A negative electrode sheet, a battery, a battery pack, and an electric device

Abstract

The provided negative electrode sheet of the present application is designed with multiple active material layers, and the crystallographic parameter C 101 + C 002 value and defect content A D / A G of the carbon material in each active material layer are controlled, so that the negative electrode sheet has both low polarization and high compaction, and the battery has both good kinetic performance and energy density.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more particularly to a negative electrode, a battery, a battery pack, and an electrical device. Background Technology

[0002] The negative electrode sheet in lithium-ion batteries plays a decisive role in achieving key battery performance. Therefore, meticulous design of the negative electrode sheet is necessary to meet the market's comprehensive demands for battery performance. Currently, lithium-ion battery negative electrodes typically employ multi-layer coating to increase the compaction density of the negative electrode sheet, thereby improving the battery's energy density. However, as the compaction density of the negative electrode sheet increases, the tortuosity and impedance of the electrolyte's liquid phase diffusion increase, leading to a decline in the kinetic performance of the negative electrode sheet and the occurrence of lithium plating problems.

[0003] Therefore, how to make batteries have both high energy density and good dynamic performance is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] This application provides a negative electrode, a battery, a battery pack, and an electrical device. This application achieves this by designing a multi-layered active material structure for the negative electrode and specifying the crystallographic parameters (C0) of the carbon material in each active material layer. 101 +C 002 By controlling the values ​​of OI and OI, the negative electrode sheet can achieve both high solid density and low impedance, thereby enabling the battery to have both excellent energy density and good kinetic performance.

[0005] This application provides a negative electrode sheet, comprising a current collector and n active material layers disposed on at least one surface of the current collector, where n is an integer greater than 1; the n active material layers are stacked in a direction perpendicular to the surface of the current collector; each active material layer comprises a carbon material; the carbon material in the (m+1)th active material layer comprises Cm+1... 101 +C 002 The value is less than the C of the carbon material in the m-th active material layer. 101 +C 002 Value; the difference between the OI value of the carbon material in the (m+1)th active material layer and the OI value of the carbon material in the mth active material layer is less than or equal to 4 and greater than or equal to -4; wherein, the mth layer is the active material layer closest to the current collector, the (m+1)th layer is the active material layer furthest from the current collector, m is an integer greater than or equal to 1 and less than n, C 101 With C 002 The two crystallographic parameters representing the carbon material, in nm, are calculated using Equations 1 and 2, respectively: C 101 =1.84×λ / (FWHM) 101 ×cosθ 101 Formula 1; C 002=0.89×λ / (FWHM) 002 ×cosθ 002 Equation 2; In Equations 1 and 2, FWHM 101 and FWHM 002 θ represents the half-width at half-maximum (FWHM) of the (101) and (002) diffraction peaks of the carbon material in the X-ray diffraction pattern of the monolayer active material layer, in radians; 101 and θ 002 The values ​​are half the 2θ values ​​of the (101) and (002) diffraction peaks of the carbon material in the X-ray diffraction pattern of the monolayer active material layer, respectively, in °; λ is the wavelength of the cathode ray used in X-ray diffraction, in nm; the OI value is the area ratio of the (004) and (110) diffraction peaks in the X-ray diffraction pattern of the monolayer active material layer.

[0006] In the negative electrode sheet described above, the difference between the OI value of the carbon material in the (m+1)th active material layer and the OI value of the carbon material in the mth active material layer is less than or equal to 3 and greater than or equal to -3.

[0007] In the negative electrode sheet described above, the OI value of the carbon material in the n-layer active material layer is 2 to 12.

[0008] The negative electrode as described above, wherein the carbon material in the m-th active material layer has C 101 +C 002 The value is related to the C of the carbon material in the (m+1)th active material layer. 101 +C 002 The difference in values ​​is 10–80 nm.

[0009] The negative electrode as described above, wherein the carbon material in the n active material layers contains C 101 +C 002 The value is 40-130nm.

[0010] The negative electrode sheet as described above, wherein the carbon material is a carbon-based negative electrode active material, and the carbon-based negative electrode active material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, and mesophase carbon microspheres.

[0011] The negative electrode as described above, where n is 2 to 4.

[0012] The negative electrode sheet described above, where n is 2, and C of the first active material layer... 101 +C 002 The value is 90–180 nm; and / or, the OI value of the first active material layer is 2–12; and / or, the C of the second active material layer is... 101 +C 002The value is 40–130 nm; and / or, the OI value of the second active material layer is 2–12.

[0013] A second aspect of this application provides a battery including the negative electrode provided in the first aspect of this application.

[0014] The battery as described above further includes a positive electrode and an electrolyte, the electrolyte being filled between the positive electrode and the negative electrode, the electrolyte comprising lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate.

[0015] The battery as described above, wherein the positive electrode comprises Li 1-x NiO2 (0≤x≤1), Li3FeO 3.5 One or more combinations of LiFeO2 with positive electrode active materials.

[0016] In the battery described above, the positive electrode includes a lithium replenishing agent.

[0017] In the battery described above, the lithium replenishing agent includes one or more combinations of Li2CO3, Li2C2O4, Li6CoO4, Li2NiO2, Li2Se, Li3N, Li2O2, Li2O, Li2S, Li2S2, Li5FeO4, lithium borate, and lithium thioborate.

[0018] A third aspect of this application provides a battery pack, and a second aspect of this application provides a battery.

[0019] The fourth aspect of this application provides an electrical device, including the negative electrode provided in the first aspect of this application, the battery provided in the second aspect of this application, or the battery pack provided in the third aspect of this application.

[0020] The negative electrode of this application has multiple active material layers, each containing carbon material. From a crystal structure perspective, this application aims to optimize the crystallographic parameters (C0, C0) of the carbon material in the active material layer near the current collector side of the negative electrode. 101 +C 002 The value is greater than the crystallographic parameter C of the carbon material in the active material layer away from the current collector side. 101 +C 002 This value is beneficial for the active material layer near the current collector to have a lower compressive modulus, increasing the high compaction density and thus ensuring the energy density of the battery. However, the crystallographic parameter C of the carbon material in the active material layer... 101 +C 002The higher the OI value, the greater the anisotropy of the carbon material. After rolling, the carbon material tends to align along the direction parallel to the current collector, increasing the tortuosity of lithium-ion liquid-phase diffusion and deteriorating the kinetic performance. The second aspect of this application addresses this by improving the tortuosity of lithium-ion liquid-phase diffusion, ensuring that the difference between the OI value of the active material layer far from the current collector and the OI value of the active material layer near the current collector is less than or equal to 4 and greater than or equal to -4. This guarantees a good ion diffusion pathway throughout the entire active material layer of the negative electrode, reducing the ion diffusion resistance of the negative electrode. In summary, this application designs a multi-layered active material layer for the negative electrode and optimizes the crystallographic parameters of the carbon material in each active material layer. 101 +C 002 By controlling the values ​​of OI and OI, the negative electrode sheet can achieve both high compaction and low impedance, thereby enabling the battery to have both excellent energy density and kinetic performance. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0022] Figure 1 The XRD pattern of the negative electrode sheet of Embodiment 1 of this application; and

[0023] Figure 2 The image shows the XRD pattern of the negative electrode of Comparative Example 1 of this application. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] For the negative electrode of a battery, the material properties of its active material layers and the electrode structure determine the battery's energy density and fast-charging performance. From a material property perspective, increasing the crystallographic parameters of carbon materials can reduce their modulus, which is beneficial for increasing compaction density. Conversely, reducing the crystallographic parameters can reduce the anisotropy of carbon materials, and increasing the proportion of carbon material end faces is beneficial for improving material kinetics. Here, end faces refer to the surfaces of carbon materials where lithium intercalation reactions can occur; for example, in graphite, the end faces are the surfaces parallel to the graphite stacking direction. However, it is difficult to achieve a balance between battery energy density and fast-charging performance solely from a material property perspective. Therefore, the structural properties of the negative electrode also need to be considered. From the perspective of negative electrode structure, multi-layer coating and other methods, combined with the arrangement characteristics of carbon materials in each active material layer, can be used to optimize and construct a negative electrode that balances high energy density and fast-charging capability.

[0026] Based on this, the first aspect of this application provides a negative electrode sheet, which includes a current collector and n active material layers disposed on at least one surface of the current collector, where n is an integer greater than 1; the n active material layers are stacked in a direction perpendicular to the surface of the current collector.

[0027] Each of the active material layers comprises carbon materials;

[0028] The carbon material in the (m+1)th active material layer 101 +C 002 The value is less than the C of the carbon material in the m-th active material layer. 101 +C 002 The difference between the OI value of the carbon material in the (m+1)th active material layer and the OI value of the carbon material in the mth active material layer is less than or equal to 4 and greater than or equal to -4.

[0029] Wherein, the m-th layer is the active material layer closest to the current collector, and the (m+1)-th layer is the active material layer furthest from the current collector, where m is an integer greater than or equal to 1 and less than n; C 101 With C 002 The two crystallographic parameters representing carbon materials, in nm, are calculated using Equations 1 and 2, respectively:

[0030] C 101 =1.84×λ / (FWHM) 101 ×cosθ 101 Formula 1;

[0031] C 002 =0.89×λ / (FWHM) 002 ×cosθ 002 Equation 2;

[0032] In Equations 1 and 2, FWHM 101 and FWHM 002θ represents the half-width at half-maximum (FWHM) of the (101) and (002) diffraction peaks of the carbon material in the X-ray diffraction pattern of the monolayer active material layer, in radians; 101 and θ 002 λ represents half the 2θ value of the (101) and (002) diffraction peaks of the carbon material in the X-ray diffraction pattern of the monolayer active material layer, in °; λ is the wavelength of the cathode ray used in X-ray diffraction, in nm; OI is the area ratio of the (004) and (110) diffraction peaks in the X-ray diffraction pattern of the monolayer active material layer.

[0033] For example, the difference can be 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.8, 0.5, 0.3, 0.1, -4, -3.5, -3, -2.5, -2, -1.5, -1, -0.8, -0.5, -0.3, -0.1, or a range of any two of these values.

[0034] In detail, the full width at half maximum (FWHM) of the (101) and (002) diffraction peaks of carbon materials in the X-ray diffraction pattern of the active material layer refers to the peak width at half the peak height of the (101) and (002) diffraction peaks. It should be noted that the (101) and (002) diffraction peaks of carbon materials in the X-ray diffraction pattern of this application refer to the (101) and (002) diffraction peaks of all types of carbon materials in the active material layer, including carbon materials existing in the form of active materials and carbon materials existing in the form of conductive agents. Since the content of conductive agents in the negative electrode active material layer is low, its impact on the test results is minimal. In the X-ray diffraction pattern, the FWHM can be used to estimate the average size of carbon material grains, crystal defects, and for phase analysis.

[0035] λ is determined by the cathode material (i.e., target material) of the X-ray tube and the operating conditions of the X-ray tube. In one specific embodiment, the cathode ray wavelength (Kα of the copper target) used for X-ray diffraction is λ, which is 0.15418 nm.

[0036] The crystallographic parameters C1 representing the (101) and (002) crystal planes of carbon materials are extracted using the evolved Scherrer formula. 101 C 002 The above C 101 It can reflect the height of the unit cell of carbon materials, C 002 It can reflect the length or width of the unit cell of carbon materials, C 101 +C 002 It can reflect the ordered cell size and the proportion of ordered structure in carbon materials.

[0037] The OI value, or orientation value, is used to represent the orientation index of carbon materials in the negative electrode, that is, the degree of anisotropy of the arrangement of carbon materials in the negative electrode.

[0038] The negative electrode of this application has multiple active material layers, each containing carbon material. From a crystal structure perspective, this application aims to optimize the crystallographic parameters (C0, C0) of the carbon material in the active material layer near the current collector side of the negative electrode. 101 +C 002 The value is greater than the crystallographic parameter C of the carbon material in the active material layer away from the current collector side. 101 +C 002 This value is beneficial for the active material layer near the current collector to have a lower compressive modulus, increasing the high compaction density and thus ensuring the energy density of the battery. However, the crystallographic parameter C of the carbon material in the active material layer... 101 +C 002 The higher the value, the higher the anisotropy of the carbon material. After rolling, the carbon material tends to align along the direction parallel to the current collector, increasing the tortuosity of lithium-ion liquid phase diffusion and deteriorating the kinetic performance. The second aspect of this invention aims to improve the tortuosity of lithium-ion liquid phase diffusion by ensuring that the difference between the OI value of the active material layer far from the current collector and the OI value of the active material layer near the current collector is less than or equal to 4 and greater than or equal to -4, so as to ensure that the entire active material layer in the negative electrode has a good ion diffusion path and reduce the ion diffusion resistance of the negative electrode.

[0039] In summary, this application designs a multi-layered active material sheet for the negative electrode and specifies the crystallographic parameters C of the carbon material in each active material layer. 101 +C 002 By controlling the values ​​of OI and OI, the negative electrode sheet can achieve both high compaction and low impedance, thereby enabling the battery to have both excellent energy density and kinetic performance.

[0040] It is understandable that the carbon content of each active material layer is C. 101 +C 002 The value can be obtained through XRD testing, using copper Kα rays as the light source, exciting X-rays at 40 kV and 20 mA, with a scan rate of 5° / min, and using K... β Filter removes K β The influence of X-rays on the shape and position of spectral peaks.

[0041] The testing steps include:

[0042] 1. After the battery is fully discharged, disassemble it to obtain the negative electrode sheet; immerse the negative electrode sheet in dimethyl carbonate (DMC) for 10-20 minutes to clean the residual electrolyte, and then dry the negative electrode sheet.

[0043] 2. Place the dried negative electrode sheet on the XRD test sample stage and perform grazing incidence XRD test (GIXRD) on the surface negative electrode active material layer (nth layer) on the side away from the current collector. The incident angle is 1-3° (corresponding to X-ray irradiation depth of 10-300nm) to obtain the XRD spectrum of this layer.

[0044] 3. From the XRD spectrum of the obtained monolayer negative electrode active material layer, read the diffraction angle 2θ (in °) of the diffraction peaks corresponding to the (101) and (002) crystal planes of the carbon material, and the half-width at half-maximum (i.e., the diffraction angle corresponding to 1 / 2 peak height, in radians) of these two diffraction peaks, and then according to formula C 101 =1.84×λ / (FWHM) 101 ×cosθ 101 C 002 =0.89×λ / (FWHM) 002 ×cosθ 002 The C values ​​for each layer were calculated separately. 101 With C 002 value.

[0045] 4. Remove the nth active material layer in the negative electrode using ion thinning or ion polishing to expose the adjacent n-1 active material layers. Then repeat steps 2) and 3) to calculate the C of the n-1th layer. 101 With C 002 value.

[0046] 5. Repeat step 4 until the C of the first layer is calculated. 101 With C 002 value.

[0047] It should be noted that in XRD patterns, the diffraction angle and full width at half maximum (FWHM) of a diffraction peak on a specific crystal plane are directly read in degrees. When calculating the FWHM... 101 and FWHM 002 When doing so, the half-peak width value, which is measured in degrees, needs to be converted to a value calculated in radians.

[0048] Understandably, the OI value of the carbon material in each active material layer can also be obtained through XRD testing.

[0049] The testing steps include:

[0050] 1. After the battery is fully discharged, disassemble it to obtain the negative electrode sheet; immerse the negative electrode sheet in dimethyl carbonate (DMC) for 10-20 minutes to clean the residual electrolyte, and then dry the negative electrode sheet.

[0051] 2. Place the dried negative electrode sheet on the XRD test sample stage and perform grazing incidence XRD test (GIXRD) on the surface negative electrode active material layer (nth layer) on the side away from the current collector. The incident angle is 1-3° (corresponding to X-ray irradiation depth of 10-300nm) to obtain the XRD spectrum of this layer.

[0052] 3. From the XRD spectrum of the obtained monolayer negative electrode active material layer, obtain the peak areas of the diffraction peaks corresponding to the (004) and (110) crystal planes of the carbon material, and calculate the area ratio of the (004) diffraction peak and the (110) diffraction peak to obtain the OI value of the layer.

[0053] 4. Use ion thinning or ion polishing to remove the nth active material layer in the above negative electrode to expose the adjacent n-1 active material layers, and then repeat steps 2) and 3) to calculate the OI value of the n-1th layer.

[0054] 5. Repeat step 4 until the OI value of layer 1 is calculated.

[0055] In a preferred embodiment, the difference between the OI value of the carbon material in the (m+1)th active material layer and the OI value of the carbon material in the mth active material layer is less than or equal to 3 and greater than or equal to -3.

[0056] When the difference between the OI value of the (m+1)th active material layer and the OI value of the mth active material layer is within the above range, the abrupt change in the contact interface between adjacent active material layers caused by the large difference in the orientation degree of carbon materials between each active material layer can be alleviated, thus improving the lithium plating problem of the negative electrode.

[0057] For example, the difference can be 3, 2.5, 2, 1.5, 1, 0.8, 0.5, 0.3, 0.1, -3, -2.5, -2, -1.5, -1, -0.8, -0.5, -0.3, -0.1, or a range of any two of these values.

[0058] In some specific implementations, the OI value of the carbon material in the n-layer active material layer is 2 to 12.

[0059] It is understandable that the OI value of the carbon material in the n-layer active material is 2 to 12, which refers to the OI value of the entire negative electrode active material layer, and can be obtained by analyzing and calculating the XRD pattern of the negative electrode sheet.

[0060] Keeping the OI value of the carbon material in the n-layer active material layer within the above range is beneficial to improving the diffusion efficiency of lithium ions and enhancing the dynamic performance of the battery. At the same time, it can also alleviate the cracking of the negative electrode active material layer caused by the breathing effect of carbon material during the lithium ion deintercalation process.

[0061] For example, the OI value of the carbon material in the n-layer active material layer can be 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2 or any two of these values.

[0062] In some specific embodiments, the carbon material in the m-th active material layer has C 101 +C 002 The value is related to the C of the carbon material in the (m+1)th active material layer. 101 +C 002 The difference in values ​​is 10–80 nm.

[0063] C in the (m+1)th active material layer 101 +C 002 When the value is less than that of the m-th active material layer, the C value between adjacent layers is reduced. 101 +C 002 The difference in values ​​is within the above range, which can avoid the formation of abrupt changes in pore size between adjacent active material layers due to excessive differences in pore structure between each negative electrode active material layer. This is conducive to further improving the diffusion efficiency of lithium ions, enhancing the dynamic performance of the battery, and improving the problem of lithium plating on the negative electrode.

[0064] For example, the difference can be a range of 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 60nm, 70nm, 80nm, or any two of these values.

[0065] In some specific embodiments, the carbon material in the m-th active material layer has C 101 +C 002 The value is related to the C of the carbon material in the (m+1)th active material layer. 101 +C 002 The difference in values ​​is 10–50 nm.

[0066] In some specific embodiments, the carbon material in the n-layer active material layer is C 101 +C 002 The value is 40-130nm.

[0067] It is understandable that the carbon material in the n-layer active material layer has C 101 +C 002 The value refers to the C of the entire negative electrode active material layer. 101 +C 002 The value can be calculated through XRD pattern analysis of the negative electrode.

[0068] C in the (m+1)th active material layer 101 +C 002 When the value is less than that of the m-th active material layer, the C of the entire negative electrode active material layer is reduced. 101 +C002 Within the above range, carbon materials can have a high overall ordered structure size, and after forming interlayer compounds, they can store more active ions. In addition, the material modulus is relatively low, which is conducive to further improving the compaction density of the negative electrode sheet.

[0069] For example, C 101 +C 002 The values ​​include, but are not limited to, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, or any two of the above values.

[0070] In some specific embodiments, the carbon material is a carbon-based anode active material, which includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, and mesophase carbon microspheres.

[0071] It is understandable that different carbon materials have different degrees of order, which in turn affects their crystallographic parameters C. 101 +C 002 Value, to meet the C values ​​in different active material layers 101 +C 002 Due to the limitation of the value, the above-mentioned carbon materials can be used alone or in combination in different active material layers.

[0072] Furthermore, when the carbon material is natural graphite, it can be modified to improve its degree of order, thereby affecting the crystallographic parameters C. 101 +C 002 The value can be adjusted. Specifically, modification methods can include coating treatment, filling treatment, pressurization treatment, calcination treatment, spheroidization, secondary granulation, etc.

[0073] Furthermore, when the carbon material is artificial graphite, the artificial graphite precursor can be selected or modified to improve its degree of order, thereby affecting the crystallographic parameter C. 101 +C 002 The value is adjusted. Specifically, modification methods can include coating treatment, filling treatment, pressure treatment, calcination treatment, etc. Artificial graphite precursors include, but are not limited to, needle coke, petroleum coke, and pitch coke.

[0074] Furthermore, when the carbon material is hard carbon or soft carbon, the hard carbon or soft carbon precursor can be selectively or modified to improve its degree of order, thereby affecting the crystallographic parameter C. 101 +C 002The value is adjusted. Specifically, modification methods can include coating treatment, filling treatment, pressure treatment, calcination treatment, etc. Hard carbon precursors include, but are not limited to, coconut shell, straw, walnut shell, starch, sucrose, phenolic resin, epoxy resin, etc. Soft carbon precursors include, but are not limited to, asphalt, anthracite, etc.

[0075] In some specific embodiments, the carbon-based negative electrode active material includes artificial graphite; based on the mass of the n active material layers, the mass content of artificial graphite is greater than or equal to 20%.

[0076] Ensuring that the mass content of the artificial graphite meets the above-mentioned range is beneficial to improving the diffusion resistance of lithium ions in the negative electrode and increasing kinetic performance.

[0077] For example, the mass content of artificial graphite is 20%, 24%, 30%, 35%, 38%, 42%, 50%, 58%, 65%, 70%, 72%, 78%, 83%, 88%, 92%, 96%, 100%, or any combination thereof.

[0078] In some specific embodiments, the carbon-based anode active material includes artificial graphite; based on the mass of the n active material layers, the mass content of artificial graphite is greater than or equal to 70%.

[0079] Ensuring that the mass content of artificial graphite meets the above range is beneficial for improving the battery's dynamic performance while maintaining a certain cycle life.

[0080] In some specific embodiments, the carbon-based negative electrode active material includes artificial graphite and natural graphite; based on the mass of a single active material layer, the mass content of artificial graphite in the (m+1)th active material layer is greater than the mass content of artificial graphite in the mth active material layer.

[0081] The (m+1)th active material layer is close to the separator side. Due to its high lithium-ion concentration and preferential lithium intercalation, it has high requirements for the intrinsic kinetics of the negative electrode active material. Therefore, the mass content of artificial graphite in the (m+1)th active material layer is greater than that in the mth active material layer. This can increase the lithium intercalation capability and prevent the formation of lithium dendrites.

[0082] In one specific embodiment, the n-layer active material layer of this application includes a negative electrode active material, a binder, an optional conductive agent, and optional other additives. The binder and conductive agent can be selected according to conventional methods in the art. Exemplary binders include, but are not limited to, one or more of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylates (such as polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, etc.), polyolefins (such as polypropylene, polyethylene, etc.), carboxymethyl cellulose (CMC), and sodium alginate. Conductive agents include, but are not limited to, one or more of carbon nanotubes, carbon black, graphene, carbon fibers, acetylene black, Ketjen black, and graphite flakes. Other additives include, but are not limited to, one or more of mesoporous silica, mesoporous alumina, silica microspheres, and alumina nanoparticles. Other additives are non-conductive and inert in the battery. When added to the electrode, they not only ensure that the electrode has good liquid absorption and retention capabilities, but also reduce the side reactions between the conductive agent and the electrolyte, thereby improving the lifespan of the electrode.

[0083] The negative electrode active material of this application may also include one or more of silicon-based materials, tin-based materials, and lithium metal materials.

[0084] Based on the total mass of the n active material layers, the mass percentage of the negative electrode active material in this application is 85-97%, the mass percentage of the binder is 0.5-2%, the mass percentage of the conductive agent is 0.5-2%, and the mass percentage of other additives is 0.5-2%.

[0085] This application does not specifically limit the type of current collector in the negative electrode sheet, which may include, but is not limited to, any one of copper foil, composite copper foil, carbon-coated copper foil, aluminum foil, composite aluminum foil, carbon-coated aluminum foil, stainless steel foil, copper alloy foil, and copper-plated film.

[0086] In some specific implementations, n is 2 to 4, meaning the negative electrode can have 2, 3, or 4 active material layers. Within this range, it is possible to ensure both excellent specific capacity and kinetic performance of the electrode, while also achieving excellent production efficiency. Increasing the number of active material layers further adds extra steps to slurry preparation, buffering, and coating, leading to increased production complexity and reduced production efficiency and electrode yield.

[0087] In one optional implementation, when n is 2, the C of the first active material layer 101 +C 002 Values ​​range from 90 to 180 nm; and / or,

[0088] The OI value of the first active material layer is 2–12; and / or,

[0089] C of the second active material layer 101 +C 002 Values ​​range from 15 to 130 nm; and / or,

[0090] The OI value of the second active material layer is 2 to 12.

[0091] Experimental verification revealed that when n is 2, the C of each active material layer is increased. 101 +C 002 When the value and / or OI value are within the above range, both the material properties in the active material layer and the electrode structure properties are satisfied, so that the negative electrode can have better specific capacity and kinetic performance, and the production efficiency is optimal.

[0092] For example, the OI value of the first active material layer is 2, 3, 3.7, 4.2, 5.03, 6.53, 6.73, 7.66, 7.68, 8.22, 9, 10, 10.56, 11.02, 11.27, 11.4, 11.58, 11.63, 12.16, or any combination thereof.

[0093] For example, the OI value of the first active material layer is 2, 3, 3.7, 4.2, 5.03, 6.53, 6.73, 7.66, 7.68, 8.22, 9, 10, 10.56, 11.02, 11.27, 11.4, 11.58, 11.63, 12.16, or any combination thereof.

[0094] For example, the first active material layer C 101 +C 002 Value

[0095] For example, the first active material layer C 101 +C 002 Value

[0096] In some specific implementations, the compressive modulus of the (m+1)th active material layer is greater than that of the mth active material layer.

[0097] Compression modulus refers to the ability of an active material layer to resist deformation under pressure. The (m+1)th active material layer, which is farther from the current collector surface, has a higher compression modulus than the mth active material layer. This is beneficial for the active material layer as a whole to have a higher resistance to compression deformation, and for the active material layer farther from the current collector surface to better maintain its pore structure, thereby having a lower liquid phase diffusion resistance and further improving the dynamic performance of the battery.

[0098] The active material layer typically includes carbon-active materials, binders, conductive agents, etc., except for the carbon material C.101 +C 002 In addition to value control, the compressive modulus of the entire active material layer can be adjusted by selecting binder and conductive agent materials and controlling particle morphology, thereby achieving a compressive modulus of the (m+1)th active material layer that is greater than that of the mth active material layer.

[0099] In some specific implementations, the porosity of the (m+1)th active material layer is greater than that of the mth active material layer.

[0100] Porosity refers to the ratio of pore volume to total volume in the active material layer, expressed as a percentage. The pores in the active material layer provide channels for electrolyte permeation, allowing active ions to migrate rapidly to the surface of the active material during charging and discharging, resulting in good electrode kinetic performance. By limiting the porosity of the (m+1)th active material layer to be greater than that of the mth active material layer, a smoother diffusion and transport channel for the electrolyte can be provided, thereby improving the battery's kinetic performance.

[0101] Similarly, except for the C of carbon materials 101 +C 002 In addition to value control, the compressive modulus of the entire active material layer can be adjusted by selecting binder and conductive agent materials and controlling particle morphology, thereby achieving a porosity greater than that of the m+1th active material layer.

[0102] In some specific implementations, the areal density of the negative electrode sheet on one side is 75 g / m². 2 ~175g / m 2 The areal density of the negative electrode refers to the mass of active material coated on one side of a unit area of ​​the current collector. A higher areal density is beneficial for increasing the energy density of the battery, but it also increases the transport paths of active ions and electrons, leading to increased internal resistance and affecting the battery's dynamic performance. Controlling the areal density of the negative electrode within the aforementioned range is beneficial for achieving both lower internal resistance and higher energy density.

[0103] For example, the areal density of one side of the negative electrode can be 75 g / m². 2 100g / m 2 125g / m 2 150g / m 2 175g / m 2 Or the range formed by any two of them.

[0104] In one specific embodiment, the compaction density of the negative electrode sheet is 1.4 g / cc to 1.8 g / cc. The compaction density of the negative electrode sheet refers to the mass of the negative electrode material per unit volume, and it is an important parameter for measuring the tightness of the negative electrode material packing. It is understood that a higher compaction density can increase the mass of the negative electrode active material per unit volume, thereby improving the energy density of the battery. However, it also increases the transport path of active ions, thus affecting the kinetic performance of the electrode. Therefore, controlling the compaction density of the negative electrode sheet within the aforementioned range is beneficial for achieving both high energy density and excellent kinetic performance in the battery.

[0105] For example, the compaction density of the negative electrode can be 1.4 g / cc, 1.45 g / cc, 1.5 g / cc, 1.55 g / cc, 1.6 g / cc, 1.65 g / cc, 1.7 g / cc, 1.75 g / cc, 1.8 g / cc, or any two of the above values.

[0106] The first aspect of this application provides a negative electrode sheet, which can be obtained by the following preparation method.

[0107] The preparation method includes:

[0108] Provide current collectors;

[0109] A series of n carbon-containing negative electrode slurries are coated on at least one side of the current collector, and the orientation of the carbon materials in the n negative electrode slurries is adjusted using a magnetic field; and

[0110] The negative electrode sheet is obtained after drying.

[0111] Each negative electrode slurry further includes a conductive agent, a binder, and optionally other additives. A first slurry is obtained by dispersing a first negative electrode active material, a first conductive agent, and a first binder in a solvent; similarly, a nth negative electrode active material, an nth conductive agent, and an nth binder are dispersed in a solvent to obtain an nth slurry. The first slurry can be first coated onto one or both surfaces of the current collector, followed by coating the nth slurry onto the surface of the (n-1)th active material layer. Finally, drying and rolling are performed to prepare the negative electrode sheet. Alternatively, the first slurry...nth slurry can be placed in a multilayer coating equipment for simultaneous coating.

[0112] This application achieves directional deflection of carbon materials by increasing the magnetic field, thereby adjusting the orientation degree (OI value) of the carbon materials and optimizing their kinetic characteristics. Since carbon-based active materials are diamagnetic, when an external magnetic field is applied, their magnetic moments align in the opposite direction to the applied magnetic field, causing the entire carbon-based material to be repelled by the magnetic field, aligning its basal planes with the magnetic field direction. For carbon materials with larger crystallographic parameters, their diamagnetic strength is higher, and their absolute magnetic susceptibility is higher than that of carbon materials with smaller crystallographic parameters. Therefore, under a uniform magnetic field strength, placing highly ordered carbon materials (i.e., high crystallographic parameters) near the current collector not only improves energy density but also allows for selective deflection, optimizing the orientation degree of the active material layer near the current collector to further enhance the kinetic performance of the negative electrode, ultimately achieving a battery that balances energy density and kinetics.

[0113] In one specific embodiment, the current collector includes a first surface and a second surface disposed opposite to each other. A magnetic field is disposed on one side of the first surface and / or the second surface, wherein the magnetic moment direction of the magnetic field makes an angle of 10° to 90° with the current collector; and / or, the strength of the magnetic field is 0.1 to 10T. In this application, by controlling the angle between the magnetic moment direction of the magnetic field and the surface of the negative electrode current collector to be 10°-90° (e.g., 20°, 30°, 40°, 50°, 60°, 70°, 75°, 80°, or 90°, etc.), the graphite in the negative electrode slurry can be oriented under the action of the magnetic field after being coated on the negative electrode current collector, achieving directional induction and obtaining a smooth ion transport and electron transport path.

[0114] In this application, the magnetic field can be generated by, but is not limited to, a magnetic field device, which can be, but is not limited to, an electromagnet, a permanent magnet, etc., and can be selected as needed. In one embodiment of this application, the magnetic field device can be disposed on the side of the first surface away from the second surface and spaced apart from the first surface; and / or, the magnetic field device can be disposed on the side of the second surface away from the first surface and spaced apart from the second surface.

[0115] In one specific embodiment, the angle between the magnetic moment direction of the magnetic field and the first surface is 30°-90°, which is beneficial for further optimizing the graphite arrangement and improving the performance of the negative electrode. In another embodiment of this application, the angle between the magnetic moment direction of the magnetic field and the first surface is 40°-80°. In yet another embodiment of this application, the angle between the magnetic moment direction of the magnetic field and the first surface is 60°-90°, which can further enable the graphite to align vertically, reduce the tortuosity of the negative electrode, optimize the ion transport path in the thickness direction of the negative electrode, and further improve the performance of the negative electrode.

[0116] In one specific embodiment, the magnetic field undergoes at least one of reciprocating and rotational motion. That is, while maintaining an angle of 10°-90° between the magnetic moment direction and the first surface, the magnetic field can undergo reciprocating and / or rotational motion, thereby further improving the graphite arrangement and enhancing the performance of the negative electrode. The magnetic field can undergo reciprocating motion, rotational motion, or both simultaneously. In one embodiment of this application, the angle between the direction of the reciprocating motion and the extension direction of the negative electrode current collector is 0°-90° (e.g., 10°, 20°, 30°, 40°, 45°, 50°, 60°, 70°, 80°, or 90°). It is understood that the extension direction of the negative electrode current collector is its length direction. By employing reciprocating motion, the graphite arrangement angle can be improved, further optimizing the diffusion paths of ions parallel to the negative electrode current collector direction and the electron transport direction, thus enhancing the performance of the negative electrode.

[0117] In one specific embodiment, the angle between the direction of the reciprocating motion and the extension direction of the negative electrode current collector is 10°-80°. In another embodiment of this application, the angle between the direction of the reciprocating motion and the extension direction of the negative electrode current collector is 30°-90°. In yet another embodiment of this application, the angle between the direction of the reciprocating motion and the extension direction of the negative electrode current collector is 40°-90°. In still another embodiment of this application, the angle between the direction of the reciprocating motion and the extension direction of the negative electrode current collector is 50°-90°.

[0118] In this application, rotational motion can improve the uniformity of graphite distribution; the rotational motion occurs along an axis. In one specific embodiment, a magnetic field device generates a magnetic field, and the magnetic field device can rotate along its central axis, thereby causing the magnetic field to rotate. Of course, in other embodiments, the magnetic field device can rotate along other axes.

[0119] In one specific embodiment, the magnetic field strength is 0.1T-10T, which can induce orientation in graphite, improve its orientation, reduce the preparation difficulty, and does not affect the negative electrode fluid, thus obtaining a negative electrode with excellent performance. Specifically, the magnetic field strength can be, but is not limited to, 0.1T, 0.5T, 1T, 2T, 3T, 4T, 5T, 6T, 7T, 8T, 9T, or 10T. In one embodiment, the magnetic field strength can be 0.2T-5T. In another embodiment, the magnetic field strength can be 0.5T-7T. In yet another embodiment, the magnetic field strength can be 0.2T-3T. In yet another embodiment, the magnetic field strength can be 0.8T-4T, which is beneficial for further improving the performance of the negative electrode.

[0120] In one specific embodiment, the process after drying includes roller pressing. Roller pressing controls the thickness of the negative electrode, improves compaction density and bonding strength, and further enhances the orderly arrangement of graphite. In one embodiment of this application, the roller pressing pressure is 5t (tons) to 40t, and the roller speed is 0.5m / s to 5m / s. Specifically, the roller pressing pressure can be, but is not limited to, 5t, 9t, 10t, 12t, 15t, 20t, 25t, 30t, 35t, or 40t, etc., and the roller speed can be, but is not limited to, 0.5m / s, 1m / s, 1.5m / s, 1.8m / s, or 5m / s, etc.

[0121] A second aspect of this application also provides a battery, including the negative electrode provided in the first aspect of this application.

[0122] Furthermore, the battery of this application also includes a positive electrode, a separator, and an electrolyte disposed between the positive electrode and the aforementioned negative electrode. This battery can use any battery including the aforementioned negative electrode, including but not limited to lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, etc.

[0123] The separator in a battery serves to isolate the positive and negative electrodes. This application does not limit the type of separator and any separator material in existing batteries can be used. For example, the separator includes, but is not limited to, single-layer PP (polypropylene) film, single-layer PE (polyethylene) film, double-layer PP / PE film, double-layer PP / PP film, and triple-layer PP / PE / PP film.

[0124] The electrolyte includes an electrolyte salt and an organic solvent. The electrolyte salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. This mixed lithium salt, due to its suitable solvation effect, is conducive to shuttling between the layers of multilayer negative electrode active material to improve fast charging performance.

[0125] The positive electrode sheet includes a positive current collector and a positive active material layer loaded on at least one side of the positive current collector. The positive active layer includes a positive active material and a lithium supplement agent.

[0126] In one specific embodiment, the positive electrode active material can be any positive electrode active material known in the art for use in lithium-ion batteries, including but not limited to one or more of phosphate-based positive electrode active materials and transition metal oxide positive electrode active materials. In some embodiments, the phosphate-based positive electrode active material can be, for example, one or more of lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate, lithium nickel phosphate, and lithium manganese iron phosphate; the transition metal oxide positive electrode active material can be, for example, one or more of ternary positive electrode materials and lithium-rich layered oxides. In some embodiments, the positive electrode active material includes, but is not limited to, a doped or coated positive electrode active material, or an undoped or uncoated positive electrode active material. In the embodiments of this application, the positive electrode active material includes, but is not limited to, the examples described above.

[0127] In some embodiments of this application, the lithium supplementer added to the positive electrode slurry includes one or more combinations of Li₂CO₃, Li₂C₂O₄, Li₆CoO₄, Li₂NiO₂, Li₂Se, Li₃N, Li₂O₂, Li₂O, Li₂S, Li₂S₂, Li₅FeO₄, lithium borate, and lithium thioborate. Different lithium supplementers correspond to different delithiation potentials and have different effects on the formation and stabilization of lithium-rich and oxygen-rich lithium compounds in the solid electrolyte interface film. They can be selected in conjunction with different electrochemical systems and formation processes.

[0128] In one specific embodiment, the mass of the lithium replenishing agent added to the positive electrode active material layer is 0.3% to 5% of the mass of the positive electrode active material. In some specific embodiments, the mass of the lithium replenishing agent can be, for example, 0.3%, 0.4%, 0.5%, 0.7%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2.0%, 2.3%, 2.5%, 2.8%, 3.0%, 3.5%, 4%, 4.5%, or 5% of the mass of the positive electrode active material. A suitable range of lithium replenishing agent content is beneficial for improving the battery's energy density, fast-charging performance, and cycle life.

[0129] In this application, the positive current collector can be any positive current collector known in the art. In some embodiments of this application, the positive current collector can be, for example, aluminum foil.

[0130] In some embodiments of this application, the positive electrode also includes Li 1-x NiO2 (0≤x≤1), Li3FeO 3.5 A combination of LiFeO2 and one or more. Li 1-x NiO2 (0≤x≤1), Li3FeO 3.5 LiFeO2 can be a residual substance remaining in the positive electrode active layer after the lithium replenishing agent undergoes an irreversible delithiation reaction. Because the lithium replenishing agent shrinks in volume after delithiation, forming gaps, these gaps can store electrolyte, further reducing the tortuosity of the electrolyte and increasing fast-charging performance.

[0131] A third aspect of this application provides a battery pack, and a second aspect of this application provides a battery.

[0132] The fourth aspect of this application provides an electrical device, including the negative electrode provided in the first aspect of this application, the battery provided in the second aspect of this application, or the battery pack provided in the third aspect of this application.

[0133] Since the electrical device of this application includes the aforementioned battery, the electrical device has advantages such as long battery life, good fast charging function, and high power output function.

[0134] This application does not impose any particular restrictions on the electrical devices that use the aforementioned batteries. Exemplary examples include, but are not limited to, mobile phones, laptops, tablets, cameras, televisions, radios, wearable devices (such as smartwatches, smart bracelets, stereo headphones, and Bluetooth headsets), electric vehicles (such as new energy vehicles and electric bicycles), electric toys, backup power supplies, and large household batteries.

[0135] The negative electrode sheet and battery provided in this application will be described in detail below through specific embodiments.

[0136] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0137] Example 1

[0138] A method for preparing a negative electrode and a lithium battery is provided:

[0139] 1. Preparation of negative electrode sheet

[0140] Carbon-based active material (petroleum coke artificial graphite, i.e., the precursor of artificial graphite is petroleum coke), conductive agent (carbon black), thickener (sodium carboxymethyl cellulose) and binder (styrene-butadiene latex) are mixed in a solid mass ratio of 100:1:1.6:1.8. The mixed powder is placed in a homogenizer, and deionized water is added as a solvent to mix and stir evenly to obtain negative electrode slurry A.

[0141] Carbon-based active material (needle coke artificial graphite, i.e., the precursor of artificial graphite is needle coke), conductive agent (carbon black), thickener (sodium carboxymethyl cellulose) and binder (styrene-butadiene latex) are mixed in a solid mass ratio of 100:1:1.6:1.8. The mixed powder is placed in a homogenizer, and deionized water is added as a solvent to mix and stir evenly to obtain negative electrode slurry B.

[0142] The difference between slurry A and slurry B lies in the choice of carbon-based active material.

[0143] The above materials can be purchased commercially or synthesized by oneself; this application does not impose any restrictions.

[0144] Slurry A and slurry B are sieved separately (using a 200-mesh sieve). Negative electrode slurries A and B, along with copper foil, are placed in a continuous coating apparatus. Negative electrode slurries A and B are coated onto the surface of the copper foil, with slurry B positioned closer to the current collector and slurry A further away. A magnetic field device is placed at the coating outlet, positioned on the side of the second surface opposite the first surface. The magnetic field strength is 2T, and the magnetic moment direction forms a 90° angle with the first surface of the copper foil. The magnetic field device reciprocates, with the direction of reciprocating motion forming a 90° angle with the extension direction (movement direction) of the copper foil, maintaining a uniform and stable magnetic field. The coated negative electrode slurry passes through the magnetic field region for 10 minutes, reaching a temperature of 40℃. After drying at 100℃ for 10 minutes, it is then rolled under a pressure of 10t and a roller speed of 0.5m / s to obtain the negative electrode. The areal density of the negative electrode sheet is 125 g / m². 2 The compaction density is 1.55 g / cc, and the thickness of the negative electrode sheet is approximately 165 μm. The first active material layer is prepared from negative electrode slurry B; the second active material layer is prepared from negative electrode slurry A, and the thicknesses of the two active material layers are similar.

[0145] Among them, the FWHM of each active material layer 101 and FWHM 002 θ 101 and θ 002 C 101 +C 002 The values ​​and OI values ​​are listed in Table 1.

[0146] 2. Preparation of lithium batteries

[0147] 1) Preparation of positive electrode sheet

[0148] The positive electrode active material (lithium iron phosphate), conductive agent (carbon black), and binder (polyvinylidene fluoride) are mixed in a mass ratio of 96:2:2. The mixed powder is placed in a vacuum mixer, and a solvent (N-methylpyrrolidone) is added. The mixture is stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is sieved (through a 200-mesh sieve) and coated onto a positive electrode current collector aluminum foil. After drying in an oven at 120°C, the positive electrode sheet is obtained by rolling and slitting.

[0149] The positive electrode aluminum foil has a thickness of 12 μm and a compaction density of 2.65 g / cc; the positive electrode sheet has a single-sided areal density of 220 g / m². 2 The thickness of the positive electrode is approximately 176 μm.

[0150] 2) Preparation of electrolyte

[0151] 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. 1 wt% of vinylene carbonate (VC) is added to the mixed solvent, and then dry lithium salt LiPF6 is added to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0152] 3) Assembly of lithium batteries

[0153] In an argon-filled glove box, the positive electrode, separator (polyethylene film), and negative electrode are stacked in sequence to obtain a battery. The separator must completely separate the positive electrode from the negative electrode. The stacked battery is then placed into an aluminum-plastic film soft pack, and the resulting lithium-ion battery is labeled as Battery-1.

[0154] Example 2

[0155] The preparation methods of the negative electrode and lithium-ion battery in this embodiment are basically the same as those in Example 1, except that the magnetic field strength is 4T during the preparation of the negative electrode. The resulting lithium-ion battery is labeled as Battery-2.

[0156] Example 3

[0157] The preparation methods of the negative electrode and lithium-ion battery in this embodiment are basically the same as those in Example 1, except that the magnetic field strength is 6T during the preparation of the negative electrode. The resulting lithium-ion battery is labeled as Battery-3.

[0158] Example 4

[0159] The preparation methods of the negative electrode and lithium-ion battery in this embodiment are basically the same as those in Example 1, except that the magnetic field strength is 8T during the preparation of the negative electrode. The resulting lithium-ion battery is labeled as Battery-4.

[0160] Example 5

[0161] The preparation methods of the negative electrode and lithium-ion battery in this embodiment are basically the same as those in Example 1, except that the magnetic field strength is 10T during the preparation of the negative electrode. The resulting lithium-ion battery is labeled as Battery-5.

[0162] Example 6

[0163] The preparation methods of the negative electrode and lithium-ion battery in this embodiment are basically the same as those in Example 1. The difference is that during the preparation of the negative electrode, the magnetic field strength is 5T, and the petroleum coke artificial graphite in slurry A is replaced with a mixture of needle coke artificial graphite and petroleum coke natural graphite, wherein the mass ratio of needle coke artificial graphite to petroleum coke natural graphite is 1:1. The resulting lithium-ion battery is labeled as Battery-6.

[0164] Example 7

[0165] The preparation methods of the negative electrode sheet and lithium-ion battery in this embodiment are basically the same as those in Example 1. The difference is that during the preparation of the negative electrode sheet, the magnetic field strength is 5T, and the petroleum coke artificial graphite in slurry A is replaced with a mixture of needle coke artificial graphite and hard carbon, wherein the mass ratio of needle coke artificial graphite to hard carbon is 1:1. At this time, the mass percentage of artificial graphite in the entire negative electrode active material layer is 72%. The resulting lithium-ion battery is labeled as Battery-7.

[0166] Example 8

[0167] The preparation method of the negative electrode sheet and lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that during the preparation of the negative electrode sheet, the magnetic field strength is 5T, and the needle-shaped coke artificial graphite in slurry B is replaced with a mixture of needle-shaped coke artificial graphite and spherical natural graphite, wherein the mass ratio of needle-shaped coke artificial graphite to spherical natural graphite is 1:1. At this time, the mass percentage of artificial graphite in the entire negative electrode active material layer is 72%. The resulting lithium-ion battery is labeled as Battery-8.

[0168] Example 9

[0169] The preparation method of the negative electrode sheet and lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that during the preparation of the negative electrode sheet, the magnetic field strength is 6.5T, and the needle-shaped coke artificial graphite in slurry B is replaced with a mixture of needle-shaped coke artificial graphite and spherical natural graphite, wherein the mass ratio of needle-shaped coke artificial graphite to spherical natural graphite is 1:4. At this time, the mass percentage of artificial graphite in the entire negative electrode active material layer is 58%. The resulting lithium-ion battery is labeled as Battery-9.

[0170] Example 10

[0171] The preparation methods of the negative electrode sheet and lithium-ion battery in this embodiment are basically the same as those in Example 1. The difference is that during the preparation of the negative electrode sheet, the magnetic field strength is 5T, the petroleum coke artificial graphite in slurry A is replaced with a mixture of needle coke artificial graphite and spherical natural graphite, wherein the mass ratio of needle coke artificial graphite to spherical natural graphite is 1:1; the needle coke artificial graphite in slurry B is replaced with spherical natural graphite; and the mass percentage of artificial graphite in the entire negative electrode active material layer is 24%. The resulting lithium-ion battery is labeled as Battery-10.

[0172] Example 11

[0173] The preparation methods of the negative electrode sheet and lithium-ion battery in this embodiment are basically the same as those in Example 1. The difference is that during the preparation of the negative electrode sheet, the magnetic field strength is 6.5T, the petroleum coke artificial graphite in slurry A is replaced with a mixture of needle coke artificial graphite and spherical natural graphite, wherein the mass ratio of needle coke artificial graphite to spherical natural graphite is 4:1; the needle coke artificial graphite in slurry B is replaced with spherical natural graphite; and the mass percentage of artificial graphite in the entire negative electrode active material layer is 38%. The resulting lithium-ion battery is labeled as Battery-11.

[0174] Example 12

[0175] The preparation methods of the negative electrode sheet and lithium-ion battery in this embodiment are basically the same as those in Example 1. The difference is that during the preparation of the negative electrode sheet, the magnetic field strength is 4T, and the petroleum coke artificial graphite in slurry A is replaced with a mixture of petroleum coke artificial graphite and hard carbon, wherein the mass ratio of petroleum coke artificial graphite to hard carbon is 1:4; the needle coke artificial graphite in slurry B is replaced with a mixture of spherical natural graphite. At this time, the mass percentage of artificial graphite in the entire negative electrode active material layer is 60%. The resulting lithium-ion battery is labeled as Battery-12.

[0176] Example 13

[0177] The preparation method of the negative electrode and lithium-ion battery in this embodiment is the same as that in Example 1, except that the lithium salt in the electrolyte also includes lithium bisfluorosulfonylimide (LiFSI), the molar ratio of LiFSI to LiPF6 is 1:1, and the sum of the concentrations of LiFSI and LiPF6 is 1 mol / L. The resulting lithium-ion battery is labeled Battery-13.

[0178] Example 14

[0179] The preparation method of the negative electrode and lithium-ion battery in this embodiment is the same as that in Example 1, except that the lithium salt in the electrolyte also includes lithium bis(fluorosulfonyl)imide (LiFSI), the molar ratio of LiFSI to LiPF6 is 1:3, and the sum of the concentrations of LiFSI and LiPF6 is 1 mol / L. The resulting lithium-ion battery is labeled Battery-14.

[0180] Example 15

[0181] The preparation method of the negative electrode and lithium-ion battery in this embodiment is the same as that in Example 1, except that the lithium salt in the electrolyte also includes lithium bis(fluorosulfonyl)imide (LiFSI), the molar ratio of LiFSI to LiPF6 is 3:1, and the sum of the concentrations of LiFSI and LiPF6 is 1 mol / L. The resulting lithium-ion battery is labeled Battery-15.

[0182] Example 16

[0183] The preparation method of the negative electrode and lithium-ion battery in this embodiment is the same as that in Example 1, except that the lithium salt in the electrolyte also includes lithium bis(fluorosulfonyl)imide (LiFSI), the molar ratio of LiFSI to LiPF6 is 1:1, and the sum of the concentrations of LiFSI and LiPF6 is 1 mol / L; at the same time, the positive electrode includes a lithium replenishing agent, which is Li5FeO4, accounting for 0.6% of the mass of lithium iron phosphate. The resulting lithium-ion battery is labeled as Battery-16.

[0184] Example 17

[0185] The preparation method of the negative electrode and lithium-ion battery in this embodiment is the same as that in Example 1, except that the positive electrode includes a lithium replenishing agent, which is Li5FeO4, accounting for 0.6% of the mass of lithium iron phosphate. The resulting lithium-ion battery is labeled as Battery-17.

[0186] Example 18

[0187] The preparation method of the negative electrode and lithium-ion battery in this embodiment is the same as that in Example 1, except that the positive electrode includes a lithium replenishing agent, which is Li5FeO4, accounting for 2% of the mass of lithium iron phosphate. The resulting lithium-ion battery is labeled as Battery-18.

[0188] Example 19

[0189] The preparation method of the negative electrode and lithium-ion battery in this embodiment is the same as that in Example 1, except that the positive electrode includes a lithium replenishing agent, which is Li5FeO4, accounting for 0.2% of the mass of lithium iron phosphate. The resulting lithium-ion battery is labeled as Battery-19.

[0190] Example 20

[0191] The preparation method of the negative electrode and lithium-ion battery in this embodiment is the same as that in Example 1, except that the positive electrode includes a lithium replenishing agent, which is a mixture of Li2CO3 and Li5FeO4, with the sum of Li2CO3 and Li5FeO4 accounting for 1% of the mass of lithium iron phosphate; the mass ratio of Li2CO3 to Li5FeO4 is 1:1. The resulting lithium-ion battery is labeled Battery-20.

[0192] Example 21

[0193] The preparation method of the negative electrode and lithium-ion battery in this embodiment is the same as that in Example 1, except that the positive electrode includes a lithium replenishing agent, which is a mixture of Li2NiO2 and Li5FeO4. The sum of Li2CO3 and Li5FeO4 accounts for 1.5% of the mass of lithium iron phosphate; the mass ratio of Li2NiO2 to Li5FeO4 is 2:1. The resulting lithium-ion battery is labeled as Battery-21.

[0194] Example 22

[0195] The preparation methods of the negative electrode and lithium-ion battery in this embodiment are the same as in Example 1, except that the lithium salt in the electrolyte also includes lithium bis(fluorosulfonyl)imide (LiFSI), the molar ratio of LiFSI to LiPF6 is 1:1, and the combined concentration of LiFSI and LiPF6 is 1 mol / L; simultaneously, the positive electrode includes a lithium replenishing agent, which is a mixture of Li2NiO2 and Li5FeO4, with the sum of Li2CO3 and Li5FeO4 accounting for 1.5% of the mass of lithium iron phosphate; the mass ratio of Li2NiO2 to Li5FeO4 is 2:1. The resulting lithium-ion battery is labeled Battery-22.

[0196] Comparative Example 1

[0197] The preparation methods of the negative electrode and lithium-ion battery in this comparative example are basically the same as those in Example 1. The difference is that the magnetic field strength is 0T during the preparation of the negative electrode, the negative electrode does not have a double-layer structure, and after the slurry A and slurry B are mixed evenly, they are covered on both sides of the current collector. The resulting lithium-ion battery is labeled as Battery-D1.

[0198] Comparative Example 2

[0199] The preparation methods of the negative electrode and lithium-ion battery in this comparative example are basically the same as those in Example 1, except that the magnetic field strength is 0T during the preparation of the negative electrode. The resulting lithium-ion battery is labeled as Battery-D2.

[0200] Comparative Example 3

[0201] The preparation methods of the negative electrode sheet and lithium-ion battery in this comparative example are basically the same as those in Example 1. The difference is that during the preparation of the negative electrode sheet, the magnetic field strength is 0T, and the petroleum coke artificial graphite in slurry A is replaced with a mixture of petroleum coke artificial graphite and spherical natural graphite, wherein the mass ratio of petroleum coke artificial graphite to hard carbon is 1:1; the needle coke artificial graphite in slurry B is replaced with petroleum coke artificial graphite; at this time, the mass percentage of artificial graphite in the entire negative electrode active material layer is 75%. The resulting lithium-ion battery is labeled as Battery-D3.

[0202] Test case

[0203] I. The following performance tests were performed on the negative electrode sheets of the above embodiments and comparative examples:

[0204] 1. XRD (C 101 +C 002 )test

[0205] The test conditions were as follows: copper Kα rays were used as the light source, X-rays were excited at 40kV and 20mA, the test scan rate was 5° / min, and a Kβ filter was used to remove the influence of Kβ rays on the peak shape and position of the spectral lines.

[0206] The specific method is as follows:

[0207] 1) After the battery is fully discharged, disassemble it to obtain the negative electrode sheet; immerse the negative electrode sheet in dimethyl carbonate (DMC) for 10-20 minutes to clean the residual electrolyte, and then dry the negative electrode sheet.

[0208] 2) Grazing incidence XRD (GIXRD) was performed on the surface negative electrode active material layer (nth layer) on the current collector side, with an incident angle of 1-3° (corresponding to X-ray irradiation depth of 10-300 nm), and the XRD spectrum of this layer was obtained.

[0209] 3) From the XRD spectrum of the obtained negative electrode active material layer, read the diffraction angle 2θ (in °) of the diffraction peaks corresponding to the (101) and (002) crystal planes of the carbon material, and the half-width at half-maximum (i.e., the diffraction angle corresponding to 1 / 2 peak height, in radians) of these two diffraction peaks, and then according to formula C 101 =1.84×λ / (FWHM) 101 ×cosθ 101 C 002 =0.89×λ / (FWHM) 002 ×cosθ 002 The C values ​​for each layer were calculated separately. 101 With C 002 value.

[0210] 4) Remove the nth active material layer using ion thinning or ion polishing to expose the adjacent n-1 active material layers. Then repeat steps 2) and 3) to calculate the C of the n-1th layer. 101 With C 002 value.

[0211] 5) Repeat step 4) until the C of the first layer is calculated. 101 With C 002 value.

[0212] It should be noted that in both methods above, the diffraction angle and full width at half maximum (FWHM) of a diffraction peak directly read from a crystal plane in the XRD pattern are measured in degrees. When calculating the FWHM... 101 and FWHM 002 When doing so, the half-peak width value, which is measured in degrees, needs to be converted to a value calculated in radians.

[0213] 2. OI value test

[0214] The test conditions were as follows: copper Kα rays were used as the light source, X-rays were excited at 40kV and 20mA, the test scan rate was 5° / min, and a Kβ filter was used to remove the influence of Kβ rays on the peak shape and position of the spectral lines.

[0215] The specific method is as follows:

[0216] 1) After the battery is fully discharged, disassemble it to obtain the negative electrode sheet; immerse the negative electrode sheet in dimethyl carbonate (DMC) for 10-20 minutes to clean the residual electrolyte, and then dry the negative electrode sheet.

[0217] 2) Grazing incidence XRD (GIXRD) was performed on the surface negative electrode active material layer (nth layer) on the current collector side, with an incident angle of 1-3° (corresponding to X-ray irradiation depth of 10-300 nm), and the XRD spectrum of this layer was obtained.

[0218] 3) From the XRD spectrum of the obtained negative electrode active material layer, obtain the peak areas of the diffraction peaks corresponding to the (004) and (110) crystal planes of the carbon material, and calculate the area ratio of the (004) diffraction peak and the (110) diffraction peak to obtain the OI value of the layer.

[0219] 4. Use ion thinning or ion polishing to remove the nth active material layer, exposing the adjacent n-1 active material layers, and then repeat steps 2) and 3) to calculate the OI value of the n-1th layer.

[0220] 5. Repeat step 4 until the OI value of layer 1 is calculated.

[0221] Figure 1 The XRD pattern of the negative electrode in Embodiment 1 of this application; Figure 2 The image shows the XRD pattern of the negative electrode in Comparative Example 1 of this application.

[0222] from Figure 1 It can be determined that the 2θ angle corresponding to the diffraction peak of the (002) crystal plane in the lower layer (n=1) is 26.515° (i.e., θ). 002 It is 13.2575°, FWHM (002) The value in degrees is 0.1618°. By multiplying this degree by π / 180°, the half-width at half-maximum (WHM) value in radians can be obtained, which is 0.0028239; (101) The 2θ angle corresponding to the diffraction peak of the crystal plane is 44.517° (i.e., θ 101 (22.2585°), FWHM (101) The value in degrees is 0.508°. Multiplying this degree by π / 180° yields the half-width in radians, which is 0.00886627. According to the formula listed earlier in this application, C can be calculated. 101 The calculated value is 34.6, C 002 The calculated value is 56.5, C101 +C 002 The value is 91.1. Calculation of OI value for the lower layer (n=1): By fitting the peak shape, the peak area of ​​the (004) diffraction peak is 3004 and the peak area of ​​the (110) diffraction peak is 266.5. The calculated OI value is 11.27.

[0223] The 2θ angle corresponding to the diffraction peak of the (002) crystal plane in the upper layer (n=2) is 26.371° (i.e., θ). 002 It is 13.1855°, FWHM (002) The value in degrees is 0.265°. By multiplying this degree by π / 180°, the half-width at half-maximum (WHM) in radians can be obtained, which is 0.00462512. (101) The 2θ angle corresponding to the diffraction peak of the crystal plane is 44.62° (i.e., θ 101 (22.31°), FWHM (101) The value in degrees is 0.967°. Multiplying this degree by π / 180° yields the half-width in radians, which is 0.016877. According to the formula listed earlier in this application, C can be calculated. 101 The calculated value is 18.17, C 002 The calculated value is 30.47, C 101 +C 002 The value is 48.6. Calculation of OI value of upper layer (n=2): Through peak shape fitting, the peak area ratio of (004) diffraction peak is 2178, and the peak area of ​​(110)(004) diffraction peak is 260. The calculated OI value is 8.38.

[0224] from Figure 2 It can be determined that the 2θ angle corresponding to the diffraction peak of the (002) crystal plane is 26.487° (i.e., θ). 002 It is 13.2435°, FWHM (002) The value in degrees is 0.273°. By multiplying this degree by π / 180°, the half-width at half-maximum (WHM) value in radians can be obtained, which is 0.00476475; (101) The 2θ angle corresponding to the diffraction peak of the crystal plane is 44.458° (i.e., θ 101 (22.229°), FWHM (101) The value in degrees is 0.574°. Multiplying this degree by π / 180° yields the half-width in radians, which is 0.01002. According to the formula listed earlier in this application, C can be calculated. 101 The calculated value is 29.6, C 002 The calculated value is 30.6, C 101 +C 002 The value is 60.2. OI value calculation: By fitting the peak shape, the peak area ratio of the (004) diffraction peak is 3140, and the peak area of ​​the (110) diffraction peak is 314. The calculated OI value is 10.

[0225] The test results for other embodiments and comparative data are listed in Table 1.

[0226] Table 1

[0227]

[0228]

[0229] Note: In the thickness direction of the active material layer of the negative electrode, from the side away from the current collector to the side closer to the current collector, the layers are 1, 2, 3, ..., n.

[0230] II. The following performance tests were conducted on the batteries of the above embodiments and comparative examples:

[0231] 1. Volumetric energy density

[0232] Test Method: At 25℃, the volume of the battery composed of the negative electrode, separator, and positive electrode was measured using the water displacement method and recorded as the battery volume. Under the same conditions, each lithium-ion battery was first charged at a 1 / 3C rate and then discharged at a 1 / 3C rate (voltage range 2V-3.8V), and the actual discharge amount was recorded. The energy of the battery is the product of the actual discharge amount at 1 / 3C and the average voltage during discharge. The ratio of the battery's energy to its weight is the actual energy density of the battery using this negative electrode.

[0233] 2. Dynamic performance

[0234] 2.1 Maximum Charging Rate: At 25℃, each lithium-ion battery was fully charged at nC and fully discharged at 1C for 10 charge-discharge cycles. Then, the battery was fully charged at nC. The negative electrode was then disassembled, and the lithium deposition on its surface was observed. If the area of ​​the lithium-deposited region on the negative electrode surface was less than 5%, it was considered slight lithium deposition; if the area of ​​the lithium-deposited region was 5%–40%, it was considered moderate lithium deposition; and if the area of ​​the lithium-deposited region was greater than 40%, it was considered severe lithium deposition. If no lithium deposition occurred on the negative electrode surface (i.e., no lithium-deposited region), the charging rate was increased from nC in increments of 0.1C, and the test was repeated until slight lithium deposition occurred on the negative electrode surface. The test was then stopped. The maximum charging rate of the battery under non-lithium deposition conditions was nC minus 0.1C.

[0235] 2.2 Discharge specific capacity ratio: The discharge capacity of the above batteries was tested at 25℃ at different rates of 0.3C and 4C, with a voltage range of 2.0V-3.8V. The ratio of the first discharge capacity at 4C to the first discharge capacity at 0.3C (4C / 0.3C discharge ratio) was calculated. The test results are shown in Table 2.

[0236] Table 2

[0237]

[0238] From Table 1 and Table 2, we can see that:

[0239] Compared to Comparative Examples 1-3, the batteries in Examples 1-12 exhibit higher energy density and kinetic performance. This demonstrates that the present application, through the design of a multi-layered active material structure for the negative electrode and the control of the crystallographic parameters C of the carbon material in each active material layer, achieves superior performance. 101 +C 002 By controlling the O1 and O2 values, secondary batteries can achieve both excellent energy density and good kinetic performance. Furthermore, when the electrolyte includes LiFSI and LiPF6 and / or the cathode includes a lithium supplement, the energy density and kinetic performance of the secondary battery can be further improved.

[0240] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A negative electrode sheet, characterized in that, It includes a current collector and n active material layers disposed on at least one surface of the current collector, where n is an integer greater than 1; the n active material layers are stacked in a direction perpendicular to the surface of the current collector; Each of the active material layers comprises carbon materials; The carbon material in the (m+1)th active material layer 101 +C 002 The value is less than the C of the carbon material in the m-th active material layer. 101 +C 002 The difference between the OI value of the carbon material in the (m+1)th active material layer and the OI value of the carbon material in the mth active material layer is less than or equal to 4 and greater than or equal to -4. Wherein, the m-th layer is the active material layer closest to the current collector, and the (m+1)-th layer is the active material layer furthest from the current collector, where m is an integer greater than or equal to 1 and less than n; C 101 With C 002 The two crystallographic parameters representing the carbon material, in nm, are calculated using Equations 1 and 2, respectively: C 101 =1.84×λ / (FWHM) 101 ×cosθ 101 Formula 1; C 002 =0.89×λ / (FWHM) 002 ×cosθ 002 Equation 2; In Equations 1 and 2, FWHM 101 and FWHM 002 θ represents the half-width at half-maximum (FWHM) of the (101) and (002) diffraction peaks of the carbon material in the X-ray diffraction pattern of the monolayer active material layer, in radians; 101 and θ 002 The values ​​are half the 2θ values ​​of the (101) and (002) diffraction peaks of the carbon material in the X-ray diffraction pattern of the monolayer active material layer, respectively, in °; λ is the wavelength of the cathode ray used in X-ray diffraction, in nm; the OI value is the area ratio of the (004) and (110) diffraction peaks in the X-ray diffraction pattern of the monolayer active material layer.

2. The negative electrode sheet according to claim 1, characterized in that, The difference between the OI value of the carbon material in the (m+1)th active material layer and the OI value of the carbon material in the mth active material layer is less than or equal to 3 and greater than or equal to -3.

3. The negative electrode sheet according to claim 1 or 2, characterized in that, The OI value of the carbon material in the n-layer active material layer is 2 to 12.

4. The negative electrode sheet according to any one of claims 1-3, characterized in that, The carbon material in the m-th active material layer (C) 101 +C 002 The value is related to the C of the carbon material in the (m+1)th active material layer. 101 +C 002 The difference in values ​​is 10–80 nm.

5. The negative electrode sheet according to any one of claims 1-4, characterized in that, The carbon material in the n-layer active material layer (C 101 +C 002 The value is 40-130nm.

6. The negative electrode sheet according to any one of claims 1-5, characterized in that, The carbon material is a carbon-based anode active material, which includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, and mesophase carbon microspheres.

7. The negative electrode sheet according to any one of claims 1-6, characterized in that, n is 2 to 4.

8. The negative electrode sheet according to claim 7, characterized in that, n is 2, C of the first active material layer 101 +C 002 Values ​​range from 90 to 180 nm; and / or, The OI value of the first active material layer is 2–12; and / or, C of the second active material layer 101 +C 002 Values ​​range from 15 to 130 nm; and / or, The OI value of the second active material layer is 2 to 12.

9. A battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-8.

10. The battery according to claim 9, characterized in that, The battery also includes a positive electrode and an electrolyte, the electrolyte being filled between the positive electrode and the negative electrode, and the electrolyte comprising lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate.

11. The battery according to claim 9 or 10, characterized in that, The positive electrode includes Li 1-x NiO2 (0≤x≤1), Li3FeO 3.5 One or more combinations of LiFeO2 with positive electrode active materials.

12. The battery according to any one of claims 9-11, characterized in that, The positive electrode includes a lithium supplement.

13. The battery according to claim 12, characterized in that, The lithium supplement includes one or more of the following: Li2CO3, Li2C2O4, Li6CoO4, Li2NiO2, Li2Se, Li3N, Li2O2, Li2O, Li2S, Li2S2, Li5FeO4, lithium borate, and lithium thioborate.

14. A battery pack, characterized in that, The battery pack includes the battery as described in any one of claims 9-13.

15. An electrical appliance, characterized in that, The electrical equipment includes the negative electrode sheet according to any one of claims 1-8, the battery according to claims 9-13, or the battery pack according to claim 14.

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