping and soft carbonization heat treatment processes. In a protective atmosphere, the heating rate is 2℃ / min to 10℃ / min, and the temperature is held at 700℃ to 1300℃ for 6h to 12h to prepare electronegative coated active materials. In this method, the doping heat treatment and soft carbonization heat treatment processes are carried out simultaneously.

[0654] Method (i) involves N-doping and / or P-doping of the carbon matrix in the coating layer: In an NH3 atmosphere, the electronegative coated active material is heated at a rate of 2℃ / min to 10℃ / min and held at 400℃ to 800℃ for 1h to 6h to obtain a new electronegative coated active material, the coating layer of which includes the electronegative dopant element N. When performing P-doping, the ammonia atmosphere is changed to a phosphorus vapor atmosphere.

[0655] Method (ii) S doping of the carbon matrix in the coating layer: The electronegative coating active material is mixed with asphalt and sulfur, and in an atmosphere of S vapor, the temperature is increased at a rate of 2℃ / min to 10℃ / min and held at 200℃ to 600℃ for 1h to 6h to obtain a new electronegative coating active material, the coating layer of which includes the electronegative doping element S.

[0656] Two electronegative dopants, S and P, are introduced using methods (a) and (b) including the following steps, wherein the step of introducing the P dopant is performed by grafting O or S (i.e., introducing O or S first to make the subsequent P introduction easier).

[0657] Method (a) S-doping (S-doping) of the carbon matrix in the coating layer: The negative electrode active matrix is ​​mixed with asphalt and sulfur, and held at 200℃ to 600℃ for 1h to 6h in an atmosphere of S vapor at a heating rate of 2℃ / min to 10℃ / min.

[0658] Oxidation pretreatment (oxidation): Electronegative coating active material is heated at a rate of 2℃ / min to 10℃ / min and held at 400℃ to 800℃ for 1h to 6h; the atmosphere during the heating process is air and the atmosphere during the holding process is nitrogen, in order to reduce or prevent the asphalt from losing weight due to oxidation.

[0659] Method (b) employs a stepwise P-chemical method: the electronegative coated active material obtained by S-chemical and / or oxidation is placed in a P vapor atmosphere and heated at a rate of 2℃ / min to 10℃ / min for 1h to 6h at 200℃ to 600℃.

[0660] (ii) The carbon matrix in the coating layer is hard carbon.

[0661] The method for preparing electronegative coated active materials with hard carbon as the carbon matrix includes the following steps S210 and S220.

[0662] S210: Preparation of hard carbon-coated negative electrode active material.

[0663] A high-N hard carbon precursor (polyacrylonitrile (PAN)) is mixed with graphite in the liquid phase and dispersed by stirring. The hard carbon precursor is dried at 100℃ to 300℃ to solidify it on the graphite surface. Then, it is carbonized at 700℃ to 1300℃ for 1h to 6h, with a heating rate of 2℃ / min to 10℃ / min. During the carbonization process, the hard carbon precursor undergoes surface polymerization on the graphite surface to transform into hard carbon. The prepared hard carbon-coated negative electrode active material includes a graphite body and a hard carbon coating layer located on at least a portion of the graphite body surface. The hard carbon coating layer has a high N content and can be referred to as a high-N hard carbon coating layer.

[0664] S220: Electronegative dopants are introduced into the hard carbon coating layer of the hard carbon-coated negative electrode active material using a gas displacement method.

[0665] N-doping and / or P-doping of the hard carbon coating: For N-doping, the hard carbon-coated negative electrode active material is heated at a rate of 2℃ / min to 10℃ / min and held at 400℃ to 800℃ for 1h to 6h in an NH3 atmosphere to obtain an electronegatively coated active material. The coating layer includes the electronegative dopant element N. For P-doping, the ammonia atmosphere is replaced with a phosphorus vapor atmosphere.

[0666] S doping of hard carbon coating layer: The hard carbon coated negative electrode active material is placed in an atmosphere of S vapor, heated at a rate of 2℃ / min to 10℃ / min, and held at 200℃ to 600℃ for 1h to 6h to obtain an electronegative coated active material, the coating layer of which includes electronegative doping element S.

[0667] Two electronegative doping elements, S and P, can also be introduced by methods (a2) and (b2) including the following steps, wherein the step of introducing the P doping element is introduced by grafting O or S (that is, O or S is introduced first to make the subsequent P introduction easier).

[0668] Method (a2) S-doping (S-doping) of the carbon matrix in the coating layer: Hard carbon coated negative electrode active material is mixed with sulfur and held at 200℃ to 600℃ for 1h to 6h in an atmosphere of S vapor at a heating rate of 2℃ / min to 10℃ / min.

[0669] Oxidation pretreatment (oxidation): Hard carbon-coated negative electrode active material is heated at a rate of 2℃ / min to 10℃ / min and held at 400℃ to 800℃ for 1h to 6h; the atmosphere during the heating process is air and the atmosphere during the holding process is nitrogen, in order to reduce or prevent the asphalt from oxidizing and losing weight.

[0670] Method (b2) adopts a stepwise P-chemical method: the electronegative coated active material obtained by S-chemical and / or oxidation is placed in an atmosphere of P vapor and heated at a rate of 2℃ / min to 10℃ / min for 1h to 6h at 200℃ to 600℃.

[0671] In some embodiments, electronegative doping elements can be introduced into the hard carbon in the coating layer based on the hard carbon-coated negative electrode active material using methods such as those described below, but are not limited to these doping methods:

[0672] 1. Perform N-doping or S-doping, that is, perform N-doping or S-doping: Place the hard carbon-coated negative electrode active material in an atmosphere of ammonia (NH3) or S vapor, and heat it at 400℃ to 700℃ for 1h to 6h at a heating rate of 2℃ / min to 10℃ / min.

[0673] 2. Oxidation treatment: Hard carbon-coated negative electrode active material is heated at a rate of 2℃ / min to 10℃ / min and held at 400℃ to 700℃ for 1h to 6h; the atmosphere during the heating process is air and the atmosphere during the holding process is nitrogen, which helps to reduce or prevent the oxidation and weight loss of the coating layer.

[0674] 3. Perform P doping: Coat the negative electrode active material with S-oxidized or oxidized hard carbon, place it in an atmosphere of P vapor, and hold it at 400℃~700℃ for 1h~6h with a heating rate of 2℃ / min~10℃ / min.

[0675] II. Preparation of negative electrode sheet and lithium-ion secondary battery

[0676] Example 1.

[0677] (1) Preparation of the positive electrode sheet:

[0678] Lithium iron phosphate (LFP, with soft carbon coating), conductive agent (Super P), and binder (PVDF) were mixed in a ratio of 96:2:2. N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred under vacuum until it became homogeneous and transparent, yielding a positive electrode slurry with a solid content of 60 wt%. The coating surface density (one-sided) was 0.18 g / 1540.25 m². 2 (approximately 11.7 mg / cm) 2 The positive electrode slurry was uniformly coated onto both sides of the positive electrode current collector aluminum foil, with the coating density on both sides being approximately the same. After drying the positive electrode current collector coated with the slurry at room temperature, it was transferred to an oven for drying, and then cold-pressed and slit to obtain the positive electrode sheet. The compacted density of the positive electrode sheet was 2.50 g / cm³. 3 .

[0679] The lithium iron phosphate-based cathode active material is lithium iron phosphate coated with soft carbon, and the mass percentage of soft carbon in the cathode active material is about 1%.

[0680] (2) Preparation of negative electrode sheet:

[0681] The powder of the first negative electrode active material (corresponding to the upper first negative electrode active layer) was mixed with thickener (sodium carboxymethyl cellulose), binder (SBR), and conductive agent (Super P) in a ratio of 97.0:0.8:1.0:1.2, and then mixed with solvent (deionized water) under vacuum stirring to prepare the first negative electrode slurry with a solid content of 48wt%.

[0682] The powder of the second negative electrode active material (corresponding to the lower second negative electrode active layer) was mixed with thickener (sodium carboxymethyl cellulose), binder (SBR), and conductive agent (Super P) in a ratio of 96.4:1.0:1.2:1.4, and then mixed with solvent (deionized water) under vacuum stirring to prepare a second negative electrode slurry with a solid content of 48 wt%.

[0683] The second negative electrode slurry and the first negative electrode slurry were uniformly coated onto both sides of the copper foil of the negative electrode current collector using an extrusion coating machine. The second negative electrode slurry (lower layer) was coated first, followed by the first negative electrode slurry (upper layer). The surface density of the coating on one side of the negative electrode current collector was controlled to be 0.13 g / 1540.25 mm. 2 (corresponding to approximately 8.44 mg / cm²) 2 The weight ratio of the upper and lower coating layers (on one side) was controlled to be approximately 4:6. The surface density of the upper and lower coating layers on both sides of the negative electrode current collector was basically the same. After drying in an oven, the negative electrode sheet was compacted using a cold press to control the compaction density of the negative electrode sheet to be 1.65 g / cm³. 3 After cold pressing, the electrode sheet is slitting and cutting to obtain the negative electrode sheet. The negative electrode sheet consists of a negative current collector and negative active material layers located on both sides of the negative current collector. The negative active material layers are composed of a first negative active layer and a second negative active layer, with the second negative active layer located between the negative current collector and the first negative active layer.

[0684] First negative electrode active layer (upper layer): The first negative electrode active material is electronegatively coated graphite, and the negative electrode active body is artificial graphite and secondary particle graphite (at this time, the first negative electrode active material is electronegatively coated secondary particle graphite, which is both electronegatively coated graphite and electronegatively coated secondary particles). The coating layer is doped soft carbon, and the carbon matrix is ​​soft carbon, which includes the electronegative dopant element N. The first negative electrode active material has D... v 50 represents 12 μm. Artificial graphite was used as the negative electrode active material, which was secondary particle graphite. Method ⑤ was employed, with simultaneous doping and soft carbonization heat treatments. In a nitrogen atmosphere, pitch was used as the soft carbon precursor, and urea as the nitrogen-containing precursor for nitrogen doping treatment of the negative electrode active material. The heating rate during doping was 5℃ / min, the holding temperature was 1000℃, and the holding time was 4 h. The mass percentage of urea relative to pitch was approximately 0.8%.

[0685] Second negative electrode active layer (lower layer): The second negative electrode active material is artificial graphite and is secondary particle graphite. The D of the second negative electrode active material... v 50 represents 15μm.

[0686] In Example 1, the ratio of the areal density of the first negative electrode active layer to the areal density of the second negative electrode active layer is approximately 4:6. The compacted powder density of the second negative electrode active material is higher than that of the first negative electrode active material. The percentage of the thickness of the first negative electrode active layer (upper layer) relative to the sum of the thicknesses of the first and second negative electrode active layers (F) is calculated on one side of the negative electrode current collector. H Within the range of 20% to 65%, and further within the range of 40% to 60%, F H Approximately 44%. At this point, the compaction density of the second negative electrode active layer is approximately 1.75 g / cm³. 3 The compaction density is higher than that of the first negative electrode active layer (approximately 1.5 g / cm³). 3 The thickness of the first negative electrode active layer on one side is in the range of 20μm to 40μm. The difference between the compaction density of the second negative electrode active layer and the compaction density of the first negative electrode active layer (which can be denoted as P) in the negative electrode sheet obtained after cold pressing. Δ0 Approximately 0.25 g / cm³ 3 P Δ0 The ratio of the compaction density of the negative electrode to that of the negative electrode (which can be denoted as R) PΔ0 The value is approximately 0.152, R PΔ0 Within the range of 0 to 2, and further within the range of 0 to 0.834.

[0687] In Example 1, the porosity of the first negative electrode active layer is higher than that of the second negative electrode active layer, wherein the porosity of the upper first negative electrode active layer is approximately 26.14%.

[0688] (3) Separation membrane: A polyethylene film with a thickness of 12 micrometers (μm) is selected.

[0689] (4) Electrolyte preparation: Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:70 to obtain an organic solvent. Then, thoroughly dried lithium hexafluorophosphate (LiPF6) was dissolved in the mixed organic solvent. Ethylene carbonate (VC), fluoroethylene carbonate (FEC), and ethylene sulfate (DTD) were added to prepare an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. The electrolyte contained 2.5 wt% VC, 1 wt% FEC, and 0.5 wt% DTD.

[0690] The electrolyte has an ionic conductivity of 15 mS / cm at 25°C.

[0691] (5) Assemble the secondary battery: Stack and wind the positive electrode, separator and negative electrode in sequence to obtain the electrode assembly; place the electrode assembly in the outer packaging, dry it and inject the electrolyte, and then go through vacuum sealing, standing, formation and shaping processes to obtain the lithium-ion secondary battery.

[0692] Example 2. A first negative electrode active material, a negative electrode sheet, and a lithium-ion secondary battery were prepared using essentially the same method as in Example 1, except that: in the step of preparing the first negative electrode active material, the N-doping treatment was changed to first perform O-doping treatment, followed by P-doping treatment, and red phosphorus was used as the P-containing precursor; different first negative electrode active materials were used to prepare the negative electrode sheet; and different negative electrode sheets were used to prepare the lithium-ion secondary battery. The remaining operation steps were the same as in Example 1.

[0693] The negative electrode active material is first subjected to O doping treatment, and then to P doping treatment.

[0694] O doping treatment: The temperature was increased at a rate of 6℃ / min in air atmosphere, and then held at 600℃ in nitrogen atmosphere for 4 hours to obtain O-doped products; the atmosphere during the heating process was air, and the atmosphere during the holding process was nitrogen.

[0695] P-doping treatment of O-doped products: In a nitrogen atmosphere, using pitch as a soft carbon precursor and red phosphorus as a P-containing precursor, the heating rate during doping was 5℃ / min, the holding temperature was 1000℃, and the holding time was 6h.

[0696] Example 3. A first negative electrode active material, a negative electrode sheet, and a lithium-ion secondary battery were prepared using essentially the same method as in Example 1, except that: in the step of preparing the first negative electrode active material, the N-doping treatment was replaced with S-doping treatment, and sulfur was used as the S-containing precursor; different first negative electrode active materials were used to prepare the negative electrode sheet; and different negative electrode sheets were used to prepare the lithium-ion secondary battery. The remaining operation steps were the same as in Example 1.

[0697] S-doping treatment: In a nitrogen atmosphere, using asphalt as a soft carbon precursor and sulfur as a S-containing precursor, the heating rate was 5℃ / min, the holding temperature was 1000℃, and the holding time was 5h.

[0698] Example 4. A first negative electrode active material, a negative electrode sheet, and a lithium-ion secondary battery were prepared using a method essentially the same as in Example 1, except that: in the step of preparing the first negative electrode active material, the N-doping treatment was changed to S-doping treatment first, followed by P-doping treatment; different first negative electrode active materials were used to prepare the negative electrode sheet; and different negative electrode sheets were used to prepare the lithium-ion secondary battery. The remaining operation steps were the same as in Example 1.

[0699] S-doping treatment: In a nitrogen atmosphere, using pitch as a soft carbon precursor and sulfur as a S-containing precursor, the heating rate was 6℃ / min, the holding temperature was 400℃, and the holding time was 4h to obtain the S-doped product.

[0700] P-doping treatment of S-doped products: In a nitrogen atmosphere, using red phosphorus as a P-containing precursor, the heating rate during doping was 5℃ / min, the holding temperature was 1000℃, and the holding time was 6h.

[0701] Example 5. A first negative electrode active material, a negative electrode sheet, and a lithium-ion secondary battery were prepared using essentially the same method as in Example 1, except that: in the step of preparing the first negative electrode active material, the mass percentage of urea relative to asphalt was approximately 1.2%; different first negative electrode active materials were used to prepare the negative electrode sheet; and different negative electrode sheets were used to prepare the lithium-ion secondary battery. The remaining operation steps were the same as in Example 1. Compared to Example 1, the mass percentage of N in the doped carbon and coating layer was increased in Example 5.

[0702] Example 6. The first negative electrode active material, negative electrode sheet, and lithium-ion secondary battery were prepared using essentially the same method as in Example 1, except that the ratio of solvent EC to EMC was changed in the electrolyte preparation step to make the electrolyte have an ionic conductivity of approximately 13.7 mS / cm at 25°C. A different electrolyte was used to prepare the lithium-ion secondary battery. The remaining operation steps were the same as in Example 1.

[0703] Example 7. A negative electrode and a lithium-ion secondary battery were prepared using essentially the same method as in Example 1, except that the composition of the electrolyte was changed in the electrolyte preparation step, and a different electrolyte was used to prepare the lithium-ion secondary battery. The remaining operation steps were the same as in Example 1.

[0704] Example 7 changed the solvent to ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:2:1; the type and amount of electrolyte lithium salt, and the type and amount of additives were the same as in Example 1.

[0705] The electrolyte in Example 7 has an ionic conductivity of approximately 17.8 mS / cm at 25°C.

[0706] Examples 8-9. The first negative electrode active material, the negative electrode sheet, and the lithium-ion secondary battery were prepared using essentially the same method as in Example 1. The difference was that in the step of preparing the negative electrode sheet, the coating weight ratio of the first and second negative electrode slurries was changed, i.e., the ratio of the areal density of the first negative electrode active layer to the areal density of the second negative electrode active layer was changed. The sum of the coating areal densities of both sides and both layers of the negative electrode sheet remained essentially unchanged. Different negative electrode sheets were used to prepare the lithium-ion secondary battery. The remaining operation steps were the same as in Example 1.

[0707] In Example 8, the ratio of the areal density of the first negative electrode active layer to the areal density of the second negative electrode active layer is 2:8.

[0708] In Example 9, the ratio of the areal density of the first negative electrode active layer to the areal density of the second negative electrode active layer is 6:4.

[0709] Examples 10-11 use essentially the same method as Example 1 to prepare the first negative electrode active material, the negative electrode sheet, and the lithium-ion secondary battery, the difference being that: in the step of preparing the negative electrode sheet, the type of electronegative coating active material in the first negative electrode active layer is changed, as is the type of negative electrode active body therein; and different negative electrode sheets are used to prepare the lithium-ion secondary battery. The remaining operation steps are the same as in Example 1.

[0710] The negative electrode active body of Example 10 uses a combination of artificial graphite and soft carbon in a mass ratio of 1:2%.

[0711] The negative electrode active body of Example 11 uses a combination of artificial graphite and hard carbon in a mass ratio of 1:2%.

[0712] Example 12. The first negative electrode active material, negative electrode sheet, and lithium-ion secondary battery were prepared using a method essentially the same as in Example 1, except that the type of positive electrode active material was changed to ternary positive electrode material NCM811 (LiNi) in the step of preparing the positive electrode sheet. 0.8 Co 0.1 Mn 0.1 O2); lithium-ion secondary batteries were prepared using different positive electrode sheets. The remaining operation steps were the same as in Example 1.

[0713] Example 13. A first negative electrode active material, a negative electrode sheet, and a lithium-ion secondary battery were prepared using essentially the same method as in Example 1, except that: in the electronegative coating active material used as the first negative electrode active material, the carbon matrix of the doped carbon in the coating layer is hard carbon, and the electronegative doping element is N; different first negative electrode active materials were used to prepare the negative electrode sheet; and different negative electrode sheets were used to prepare the lithium-ion secondary battery. The remaining operation steps were the same as in Example 1.

[0714] (1) Preparation of hard carbon coated negative electrode active material

[0715] A high-nitrogen hard carbon precursor (polyacrylonitrile (PAN)) was mixed with graphite in the liquid phase and dispersed by stirring. The hard carbon precursor was dried at 200℃ to solidify it on the graphite surface. Then, it was carbonized at 1000℃ for 3 hours with a heating rate of 5℃ / min to prepare a hard carbon-coated negative electrode active material with a high nitrogen content in the hard carbon coating layer on its surface.

[0716] (2) The electronegative dopant element N is introduced into the hard carbon coating layer of the hard carbon coated negative electrode active material by gas displacement method.

[0717] N doping of hard carbon coating layer: In NH3 atmosphere, hard carbon coated negative electrode active material is heated at 600℃ for 4h at a heating rate of 5℃ / min to obtain electronegative coated active material. The coating layer includes carbon matrix and electronegative dopant element N, and the carbon matrix is ​​hard carbon.

[0718] Example 14. A negative electrode sheet and a lithium-ion secondary battery were prepared using essentially the same method as in Example 1, except that the negative electrode active material layer of the negative electrode sheet adopted a single-layer structure. The first negative electrode active material of Example 1 was used as the negative electrode active material of Example 14, and different negative electrode sheets were used to prepare lithium-ion secondary batteries. The negative electrode sheet was prepared using the following method:

[0719] The powder of negative electrode active material (electrone coated graphite) was mixed with thickener (sodium carboxymethyl cellulose), binder (SBR), and conductive agent (Super P) in a ratio of 96:0.8:2.0:1.2. The mixture was then mixed with solvent (deionized water) under vacuum stirring to prepare a negative electrode slurry with a solid content of 48 wt%.

[0720] The negative electrode slurry was uniformly coated onto both sides of the copper foil of the negative electrode current collector using an extrusion coating machine (the coating parameters on both sides of the negative electrode current collector were basically the same). The coating weight on one side of the negative electrode current collector was 0.13g / 1540.25mm. 2 After drying in an oven, the negative electrode sheet is compacted using a cold press to control its compaction density to 1.60 g / cm³. 3 The cold-pressed electrode sheet is then slitting and cutting to obtain the negative electrode sheet. Based on one side of the negative current collector, the areal density of the negative electrode sheet is approximately 8.44 mg / cm³. 2 .

[0721] The negative electrode active material is electronegatively coated graphite, and the negative electrode active body is artificial graphite, specifically secondary particle graphite (in this case, the negative electrode active material is both electronegatively coated secondary particle graphite and electronegatively coated secondary particles). The coating layer is doped soft carbon, and the carbon matrix is ​​soft carbon, including the electronegative dopant element N. The D of the negative electrode active material... v 50 represents 12μm. Artificial graphite is used as the negative electrode active material, which is secondary particle graphite.

[0722] In this example, the porosity of the negative electrode active material layer is approximately 28.91%.

[0723] Comparative Examples 1-4: The first negative electrode active material, the negative electrode sheet, and the lithium-ion secondary battery were prepared using the same method as in Example 1, except that the doping precursor in the coating step was omitted and electronegativity doping was not performed when preparing the first negative electrode active material.

[0724] Comparative Examples 1-4 were prepared using essentially the same methods as Examples 1 and 10-12, with the following differences: no doped precursor was introduced during the soft carbon coating of the first negative electrode active material; only asphalt was used for coating. The mass ratio of the first negative electrode active material, conductive agent, stabilizer, and binder was the same as in Examples 1 and 10-12. Different first negative electrode active materials were used to prepare the negative electrode sheets; different negative electrode sheets were used to prepare the lithium-ion secondary batteries. The remaining operational steps were the same as in the corresponding Examples 1 and 10-12. The sum of the surface densities of the coatings on both sides of the negative electrode sheet was the same as in the corresponding Examples 1 and 10-12.

[0725] Comparative Example 5. A first negative electrode active material, a negative electrode sheet, and a lithium-ion secondary battery were prepared using essentially the same method as in Example 13, except that: no electronegative dopant elements were introduced when preparing the first negative electrode active material; different first negative electrode active materials were used to prepare the negative electrode sheet; and different negative electrode sheets were used to prepare the lithium-ion secondary battery. The first negative electrode active material in Comparative Example 5 was a hard carbon-coated negative electrode active material, in which no electronegative dopant elements were doped.

[0726] As a non-limiting example, in the electronegative coated active materials of Examples 1-13, the average thickness of the coating layer is in the range of 1 nm to 500 nm, further in the range of 100 nm to 500 nm, and further in the range of 100 nm to 200 nm; respectively satisfying that at least a portion of the coating layer has a thickness in the range of 1 nm to 1000 nm; respectively satisfying that at least a portion of the coating layer has a thickness in the range of 100 nm to 1000 nm; respectively satisfying that at least a portion of the coating layer has a thickness in the range of 100 nm to 200 nm.

[0727] As a non-limiting example, in the electronegative coated active materials of Examples 1-13, the mass percentage of electronegative doping elements in the doped carbon and the coating layer is in the range of 0.1% to 1%, and in some examples it is in the range of 0.2% to 0.6%.

[0728] As a non-limiting example, in the electronegative coated active materials of Examples 1-13, the mass percentage of the coating layer in the electronegative coated active material is in the range of 0.2% to 5%, and further in the range of 0.5% to 3%.

[0729] As a non-limiting example, in the electronegativity-coated active materials of Examples 1-13, the average thickness of the coating layer is similar to the D of the first negative electrode active material. v The ratios of 50 were all in the range of 0.5% to 12.5%, and further in the range of 1% to 10%.

[0730] As a non-limiting example, in Examples 1-13, the ratio (F) of the thickness of the first negative electrode active layer (upper layer) to the sum of the thicknesses of the first negative electrode active layer and the second negative electrode active layer is... H The thickness of the first negative electrode active layer is in the range of 20% to 65%, and further in the range of 40% to 60%. The thickness of the first negative electrode active layer on one side is in the range of 10 μm to 50 μm, and further in the range of 20 μm to 40 μm.

[0731] In Examples 1-13, the porosity of the first negative electrode active layer is higher than that of the second negative electrode active layer, with the porosity of the first negative electrode active layer ranging from 24% to 28%. The ratio (R2) of the difference in compaction density between the second and first negative electrode active layers relative to the compaction density of the negative electrode sheet obtained after cold pressing is also considered. PΔ0 The values ​​are all in the range of -0.834 to 2, with most in the range of 0 to 2.

[0732] III. Testing Methods and Analysis

[0733] (I) Negative electrode sheet and negative electrode active material layer

[0734] The first negative electrode active layer is designated as the upper layer, and the second negative electrode active layer is designated as the lower layer.

[0735] 1. X-ray photoelectron spectroscopy (XPS) test.

[0736] XPS instrument: Thermo Scientific ESCALAB Xi+.

[0737] A clean and uncontaminated sample is placed in an ultra-high vacuum environment to prevent interference from airborne molecules. Then, high-energy X-rays (1486.6 eV aluminum Kα radiation) irradiate the sample...

Claims

1. A lithium-ion secondary battery, comprising a negative electrode sheet and an electrolyte; the negative electrode sheet comprising a negative current collector and a negative active material layer located on at least one side of the negative current collector, the negative active material layer comprising a first negative active layer; The first negative electrode active layer includes a first negative electrode active material, which includes an electronegatively coated active material. The electronegatively coated active material includes a negative electrode active body and a coating layer located on at least a portion of the surface of the negative electrode active body. The coating layer includes doped carbon, which includes a carbon matrix and an electronegatively dopant element. The carbon matrix includes one or more of soft carbon and hard carbon. The Pauling electronegativity scale of the electronegatively dopant element is denoted as χ1, and the Pauling electronegativity scale of carbon element is denoted as χ. C Then χ1 and χ C The difference between them, expressed in absolute terms, ranges from 0.03 to 0.

49.

2. The lithium-ion secondary battery according to claim 1, wherein, The electronegative doping element includes nitrogen, and the doping form of the electronegative doping element in the doped carbon includes at least one of pyridine nitrogen type and pyrrole nitrogen type.

3. The lithium-ion secondary battery according to claim 1 or 2, wherein, The negative electrode active material layer further includes a second negative electrode active layer, which is located between the negative electrode current collector and the first negative electrode active layer.

4. The lithium-ion secondary battery according to any one of claims 1 to 3, wherein, χ1 and χ C The difference between them, expressed in absolute terms, ranges from 0.04 to 0.

49.

5. The lithium-ion secondary battery according to any one of claims 1 to 3, wherein, The electronegative doping element is covalently bonded to the carbon matrix; Optionally, at least a portion of the electronegative dopant elements are covalently bonded to two or three carbon atoms simultaneously; Optionally, 80% to 100% of the electronegative dopant elements are simultaneously covalently bonded to 2 or 3 carbon atoms; Optionally, any one atom of the electronegative dopant element is covalently bonded to two or three carbon atoms simultaneously.

6. The lithium-ion secondary battery according to any one of claims 1, 3, and 5, wherein, The electronegative doping element in the doped carbon includes one or more of N, P, and S.

7. The lithium-ion secondary battery according to claim 6, wherein, The doped carbon satisfies one or more of the following characteristics: (ta1) The electronegative doping element includes a bridged N atom, wherein the bridged N atom is covalently bonded to at least one carbon atom; (ta2) The electronegative doping element includes a bridged S atom, which is covalently bonded to at least one carbon atom; (ta3) The electronegative doping element includes bridging P atoms, and at least a portion of the bridging P atoms have any covalent sites independently covalently bonded in a COP or CSP manner; optionally, 80% to 100% of the bridging P atoms have any covalent sites independently covalently bonded in a COP or CSP manner. (ta4) Among the electronegative doping elements of the doped carbon, the doping amount of N is higher than that of S. Optionally, among the electronegative doping elements of the doped carbon, the doping amount of N is higher than that of P, and the doping amount of N is higher than that of S.

8. The lithium-ion secondary battery according to any one of claims 1 to 7, wherein, The electronegative coated active material satisfies one or more of the following characteristics: (tb1) The average thickness of the coating layer is 1nm to 500nm, optionally 100nm to 500nm, and further optionally 100nm to 200nm; (tb2) The thickness of at least one of the coating layers is 1 nm to 1000 nm, optionally 100 nm to 1000 nm, and further optionally 100 nm to 200 nm; (tb3) The electronegative doping element in the doped carbon has a mass percentage of 0.1% to 0.6%, optionally 0.2% to 0.6%, and more preferably 0.2% to 0.4%; (tb4) The electronegative dopant element in the coating layer has a mass percentage of 0.1% to 0.6%, optionally 0.2% to 0.6%, and more preferably 0.2% to 0.4%; (tb5) The coating layer has a mass percentage of 0.2% to 5% in the electronegative coating active material, and can be optionally 0.5% to 3%; (tb6) The average thickness of the coating layer is related to the D of the first negative electrode active material. v The ratio of 50 is 0.5% to 12.5%, and can be selected as 1% to 10%; (tb7) The mass percentage of the doped carbon in the coating layer is 80% to 100%, and optionally 90% to 100%; (tb8) The mass percentage of soft carbon and hard carbon in the carbon matrix is ​​80% to 100%, optionally 90% to 100%; optionally, the mass percentage of soft carbon in the carbon matrix is ​​80% to 100%, further optionally 90% to 100%, or the mass percentage of hard carbon in the carbon matrix is ​​80% to 100%, further optionally 90% to 100%. (tb9) The carbon matrix is ​​soft carbon.

9. The lithium-ion secondary battery according to any one of claims 1 to 8, wherein, The electronegative coating active material accounts for 20% to 100% of the first negative electrode active material, and can be selected as 40% to 100%. Alternatively, the electronegative coating active material accounts for 20% to 80% of the amount of the first negative electrode active material, and more preferably 40% to 80%.

10. The lithium-ion secondary battery according to claim 9, wherein, The electronegatively coated active material includes electronegatively coated secondary particles, wherein the negative electrode active body in the electronegatively coated secondary particles is a secondary particle. Optionally, the electronegatively coated secondary particles account for 20% to 100% of the amount in the first negative electrode active material, and more preferably 40% to 100%. Alternatively, the electronegatively coated secondary particles account for 20% to 80% of the amount in the first negative electrode active material, and more preferably 40% to 80%.

11. The lithium-ion secondary battery according to any one of claims 1 to 10, wherein, The negative electrode active body includes one or more of carbon-based active materials and silicon-based active materials; Optionally, the first negative electrode active material satisfies one or more of the following characteristics: (tc1) The carbon-based active material includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon; (tc2) The first negative electrode active material includes a carbon-based material, wherein the mass percentage of the carbon-based material in the first negative electrode active material is 20% to 100%, optionally 20% to 80%, and further optionally 40% to 80%.

12. The lithium-ion secondary battery according to any one of claims 1 to 11, wherein, The lithium-ion secondary battery satisfies one or more of the following characteristics: (td1) The negative electrode active body in the electronegative coated active material includes graphite; (td2) The electronegatively coated active material includes electronegatively coated secondary particulate graphite, wherein the negative electrode active body in the electronegatively coated secondary particulate graphite is secondary particulate graphite, and the electronegatively coated secondary particulate graphite accounts for 20% to 100% of the first negative electrode active material, optionally 40% to 100%, and further optionally 40% to 80%. (td3) D of the first negative electrode active material v 50 is 8μm to 16μm, and can be selected as 10μm to 14μm; (td4) The porosity of the first negative electrode active layer is 22% to 32%, and can be selected as 26% to 30%; (td5) At at least one temperature condition from 20°C to 35°C, the ionic conductivity of the electrolyte is 13 mS / cm to 18 mS / cm; optionally, at 25°C, the ionic conductivity of the electrolyte is 13 mS / cm to 18 mS / cm.

13. The lithium-ion secondary battery according to any one of claims 1 to 12, wherein, The negative electrode active material layer further includes a second negative electrode active layer, which is located between the negative electrode current collector and the first negative electrode active layer. The lithium-ion secondary battery satisfies one or more of the following characteristics: (t1) The porosity of the first negative electrode active layer is higher than that of the second negative electrode active layer; (t2) The ratio of the difference in compaction density between the second negative electrode active layer and the first negative electrode active layer to the compaction density of the negative electrode sheet is denoted as R. PΔ R PΔ The range is 0 to 2, and can be selected as 0 to 0.

834. Further optionally, 0 <R PΔ ≤0.834; (t3) The charging rate of the first negative electrode active layer is higher than that of the second negative electrode active layer; optionally, the charging rate of the first negative electrode active layer is higher than that of the second negative electrode active layer.

14. The lithium-ion secondary battery according to any one of claims 13, wherein, The negative electrode active material layer further includes a second negative electrode active layer, which is located between the negative electrode current collector and the first negative electrode active layer; the second negative electrode active layer includes a second negative electrode active material, and the negative electrode sheet satisfies one or more of the following characteristics: (te1) D of the second negative electrode active material v 50 is 10μm to 20μm, and can be selected as 13μm to 17μm; (te2) D of the second negative electrode active material v 50 is higher than the D of the first negative electrode active material v 50; (te3) The compaction density of the second negative electrode active layer is higher than that of the first negative electrode active layer; (te4) The compaction density of the powder in the second negative electrode active layer is higher than that in the first negative electrode active layer.

15. The lithium-ion secondary battery according to any one of claims 1 to 14, wherein, The negative electrode active material layer further includes a second negative electrode active layer, which is located between the negative electrode current collector and the first negative electrode active layer; the negative electrode sheet satisfies one or more of the following characteristics: (tf1) On one side of the negative electrode current collector, the ratio of the areal density of the first negative electrode active layer to the areal density of the second negative electrode active layer is 2:8 to 6:4, and optionally 4:6 to 5:

5. (tf2) Taking the negative electrode current collector as a single side, the ratio of the thickness of the first negative electrode active layer to the sum of the thicknesses of the first negative electrode active layer and the second negative electrode active layer is denoted as F. H Satisfying 20% ​​≤ F H ≤65%, optionally, 40% ≤F H ≤60%; (tf3) The thickness of the first negative electrode active layer is 10 μm to 50 μm, and optionally 20 μm to 40 μm, depending on the single side of the negative electrode current collector.

16. The lithium-ion secondary battery according to any one of claims 1 to 15, wherein, The areal density of the negative electrode sheet is 5 mg / cm³, calculated on one side of the negative electrode current collector. 2 ~15mg / cm 2 .

17. The lithium-ion secondary battery according to any one of claims 1 to 16, wherein, The lithium-ion secondary battery further includes a positive electrode sheet, the positive electrode sheet includes a positive active layer, the positive active layer includes a positive active material, and the positive active material includes one or more of lithium phosphate active materials and lithium composite metal oxide active materials.

18. The lithium-ion secondary battery according to claim 17, wherein, The positive electrode active material includes a lithium phosphate-containing active material, and the positive electrode active material satisfies one or more of the following characteristics: (tg1) The mass percentage of the lithium phosphate-containing active material in the positive electrode active layer is greater than or equal to 80%, and can be selected as 80% to 97%; (tg2) The lithium-containing phosphate active materials include one or more of lithium iron phosphate, lithium iron phosphate and carbon composite materials, lithium manganese phosphate, lithium manganese phosphate and carbon composite materials, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composite materials. (tg3) The lithium phosphate active material includes a lithium phosphate active body and a carbon coating layer located on at least a portion of the surface of the lithium phosphate active body, wherein the carbon coating layer includes one or more of soft carbon, hard carbon and amorphous carbon.

19. A method for preparing a lithium-ion secondary battery, comprising preparing a negative electrode sheet; The preparation of the negative electrode sheet includes the following steps: A negative electrode active material layer is disposed on at least one side of the negative electrode current collector; wherein, The negative electrode active material layer includes a first negative electrode active layer, which includes a first negative electrode active material. The first negative electrode active material includes an electronegatively coated active material, which includes a negative electrode active body and a coating layer located on at least a portion of the surface of the negative electrode active body. The coating layer includes doped carbon, which includes a carbon matrix and an electronegatively dopant element. The carbon matrix includes one or more of soft carbon and hard carbon. The Pauling electronegativity scale of the electronegatively dopant element is denoted as χ1, and the Pauling electronegativity scale of carbon element is denoted as χ. C Then χ1 and χ C The absolute value of the difference is between 0.03 and 0.49, which means that 0.03 ≤ |χ1-χ C |≤0.

49.

20. The method for preparing a lithium-ion secondary battery according to claim 19, wherein, The carbon matrix in the doped carbon includes soft carbon, and the electronegative coated active material is prepared by an in-situ coating method; Optionally, the electronegative coated active material is prepared by a method comprising the following steps: In the presence of a doped precursor, the negative electrode active body and the soft carbon precursor are mixed and subjected to doping heat treatment and soft carbonization heat treatment, so that the soft carbon precursor and the doped precursor together form a doped soft carbon coating on at least a portion of the surface of the negative electrode active body; wherein, the doped precursor includes the electronegative doping element.

21. The method for preparing a lithium-ion secondary battery according to claim 20, wherein, The preparation method of the electronegative coated active material satisfies one or more of the following characteristics: (th1) The doped precursor includes an N-containing precursor, which includes one or more of urea and ammonia; (th2) The doped precursor includes an S-containing precursor, which includes one or more of sulfur and sulfur vapor; (th3) The doped precursor includes a P-containing precursor, which includes one or more of red phosphorus and phosphorus vapor; (th4) The doping heat treatment includes N doping treatment, and the conditions for carrying out the N doping treatment include: heating rate of 2℃ / min~10℃ / min, holding temperature of 400℃~800℃, and holding time of 1h~6h. (th5) The doping heat treatment includes S doping treatment, and the conditions for carrying out the S doping treatment include: heating rate of 2℃ / min~10℃ / min, holding temperature of 200℃~600℃, and holding time of 1h~6h. (th6) The doping heat treatment includes P doping treatment. The steps of performing the heat treatment include: performing one or both of O doping treatment and S doping treatment, followed by P doping treatment. The conditions for performing the P doping treatment include: a heating rate of 2℃ / min to 10℃ / min, a holding temperature of 200℃ to 600℃, and a holding time of 1h to 6h. The conditions for performing the O doping treatment include: heating at a heating rate of 2℃ / min to 10℃ / min in an air atmosphere, holding at a nitrogen atmosphere and at 400℃ to 800℃, and holding for 1h to 6h. (th7) In the steps of performing doping heat treatment and performing soft carbonization heat treatment, the soft carbon precursor includes pitch; (th8) The conditions for carrying out the soft carbonization heat treatment include: heat treatment in an inert gas atmosphere and at 700℃~1300℃.

22. The method for preparing a lithium-ion secondary battery according to claim 19, wherein, The carbon matrix in the doped carbon includes hard carbon, and the electronegative coated active material is prepared by an in-situ coating method; Optionally, the electronegative coated active material is prepared by a method comprising the following steps: At least a portion of the surface of the negative electrode active body is coated with hard carbon, a doping source including an electronegative doping element is introduced, and the electronegative doping element is introduced into the hard carbon by gas displacement method to form a doped hard carbon coating at least a portion of the surface of the negative electrode active body. Optionally, the gas replacement method may employ one of ammonia, sulfur vapor, and phosphorus vapor.

23. An electrical device comprising at least one of the lithium-ion secondary batteries according to any one of claims 1 to 18 and lithium-ion secondary batteries prepared by the preparation method of the lithium-ion secondary batteries according to any one of claims 19 to 22.

24. The use of the lithium-ion secondary battery according to any one of claims 1 to 18 in supplying and / or storing electrical energy; The application includes the process of charging the lithium-ion secondary battery at a rate of 2C or higher; Optionally, the application includes the process of charging the lithium-ion secondary battery at at least one rate from 2C to 6C. Optionally, the application includes the process of charging the lithium-ion secondary battery at at least one rate of 2C to 4C or 4C to 6C. Optionally, the maximum charging rate of the lithium-ion secondary battery is greater than or equal to 2C, and can be selected as 2C to 6C, or further selected as 2C to 4C or 4C to 6C.

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