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

Abstract

A lithium-ion secondary battery, a preparation method, and an electric device. The lithium-ion secondary battery comprises an electrolytic solution. A non-aqueous solvent in the electrolytic solution comprises a chain carboxylic ester compound, and the chain carboxylic ester compound comprises a solvent of formula I having a structural formula of R11-C(=O)-O-R12, wherein R11 and R12 are each independently methyl or ethyl. An additive in the electrolytic solution comprises a first additive and a second additive, wherein the first additive is a non-ionic organic additive containing a carbon-carbon triple bond, and the second additive is a negative electrode film-forming additive different from the first additive.

Description

Lithium-ion secondary batteries, preparation methods and electrical devices

[0001] Related applications

[0002] This application claims priority to Chinese patent application filed on March 28, 2025, with application number CN2025103784038, entitled "Lithium-ion secondary battery, preparation method and power device", 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 lithium-ion secondary batteries, preparation methods, and electrical devices. 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 smartphones, tablets, laptops, power tools, electric bicycles, electric motorcycles, electric vehicles, 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 fast-charging capability of lithium-ion rechargeable batteries has attracted significant attention. However, fast-charging systems for lithium-ion rechargeable batteries typically face gas generation issues. The interfacial side reactions associated with gas generation degrade the cycle performance of fast-charging batteries, hindering the further development of fast-charging systems. Summary of the Invention

[0006] According to various embodiments and examples of this application, this application provides a lithium-ion secondary battery, a preparation method, and an electrical device. This lithium-ion secondary battery has improved fast-charging performance and can extend the cycle life of the fast-charging battery system.

[0007] In some embodiments of the first aspect of this application, a lithium-ion secondary battery is provided, comprising a positive electrode, a negative electrode, and an electrolyte, wherein a separator is disposed between the positive electrode and the negative electrode; the electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent comprises a chain-like carboxylic acid ester compound, wherein the chain-like carboxylic acid ester compound comprises a solvent of formula I, the structure of which is shown in formula (I): In equation (I), R 11 and R 12 Each can be independently methyl or ethyl;

[0008] The additives include a first additive and a second additive. The first additive is a nonionic organic additive containing carbon-carbon triple bonds, and the second additive is a negative electrode film-forming additive that is different from the first additive.

[0009] The "first additive" used in this application is a nonionic organic additive containing a carbon-carbon triple bond, specifically a nonionic acetylene organic additive. It is understood that additives in the electrolyte include acetylene additives.

[0010] This lithium-ion secondary battery introduces a non-ionic alkyne-based organic additive (denoted as the first additive) and a second additive (a negative electrode film-forming additive different from the first additive) when using a highly conductive solvent. The first additive is R in the solvent of formula I. 11 and R 12 Both additives have fewer carbon atoms, resulting in lower viscosity and higher conductivity for the solvent in Formula I. Secondly, the first additive can participate in the formation and repair of the solid electrolyte interphase (SEI) film at the negative electrode, significantly improving the stability of the SEI film. This significantly suppresses interfacial side reactions between the negative electrode and the electrolyte during fast charging, effectively inhibiting the problem of easy decomposition and gas generation of the solvent in Formula I. Thirdly, the second additive can competitively participate in the negative electrode film formation, reducing or delaying the consumption of the first additive in the negative electrode film formation and suppressing the increase in negative electrode interfacial impedance caused by the participation of the first additive in the negative electrode film formation. Based on the synergistic effects of the above-mentioned actions, but not limited to the aforementioned theories, lithium-ion secondary batteries have improved fast charging performance, including extending the cycle life of fast charging battery systems.

[0011] In some embodiments, the chain carboxylic acid ester compound includes one or more of methyl formate, ethyl formate, methyl acetate, and ethyl acetate.

[0012] In some embodiments, the negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material, and the average particle size of the primary particles in the negative electrode active material is denoted as D1, wherein D1 is 0.1μm to 2μm, and can be selected as 0.5μm to 1.2μm.

[0013] By controlling the average particle size (denoted as D1) of the primary particles in the negative electrode active material within the aforementioned range, it is possible to control the negative electrode active material to have a more suitable ion transport path, achieve a better rate capability, and simultaneously control the negative electrode interface reaction, control the consumption of the first additive in negative electrode film formation, better optimize the SEI film and suppress gas generation. Based on the synergistic effect of the aforementioned effects, but not limited to the aforementioned theory, it is beneficial to better control the battery internal resistance and enable lithium-ion secondary batteries to achieve better fast charging performance.

[0014] In some embodiments, the D of the negative electrode active material v 50 ranges from 5μm to 18μm.

[0015] In some embodiments, the D of the negative electrode active material v 50 is 6μm to 15μm.

[0016] By using the D of the negative electrode active material v By controlling the specific surface area of ​​the negative electrode active material within the aforementioned range, it is possible to keep the specific surface area of ​​the negative electrode active material within a relatively low range. This is beneficial for reducing side reactions at the negative electrode interface during fast charging, reducing or delaying the consumption of the first additive at the negative electrode interface, optimizing the SEI film, and suppressing gas generation. It is also beneficial for better control of the overall ion transport path of the negative electrode active material particles. Based on the synergistic effect of the aforementioned effects, but not limited to the aforementioned theory, it is beneficial for better control of the battery internal resistance and for enabling lithium-ion secondary batteries to achieve better fast charging performance.

[0017] By using the D of the negative electrode active material v If the value is controlled within the aforementioned range, it can be paired with a relatively small average primary particle size.

[0018] By synergistically controlling the D of the negative electrode active material v The average particle size of the primary particles in the 50 and negative electrode active materials is beneficial to taking into account the ion transport path of the primary particles and the particles as a whole in the negative electrode active materials. It also effectively suppresses the side reactions at the negative electrode interface and suppresses gas generation. Based on the synergistic effect of the above, but not limited to the above theory, it is beneficial to better control the internal resistance of the battery and to enable the lithium-ion secondary battery to achieve better fast charging performance.

[0019] In some embodiments, the negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material, and the average particle size of the primary particles in the negative electrode active material is denoted as D1;

[0020] The negative electrode active material D v The ratio of 50 to D1 is 5 to 50, and can be selected as 8 to 30.

[0021] By using the D of the negative electrode active material v Controlling the ratio of 50 to D1 within the aforementioned range is beneficial for balancing the ion transport paths of primary particles and the particles as a whole in the negative electrode active material, while also effectively suppressing side reactions at the negative electrode interface and inhibiting gas generation.

[0022] In some embodiments, the negative electrode active material includes a coated negative electrode material, which includes a negative electrode active body and a carbon coating layer located on the negative electrode active body, comprising at least a portion thereof.

[0023] In some embodiments, the negative electrode sheet satisfies one or more of the following characteristics:

[0024] (a1) The mass percentage of the coated negative electrode material in the negative electrode active material is 80% to 100%;

[0025] (a2) The coated negative electrode material includes coated graphite, and the negative electrode active body in the coated graphite includes graphite body, and the mass percentage of the coated graphite in the negative electrode active material is 80% to 100%.

[0026] By incorporating a coated anode material (such as coated graphite) with a carbon coating layer into the anode active material, the lithium-ion transport channels on the surface of the anode active material can be optimized, promoting lithium-ion transport and improving the kinetics of lithium-ion secondary batteries. At the same time, it is also beneficial to suppress side reactions at the anode interface and suppress the increase in interface impedance caused by the participation of the first additive in film formation, which is conducive to better improving the fast-charging performance of lithium-ion secondary batteries.

[0027] By incorporating a coated anode material (such as coated graphite) with a carbon coating layer into the anode active material, rate performance can be optimized by using a relatively small average primary particle size.

[0028] In some embodiments, the positive electrode sheet includes a positive active layer, and the positive active layer includes a positive active material; the positive active material includes one or more of lithium phosphate-based positive electrode materials and lithium transition metal oxide-based positive electrode materials;

[0029] Optionally, the positive electrode sheet satisfies one or more of the following characteristics:

[0030] (b1) The positive electrode active material includes a lithium phosphate-containing positive electrode material, wherein the lithium phosphate-containing positive electrode material has a D... v 50 is 0.3μm to 2μm;

[0031] (b2) The positive electrode active material includes a lithium transition metal oxide positive electrode material, wherein the lithium transition metal oxide positive electrode material has a D v 50 is 2μm to 10μm.

[0032] By controlling the type of positive electrode active material and combining it with the aforementioned D v A value of 50 helps to better coordinate the lithium-ion desorption kinetics of the positive electrode with the lithium insertion kinetics of the negative electrode, which helps to reduce the internal resistance of the battery and improve fast charging performance.

[0033] In some embodiments, the negative electrode includes a negative active layer, the negative active layer including a negative active material; the positive electrode includes a positive active layer, the positive active layer including a positive active material.

[0034] (c1) The D of the negative electrode active material v 1 is greater than or equal to 1.5 μm;

[0035] (c2) The positive electrode active material includes a lithium transition metal oxide positive electrode material, wherein the lithium transition metal oxide positive electrode material has a D v 10 is greater than or equal to 1 μm;

[0036] (c3) The positive electrode active material includes a lithium phosphate-containing positive electrode material, wherein the lithium phosphate-containing positive electrode material has a D... v 10 is greater than or equal to 0.2 μm.

[0037] By controlling the D of the negative electrode active material v 1. D of positive electrode active material v Controlling one or both of 10 within the aforementioned range is beneficial for reducing the content of small particles with extremely small size and extremely large specific surface area at the negative electrode and / or positive electrode, which is beneficial for better suppressing the interfacial side reactions of the negative electrode and / or positive electrode, and better suppressing gas generation during fast charging.

[0038] By controlling the D of the negative electrode active material v 1. Within the aforementioned range, the negative electrode interface side reactions can be significantly suppressed, the consumption rate of the first additive can be reduced, and the battery internal resistance growth rate can be reduced, which is conducive to maintaining better fast charging performance for a longer period of time.

[0039] The first additive can adsorb transition metal ions in the electrolyte. This is achieved by controlling the D… of the lithium transition metal oxide cathode material… v 10 Within the aforementioned range, it is beneficial to better control the dissolution of transition metal ions in the positive electrode, allowing the first additive to participate more in the formation and repair of the negative electrode interface film, which is conducive to maintaining better fast charging performance for a longer period of time.

[0040] By controlling the D of lithium phosphate-containing cathode materials v 10 Within the aforementioned range, it is beneficial to better control the water content of the positive electrode active material, thereby reducing acid byproducts (such as hydrofluoric acid), which in turn helps to improve the stability of the negative electrode interface and the negative electrode active material, reduces the consumption rate of the first additive, reduces the growth rate of battery internal resistance, and helps to maintain better fast charging performance for a longer period of time.

[0041] In some embodiments, the negative electrode sheet includes a negative electrode active layer, and the negative electrode active layer includes a negative electrode active material; the negative electrode active material includes at least one of carbon-based materials and silicon-based materials; optionally, the silicon-based material accounts for 0-40% of the mass of the negative electrode active material.

[0042] In some embodiments, the negative electrode sheet satisfies one or more of the following characteristics:

[0043] (d1) The silicon-based material accounts for 0-25% of the mass of the negative electrode active material;

[0044] (d2) The silicon-based material includes a silicon-carbon composite material, which includes a porous carbon matrix and elemental silicon located in the pores of the porous carbon matrix; optionally, the silicon-carbon composite material accounts for 80% to 100% of the mass of the silicon-based material.

[0045] By controlling the silicon content of the negative electrode within the aforementioned range, it is beneficial to better control the expansion and contraction changes of the negative electrode, reduce the generation of fresh interfaces, suppress side reactions at the negative electrode interface, reduce the consumption rate of the first additive, decrease the growth rate of battery internal resistance, and maintain superior fast-charging performance for a longer period. For example, in silicon-based materials, silicon-carbon composite materials exhibit relatively low volume expansion and contraction changes.

[0046] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0047] (e1) The first additive in the electrolyte has a mass percentage of 0.01% to 3.2%;

[0048] (e2) The mass ratio of the second additive to the first additive is 0.01 to 50.

[0049] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0050] (e1') The first additive is present in the electrolyte at a mass percentage of 0.05% to 1.6%;

[0051] (e2') The mass ratio of the second additive to the first additive is 0.1 to 30.

[0052] By controlling the mass percentage of the first additive in the electrolyte within the aforementioned range, the first additive can continuously play a role in repairing the SEI film during fast charging and cycling, and can maintain superior fast charging performance for a longer period of time.

[0053] By controlling the mass ratio of the second additive to the first additive within the aforementioned range, it is beneficial for the first and second additives to work synergistically, which helps to improve the negative electrode SEI film and suppress gas generation during fast charging, while also better suppressing the increase in negative electrode interface impedance, thereby improving the fast charging performance of lithium-ion secondary batteries.

[0054] By controlling the mass percentage of the first additive in the electrolyte and the mass ratio of the second additive to the first additive within the aforementioned range, it is beneficial to better leverage the synergistic effect between the first and second additives and improve the fast-charging performance of lithium-ion secondary batteries.

[0055] In some embodiments, the second additive includes one or more of lithium salt additives, phosphate ester additives, vinylene carbonate, fluorocarbonate additives, saturated sulpholactones, and cyclic sulfates.

[0056] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0057] (f1) The lithium salt additive includes one or more of oxalate lithium salts, lithium tetrafluoroborate, lithium difluorophosphate, and fluorosulfonic acid lithium salts; the oxalate lithium salt includes one or more of lithium difluorooxalateborate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate; the fluorosulfonic acid lithium salt includes one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

[0058] (f2) The phosphate ester additives include silicon-based phosphate ester additives; the silicon-based phosphate ester additives include one or more of tris(trimethylsilane) phosphate (TMSP) and tris(trimethylsilyl) phosphite (TMSPi);

[0059] (f3) The second additive includes fluorocarbonate additives, wherein the fluorocarbonate additives include fluoroethylene carbonate;

[0060] (f4) The cyclic sulfates include one or more of monocyclic sulfates and polycyclic sulfates.

[0061] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0062] (g1) The lithium salt additive in the electrolyte has a mass percentage of 0-3%;

[0063] (g2) The lithium salt additive includes lithium difluorooxalate borate, wherein the mass percentage of lithium difluorooxalate borate in the electrolyte is 0-3%;

[0064] (g3) The lithium salt additive includes lithium bis(fluorosulfonyl)imide;

[0065] (g4) The phosphate ester additives in the electrolyte have a mass percentage of 0-2%;

[0066] (g5) The mass percentage of the vinylene carbonate in the electrolyte is 0-3%;

[0067] (g6) The fluorocarbonate additives in the electrolyte are 0-10% by mass;

[0068] (g7) The fluorocarbonate additives include fluoroethylene carbonate, wherein the mass percentage of fluoroethylene carbonate in the electrolyte is 0-10%, and optionally 0-5%;

[0069] (g8) The mass percentage of the saturated sulfonyl lactone in the electrolyte is 0-3%;

[0070] (g9) The cyclic sulfate ester in the electrolyte has a mass percentage of 0-3%;

[0071] (g10) The cyclic sulfate esters include polycyclic sulfate esters, wherein the mass percentage of the polycyclic sulfate esters in the electrolyte is 0 to 3%.

[0072] By selecting a second additive with the aforementioned type and / or dosage, it is beneficial to better leverage the competitive and synergistic effects between the first and second additives, thereby improving battery performance.

[0073] For example, lithium salt additives and phosphate ester additives have low negative electrode film resistance. By introducing one or more of lithium salt additives and phosphate ester additives into the electrolyte, it is beneficial to reduce the interfacial resistance of the negative electrode SEI film and improve the fast charging performance of lithium-ion secondary batteries.

[0074] For example, vinylene carbonate (VC) can optimize the SEI film. By introducing VC into the electrolyte, it is beneficial to reduce or delay the consumption of the first additive in the negative electrode film formation, and better control the charge transfer impedance of the negative electrode surface and the internal resistance of the battery.

[0075] For example, fluorocarbonate additives (such as fluoroethylene carbonate (FEC)) can form a robust interfacial film with low ion transport impedance on the negative electrode surface at room temperature. By introducing fluorocarbonate additives (such as FEC) into the electrolyte, it is beneficial to reduce or delay the consumption of the first additive in the negative electrode film formation, and to better control the negative electrode interfacial impedance and battery internal resistance.

[0076] For example, saturated sulfonyl lactones (such as 1,3-propanesulfonyl lactone (PS)) can participate in the formation of the negative electrode film, forming a dense and stable negative electrode SEI film, which is beneficial to reduce or delay the consumption of the first additive in the negative electrode film formation and better control the negative electrode interface impedance and battery internal resistance.

[0077] For example, by introducing cyclic sulfates into the electrolyte, the negative electrode interface film can be optimized, the stability of the negative electrode SEI film can be improved, the negative electrode interface side reactions can be reduced and gas generation can be suppressed during fast charging, and the negative electrode interface impedance and battery internal resistance can be better controlled.

[0078] In some embodiments, the electrolyte comprises lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; optionally, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.01 mol / L to 0.5 mol / L.

[0079] Lithium bisfluorosulfonyl imide (LiFSI) can participate in the formation of a stable solid electrolyte interfacial film at both the positive and negative electrodes. On the one hand, introducing LiFSI into the electrolyte can improve the stability of the positive and negative electrode interfacial film, effectively reducing side reactions at the electrolyte interface and suppressing gas generation during fast charging. On the other hand, LiFSI has a better ability to dissociate lithium ions than lithium hexafluorophosphate (LiPF6), therefore, the addition of LiFSI is also beneficial to improving the liquid phase conductivity. Thus, introducing LiFSI into the electrolyte can better improve the fast charging performance of lithium-ion secondary batteries.

[0080] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0081] (h1) The molecular weight of the first additive is less than or equal to 500 Da;

[0082] (h2) The molecule of the first additive contains 1 to 4 carbon-carbon triple bonds;

[0083] (h3) The carbon-carbon triple bond in the first additive is CH≡C-;

[0084] (h4) The first additive comprises one or more of a first alkynyl compound and a second alkynyl compound; wherein the first alkynyl compound contains a carbon-carbon triple bond and a Lewis base nitrogen heterocycle, and the carbon-carbon triple bond and the Lewis base nitrogen heterocycle in the first alkynyl compound are linked by a linker L1, wherein the linker L1 contains a C-type carbon bond covalently bonded to the carbon-carbon triple bond. 1-3 Alkylene; the second alkynyl compound contains a carbon-carbon triple bond and an alkyl carbonate group, wherein the alkyl carbonate group has the structure R2-OC(=O)-O-*, where * is the bonding site attached to a carbon atom, and R2 is C 1-3 Alkyl group; the carbon-carbon triple bond and alkyl carbonate group in the second alkynyl compound are linked by a linker L2, wherein the linker L2 contains a C- group covalently bonded to the carbon-carbon triple bond. 1-3 Alkylene.

[0085] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0086] (i1) The molecular weight of the first additive is less than or equal to 300 Da;

[0087] (i2) The molecule of the first additive contains 1 to 4 Lewis base nitrogen heterocycles;

[0088] (i3) The Lewis base nitrogen heterocycle comprises a substituted or unsubstituted imidazole group, wherein the imidazole ring in the substituted or unsubstituted imidazole group is substituted by 0, 1 or more substituents Q2, and each substituent Q2 in the substituted imidazole group is independently C. 1-3 Alkyl, cyano, or fluorine atom;

[0089] (i4) The first alkynyl compound consists of a carbon-carbon triple bond, C, and C bonds connected in sequence. 1-3 Alkylene and -OC(=O)-R 10 Composition, R 10 It is a Lewis base nitrogen heterocycle; the second alkynyl compound consists of a carbon-carbon triple bond, C, and C bonds connected in sequence. 1-3 Alkylene and -OC(=O)-OR 20 Composition, R 20 C 1-3 alkyl.

[0090] In some embodiments, the first additive includes one or more of compound II and compound III;

[0091] The structure of compound II is as follows: Among them, L 11 C 1-3 Alkylene, Q2 is independently C 1-3 Alkyl, cyano, or fluorine atom, p2 is 0, 1, 2, or 3;

[0092] The structure of compound III is as follows: Among them, L 21 C 1-3 Alkylene, R 22 C 1- 3-alkyl group.

[0093] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0094] (j1) The first additive includes compound II, wherein the mass percentage of compound II in the first additive is 80% to 100%;

[0095] (j2) The first additive comprises the structure as follows The compound IIa, wherein the mass percentage of compound IIa in the first additive is 80% to 100%.

[0096] By controlling the molecular weight of the first additive within the aforementioned lower range, the first additive can have a smaller molecular size, which is beneficial for better control of the low viscosity characteristics of the electrolyte, and makes the electrolyte have higher conductivity, which can better synergize with the solvent of Formula I to improve battery dynamics.

[0097] By controlling the number of carbon-carbon triple bonds in the first additive within the aforementioned range, the first additive can better synergistically improve the fast-charging performance of lithium-ion secondary batteries with the solvent of Formula I. It also helps to suppress the increase in interfacial impedance caused by the first additive participating in the formation and repair of the SEI film, and helps to control the influence of the first additive on the liquid phase impedance. As a result, battery kinetics can be better improved, and the fast-charging performance of lithium-ion secondary batteries can be better improved.

[0098] The first alkynyl compound, which includes both a carbon-carbon triple bond and a Lewis base nitrogen heterocycle, can promote the formation of an interface film with dual organic / inorganic properties during the negative electrode interface reaction, thereby improving the stability of the negative electrode SEI film. It can also work synergistically with the solvent of formula I to comprehensively improve the fast-charging performance of lithium-ion secondary batteries. The Lewis base nitrogen heterocycle can also absorb acid byproducts in the electrolyte, which is beneficial to improving the stability of the negative electrode interface and the negative electrode active material, reducing the consumption rate of the first additive, reducing the growth rate of battery internal resistance, and maintaining superior fast-charging performance for a longer period of time.

[0099] By controlling the number of Lewis base nitrogen heterocycles in the first additive within the aforementioned range, it is beneficial to better absorb acid byproducts in the electrolyte, and at the same time, it is also beneficial to control the steric hindrance effect of Lewis base nitrogen heterocycles on carbon-carbon triple bonds.

[0100] Examples of Lewis base nitrogen heterocycles include the imidazole ring in compounds II and IIa.

[0101] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0102] (k1) The solvent of Formula I in the chain carboxylic acid ester compound accounts for 75% to 100% by mass;

[0103] (k2) The chain carboxylic acid ester compound accounts for 5% to 80% of the mass in the non-aqueous solvent;

[0104] (k3) The conductivity of the electrolyte at 25°C is 9mS / cm~25mS / cm.

[0105] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0106] (k1') The solvent of Formula I accounts for 90% to 100% of the mass of the chain carboxylic acid ester compound;

[0107] (k2') The chain carboxylic acid ester compound in the non-aqueous solvent accounts for 10% to 60% by mass;

[0108] (k3') The conductivity of the electrolyte at 25°C is 10 mS / cm to 18 mS / cm.

[0109] By controlling one or more parameters—such as the mass percentage of the solvent of Formula I in the chain carboxylic acid ester compound, the mass percentage of the chain carboxylic acid ester compound in the non-aqueous solvent, and the conductivity of the electrolyte at 25°C—within the aforementioned ranges, it is beneficial to improve battery kinetics and thus impart better fast-charging performance to lithium-ion secondary batteries. Among these, the chain carboxylic acid ester compound (solvent of Formula I) has a relatively low viscosity, which is beneficial for improving the conductivity of the electrolyte.

[0110] In some embodiments of the second aspect of this application, a method for preparing a lithium-ion secondary battery is provided, comprising the following steps:

[0111] An electrode assembly comprising a positive electrode, a separator, and a negative electrode is placed inside a battery casing; wherein the separator is disposed between the positive electrode and the negative electrode.

[0112] An electrolyte is injected into the battery casing, and the battery is allowed to stand to allow the electrolyte to wet the positive and negative electrode plates, thus forming the battery. The electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives. The non-aqueous solvent comprises a chain-like carboxylic acid ester compound, which includes a solvent of formula I, the structure of which is shown in formula (I). In equation (I), R 11 and R 12 Each is independently methyl or ethyl; the additives are a first additive and a second additive, wherein the first additive is a nonionic organic additive containing a carbon-carbon triple bond, and the second additive is a negative electrode film-forming additive different from the first additive.

[0113] The prepared lithium-ion secondary battery has the advantages of the lithium-ion secondary battery described in the first aspect of this application.

[0114] In some embodiments, during the step of injecting electrolyte into the battery casing, the initial mass percentage of the first additive in the electrolyte is 0.1% to 5%.

[0115] In some embodiments, during the step of injecting electrolyte into the battery casing, the initial mass percentage of the first additive in the electrolyte is 0.1% to 3%.

[0116] In some embodiments, the lithium-ion secondary battery described in the first aspect of this application is prepared.

[0117] In some embodiments of the third aspect of this application, an electrical device is provided, which includes 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. Attached Figure Description

[0118] 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.

[0119] 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:

[0120] Figure 1 is a schematic diagram of a battery cell according to an embodiment of this application.

[0121] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1.

[0122] Figure 3 is a schematic diagram of a battery device according to an embodiment of this application.

[0123] Figure 4 is a schematic diagram of a battery pack according to one embodiment of this application.

[0124] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4.

[0125] 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.

[0126] 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, battery casing; 52, electrode assembly; 53, cover plate; 6, electrical device. Detailed Implementation

[0127] The following describes in detail some embodiments and examples of the lithium-ion secondary battery, its preparation method, and its power application device, with appropriate reference to the accompanying drawings. However, some unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially the same 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.

[0128] 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.

[0129] In this application, the term "numerical value" includes the number itself and its reasonable approximations. The definition of "numerical value" can apply to discrete numerical points or to the endpoints of a numerical range. Unless otherwise specified, the term "approximation" covers a numerical interval based on a reasonable range of fluctuations of the number itself. This reasonable range of fluctuations can vary depending on the type and magnitude of the number. This reasonable range of fluctuations can be reasonably determined based on the accuracy of the testing or measurement method. Therefore, when referring to a numerical value or a numerical range, unless otherwise specified, it should be understood that the numerical value includes its reasonable approximation, and the numerical range includes reasonable approximations at both endpoints. Those skilled in the art will understand that acceptable fluctuation ranges of the relevant approximations can be included within the definition of the numerical value or the numerical range. In this application, unless otherwise specified, "N1" can be reasonably understood as "about N1," and "N1~N2" can be reasonably understood as "about N1 to about N2," where N1 and N2 are two unequal numerical values.

[0130] 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".

[0131] In this application, the terms "multiple," "multi-item," or "multiple items" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one item or two or more (greater than or equal to) items. 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.

[0132] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0133] 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.

[0134] Those skilled in the art will understand that, unless otherwise specified, the order in which the steps are written in the various embodiments or methods of this application does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but are preferably performed sequentially. For example, if method M includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, method M may also include step (c), meaning that step (c) can be added to method M in any order. For example, method M may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0135] 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."

[0136] 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.

[0137] 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."

[0138] 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.

[0139] In this document, the word "suitable" in "suitable combination" or "suitable method" refers to the technical solution that can implement this application.

[0140] In this document, terms such as "preferred," "better," and "good" are merely descriptions of implementation methods or embodiments that achieve better results, and should be understood as not constituting a limitation on 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.

[0141] 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.

[0142] In this application, the terms "first aspect," "second aspect," "third 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," and "third" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0143] In the description of this application, it should be understood that the terms "thickness", "height", "upper", "lower", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0144] In this application, unless otherwise expressly specified and limited, terms such as "connected" and "joined" in relation to mechanical structures should be interpreted broadly, for example, they can refer to a fixed connection, a detachable connection, or an integral part. Those skilled in the art can understand the meaning of the above terms in this application according to the circumstances.

[0145] 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.

[0146] In this application, the terms "room temperature" or "normal temperature" generally refer 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℃. In some embodiments or examples of this application, "normal temperature" is 20℃ to 35℃, and may be 20℃ to 30℃.

[0147] 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.

[0148] In this application, unless otherwise stated, "molecular weight" refers to molecular mass measured in Daltons (Da), where 1 Dalton equals 12 One-twelfth of the mass of a carbon atom.

[0149] In this application, "greater than or equal to", "greater than or equal to", and "≥" have the same meaning and can be used interchangeably; "less than or equal to", "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".

[0150] 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.

[0151] Unless otherwise stated, the improvements described in this application are not intended to be limited to any theoretical constraints.

[0152] For traditional lithium-ion rechargeable batteries, the electrolyte is prone to decomposition and gas production during fast charging. As the internal temperature of the battery increases during fast charging, the reaction rate accelerates, exacerbating interfacial side reactions and gas production. This gas production associated with interfacial side reactions degrades the cycle performance of fast-charging batteries.

[0153] According to various embodiments and examples of this application, this application provides a lithium-ion secondary battery, a preparation method, and an electrical device. This lithium-ion secondary battery has improved fast-charging performance.

[0154] In some embodiments of this application, the lithium-ion secondary battery includes an electrolyte; the non-aqueous solvent in the electrolyte includes chain-like carboxylic acid ester compounds, and the chain-like carboxylic acid ester compounds include those with the structural formula R. 11 -C(=O)-OR 12 Solvent of formula I, R 11 and R 12 Each is independently methyl or ethyl; the additives in the electrolyte include a first additive and a second additive, the first additive being a nonionic organic additive containing a carbon-carbon triple bond, and the second additive being a negative electrode film-forming additive different from the first additive.

[0155] 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. A separator is disposed between the positive and negative electrodes; the separator primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0156] 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. It is understood that the positive active material layer contains positive active material, and the negative active material layer contains negative active material. In this application, "electrode active material layer" may also be referred to as "active material layer," "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."

[0157] In this application, the terms "electrode sheet" and "electrode plate" have the same meaning and can be used interchangeably. An electrode sheet can be a positive electrode sheet or a negative electrode sheet, and the "active material" or "active substance" in the electrode sheet has the ability to reversibly insert and extract active ions.

[0158] In this application, the term "negative electrode sheet" includes a negative electrode active 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.

[0159] 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.

[0160] In this application, the term "positive electrode sheet" includes a positive electrode active layer, and the positive electrode active layer 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.

[0161] 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.

[0162] In this application, unless otherwise specified, "separation membrane" and "diaphragm" have the same meaning and can be used interchangeably.

[0163] In a first aspect of this application, a lithium-ion secondary battery is provided that has improved fast-charging performance.

[0164] In some embodiments, the lithium-ion secondary battery includes an electrolyte comprising an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent includes a chain-like carboxylic acid ester compound, which includes compounds with the structure R. 11 -C(=O)-OR 12 Solvent of formula I, R 11 and R 12 Each component is independently methyl or ethyl; the additives include a first additive and a second additive, wherein the first additive is a nonionic organic additive containing a carbon-carbon triple bond, and the second additive is a negative electrode film-forming additive different from the first additive. This lithium-ion secondary battery exhibits significantly improved fast-charging performance.

[0165] In some embodiments, a lithium-ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte, with a separator disposed between the positive and negative electrodes; the electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent includes chain-like carboxylic acid ester compounds, and the chain-like carboxylic acid ester compounds include those with the structural formula R. 11 -C(=O)-OR 12 Solvent of formula I, R11 and R 12 Each component is independently methyl or ethyl; the additives include a first additive and a second additive. The first additive is a nonionic organic additive containing a carbon-carbon triple bond, and the second additive is a negative electrode film-forming additive different from the first additive. This lithium-ion secondary battery exhibits superior fast-charging performance. Not limited to the following mechanisms, viscosity can be reduced and conductivity increased by the solvent of formula I; the stability of the SEI film can be improved and negative electrode interface side reactions and gas generation problems can be suppressed by the first additive; and the second additive can competitively participate in negative electrode film formation, suppressing the increase in negative electrode interface impedance caused by the participation of the first additive in negative electrode film formation.

[0166] In some embodiments of the first aspect of this application, a lithium-ion secondary battery is provided, comprising a positive electrode, a negative electrode, and an electrolyte, wherein a separator is disposed between the positive and negative electrode; the electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent comprises a chain-like carboxylic acid ester compound, which comprises a solvent of formula I, the structure of which is shown in formula (I): In equation (I), R 11 and R 12 Each is independently methyl or ethyl; the additives include a first additive and a second additive, the first additive being a nonionic organic additive containing a carbon-carbon triple bond, and the second additive being a negative electrode film-forming additive different from the first additive.

[0167] In this application, unless otherwise specified, "non-aqueous solvent" means a solvent that is not water.

[0168] In this application, unless otherwise specified, "chain carboxylic acid ester compounds" refers to chain compounds having a -C(=O)-O- structure. Chain carboxylic acid ester compounds used as non-aqueous solvents in electrolytes typically have low viscosity, which is beneficial for providing high conductivity. Among them, "solvent of formula I" has even lower viscosity and higher conductivity.

[0169] In this application, unless otherwise specified, a "carbon-carbon triple bond" is an unsaturated bond with a —C≡C— framework.

[0170] In this application, unless otherwise specified, "acetylene additive" refers to a compound containing a carbon-carbon triple bond (—C≡C—), and "first additive" refers to a nonionic acetylene organic additive, which is a nonionic organic additive containing a carbon-carbon triple bond. It is understood that salt additives are not within the scope of the first additive. The first additive can participate in the formation of the negative electrode solid electrolyte interphase (SEI) film. The first additive can significantly improve the high-temperature performance of the battery, including extending high-temperature cycling and storage life, and can be used as a high-temperature additive. However, using the first additive as a single additive can easily lead to a large negative electrode interfacial impedance at room temperature.

[0171] In this application, unless otherwise specified, "second additive" refers to a negative electrode film-forming additive different from the first additive. "Negative electrode film-forming additive" refers to an additive capable of decomposing at the negative electrode operating potential and participating in the formation of the negative electrode SEI film. The higher the reduction potential of the negative electrode film-forming additive, that is, relative to Li / Li... + The more positive the potential value, the earlier the negative electrode film-forming additive decomposes, and thus the earlier it participates in the formation of the negative electrode SEI film. It is understood that some negative electrode film-forming additives can also participate in the formation of the interface film (CEI film) at the positive electrode. Typically, those skilled in the art can determine whether an additive can participate in the formation of the negative electrode SEI film based on methods such as reduction potential analysis, analysis of decomposition products and SEI film composition, and electrochemical performance verification. For example, the reduction potential of an additive can be measured by cyclic voltammetry in a simulated battery environment (such as a lithium metal-pair working electrode). For example, the composition of the SEI film can be analyzed using chemical composition analysis methods including but not limited to X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). For example, the change in performance indicators such as initial coulombic efficiency, cycle stability, and impedance spectrum before and after the introduction of the additive can determine whether an introduced additive can participate in the formation of the negative electrode SEI film.

[0172] In the lithium-ion secondary battery provided in the first aspect of this application, it is understood that the positive electrode and the negative electrode are wetted by the electrolyte.

[0173] This lithium-ion secondary battery introduces a non-ionic alkyne-based organic additive (denoted as the first additive) and a second additive (a negative electrode film-forming additive different from the first additive) when using a highly conductive solvent. The first additive is R in the solvent of formula I. 11 and R 12 Both additives have fewer carbon atoms, resulting in lower viscosity and higher conductivity for the solvent in Formula I. Secondly, the first additive can participate in the formation and repair of the solid electrolyte interphase (SEI) film at the negative electrode, significantly improving the stability of the SEI film. This significantly suppresses interfacial side reactions between the negative electrode and the electrolyte during fast charging, effectively inhibiting the problem of easy decomposition and gas generation of the solvent in Formula I. Thirdly, the second additive can competitively participate in the negative electrode film formation, reducing or delaying the consumption of the first additive in the negative electrode film formation and suppressing the increase in negative electrode interfacial impedance caused by the participation of the first additive in the negative electrode film formation. Based on the synergistic effects of the above-mentioned actions, but not limited to the aforementioned theories, lithium-ion secondary batteries have improved fast charging performance and extended cycle life of fast charging battery systems.

[0174] The types and concentrations of inorganic components (including electrolyte salts and inorganic additives) in the electrolyte can be tested with reference to relevant standards such as GB / T 34672-2017 General Rules for Determination of Chemical Reagents by Ion Chromatography and GB / T 6040-2019 General Rules for Infrared Spectroscopic Analysis, and the latest version of the standard method can be preferred. The types and contents of organic components (including non-aqueous solvents and organic additives) in the electrolyte can be tested with reference to relevant standards such as GB / T 9722-2023 General Rules for Gas Chromatography of Chemical Reagents.

[0175] Furthermore, those skilled in the art can also identify the components of the electrolyte in a lithium-ion secondary battery using one or more of the following detection methods, including but not limited to: 1H NMR (1H NMR) spectroscopy. 1 Methods such as 1H NMR, high-performance liquid chromatography (HPLC), matrix-assisted laser desorption / ionization mass spectrometry (MADI-TOF), Fourier transform infrared spectroscopy (FT-IR), ultraviolet spectroscopy, and gas chromatography (GC) are available. 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. As a non-limiting example, FT-IR, ultraviolet spectroscopy, etc., can be used. 1 One or more of the following methods may be used to detect the types and contents of electrolyte components: ¹H NMR, mass spectrometry, MADI-TOF, GC, etc., but not limited to these.

[0176] The electrolyte sample can be obtained by disassembling the battery cell.

[0177] In some embodiments, the chain carboxylic acid ester compound includes one or more of methyl formate, ethyl formate, methyl acetate, and ethyl acetate.

[0178] In some embodiments of this application, the chain carboxylic acid ester compound includes ethyl acetate.

[0179] In some embodiments of this application, the chain carboxylic acid ester compound includes ethyl acetate, and further, the chain carboxylic acid ester compound also includes one or more of methyl formate, ethyl formate and methyl acetate.

[0180] In some embodiments of this application, R 11 For methyl, R 12 It is an ethyl group.

[0181] In some embodiments, the negative electrode sheet includes a negative electrode active layer, which includes a negative electrode active material. The average particle size of the primary particles in the negative electrode active material is denoted as D1, wherein D1 is 0.1 μm to 2 μm, optionally 0.5 μm to 1.2 μm, further optionally 0.5 μm to 1.0 μm, and may also be any of the following values ​​or a range selected from any two of the following values: 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, etc. For example, the D1 of the negative electrode active material can also be selected from any of the following suitable ranges: 0.1μm to 1.6μm, 0.5μm to 1.8μm, 0.6μm to 1.5μm, etc.

[0182] In this application, unless otherwise specified, the "average particle size of primary particles" or "average particle size of primary particles" in the negative electrode active material refers to the average particle size of each primary particle in the negative electrode active material. The "particle size of primary particles" refers to the maximum diameter of the primary particles in each direction.

[0183] In this application, unless otherwise specified, "primary particles" in the negative electrode active material refer to the basic particle unit in the negative electrode active material. It is understood that primary particles exist in the negative electrode active material. In the negative electrode active material, primary particles can exist in a non-agglomerated state, or multiple primary particles can form aggregates. Non-agglomerated primary particles can be called "non-agglomerated primary particles," and aggregates formed by multiple primary particles can be called "secondary particles."

[0184] By controlling the average particle size (denoted as D1) of the primary particles in the negative electrode active material within the aforementioned range, it is possible to control the negative electrode active material to have a more suitable ion transport path, achieve a better rate capability, and simultaneously control the negative electrode interface reaction, control the consumption of the first additive in negative electrode film formation, better optimize the SEI film and suppress gas generation. Based on the synergistic effect of the aforementioned effects, but not limited to the aforementioned theory, it is beneficial to better control the battery internal resistance and enable lithium-ion secondary batteries to achieve better fast charging performance.

[0185] The particle morphology of the negative electrode active material can be used to statistically analyze the particle size and average value of the primary particles in the negative electrode active material. The particle morphology of the negative electrode active material can be obtained using scanning electron microscopy (SEM) results (e.g., ZEISS Sigma 300, JEOL SEM, Axia Chemi SEM, etc.). The sample to be tested can be obtained by laying a powder sample of the negative electrode active material on conductive adhesive. Non-limitingly, SEM testing can refer to JY / T(001)-1996. One or more regions are randomly selected from the sample to be tested for scanning. Based on the SEM image at a certain magnification, the particle size of each primary particle in the scanned region and the frequency of occurrence of different particle sizes are statistically analyzed, and the average particle size of the statistically analyzed primary particles can then be calculated. Non-limitingly, the magnification of a single scanned region can be, for example, 1000X, but is not limited to this. To improve the accuracy of the statistical results, multiple regions can be randomly selected for scanning.

[0186] In some embodiments, the D of the negative electrode active material v The micrometer value of 50 is 5μm to 18μm, optionally 6μm to 15μm, and further optionally 8μm to 12.5μm. It can also be any of the following values ​​or a range selected from any two of the following values: 5μm, 5.5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 16μm, 17μm, 18μm, etc. For example, the D of the negative electrode active material... v 50 can also be selected from any of the following suitable ranges: 10μm~13μm, 11μm~12.5μm, etc.

[0187] In the context of this application, the volumetric cumulative distribution particle size D can be used. v N (where N represents any value selected from 0 to 100) is used to characterize the particle size of the material, referring to the particle size corresponding to the cumulative volume distribution percentage of the material reaching N%, where the particle size is less than or equal to D. v N's volume percentage is N%. D v N can be obtained from the volumetric cumulative distribution curve of the material particles. Unless otherwise specified, the volumetric cumulative distribution curve is accumulated from zero on the smaller particle size side. Let D... v Taking 50 as an example for illustration. In this application, unless otherwise stated, 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 v50. D v 10. D v The meaning of 1 can be determined using instruments and methods known in the art. For example, particle size distribution can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer or the LS-909 laser particle size analyzer from Malvern Instruments Ltd. (UK). Furthermore, for equipment models such as the Malvern 2000 laser particle size analyzer, the standard procedure GB / T19077-2016 / ISO 13320:2009 can be referenced for testing.

[0188] By using the D of the negative electrode active material v By controlling the specific surface area of ​​the negative electrode active material within the aforementioned range, it is possible to keep the specific surface area of ​​the negative electrode active material within a relatively low range. This is beneficial for reducing side reactions at the negative electrode interface during fast charging, reducing or delaying the consumption of the first additive at the negative electrode interface, optimizing the SEI film, and suppressing gas generation. It is also beneficial for better control of the overall ion transport path of the negative electrode active material particles. Based on the synergistic effect of the aforementioned effects, but not limited to the aforementioned theory, it is beneficial for better control of the battery internal resistance and for enabling lithium-ion secondary batteries to achieve better fast charging performance.

[0189] By synergistically controlling the D of the negative electrode active material v The average particle size of the primary particles in the 50 and negative electrode active materials is beneficial to taking into account the ion transport path of the primary particles and the particles as a whole in the negative electrode active materials. It also effectively suppresses the side reactions at the negative electrode interface and suppresses gas generation. Based on the synergistic effect of the above, but not limited to the above theory, it is beneficial to better control the internal resistance of the battery and to enable the lithium-ion secondary battery to achieve better fast charging performance.

[0190] In some embodiments of this application, the negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material, and the average particle size of the primary particles in the negative electrode active material is denoted as D1, wherein D1 is 0.1 μm to 2 μm; the D of the negative electrode active material... v 50 has a diameter of 5μm to 18μm. The D of the negative electrode active material... v 50 and D1 can also be further combined with values ​​or ranges in other implementations.

[0191] By controlling the size of the negative electrode active material and the agglomeration state of the primary particles in the negative electrode active material, a large number of lithium ion insertion sites can be provided on the surface of the negative electrode active material, while controlling the solid-phase transport path of lithium ions.

[0192] By synergistically controlling the Dv50 of the negative electrode active material and the average particle size D1 of the primary particles in the negative electrode active material, it is beneficial to take into account the ion transport path of the primary particles and the particles as a whole in the negative electrode active material, and at the same time, it can better suppress the side reactions at the negative electrode interface and suppress gas production.

[0193] In some embodiments, the D of the negative electrode active material v The particle size of the primary particles ranges from 5 μm to 18 μm, and the average particle size (D1) of the primary particles ranges from 0.1 μm to 1.8 μm; optionally, the D1 of the negative electrode active material ranges from 0.4 μm to 1.1 μm. The D1 of the negative electrode active material... v 50 and D1 can also be further combined with values ​​or ranges in other embodiments. By using the D of the negative electrode active material... v By keeping the value of 50 within the aforementioned range, a relatively small average primary particle size can be used to shorten the lithium-ion diffusion path.

[0194] In some embodiments, the D of the negative electrode active material or the positive electrode active material can be tested using the following methods. v 50. D v 10. D v 1. A Malvern 2000 (MasterSizer 2000) laser particle size analyzer was used, following the standard procedure GB / T19077-2016 / ISO 13320:2009. The detailed test procedure included: taking an appropriate amount of the sample to be tested, adding a solvent (deionized water is acceptable, and the sample concentration can be controlled at 8%–12% opacity), and sonicating for 5 minutes (53 kHz / 120 W) to ensure thorough dispersion. The sample was then measured according to GB / T19077-2016 / ISO 13320:2009. Non-limiting examples of solvents include deionized water and anhydrous ethanol. After the sample was poured into the injection tower, it circulated with the solution to the test optical path system. Under the irradiation of the laser beam, the particle size distribution characteristics could be obtained by receiving and measuring the energy distribution of the scattered light. Based on the test data, a particle size distribution map was plotted, and the Dsize was obtained from the distribution map. v 50. D v 10. D v Parameter 1. To avoid agglomeration during the drying process affecting particle size testing, a dispersion test was performed on a washed and moistened sample.

[0195] In some embodiments, the D of the negative electrode active material v The ratio of 50 to D1 is 5 to 50, can be selected from 8 to 30, can be further selected from 10 to 20, and can also be any of the following values ​​or a range selected from any two of the following values: 5, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, etc.

[0196] D of negative electrode active materialv The ratio of 50 to D1 can reflect the agglomeration state of primary particles in the negative electrode active material. The larger the ratio, the more primary particles are contained in the secondary particles of the negative electrode active material, and the higher the degree of agglomeration. Conversely, the smaller the ratio, the fewer primary particles are contained in the secondary particles of the negative electrode active material, and the lower the degree of agglomeration.

[0197] By using the D of the negative electrode active material v Controlling the ratio of 50 to D1 within the aforementioned range is beneficial for balancing the ion transport paths of primary particles and the particles as a whole in the negative electrode active material, while also effectively suppressing side reactions at the negative electrode interface and inhibiting gas generation.

[0198] In some embodiments, the negative electrode active material includes a coated negative electrode material, which includes a negative electrode active body and a carbon coating layer located on at least a portion of the negative electrode active body. It is understood that the carbon coating layer in the coated negative electrode material has a different chemical composition from the negative electrode active body. The negative electrode active body can be selected from at least one material known in the art suitable for negative electrode active materials. Non-limitingly, the negative electrode active body can include one or more of graphite and silicon-based materials. Non-limitingly, graphite can include one or more of natural graphite and artificial graphite. Non-limitingly, silicon-based materials can include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Non-limitingly, the carbon coating layer in the coated negative electrode material can include one or more of soft carbon, hard carbon, and amorphous carbon. Non-limitingly, the average thickness of the carbon coating in the coated negative electrode material can be 1 nm to 500 nm, optionally 100 nm to 500 nm, and further optionally 100 nm to 200 nm. Non-limitingly, the coating layer constitutes 0.2% to 5% of the mass percentage of the coated active material, optionally 0.5% to 3%.

[0199] "Soft carbon" and "hard carbon" have well-known meanings in the art. Soft carbon can be graphitized by further high-temperature treatment, while hard carbon is difficult to graphitize even with further high-temperature treatment. In this application, unless otherwise specified, "amorphous carbon" refers to transitional carbon materials with a very low degree of graphitization and crystallization, which are approximately amorphous (or have no fixed shape and periodic structural regularity).

[0200] In some embodiments, the carbon coating layer in the coated negative electrode material is one of a soft carbon coating layer, a hard carbon coating layer, and an amorphous carbon coating layer. It can be understood that the material composition of the soft carbon coating layer is mainly soft carbon, the material composition of the hard carbon coating layer is mainly hard carbon, and the material composition of the amorphous carbon coating layer is mainly amorphous carbon.

[0201] In some embodiments, the negative electrode active material includes a coated negative electrode material, wherein the average particle size D1 of the primary particles of the negative electrode active material is 0.1 μm to 1.6 μm, optionally 0.4 μm to 1.0 μm, or any of the following values ​​or a range selected from any two of the following values: 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, etc.

[0202] In some implementations, the negative electrode sheet satisfies one or more of the following characteristics:

[0203] (a1) The mass percentage of the coated negative electrode material in the negative electrode active material is 80% to 100%, which can be selected as 90% to 100%, or it can be 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.

[0204] (a2) The coated negative electrode material includes coated graphite, and the negative electrode active body in the coated graphite includes graphite body; without limitation, the mass percentage of coated graphite in the negative electrode active material is 80% to 100%, optionally 90% to 100%, and may 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%, 94%, 95%, 96%, 98%, 100%, etc.

[0205] In this application, "coated graphite" is a coated anode material, wherein the anode active body in coated graphite includes a graphite body; coated graphite includes a graphite body and a carbon coating layer located on at least a portion of the surface of the graphite body.

[0206] In this application, the “graphite body” is composed of graphite.

[0207] By incorporating a coated anode material (such as coated graphite) with a carbon coating layer into the anode active material, the lithium-ion transport channels on the surface of the anode active material can be optimized, promoting lithium-ion transport and improving the kinetics of lithium-ion secondary batteries. At the same time, it is also beneficial to suppress side reactions at the anode interface and suppress the increase in interface impedance caused by the participation of the first additive in film formation, which is conducive to better improving the fast-charging performance of lithium-ion secondary batteries.

[0208] By incorporating a coated anode material (such as coated graphite) with a carbon coating layer into the anode active material, rate performance can be optimized by using a relatively small average primary particle size.

[0209] In some implementations, the coated negative electrode material is coated graphite.

[0210] In some embodiments, the positive electrode includes a positive active layer, which includes a positive active material; the positive active material includes one or more of lithium phosphate-based positive electrode materials and lithium transition metal oxide-based positive electrode materials.

[0211] In some embodiments, the positive electrode active material includes a lithium phosphate positive electrode material. Non-limitingly, the lithium phosphate positive electrode material constitutes 80% to 100% of the positive electrode active material by mass, optionally 90% to 100%, further optionally 95% to 100%, and may 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%, 94%, 95%, 96%, 98%, 100%, etc.

[0212] In some embodiments, the positive electrode active material includes a lithium transition metal oxide (LiMe) positive electrode material. Non-limitingly, the LiMe is present in the positive electrode active material at a mass percentage of 80%–100%, optionally 90%–100%, further optionally 95%–100%, and may 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%, 94%, 95%, 96%, 98%, 100%, etc.

[0213] In some embodiments, the positive electrode sheet satisfies one or more of the following characteristics:

[0214] (b1) Positive electrode active materials include lithium phosphate-containing positive electrode materials, and the D of lithium phosphate-containing positive electrode materials v 50 is 0.3μm to 2μm, and can also be any of the following values ​​or a range selected from any two of the following values: 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.8μm, 1μm, 1.2μm, 1.4μm, 1.5μm, 1.6μm, 1.8μm, 2μm, etc.;

[0215] (b2) Positive electrode active materials include lithium transition metal oxide positive electrode materials, and the D of lithium transition metal oxide positive electrode materials. v 50 is 2μm to 10μm, and can also be any of the following values ​​or a range composed of any two of the following values: 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc.

[0216] By controlling the type of positive electrode active material and combining it with the aforementioned D vA value of 50 helps to better coordinate the lithium-ion desorption kinetics of the positive electrode with the lithium insertion kinetics of the negative electrode, which helps to reduce the internal resistance of the battery and improve fast charging performance.

[0217] In this application, unless otherwise specified, "lithium phosphate-containing cathode material" refers to a class of cathode active materials that include lithium phosphate components (e.g., lithium iron phosphate components), and more specifically, materials that include lithium, transition metal elements, and phosphate ions (PO4). 3- The positive electrode active material is lithium phosphate. Unless otherwise specified, "lithium phosphate positive electrode material" may be olivine structure.

[0218] In some embodiments, the positive electrode active material includes a lithium phosphate-based positive electrode material with an olivine structure. Non-limiting examples of lithium phosphate-based positive electrode materials 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.

[0219] Non-limiting examples of lithium phosphate cathode materials include lithium iron phosphate cathode materials.

[0220] In this application, unless otherwise specified, "lithium iron phosphate cathode material" refers to a class of cathode active materials containing lithium iron phosphate components. Unless otherwise specified, "lithium iron phosphate cathode material" may have an olivine structure.

[0221] In some embodiments, the positive electrode active material includes lithium iron phosphate-based positive electrode materials. Further, the lithium iron phosphate-based positive electrode material may include at least one of lithium iron phosphate and a composite material of lithium iron phosphate and carbon.

[0222] In some embodiments, the composite material of lithium iron phosphate and carbon is carbon-coated lithium iron phosphate.

[0223] In some implementations, lithium iron phosphate cathode materials include carbon-coated lithium iron phosphate.

[0224] In this application, the term "carbon-coated lithium iron phosphate" includes 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, wherein the lithium iron phosphate body contains lithium iron phosphate. Non-limitingly, the carbon coating layer in the carbon-coated lithium iron phosphate may include one or more of soft carbon, hard carbon, and amorphous carbon. Non-limitingly, the mass percentage of the carbon coating layer in the lithium iron phosphate cathode material may be 1% to 1.5%.

[0225] In some embodiments, lithium iron phosphate cathode materials include lithium iron phosphate-based cathode materials. Lithium iron phosphate-based cathode materials refer to a class of cathode active materials containing lithium iron phosphate.

[0226] In some implementations, the lithium iron phosphate body includes lithium iron phosphate.

[0227] In some embodiments, the lithium iron phosphate-based cathode material includes carbon-coated lithium iron phosphate. In this case, the carbon-coated lithium iron phosphate comprises carbon-coated lithium iron phosphate.

[0228] In this application, the term "carbon-coated lithium iron phosphate" includes lithium iron phosphate and a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate. Further, the carbon coating layer may include one or more of soft carbon, hard carbon, and amorphous carbon.

[0229] In some embodiments, the carbon coating layer in carbon-coated lithium iron phosphate includes soft carbon. In some embodiments, the carbon coating layer is a soft carbon coating layer, and in this case, the carbon-coated lithium iron phosphate can be referred to as soft carbon-coated lithium iron phosphate. "Soft carbon coating layer" refers to a coating layer mainly composed of soft carbon, and the mass percentage of soft carbon in the coating layer can be close to 100%. The mass percentage of soft carbon in the soft carbon coating layer in the carbon-coated lithium iron phosphate can be 1% to 1.5%, optionally 1.4% to 1.5%, but is not limited thereto.

[0230] In this application, unless otherwise specified, "lithium transition metal oxide cathode material" refers to a cathode active material containing lithium, non-lithium metal elements, and oxygen. Typically, the non-lithium metal elements in lithium transition metal oxide cathode materials include transition metal elements. Non-limitingly, in lithium transition metal oxide cathode materials, the molar percentage of transition metal elements relative to non-lithium metal elements can be 90% to 100%, and can also be any of the following percentages or a range selected from any two of the following percentages: 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0231] In this application, unless otherwise specified, "non-lithium metal element" refers to a metal element that is not lithium (Li).

[0232] In some embodiments, lithium transition metal oxide cathode materials include lithium nickel cobalt-based oxide cathode materials. In this application, "lithium nickel cobalt-based oxide cathode materials" includes lithium (Li), nickel (Ni), cobalt (Co), and oxygen (O).

[0233] In some embodiments, the lithium nickel cobalt-based oxide cathode material may further include an M2 element, which can be either manganese (Mn) or aluminum (Al). When the M2 element is manganese (Mn), the lithium nickel cobalt-based oxide cathode material is a lithium nickel cobalt manganese-based oxide cathode material, which can be denoted as an NCM-based cathode material. When the M2 element is aluminum (Al), the lithium nickel cobalt-based oxide cathode material is a lithium nickel cobalt aluminum-based oxide cathode material, which can be denoted as an NCA-based cathode material.

[0234] In some embodiments, the lithium composite metal oxide cathode material includes a ternary cathode material, which may be selected as a ternary cathode material. In this application, the "ternary cathode material" is composed of Li, nickel, cobalt, M2, and oxygen; wherein, M2 can be manganese or aluminum. When M2 is manganese (Mn), the ternary cathode material is lithium nickel cobalt manganese oxide, which can be denoted as NCM; when M2 is aluminum (Al), the ternary cathode material is lithium nickel cobalt aluminum oxide, which can be denoted as NCA.

[0235] In some embodiments, the positive electrode active material includes lithium transition metal oxide-based positive electrode materials, and the D of the lithium transition metal oxide-based positive electrode material... v 10 is greater than or equal to 1 μm.

[0236] In some embodiments, the positive electrode active material includes a lithium phosphate-based positive electrode material, and the D of the lithium phosphate-based positive electrode material... v 10 is greater than or equal to 0.2 μm.

[0237] In some embodiments, the negative electrode includes a negative active layer, which includes a negative active material; the positive electrode includes a positive active layer, which includes a positive active material.

[0238] (c1) D of the negative electrode active material v 1 is greater than or equal to 1.5 μm;

[0239] (c2) Positive electrode active materials include lithium transition metal oxide positive electrode materials, and the D of lithium transition metal oxide positive electrode materials. v 10 is greater than or equal to 1 μm;

[0240] (c3) Positive electrode active materials include lithium phosphate-containing positive electrode materials, and the D of lithium phosphate-containing positive electrode materials v 10 is greater than or equal to 0.2 μm.

[0241] By controlling the D of the negative electrode active material v 1. D of positive electrode active material vControlling one or both of 10 within the aforementioned range is beneficial for reducing the content of small particles with extremely small size and extremely large specific surface area at the negative electrode and / or positive electrode, which is beneficial for better suppressing the interfacial side reactions of the negative electrode and / or positive electrode, and better suppressing gas generation during fast charging.

[0242] By controlling the D of the negative electrode active material v 1. Within the aforementioned range, the negative electrode interface side reactions can be significantly suppressed, the consumption rate of the first additive can be reduced, and the battery internal resistance growth rate can be reduced, which is conducive to maintaining better fast charging performance for a longer period of time.

[0243] The first additive can adsorb transition metal ions in the electrolyte. This is achieved by controlling the D… of the lithium transition metal oxide cathode material… v 10 Within the aforementioned range, it is beneficial to better control the dissolution of transition metal ions in the positive electrode, allowing the first additive to participate more in the formation and repair of the negative electrode interface film, which is conducive to maintaining better fast charging performance for a longer period of time.

[0244] By controlling the D of lithium phosphate-containing cathode materials v 10 Within the aforementioned range, it is beneficial to better control the water content of the positive electrode active material, thereby reducing acid byproducts (such as hydrofluoric acid), which in turn helps to improve the stability of the negative electrode interface and the negative electrode active material, reduces the consumption rate of the first additive, reduces the growth rate of battery internal resistance, and helps to maintain better fast charging performance for a longer period of time.

[0245] In some embodiments, the D of the negative electrode active material v 50 is 5μm~18μm (optional 6μm~15μm), the D of the negative electrode active material v 1 is greater than or equal to 1.5 μm.

[0246] In some embodiments, the positive electrode active material includes a lithium phosphate-based positive electrode material, and the D of the lithium phosphate-based positive electrode material... v 50 has a diameter of 0.3μm to 2μm and contains lithium phosphate cathode materials. v 10 is greater than or equal to 0.2 μm.

[0247] In some embodiments, the positive electrode active material includes lithium transition metal oxide-based positive electrode materials, and the D of the lithium transition metal oxide-based positive electrode material... v 50 is 2μm to 10μm, D of lithium transition metal oxide cathode materials v 10 is greater than or equal to 1 μm.

[0248] In this application, the test sample of the "negative electrode active material" in the negative electrode sheet of a lithium-ion secondary battery can be obtained by disassembling the battery, removing the negative electrode sheet, and extracting the negative electrode active material from the negative electrode active layer of the negative electrode sheet using methods such as solvent washing, ultrasonic dispersion, centrifugation, and fractional sedimentation. The extracted material is then dried to obtain a powder sample. The obtained powder sample can be used for laser particle size analysis or other tests.

[0249] In this application, the test sample of the "positive electrode active material" in the positive electrode sheet of a lithium-ion secondary battery can be obtained by disassembling the battery, removing the positive electrode sheet, and extracting the positive electrode active material from the positive electrode active layer of the positive electrode sheet using methods such as solvent washing, ultrasonic dispersion, centrifugation, fractionation sedimentation, and sintering. The extracted powder sample is then dried to obtain a powder sample. The obtained powder sample can be used for laser particle size analysis or other tests. Furthermore, the powder material extracted from the positive electrode active layer can be sintered to remove organic components, thereby obtaining a powder sample of the positive electrode active material.

[0250] For example, the preparation of powder samples of positive electrode active materials can be carried out by the following method: disassemble the battery, take out the positive electrode sheet, soak and clean it with a solvent such as dimethyl carbonate to remove residual electrolyte; scrape the powder material of the positive electrode active layer, soak the powder material extracted from the positive electrode active layer with a solvent (such as N-methylpyrrolidone (NMP) etc.) to dissolve organic components such as binders in the solvent (ultrasonic dispersion and other methods can also be combined to promote dissolution), wash and filter, collect the solid phase, and then use density difference to centrifuge to separate the relatively low-density conductive agent from the suspension, collect the centrifuged precipitate to obtain the test powder of positive electrode active material.

[0251] In some embodiments, the negative electrode includes a negative electrode active layer, which includes a negative electrode active material; the negative electrode active material includes at least one of carbon-based materials and silicon-based materials.

[0252] Non-limiting, the carbon-based material may include one or more of graphite, soft carbon, and hard carbon. Graphite may include one or more of artificial graphite and natural graphite. Non-limiting, the carbon-based material may include one or more of artificial graphite, natural graphite, soft carbon, and hard carbon. Non-limiting, the mass percentage of silicon-based material in the negative electrode active material may be 0% to 40%, optionally 1% to 40%, further optionally 1% to 25%, and may also be 0% to 25%, or may be any of the following percentages or a range selected from any two of the following percentages: 0, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, 30%, 35%, 40%, etc.

[0253] In some embodiments, the negative electrode active material includes a graphite-based material.

[0254] In this application, "graphite-based material" refers to a negative electrode active material containing a graphite bulk, and the graphite-based material includes at least a graphite bulk. Unless otherwise specified, the mass percentage of the graphite bulk in the graphite-based material can be 90% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%. Non-limitingly, the graphite-based material can include one or more of coated graphite-based materials and uncoated graphite. Coated graphite-based materials include a graphite bulk and a coating layer located on at least a portion of the surface of the graphite bulk; it is understood that the coating layer is a different material from the graphite bulk. The graphite-based material can include one or more of artificial graphite and natural graphite. In some embodiments, the carbon-based material is a graphite-based material. In some embodiments, the negative electrode active material is a graphite-based material.

[0255] In some embodiments, the graphite-based material accounts for 60% to 100% of the mass of the negative electrode active material, optionally 70% to 100%, further optionally 75% to 100%, even further optionally 80% to 100%, even further optionally 90% to 100%, even further optionally 95% to 100%, even further optionally 97% to 100%, and may also be any of the following percentages or a range selected from any two of the following percentages: 60%, 65%, 70%, 75%, 80%, 85%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0256] In some embodiments, the negative electrode active material includes a carbon-based material. Non-limitingly, the carbon-based material constitutes 60% to 100% of the mass of the negative electrode active material, optionally 60% to 99%, further optionally 75% to 99%, also 70% to 100%, further 75% to 100%, even further 80% to 100%, even further 90% to 100%, even further 95% to 100%, even further 97% to 100%, and may also be any of the following percentages or a range selected from any two of the following percentages: 60%, 65%, 70%, 75%, 80%, 85%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0257] Non-limitingly, the mass percentage of silicon-based material in the negative electrode active material can be 0-40%, further preferably 0-30%, even more preferably 0-25%, even more preferably 0-20%, even more preferably 0-10%, even more preferably 0-5%, even more preferably 0-3%, and can also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.01%, 0.02%, 0.04%, 0.05%, 0.08%, 0.1%, 0.12%, 0. 14%, 0.15%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.25%, 0.26%, 0.28%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, 4%, 5%, 6%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc.

[0258] In some embodiments, the negative electrode active material includes a silicon-based material. Non-limitingly, the silicon-based material may constitute 1% to 40% of the negative electrode active material by mass, optionally 1% to 25%, further optionally 1% to 10%, and even more preferably 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%, 7%, 8%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, 30%, 35%, 40%, etc.

[0259] In some implementations, the negative electrode sheet satisfies one or more of the following characteristics:

[0260] (d1) The mass percentage of silicon-based material in the negative electrode active material is 0-40%, and can be selected as 0-25% (see also the appropriate values ​​or ranges in any of the embodiments in the context).

[0261] (d2) Silicon-based materials include silicon-carbon composite materials, which include a porous carbon matrix and elemental silicon located in the pores of the porous carbon matrix; without limitation, the mass percentage of silicon-carbon composite materials in silicon-based materials 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.

[0262] "Silicon-carbon composite material" is a silicon-based material comprising a porous carbon matrix and elemental silicon located within the pores of the porous carbon matrix. Silicon-carbon composite materials can be obtained using vapor deposition methods. Those skilled in the art can prepare silicon-carbon composite materials using conventional methods in the field.

[0263] By controlling the silicon content of the negative electrode within the aforementioned range, it is beneficial to better control the expansion and contraction changes of the negative electrode, reduce the generation of fresh interfaces, suppress side reactions at the negative electrode interface, reduce the consumption rate of the first additive, decrease the growth rate of battery internal resistance, and maintain superior fast-charging performance for a longer period. For example, in silicon-based materials, silicon-carbon composite materials exhibit relatively low volume expansion and contraction changes.

[0264] In some embodiments, the positive electrode active material includes a positive electrode active body and a coating layer located on at least a portion of the surface of the positive electrode active material.

[0265] The elemental composition of the positive electrode active material in the positive electrode active layer can be analyzed using methods known in the art, including but not limited to the following: inductively coupled plasma atomic emission spectrometry (ICP), X-ray diffraction (XRD), single-crystal X-ray diffraction (SCXRD), 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 sample characteristics. ICP can be used for quantitative analysis of the component content in the positive electrode active material.

[0266] 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.

[0267] For positive or negative electrode 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 the coating layer and the positive electrode active material, or vice versa.

[0268] Those skilled in the art can identify the components in the positive and negative active layers 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.

[0269] 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.

[0270] 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.

[0271] 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 between the D and G peaks in the Raman spectrum can be used to distinguish between graphite and hard carbon. Likewise, the difference between the D and G peaks in the Raman spectrum can be used to distinguish between natural graphite and synthetic graphite.

[0272] In some embodiments, the mass percentage of the first additive in the electrolyte is greater than 0 and less than or equal to 3.2%, optionally 0.01% to 3.2%, further optionally 0.05% to 1.6%, and even more preferably 0.1% to 1.6%. It can also be any of the following percentages, and can be greater than 0 and less than or equal to any of the following percentages, or can be selected from any two of the following percentage ranges: 0.05%, 0.08%, 0.1%. The percentages are as follows: 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.25%, 0.26%, 0.28%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, 3.2%, etc.

[0273] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0274] (e1) The first additive has a mass percentage in the electrolyte that is greater than 0 and less than or equal to 3.2%, optionally from 0.01% to 3.2%, further optionally from 0.05% to 1.6%, and even further optionally from 0.1% to 1.6%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0.01%, 0.02%, 0.04%, 0.05%, 0.08%, 0.1%, 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.25%, 0.2 6%, 0.28%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, 3.2%, etc.; Exemplarily, the mass percentage of the first additive in the electrolyte may also be selected from any suitable range of the following: 0.05%–3.2%, 0.1%–3.2%, 0.05%–3%, 0.1%–3%, 0.05%–2%, 0.1%–2%, 0.05%–1.6%, etc.

[0275] (e2) The mass ratio of the second additive to the first additive is 0.01 to 50, optionally 0.1 to 50, further optionally 0.1 to 30, even further optionally 0.5 to 30, even further optionally 0.5 to 25, even further optionally 1 to 20, and may also be any of the following values ​​or a range selected from any two of the following values: 0.01, 0.02, 0.025, 0.03, 0.033, 1 / 30, 0.04, 0 .05, 0.075, 0.1, 0.2, 0.25, 0.3, 1 / 3, 0.4, 0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 1, 1.1, 1.2, 1.25, 1.4, 1.5, 1.75, 1.8, 2, 2.25, 2.5, 2.75, 3, 3.3, 10 / 3, 3.5, 4, 5, 6, 8, 10, 15, 20, 22, 24, 25, 26, 28, 30, etc.

[0276] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0277] (e1') The mass percentage of the first additive in the electrolyte is 0.05% to 0.2%;

[0278] (e2') The mass ratio of the second additive to the first additive is 0.1 to 50.

[0279] By controlling the mass percentage of the first additive in the electrolyte within the aforementioned range, the first additive can continuously play a role in repairing the SEI film during fast charging and cycling, and can maintain superior fast charging performance for a longer period of time.

[0280] By controlling the mass ratio of the second additive to the first additive within the aforementioned range, it is beneficial for the first and second additives to work synergistically, which helps to improve the negative electrode SEI film and suppress gas generation during fast charging, while also better suppressing the increase in negative electrode interface impedance, thereby improving the fast charging performance of lithium-ion secondary batteries.

[0281] By controlling the mass percentage of the first additive in the electrolyte and the mass ratio of the second additive to the first additive within the aforementioned range, it is beneficial to better leverage the synergistic effect between the first and second additives and improve the fast-charging performance of lithium-ion secondary batteries.

[0282] In some embodiments, the second additive includes one or more of lithium salt additives, phosphate ester additives, vinylene carbonate, fluorocarbonate additives, saturated sulpholactones, and cyclic sulfates.

[0283] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0284] (f1) The lithium salt additives include one or more of the following: lithium oxalate, lithium tetrafluoroborate, lithium difluorophosphate, and lithium fluorosulfonic acid; lithium oxalate includes one or more of the following: lithium difluorooxalateborate (LiDFOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP); lithium fluorosulfonic acid includes one or more of the following: lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI);

[0285] (f2) Phosphate ester additives include silicon-based phosphate ester additives; silicon-based phosphate ester additives include one or more of tris(trimethylsilane) phosphate (TMSP) and tris(trimethylsilyl) phosphite (TMSPi);

[0286] (f3) The second additive includes fluorocarbonate additives; further, fluorocarbonate additives include fluoroethylene carbonate (FEC);

[0287] (f4) Cyclic sulfates include one or more of monocyclic sulfates and polycyclic sulfates.

[0288] In this application, "cyclic sulfate" contains one or more monocyclic sulfate units, and "monocyclic sulfate unit" contains *-OS(=O)2-O-*, where each * independently represents a bonding site with a carbon atom.

[0289] In some embodiments, the additive includes a polycyclic sulfate ester, which contains a plurality of monocyclic sulfate ester units.

[0290] In some embodiments, the multiple monocyclic sulfate units in the polycyclic sulfate ester are linked in a chain-like manner.

[0291] In some embodiments, the number of monocyclic sulfate units in the polycyclic sulfate ester is 2 to 4, and may further be 2, 3 or 4.

[0292] In some embodiments, the monocyclic sulfate unit is a 5- to 7-membered monocyclic ring, which can be a 5-membered ring, a 6-membered ring, or a 7-membered ring, and more specifically, a 5-membered ring or a 6-membered ring.

[0293] In some embodiments, the monocyclic ring in the monocyclic sulfate unit is replaced by 0, 1, or more substituents Q3, each of which is independently a halogen, C, or C. 1-3 Alkyl or C 1-3 Alkoxy group. Optionally, the substituent Q3 in the monocyclic sulfate unit is each independently a fluorine atom, a methyl group, or a methoxy group.

[0294] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0295] (g1) The mass percentage of lithium salt additive in the electrolyte is 0-3%, optionally 0.05%-3%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.01%, 0.02%, 0.04%, 0.05%, 0.08%, 0.1%, 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.25%, 0.26%, 0.28%, 0.3%, etc.;

[0296] (g2) The lithium salt additive includes lithium difluorooxalate borate. Non-limitingly, the mass percentage of lithium difluorooxalate borate in the electrolyte can be 0–3%, optionally 0.05%–3%, or any of the following percentages or a range selected from any two of the following percentages: 0, 0.01%, 0.02%, 0.04%, 0.05%, 0.08%, 0.1%, 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.25%, 0.26%, 0.28%, 0.3%, etc.

[0297] (g3) Lithium salt additives include lithium bis(fluorosulfonyl)imide;

[0298] (g4) The mass percentage of phosphate ester additives in the electrolyte is 0-2%, optionally 0.1%-2%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.01%, 0.02%, 0.04%, 0.05%, 0.08%, 0.1%, 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.25%, 0.26%, 0.28%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.6%, 0.75%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.25%, 1.3%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, etc.

[0299] (g5) The mass percentage of vinylene carbonate in the electrolyte is 0-3%, optionally 0.1%-3%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.01%, 0.02%, 0.04%, 0.05%, 0.08%, 0.1%, 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2%, 0.22%, 0 0.24%, 0.25%, 0.26%, 0.28%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.6%, 0.75%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.25%, 1.3%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, etc.;

[0300] (g6) The fluorocarbonate additive in the electrolyte is 0-10% by mass, optionally 0.1%-10%, further optionally 0.5%-6%, and even further optionally 1%-5%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.01%, 0.02%, 0.04%, 0.05%, 0.08%, 0.1%, 0.12%, 0.14%, 0.15%, 0 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.25%, 0.26%, 0.28%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.6%, 0.75%, 0.8%, 0.9%, 1%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 7.5%, 8%, 9%, 10%, etc.;

[0301] (g7) Fluorocarbonate additives include fluoroethylene carbonate. Non-limitingly, the mass percentage of fluoroethylene carbonate in the electrolyte can be 0–10%, optionally 0–5%, and further optionally 0.1%–10%, or 1%–10%, or 1%–6%, or further optionally 1%–5%, or any of the following percentages or a range selected from any two of the following percentages: 0, 0.01%, 0.02%, 0.04%, 0.05%, 0.08%, 0.1%. %, 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.25%, 0.26%, 0.28%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.6%, 0.75%, 0.8%, 0.9%, 1%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 7.5%, 8%, 9%, 10%, etc.;

[0302] (g8) The mass percentage of saturated sulfonyl lactone in the electrolyte is 0-3%, optionally 0.1%-3%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.01%, 0.02%, 0.04%, 0.05%, 0.08%, 0.1%, 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2%, 0.22%, 0. 24%, 0.25%, 0.26%, 0.28%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.6%, 0.75%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.25%, 1.3%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, etc.;

[0303] (g9) The mass percentage of cyclic sulfate esters in the electrolyte is 0-3%, optionally 0.1%-3%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.01%, 0.02%, 0.04%, 0.05%, 0.08%, 0.1%, 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2%, 0.22%, 0. 24%, 0.25%, 0.26%, 0.28%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.6%, 0.75%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.25%, 1.3%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, etc.;

[0304] (g10) Cyclic sulfates include polycyclic sulfates. Non-limitingly, the mass percentage of polycyclic sulfates in the electrolyte can be 0–3%, optionally 0.1%–3%, or any of the following percentages or a range selected from any two of the following percentages: 0, 0.01%, 0.02%, 0.04%, 0.05%, 0.08%, 0.1%, 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0. 2%, 0.22%, 0.24%, 0.25%, 0.26%, 0.28%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.6%, 0.75%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.25%, 1.3%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, etc.

[0305] By selecting a second additive with the aforementioned type and / or dosage, it is beneficial to better leverage the competitive and synergistic effects between the first and second additives, thereby improving battery performance.

[0306] In some embodiments of this application, the first additive has a mass percentage of 0.1% to 1.6% in the electrolyte, and the fluorocarbonate additive has a mass percentage of 0.5% to 6% in the electrolyte.

[0307] In some embodiments of this application, the mass percentage of fluoroethylene carbonate in the electrolyte is 0.5% to 6%.

[0308] In some embodiments of this application, the second additive includes fluorocarbonate additives. In some of these embodiments, the fluorocarbonate additive includes fluoroethylene carbonate.

[0309] For example, lithium salt additives and phosphate ester additives have low negative electrode film resistance. By introducing one or more of lithium salt additives and phosphate ester additives into the electrolyte, it is beneficial to reduce the interfacial resistance of the negative electrode SEI film and improve the fast charging performance of lithium-ion secondary batteries.

[0310] For example, vinylene carbonate (VC) can optimize the SEI film. By introducing VC into the electrolyte, it is beneficial to reduce or delay the consumption of the first additive in the negative electrode film formation, and better control the charge transfer impedance of the negative electrode surface and the internal resistance of the battery.

[0311] For example, fluorocarbonate additives (such as fluoroethylene carbonate (FEC)) can form a robust interfacial film with low ion transport impedance on the negative electrode surface at room temperature. By introducing fluorocarbonate additives (such as FEC) into the electrolyte, it is beneficial to reduce or delay the consumption of the first additive in the negative electrode film formation, and to better control the negative electrode interfacial impedance and battery internal resistance.

[0312] For example, saturated sulfonyl lactones (such as 1,3-propanesulfonyl lactone (PS)) can participate in the formation of the negative electrode film, forming a dense and stable negative electrode SEI film, which is beneficial to reduce or delay the consumption of the first additive in the negative electrode film formation and better control the negative electrode interface impedance and battery internal resistance.

[0313] For example, by introducing cyclic sulfates into the electrolyte, the negative electrode interface film can be optimized, the stability of the negative electrode SEI film can be improved, the negative electrode interface side reactions can be reduced and gas generation can be suppressed during fast charging, and the negative electrode interface impedance and battery internal resistance can be better controlled.

[0314] In some embodiments, the electrolyte includes one or both of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and in some of these embodiments, the electrolyte includes at least lithium hexafluorophosphate.

[0315] In some embodiments, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0–0.5 mol / L, optionally 0.01 mol / L–0.5 mol / L, or any of the following concentrations or a range selected from any two of the following concentrations: 0 mol / L, 0.01 mol / L, 0.02 mol / L, 0.025 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L. mol / L, 0.075mol / L, 0.08mol / L, 0.09mol / L, 0.1mol / L, 0.12mol / L, 0.14mol / L, 0.15mol / L, 0.16m ol / L, 0.18mol / L, 0.2mol / L, 0.25mol / L, 0.3mol / L, 0.35mol / L, 0.4mol / L, 0.45mol / L, 0.5mol / L, etc.

[0316] Lithium bis(fluorosulfonyl)imide can be used as both a film-forming additive and an electrolyte salt in electrolytes.

[0317] In this application, when the mass percentage of lithium salt additives (such as LiFSI) in the electrolyte is greater than 0.5%, the mass percentage of lithium salt additives (such as LiFSI) in the electrolyte in the second additive is recorded as 0.5%.

[0318] In some embodiments, the electrolyte comprises lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. Non-limitingly, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte may be greater than 0 mol / L and less than or equal to 0.5 mol / L, optionally from 0.01 mol / L to 0.5 mol / L, or may be selected from suitable ranges or values ​​in any of the embodiments described above.

[0319] Lithium bisfluorosulfonyl imide (LiFSI) can participate in the formation of a stable solid electrolyte interfacial film at both the positive and negative electrodes. On the one hand, introducing LiFSI into the electrolyte can improve the stability of the positive and negative electrode interfacial film, effectively reducing side reactions at the electrolyte interface and suppressing gas generation during fast charging. On the other hand, LiFSI has a better ability to dissociate lithium ions than lithium hexafluorophosphate (LiPF6), therefore, the addition of LiFSI is also beneficial to improving the liquid phase conductivity. Thus, introducing LiFSI into the electrolyte can better improve the fast charging performance of lithium-ion secondary batteries.

[0320] In some embodiments of this application, a lithium-ion secondary battery is provided, comprising a positive electrode, a negative electrode, and an electrolyte, wherein a separator is disposed between the positive and negative electrodes; the electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent comprises a chain-like carboxylic acid ester compound, which comprises a solvent of formula I, the structure of which is shown in formula (I): In equation (I), R 11 and R 12 Each is independently methyl or ethyl; chain carboxylic acid esters include ethyl acetate;

[0321] The additives include a first additive and a second additive. The first additive is a nonionic organic additive containing a carbon-carbon triple bond, and the second additive is a negative electrode film-forming additive that is different from the first additive. The second additive includes fluorocarbonate additives, and fluorocarbonate additives include fluoroethylene carbonate.

[0322] The negative electrode sheet includes a negative electrode active layer, which in turn includes a negative electrode active material. The average particle size of the primary particles in the negative electrode active material is denoted as D1, where D1 is 0.1 μm to 2 μm. v 50 ranges from 5μm to 18μm.

[0323] By controlling the size of the negative electrode active material and the agglomeration state of the primary particles within it, a large number of lithium-ion intercalation sites can be provided on the surface of the negative electrode active material, while simultaneously controlling the solid-phase transport path of lithium ions. Furthermore, by introducing FEC after significantly improving the negative electrode SEI film using a first additive, the competitive anode film formation of the two is utilized. This suppresses high-temperature anode interface reactions in negative electrode active materials with the aforementioned size and agglomeration state, and also controls a lower interface impedance in both fast-charging and room-temperature modes. This allows the lithium intercalation capability of the negative electrode active material in fast-charging mode to match the lithium-ion liquid-phase transport rate of the electrolyte containing the solvent of Formula I, reducing lithium plating during fast charging and the battery life degradation at high and room temperatures caused by lithium plating.

[0324] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0325] (h1) The molecular weight of the first additive is less than or equal to 500 Da;

[0326] (h2) The molecule of the first additive contains 1 to 4 carbon-carbon triple bonds. Without limitation, the number of carbon-carbon triple bonds in the molecule of the first additive can be 1, 2, 3 or 4.

[0327] (h3) The carbon-carbon triple bond in the first additive is CH≡C-;

[0328] (h4) The first additive includes one or more of a first alkynyl compound and a second alkynyl compound; wherein the first alkynyl compound contains a carbon-carbon triple bond and a Lewis base nitrogen heterocycle, the carbon-carbon triple bond and the Lewis base nitrogen heterocycle in the first alkynyl compound are linked by a linker L1, and the linker L1 contains a C-type carbon bond covalently bonded to the carbon-carbon triple bond. 1-3 Alkylene; the second alkynyl compound contains a carbon-carbon triple bond and an alkyl carbonate group. The structure of the alkyl carbonate group is R2-OC(=O)-O-*, where * is the bonding site to the carbon atom, and R2 is C. 1-3 In alkyl and diynyl compounds, the carbon-carbon triple bond and the alkyl carbonate group are linked by a linker L2, which contains a C-type carbon bond covalently bonded to the carbon-carbon triple bond. 1-3 Alkylene.

[0329] In this application, unless otherwise specified, "Lewis base nitrogen heterocycle" refers to a nitrogen heterocycle possessing Lewis base properties. This concept is based on the Lewis acid-base theory. Lewis base nitrogen heterocycles can donate electron pairs and are electron-rich. Therefore, Lewis base nitrogen heterocycles can attract and bind acidic substances. Non-limiting examples of Lewis base nitrogen heterocycles include imidazole rings, but are not limited to these.

[0330] In this application, unless otherwise specified, "nitrogen heterocyclic structure" refers to a ring structure in which the cyclic atoms include nitrogen atoms. The term "cyclic atom" refers to the constituent atom of the ring skeleton. As a non-limiting example, the three carbon atoms and two nitrogen atoms in an imidazole ring are cyclic atoms, and the imidazole ring is a 5-membered ring. "Ringed nitrogen atom" refers to the nitrogen atom in the cyclic atom.

[0331] In this application, "C" is involved. 1-3 "alkylene" can be methylene, ethylene, or propylene unless otherwise specified, and can further be methylene, 1,2-ethylene, or 1,3-propylene.

[0332] In this application, "C" is involved. 1-3 "alkyl" can be methyl, ethyl, or propyl unless otherwise specified, and may further be methyl, ethyl, n-propyl, or isopropyl.

[0333] In some implementations, R2 is a methyl group.

[0334] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0335] (i1) The molecular weight of the first additive is less than or equal to 300 Da;

[0336] (i2) The molecule of the first additive contains 1 to 4 Lewis base nitrogen heterocycles. Without limitation, the number of Lewis base nitrogen heterocycles in the first additive can be 1, 2, 3 or 4.

[0337] (i3) Lewis base nitrogen heterocycles include substituted or unsubstituted imidazole groups, wherein the imidazole ring in the substituted or unsubstituted imidazole group is substituted by 0, 1 or more substituents Q2, and each substituent Q2 in the substituted imidazole group is independently C 1-3 Alkyl, cyano (-CN), or fluorine atom; optionally, the substituent Q2 in the substituted imidazolium group is independently methyl, cyano, or fluorine atom;

[0338] (i4) The first ynyl compound consists of a carbon-carbon triple bond, C, and C bonds connected in sequence. 1-3 Alkylene and -OC(=O)-R 10 Composition, R 10 It is a Lewis base nitrogen heterocycle; the second alkynyl compound consists of a series of carbon-carbon triple bonds, C 1-3 Alkylene and -OC(=O)-OR 20 Composition, R 20 It is an alkyl group, and can be C10 or C20. 1-3 alkyl.

[0339] In some embodiments, the first alkynyl compound may be composed of a carbon-carbon triple bond, a C-carbon triple bond, and a C-carbon triple bond connected in sequence. 1-3 Alkylene and -OC(=O)-R 10 Composition, R 10 It is a Lewis base nitrogen heterocycle.

[0340] In some embodiments, the second alkynyl compound may be composed of a carbon-carbon triple bond, a C-carbon triple bond, and a C-carbon triple bond connected in sequence. 1-3 Alkylene and -OC(=O)-OR 20 Composition, R 20 It is an alkyl group, and can further be C 1-3 alkyl.

[0341] Non-limitingly, in the electrolyte, the total mass percentage of the first additive in the acetylene additives may be greater than 50%, further may be 80% to 100%, even further may be 90% to 100%, and may 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%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0342] In some embodiments, the acetylene additive in the electrolyte is the first additive.

[0343] Non-limitingly, in the electrolyte, the sum of the mass percentages of the first alkynyl compound and the second alkynyl compound in the first additive may be greater than 50%, further may be 80% to 100%, even further may be 90% to 100%, and may 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%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0344] In some embodiments, the mass percentage of the first alkynyl compound in the electrolyte may be 80% to 100%, more specifically 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%, 97%, 98%, 99%, 100%, etc.

[0345] In some embodiments, the second alkynyl compound in the electrolyte may account for 80% to 100% by mass, more preferably 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%, 97%, 98%, 99%, 100%, etc.

[0346] In some embodiments, the first additive in the electrolyte is a combination of a first alkynyl compound and a second alkynyl compound; further, the first additive may be a first alkynyl compound.

[0347] In some embodiments, the first alkynyl compound includes, and may further be, compound II. In some embodiments, the first additive is compound II.

[0348] In some embodiments, the second alkynyl compound includes, and may further be, compound III. In some embodiments, the first additive is compound III.

[0349] In some embodiments, the first additive includes one or more of compound II and compound III.

[0350] In some embodiments, the first additive includes one or more of compounds IIa and IIIa.

[0351] In some embodiments, the first additive includes one or more of compound II and compound III;

[0352] The structure of compound II is Among them, L 11 C 1-3 Alkylene, Q2 is independently C 1-3 Alkyl, cyano, or fluorine atom, p2 is 0, 1, 2, or 3;

[0353] The structure of compound III is Among them, L 21 C 1-3 Alkylene, R 22 C 1-3 alkyl.

[0354] In some implementations, L 11 It is a methylene group.

[0355] In some implementations, p2 is 0.

[0356] In some implementations, L 21 It is a methylene group.

[0357] In some implementations, R 22 It is a methyl group.

[0358] In some embodiments, compound II is compound IIa.

[0359] In some embodiments, compound III is It can be denoted as compound IIIa.

[0360] In some embodiments, the first alkynyl compound includes, and may further be, compound IIa. In some embodiments, the first additive is compound IIa.

[0361] In some embodiments, the second alkynyl compound includes, and may further be, compound IIIa. In some embodiments, the first additive is compound IIIa.

[0362] In some embodiments, the sum of the mass percentages of compounds IIa and IIIa in the first additive in the electrolyte can be 80% to 100%, more specifically 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%, 97%, 98%, 99%, 100%, etc.

[0363] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0364] (j1) The first additive includes compound II. Without limitation, the mass percentage of compound II in the first additive may be 80% to 100%, optionally 90% to 100%, or may be 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.

[0365] (j2) The first additive includes the structure as follows Compound IIa, without limitation, may constitute 80% to 100% by mass in the first additive, 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.

[0366] By controlling the molecular weight of the first additive within the aforementioned lower range, the first additive can have a smaller molecular size, which is beneficial for better control of the low viscosity characteristics of the electrolyte, and makes the electrolyte have higher conductivity, which can better synergize with the solvent of Formula I to improve battery dynamics.

[0367] By controlling the number of carbon-carbon triple bonds in the first additive within the aforementioned range, the first additive can better synergistically improve the fast-charging performance of lithium-ion secondary batteries with the solvent of Formula I. It also helps to suppress the increase in interfacial impedance caused by the first additive participating in the formation and repair of the SEI film, and helps to control the influence of the first additive on the liquid phase impedance. As a result, battery kinetics can be better improved, and the fast-charging performance of lithium-ion secondary batteries can be better improved.

[0368] The first alkynyl compound, which includes both a carbon-carbon triple bond and a Lewis base nitrogen heterocycle, can promote the formation of an interface film with dual organic / inorganic properties during the negative electrode interface reaction, thereby improving the stability of the negative electrode SEI film. It can also work synergistically with the solvent of formula I to comprehensively improve the fast-charging performance of lithium-ion secondary batteries. The Lewis base nitrogen heterocycle can also absorb acid byproducts in the electrolyte, which is beneficial to improving the stability of the negative electrode interface and the negative electrode active material, reducing the consumption rate of the first additive, reducing the growth rate of battery internal resistance, and maintaining superior fast-charging performance for a longer period of time.

[0369] By controlling the number of Lewis base nitrogen heterocycles in the first additive within the aforementioned range, it is beneficial to better absorb acid byproducts in the electrolyte, and at the same time, it is also beneficial to control the steric hindrance effect of Lewis base nitrogen heterocycles on carbon-carbon triple bonds.

[0370] Examples of Lewis base nitrogen heterocycles include the imidazole ring in compounds II and IIa.

[0371] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0372] The mass percentage of solvent in formula (k1) I in the chain carboxylic acid ester compound can be 75% to 100%, optionally 90% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 75%, 76%, 78%, 80%, 82%, 84%, 85%, 86%, 88%, 90%, 94%, 95%, 96%, 98%, 100%, etc.

[0373] (k2) The mass percentage of the chain carboxylic acid ester compound in the non-aqueous solvent can be 5% to 80%, optionally 10% to 60%, or any of the following percentages or a range selected from any two of the following percentages: 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 50%, 60%, 70%, 75%, 80%, etc.

[0374] (k3) The conductivity of the electrolyte at 25°C can be 9mS / cm to 25mS / cm, and can be selected from 10mS / cm to 18mS / cm. It can also be any of the following conductivity values ​​or a range consisting of any two of the following conductivity values: 9mS / cm, 10mS / cm, 11mS / cm, 12mS / cm, 13mS / cm, 14mS / cm, 15mS / cm, 16mS / cm, 18mS / cm, 20mS / cm, 21mS / cm, 22mS / cm, 23mS / cm, 24mS / cm, 25mS / cm, etc.

[0375] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0376] The solvent of formula (k1') accounts for 90% to 100% of the mass of the chain carboxylic acid ester compound;

[0377] (k2') Chain carboxylic acid esters account for 10% to 60% of the mass of non-aqueous solvents;

[0378] The conductivity of the (k3') electrolyte at 25°C is 10 mS / cm to 18 mS / cm.

[0379] By controlling one or more parameters—such as the mass percentage of the solvent of Formula I in the chain carboxylic acid ester compound, the mass percentage of the chain carboxylic acid ester compound in the non-aqueous solvent, and the conductivity of the electrolyte at 25°C—within the aforementioned ranges, it is beneficial to improve battery kinetics and thus impart better fast-charging performance to lithium-ion secondary batteries. Among these, the chain carboxylic acid ester compound (solvent of Formula I) has a relatively low viscosity, which is beneficial for improving the conductivity of the electrolyte.

[0380] In this application, unless otherwise specified, the "conductivity" of the electrolyte refers to ionic conductivity, which 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 testing temperature can be 25±0.1℃. The testing method can be performed according to HG / T 4067-2015. Unless otherwise specified, the unit of conductivity of the electrolyte is Siemens per centimeter (S / cm) or mS / cm.

[0381] Unless otherwise specified, the following steps may be used for testing:

[0382] 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℃);

[0383] 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.

[0384] In some implementations, the lithium-ion secondary battery includes a single lithium-ion secondary battery cell.

[0385] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0386] The following is a description of the positive electrode sheet.

[0387] 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.

[0388] Without limitation, the weight percentage of the positive electrode active material in the positive electrode active layer may be greater than or equal to 80 wt%, and may further be greater than or equal to 90 wt%.

[0389] 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.

[0390] 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).

[0391] The positive electrode active material may be any positive electrode active material known in the art for use in batteries. These positive electrode active materials may be used alone or in combination of two or more.

[0392] 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 Co0.1 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, etc.

[0393] For a further explanation of the types of positive electrode active materials, please refer to the context of this application.

[0394] 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.

[0395] 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.

[0396] 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 wt% of the weight of the positive electrode active layer, more commonly 0–8 wt%, and even more commonly 1 wt%–5 wt%, based on the total weight of the positive electrode active layer.

[0397] 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 weight percentage of the conductive agent in the positive electrode active layer can be 0–10 wt%, more commonly 0–8 wt%, and even more commonly 0–5 wt%, based on the total weight of the positive electrode active layer.

[0398] 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.

[0399] In some embodiments, the positive electrode active material includes a lithium phosphate-based positive electrode material. Further, the mass percentage of the lithium phosphate-based positive electrode material in the positive electrode active material can be greater than or equal to 50%, and can be 100%, 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 one side) can also be (0.1–0.5) g / 1540.25 mm². 2 However, this is not the only possibility. The compaction density of the positive electrode sheet can be 2.0 g / cm³. 3 ~2.8g / cm 3 2.3g / cm³ is an option. 3 ~2.6g / cm 3 .

[0400] In some embodiments, the positive electrode active material includes a lithium composite metal oxide-based positive electrode material. Further, the mass percentage of the lithium composite metal oxide-based positive electrode material in the positive electrode active material can be greater than or equal to 50%, and more preferably 95% to 100%, but is not limited thereto. When coating the positive electrode slurry, the coating areal density (based on the coating areal density of one side) on a dry weight basis (excluding solvent) can be (0.05 to 0.6) g / 1540.25 mm². 2 The optional value is (0.1~0.3)g / 1540.25mm. 2The compaction density of the positive electrode sheet can be 3.0 g / cm³. 3 ~4.2g / cm 3 3.3g / cm³ is an option. 3 ~3.8g / cm 3 .

[0401] The term "compacted density" as used in this application has a meaning known in the art and is one of the reference indicators for the energy density of materials. In this application, unless otherwise specified, the compacted density of the positive electrode refers to the ratio of the mass of the positive electrode active layer to its volume, and the compacted density of the negative electrode refers to the ratio of the mass of the negative electrode active layer to its volume.

[0402] The following are some other descriptions of the negative electrode plate.

[0403] The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector, the negative active layer including a negative active material.

[0404] Without limitation, the weight percentage of the negative electrode active material in the negative electrode active layer may be greater than or equal to 80 wt%, and may further be greater than or equal to 90 wt%.

[0405] 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 layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0406] 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).

[0407] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As a non-limiting example, the 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, etc. 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. However, this application is not limited to these materials or substances, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0408] In some embodiments, the negative electrode active layer optionally includes a binder. Non-limitingly, 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). Non-limitingly, the weight percentage of the binder in the negative electrode active layer may be 0 wt% to 20 wt%, more further 0 wt% to 10 wt%, even further 0 to 5 wt%, even further 1 wt% to 5 wt%, and even more preferably 1 wt% to 3 wt%.

[0409] For further information on the types of negative electrode active materials, please refer to the context of this application.

[0410] In some embodiments, the negative electrode active layer optionally includes a conductive agent. Non-limitingly, 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. Non-limitingly, the weight percentage of the conductive agent in the negative electrode active layer may be 0 wt% to 15 wt%, more preferably 0 wt% to 10 wt%, and even more preferably 0 wt% to 5 wt%.

[0411] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). Non-limitingly, the weight percentage of other additives in the negative electrode active layer may be 0 wt% to 15 wt%, more preferably 0 wt% to 10 wt%, even more preferably 0 wt% to 5 wt%, even more preferably 0 wt% to 3 wt%, and even more preferably 0 wt% to 2 wt%.

[0412] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry. Further, the negative electrode slurry is coated onto at least one surface of the negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode sheet is obtained. 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 of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 30wt% to 70wt%, optionally 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s, optionally 3000 mPa·s to 10000 mPa·s. When coating the negative electrode slurry, the surface density of the coating on one side of the negative electrode current collector can be 7.5 mg / cm³, based on dry weight (excluding solvent). 2 ~22mg / cm 2 The optional value is (0.12~0.2)g / 1540.25mm. 2 The compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 ~2.0g / cm 3 1.0g / cm can be selected. 3 ~1.8g / cm 3 .

[0413] The electrolyte is described below as an example.

[0414] The electrolyte serves to conduct ions between the positive and negative electrodes. The electrolyte consists of an electrolyte salt and a solvent.

[0415] In some embodiments, the electrolyte is a non-aqueous electrolyte. A non-aqueous electrolyte may include an electrolyte salt and a non-aqueous solvent.

[0416] Non-limiting, the concentration of the electrolyte salt in the electrolyte is typically from 0.5 mol / L to 5 mol / L, optionally from 0.5 mol / L to 2 mol / L, and may also be any of the following concentrations or a range selected from any two of the following concentrations: 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, etc. For non-aqueous solvent electrolyte salts in the electrolyte, please refer to the description in the context of this application.

[0417] In some embodiments, the electrolyte salt includes an electrolyte lithium salt, and more particularly, it can be an electrolyte lithium salt. Non-limitingly, other types of electrolyte salts may also be introduced into the electrolyte.

[0418] In some embodiments, the electrolyte salt includes an electrolyte lithium salt. Non-limitingly, the electrolyte lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0419] The types of non-aqueous solvents in the electrolyte can be described in the context of this application. Non-limitingly, other types of non-aqueous solvents may also be introduced into the electrolyte. In some embodiments, the non-aqueous solvent may further include ethylene carbonate (EC). ), propylene carbonate (PC, ), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), ( ), 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl sulfone and diethyl sulfone.

[0420] The electrolyte includes additives, including at least the first additive mentioned above.

[0421] The types of additives in the electrolyte can be found in the description within the context of this application. Without limitation, other types of additives may also be introduced into the electrolyte. These other types of additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance characteristics, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0422] The following is an exemplary description of the separator membrane.

[0423] In some embodiments, the lithium-ion secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0424] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0425] In some embodiments, the thickness of the separator is 6 μm to 40 μm, and optionally 6 μm to 20 μm.

[0426] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0427] In some embodiments, the lithium-ion secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0428] 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.

[0429] A lithium-ion secondary battery includes at least one battery cell. A lithium-ion secondary battery may include one or more battery cells.

[0430] 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.

[0431] In some embodiments, referring to FIG2, the outer packaging may include a battery casing 51 and a cover plate 53. The battery casing 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 battery casing 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. Positive electrode sheets, negative electrode sheets, and a separator may be formed into electrode assemblies 52 by a winding process or a stacking process. The electrode assemblies 52 are encapsulated within the receiving cavity. The electrode assemblies 52 are immersed in an electrolyte. The number of electrode assemblies 52 contained in a single battery cell 5 may be one or more, which can be selected by those skilled in the art according to actual needs. In some embodiments, the electrolyte injection coefficient is greater than or equal to 1.6 g / Ah.

[0432] The lithium-ion secondary battery can be a battery device 4 or a battery pack 1.

[0433] 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.

[0434] 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.

[0435] Optionally, the battery device 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0436] 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.

[0437] 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.

[0438] 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.

[0439] In some embodiments, a method for preparing a lithium-ion secondary battery is provided, which includes the following steps: immersing an electrode assembly, including a positive electrode, a separator, and a negative electrode, in an electrolyte to form a battery.

[0440] In some embodiments, a method for preparing a lithium-ion secondary battery is provided, which includes the following steps:

[0441] S100: An electrode assembly including a positive electrode, a separator, and a negative electrode is placed inside a battery casing; wherein a separator is provided between the positive electrode and the negative electrode.

[0442] S200: Electrolyte is injected into the battery casing, and the battery is allowed to stand to allow the electrolyte to wet the positive and negative electrode plates, thus forming the battery. The electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives. The non-aqueous solvent includes chain-like carboxylic acid ester compounds, which include solvents of formula I. The structure of solvent I is shown in formula (I). In equation (I), R 11 and R 12Each is independently methyl or ethyl; the additives are a first additive and a second additive, wherein the first additive is a nonionic organic additive containing a carbon-carbon triple bond, and the second additive is a negative electrode film-forming additive different from the first additive.

[0443] The prepared lithium-ion secondary battery has the advantages of the lithium-ion secondary battery described in the first aspect of this application, and has improved fast charging performance, which will not be elaborated here.

[0444] In some embodiments, in step 200, after injecting electrolyte into the battery casing, a lithium-ion secondary battery assembly is obtained.

[0445] In some implementations, the lithium-ion secondary battery assembly may correspond to the state before formation treatment.

[0446] The formation temperature can be 45°C, but is not limited to this.

[0447] In some embodiments, the formation can be performed at 45°C using a method comprising the following steps (steps S1, S2, S3, and S4 are performed sequentially):

[0448] S1) Charge at 0.05C for 14 minutes to 3V, then let stand for 10 minutes;

[0449] S2) Charge to 3.4V at 0.1C and let stand for 10 minutes;

[0450] S3) Charge to 3.65V at 0.2C and let stand for 10 minutes;

[0451] S4) Charge to 3.75V at 0.2C and let stand for 10 minutes;

[0452] The transformation ends.

[0453] In this application, the concentrations of additives and electrolyte salts involved in "injecting electrolyte into the battery casing" correspond to "initial concentrations," which can respectively correspond to the initial mass percentage of the additives in the electrolyte and the initial molar volume concentration of the electrolyte salts in the electrolyte. Similarly, it also involves the initial mass percentage of the solvent of Formula I in the chain carboxylic acid ester compound and the initial mass percentage of the chain carboxylic acid ester compound in the electrolyte.

[0454] In some embodiments, during the step of injecting electrolyte into the battery casing, the initial mass percentage of the first additive in the electrolyte is 0.1% to 5%, optionally 0.1% to 3%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0.1%, 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.25%, 0.26%, 0.28%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.6%, 0.75%, 0.8%, 0.9%, 1%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0455] Those skilled in the art will understand that the content of some additive components in the electrolyte may change after formation treatment. As a non-limiting example, for instance, the content of some film-forming additive components may decrease due to their participation in the formation of the solid electrolyte interface film of the positive and / or negative electrodes. As a non-limiting example, the content of a first additive in the electrolyte is typically reduced after formation treatment compared to the electrolyte before formation treatment.

[0456] In some embodiments, after formation treatment, the content of each additive in the prepared lithium-ion secondary battery can be referred to the first aspect of this application.

[0457] In lithium-ion secondary battery components, the types of electrolyte salts and non-aqueous solvents in the electrolyte are described in the first aspect of this application. After formation treatment, the mass ratios of both electrolyte salts and solvents in the electrolyte may change.

[0458] In lithium-ion secondary battery modules, the material composition and dimensions of the positive electrode, negative electrode, and separator can be found in the first aspect of this application. The dimensions of the positive electrode, negative electrode, and separator in the lithium-ion secondary battery module may differ somewhat from those in the lithium-ion secondary battery of the first aspect.

[0459] In some embodiments, the lithium-ion secondary battery described in the first aspect of this application is prepared.

[0460] In some embodiments of the third aspect of this application, an electrical device is provided, which includes 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.

[0461] 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.

[0462] In some embodiments, the electrical device includes a lithium-ion secondary battery according to any of the embodiments provided in this application.

[0463] 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 in aerospace and other fields, and can also be used in energy storage power systems such as hydroelectric, thermal, wind, and solar power plants.

[0464] As an electrical device, lithium-ion rechargeable batteries can be selected according to its usage requirements.

[0465] 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.

[0466] 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.

[0467] In a fourth aspect of this application, a lithium-ion secondary battery assembly is provided, which is the lithium-ion secondary battery assembly in the preparation method of the lithium-ion secondary battery described in the second aspect of this application.

[0468] In a fifth aspect of this application, the use of the lithium-ion secondary battery described in the first aspect of this application in supplying and / or storing electrical energy is provided.

[0469] 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.

[0470] 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.

[0471] 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.

[0472] 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.

[0473] In some embodiments, the application includes a process of charging a lithium-ion secondary battery at at least one rate from 2C to 4C.

[0474] In some embodiments, the application includes a process of charging a lithium-ion secondary battery at at least one rate from 4C to 6C.

[0475] 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.

[0476] In some implementations, lithium-ion secondary batteries can provide a charging rate of 2C or higher.

[0477] In some implementations, lithium-ion secondary batteries can provide charging rates of 2C to 6C.

[0478] 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.

[0479] 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.

[0480] 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).

[0481] 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.

[0482] In this application, the "maximum charging rate (which can be denoted as C)" of the lithium-ion secondary battery is defined as... max The 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.

[0483] 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.

[0484] 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.

[0485] In the following examples, room temperature refers to 20°C to 30°C.

[0486] In the following examples, unless otherwise specified, the parameters involved can be confirmed by referring to the test methods described above. For example, D v 50. D v 10. D v 1. Particle size-related parameters, such as the average particle size (D1) of primary particles in the negative electrode active material, the conductivity of the electrolyte, and coating amount-related parameters (such as the mass ratio of the coating layer).

[0487] I. Preparation of Lithium-ion Secondary Batteries

[0488] Example 1.

[0489] (1) Positive electrode sheet: Positive active material (carbon-coated lithium iron phosphate), conductive agent carbon black (Super P) and binder polyvinylidene fluoride (PVDF) are mixed evenly in solvent N-methylpyrrolidone (NMP) at a weight ratio of 96:2:2 to obtain a positive electrode slurry with a solid content of 60wt%. The positive electrode slurry is coated on both sides of the positive electrode current collector aluminum foil, with a coating density of 0.18g / 1540.25mm on one side. 2 The positive electrode sheet is obtained through processes such as drying, cold pressing, slitting, and cutting. The compacted density of the positive electrode sheet is approximately 2.50 g / cm³. 3 .

[0490] In this example, the positive electrode active material is a lithium phosphate-based positive electrode material, further a lithium iron phosphate-based positive electrode material, and even further a soft carbon-coated lithium iron phosphate, which can be referred to as "carbon-coated LFP"; the soft carbon-coated lithium iron phosphate includes lithium iron phosphate and a soft carbon coating layer on the surface of lithium iron phosphate, and the mass percentage of the soft carbon coating layer in the soft carbon-coated lithium iron phosphate is about 1%.

[0491] D of positive electrode active material v 10 and D v The values ​​for 50 are 0.4 μm and 1.2 μm, respectively. Please refer to Table 1.

[0492] (2) Negative electrode sheet: The negative electrode active material (carbon-based material), conductive agent carbon black (Super P), binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) are mixed evenly in deionized water at a mass ratio of 97.0:1.2:1.0:0.8, with a solid content of 48wt%, to obtain a negative electrode slurry; the negative electrode slurry is coated on both sides of the negative electrode current collector copper foil, with a coating surface density of 0.13g / 1540.25mm on one side. 2 The negative electrode sheet is obtained through drying, cold pressing, slitting, and cutting processes. The compacted density of the negative electrode sheet is 1.65 g / cm³. 3 .

[0493] In this example, the negative electrode active material is a carbon-based material, further comprising coated graphite (the negative electrode active body is artificial graphite with a soft carbon coating layer on its surface, the soft carbon coating layer accounting for approximately 2% of the mass of the coated graphite), and the D of the negative electrode active material... v 1 and D v The sizes of 50 particles are 4.7 μm and 12.1 μm, respectively, and the average particle size of the primary particles is approximately 0.8 μm, as shown in Table 1.

[0494] (3) Separating membrane:

[0495] A polyethylene (PE) film with a thickness of 13 μm is used.

[0496] (4) Preparation of electrolyte:

[0497] Add additives to a non-aqueous solvent, mix thoroughly, then add fully dried lithium electrolyte salt, mix thoroughly to ensure the lithium electrolyte salt is fully dissolved, and prepare the electrolyte solution.

[0498] The electrolyte salt in the electrolyte is a lithium electrolyte salt, specifically lithium hexafluorophosphate, with an initial concentration of 1 mol / L. The non-aqueous solvent is ethyl acetate, ethyl methyl carbonate (EMC), and ethylene carbonate (EC) in a mass ratio of 5:2:3. The additives are 2-propynyl-1-1H-imidazolium-1-carboxylic acid ester (as the first additive) and fluoroethylene carbonate (FEC). The structure of the first additive is shown in formula (IIa), also referred to as compound IIa. The initial mass percentage of compound IIa in the electrolyte is 3 wt%, and the initial concentration of FEC in the electrolyte is 2.5%.

[0499] In Example 1, the solvent of Formula I is ethyl acetate; the chain carboxylic acid ester compound is composed of the solvent of Formula I, the mass percentage of the solvent of Formula I in the chain carboxylic acid ester compound is 100%, and the mass percentage of the chain carboxylic acid ester compound in the non-aqueous solvent is 50%.

[0500] (5) Preparation of lithium-ion secondary battery: The positive electrode, separator and negative electrode are stacked and wound in sequence to obtain bare cell (electrode assembly); tabs are welded to the bare cell and the bare cell is put into aluminum shell and baked at 80°C to remove water. Then the electrolyte is injected and sealed. Then the battery is subjected to static standing, hot and cold pressing, formation, shaping and capacity testing in sequence to obtain lithium-ion secondary battery.

[0501] After injecting electrolyte, a lithium-ion secondary battery assembly is obtained.

[0502] In this example, the standing soaking parameters are: standing at room temperature for 18 hours, and then standing at 45°C for 6 hours.

[0503] In this example, the formation parameters are as follows: at 45℃,

[0504] Charge at 0.05C for 14 minutes to 3.0V, then let stand for 10 minutes;

[0505] Charge to 3.4V at 0.1C and let stand for 10 minutes;

[0506] Charge at 0.2C to 3.65V and let stand for 10 minutes;

[0507] Charge at 0.2C to 3.75V and let stand for 10 minutes;

[0508] The transformation has ended.

[0509] Examples 2-3. Lithium-ion secondary batteries were prepared using essentially the same method as in Example 1, except that the composition of the electrolyte was different, the composition of the non-aqueous solvent in the electrolyte was different, and the types of chain carboxylic acid ester compounds and solvents of Formula I were changed. The remaining operating steps were the same as in Example 1. See Table 1 for details.

[0510] In Example 2, the non-aqueous solvent was ethyl acetate: methyl acetate: ethyl methyl carbonate (EMC): ethylene carbonate (EC) in a mass ratio of 3:2:2:3.

[0511] In Example 3, the non-aqueous solvent was a mixture of methyl acetate: ethyl methyl carbonate (EMC): ethylene carbonate (EC) in a mass ratio of 5:2:3.

[0512] Examples 4-5. Lithium-ion secondary batteries were prepared using essentially the same method as in Example 1, except that the composition of the electrolyte was different, the composition of the non-aqueous solvent in the electrolyte was different, and the mass percentage of the chain carboxylic acid ester compound in the non-aqueous solvent was changed. The remaining operating steps were the same as in Example 1. See Table 1 for details.

[0513] In Example 4, the chain carboxylic acid ester compound (ethyl acetate) accounted for 10% of the mass in the non-aqueous solvent, and the mass ratio of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) was the same as in Example 1.

[0514] In Example 5, the chain carboxylic acid ester compound (ethyl acetate) accounted for 80% of the mass in the non-aqueous solvent, and the mass ratio of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) was the same as in Example 1.

[0515] Example 6. A lithium-ion secondary battery was prepared using a method essentially the same as that in Example 1, except that the particle size distribution of the positive electrode active material used in the preparation of the positive electrode sheet was different. The remaining steps were the same as in Example 1. See Table 1 for details.

[0516] In Example 6, the D of the positive electrode active material v10 and D v The thicknesses of 50 are 0.5 μm and 1.4 μm, respectively.

[0517] Example 7. A lithium-ion secondary battery was prepared using a method essentially the same as that in Example 1, except that the particle size distribution of the negative electrode active material used in the negative electrode preparation step was different. The remaining steps were the same as in Example 1. See Table 1 for details.

[0518] In Example 7, the D of the negative electrode active material v 1 and D v The sizes of particles 50 and 50 are 6.9 μm and 14.2 μm, respectively, and the average particle size of the primary particles is 1.18 μm.

[0519] Examples 8-9. Lithium-ion secondary batteries were prepared using essentially the same method as in Example 1, except that the composition of the electrolyte was different, and the initial mass percentage of the first additive in the electrolyte was different. The remaining operating steps were the same as in Example 1. See Table 1 for details.

[0520] In Example 8, the initial mass percentage of the first additive (compound IIa) in the electrolyte was 0.1%, and the initial mass percentage of the FEC was 2%.

[0521] In Example 9, the initial mass percentage of the first additive (compound IIa) in the electrolyte was 5%, and the initial mass percentage of the FEC was 3%.

[0522] Example 10. A lithium-ion secondary battery was prepared using a method essentially the same as that in Example 1, except that the electrolyte composition and the composition of the non-aqueous solvent in the electrolyte were different. PS (1,3-propenyl sulfonate) was added at a mass ratio of 1%, and the initial mass ratio of FEC was 2%. The remaining operating steps were the same as in Example 1. See Table 1 for details.

[0523] Examples 11-15. Lithium-ion secondary batteries were prepared using essentially the same method as in Example 1, except that the composition of the electrolyte and the composition of the additives in the electrolyte were different. The remaining operating steps were the same as in Example 1. See Table 1 for details.

[0524] In Example 11, based on the initial mass percentage in the electrolyte, the additives in the electrolyte consisted of 1% of a first additive, 1% of a bicyclic sulfate ester (which can be denoted as "di-DTD"), and 2% of FEC. The structure of the first additive was as follows:

[0525] In Example 12, the additives in the electrolyte, based on their initial mass percentage in the electrolyte, were 1% of a first additive, 1% of lithium difluorophosphate, and 2% of FEC.

[0526] In Example 13, the additives in the electrolyte, based on their initial mass percentage in the electrolyte, were 1% of a first additive, 1% of LiDFOB (lithium difluorooxalate borate), and 2% of FEC.

[0527] In Example 14, the additives in the electrolyte were 1% of the first additive, 0.5% of TMSP (tris(trimethylsilane)phosphate) and 2% of FEC, based on their initial mass percentage in the electrolyte.

[0528] In Example 15, the additives in the electrolyte were 1% of the first additive, 1% of LiDFOB and 2% of VC (ethylene carbonate), based on their initial mass percentages in the electrolyte.

[0529] Example 16. A lithium-ion secondary battery was prepared using a method essentially the same as that in Example 1, except that the composition of the electrolyte, the composition of the additives in the electrolyte, and the composition of the lithium salt in the electrolyte were different. The remaining operating steps were the same as in Example 1. See Table 1 for details.

[0530] In Example 16, the additives in the electrolyte, based on their initial mass percentage in the electrolyte, were 1% of the first additive, 1% of "di-DTD", 1% of LiDFOB and 2% of VC (ethylene carbonate); and based on their initial molar volume concentration in the electrolyte, the electrolyte lithium salts were 0.3 mol / L LiFSI (lithium bis(fluorosulfonyl)imide) and 0.7 mol / L LiPF6 (lithium hexafluorophosphate).

[0531] Example 17. A lithium-ion secondary battery was prepared using a method essentially the same as that in Example 1, except that the composition of the electrolyte was different, the type of the first additive in the electrolyte was different, and the remaining operating steps were the same as in Example 1. See Table 1 for details.

[0532] In Example 17, the first additive compound IIa was replaced with methylcarboxylic acid-2-propynyl ester.

[0533] Example 18. A lithium-ion secondary battery was prepared using a method essentially the same as that in Example 4, except that the negative electrode active material was different in the step of preparing the negative electrode sheet; the remaining steps were the same as in Example 4. See Table 1 for details.

[0534] In Example 18, the negative electrode active material is a carbon-based material and a silicon-based material in a mass ratio of 95:5, meaning the silicon-based material accounts for 5% of the negative electrode active material by mass. The carbon-based material is the same as in Example 1; the silicon-based material is a silicon-carbon composite material, comprising a porous carbon matrix and elemental silicon deposited within the pores of the porous carbon matrix, with a silicon to carbon mass ratio of 1:1. The negative electrode active material's D... v 1 and D v50 is similar to Example 1.

[0535] Example 19. A lithium-ion secondary battery was prepared using a method essentially the same as in Example 1, except that the positive electrode active material was different in the positive electrode preparation step, and the coating density on one side of the positive electrode current collector was 0.27 g / 1540.25 mm. 2 The compaction density of the positive electrode sheet was adjusted to 3.4 g / cm³. 3 The surface area density of the coating on one side of the negative electrode current collector is 0.16 g / 1540.25 mm. 2 The compaction density of the negative electrode sheet is 1.65 g / cm³. 3 The remaining operating steps are the same as in Example 1. Please refer to Table 1.

[0536] In Example 19, the positive electrode active material is the ternary positive electrode material NCM622 (LiNi). 0.6 Co 0.2 Mn 0.2 O2).

[0537] D of positive electrode active material v 10 and D v The thicknesses of 50 are 1.8 μm and 6.2 μm, respectively, as shown in Table 1.

[0538] Comparative Example 1. A lithium-ion secondary battery was prepared using essentially the same method as in Example 1, except that the composition of the electrolyte was different, the first additive was omitted from the electrolyte, and the initial concentration of the lithium salt remained unchanged. The remaining operating steps were the same as in Example 1.

[0539] Comparative Example 2. A lithium-ion secondary battery was prepared using essentially the same method as in Example 16, except that the composition of the electrolyte was different, the first additive was omitted from the electrolyte, and the initial concentration of the lithium salt remained unchanged. The remaining operating steps were the same as in Example 16.

[0540] Comparative Example 3. A lithium-ion secondary battery was prepared using essentially the same method as in Example 17, except that the composition of the electrolyte was different, the first additive was omitted from the electrolyte, and the initial concentration of the lithium salt remained unchanged. The remaining operating steps were the same as in Example 17.

[0541] Comparative Example 4. A lithium-ion secondary battery was prepared using essentially the same method as in Example 1, except that the electrolyte composition was different, ethyl acetate (solvent formula I) was replaced with propyl propionate, and the initial concentration of the lithium salt electrolyte remained unchanged. The remaining operating steps were the same as in Example 1.

[0542] Comparative Example 5. A lithium-ion secondary battery was prepared using essentially the same method as in Example 1, except that the composition of the electrolyte was different, ethyl acetate (a non-aqueous solvent) was omitted from the electrolyte, and the initial concentrations of the first additive and the electrolyte lithium salt remained unchanged. The remaining operating steps were the same as in Example 1.

[0543] Comparative Example 6. A lithium-ion secondary battery was prepared using essentially the same method as in Example 19, except that the composition of the electrolyte was different, the first additive was omitted from the electrolyte, and the initial concentration of the lithium salt remained unchanged. The remaining operating steps were the same as in Example 19.

[0544] The relevant parameters for the above embodiments and comparative examples can also be found in Tables 1-2.

[0545] II. Test and Analysis Methods

[0546] 1. Electrolyte conductivity

[0547] A DDSJ-318 conductivity meter was used. Reference was made to page 5 of the industry standard HG / T4067-2015, "Lithium Hexafluorophosphate Electrolyte".

[0548] Test procedure (densitometer method):

[0549] Take about 100 mL of sample in a dry, clean, corrosion-resistant sample bottle, seal it and place it in a constant temperature water bath at 25℃±0.5℃, shake it from time to time. When the sample temperature is constant, replace the bottle cap with a rubber stopper with an electrode inserted. When the temperature is within the range of 25℃±0.5℃, read the data in the conductivity meter, which is the conductivity of the tested sample.

[0550] 2. Initial DC internal resistance (DCR) test and DCR growth rate:

[0551] (1) Initial DC internal resistance (DCR0)

[0552] At 25℃, the battery under test was charged at a constant current of 0.5C to 3.65V, and then charged at a constant voltage until the current was 0.05C. The battery was then discharged at a constant current of 0.5C for 30 minutes to adjust the battery to 50% SOC, and the voltage of the battery at this time was recorded as U1. The battery was then discharged at a constant current of 4C for 30 seconds, and the voltage at the end of the discharge was recorded as U2. The initial DCR of the battery (denoted as DCR0) is represented by the discharge DCR at 50% SOC. The initial DCR0 of the battery is (U1-U2) / I, where I is the current corresponding to the 4C rate.

[0553] (2) DCR growth rate after 45℃ cycling

[0554] Examples 1-8 and Comparative Examples 1-5: At 45°C, the battery under test was charged to 3.65V with a constant current of 1C, then charged at a constant voltage of 3.65V until the current dropped to 0.05C. After resting for 5 minutes, it was discharged to 2.1V with a constant current of 1C. This is the first charge / discharge cycle of the battery, and the discharge capacity of this cycle is recorded as the discharge capacity of the battery in the first cycle (C1). The above steps were repeated for the same battery. The process capacity of the battery after the nth cycle (Cn) was recorded. The capacity retention rate after 500 cycles was calculated as C500 / C1 × 100%. The capacity retention rate after 500 cycles was recorded.

[0555] In Example 19 and Comparative Example 6, the test procedure was changed as follows: At 45°C, the battery under test was charged to 3.65V at a constant current of 1C, then charged at a constant voltage of 3.65V until the current dropped to 0.05C. After resting for 10 minutes, it was discharged to 2.5V at a constant current of 1C and then rested for 5 minutes. This constitutes one charge-discharge cycle. The above steps were repeated for the same battery. The capacity retention rate was recorded after 500 cycles.

[0556] After the high-temperature cycling performance test is completed, the DCR is tested using the above method and denoted as DCR2. Then, the DCR growth rate = (DCR2 - DCR0) / DCR0 × 100%.

[0557] The test results are recorded as “Battery DCR0” and “DCR growth rate after 500 cycles at 45℃”, see Table 3-4.

[0558] 3. Fast charging time

[0559] The battery under test was charged and discharged for the first time at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour). The detailed steps included: at 35°C, the battery was charged at a constant current rate of 1C to a voltage of 3.65V, then charged at a constant voltage rate to a current ≤0.05C, left to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to a voltage of 2.5V. Its actual capacity was recorded as C0. Then, the battery was sequentially charged at constant current rates of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, and 5C0 until the full battery charging cutoff voltage of 3.65V or the negative terminal cutoff voltage of 0V (whichever comes first). After each charging, the battery was discharged at 1C0 until the full battery discharge cutoff voltage of 2.1V. The negative terminal cutoff voltage at different charging rates to 10%, 20%, 30%, ..., 80% SOC was recorded. By plotting the charging rate-negative electrode potential curves under different SOC states, and performing linear fitting, the charging rate corresponding to the negative electrode potential of 0V under different SOC states is obtained. This charging rate is the charging window under that SOC state, denoted as C(10% SOC), C(20% SOC), C(30% SOC), C(40% SOC), C(50% SOC), C(60% SOC), C(70% SOC), and C(80% SOC). The maximum charging rate under the corresponding state of charge is obtained, which is the fast charging window. The charging time from 10% to 80% is calculated as 6 / C (20% SOC) + 6 / C (30% SOC) + 6 / C (40% SOC) + 6 / C (50% SOC) + 6 / C (60% SOC) + 6 / C (70% SOC) + 6 / C (80% SOC). Therefore, the charging time t0 for the battery under test to charge from 10% SOC to 80% SOC can be calculated. The shorter the time t0, the better the fast-charging capability of the battery under test.

[0560] Among them, SOC (State of Charge) indicates that the battery is fully discharged when "SOC = 0" and fully charged when "SOC = 100%".

[0561] For example, “C(10% SOC)” corresponds to the charging rate when the negative electrode potential is 0V at 10% SOC obtained by linear fitting.

[0562] The test results can be found in Table 3 under "Charging Time t0".

[0563] 4. High-temperature cycling performance test (1C)

[0564] At 60°C (Examples 1-18 and Comparative Examples 1-5) or 45°C (Example 19 and Comparative Example 6), the battery under test was charged to 3.65V with a constant current of 1C, then charged at a constant voltage of 3.65V until the current dropped to 0.05C. After resting for 5 minutes, it was discharged to 2.1V (Examples 1-18 and Comparative Examples 1-5) or 2.5V (Examples 19 and Comparative Example 6) with a constant current of 1C. This is the first charge / discharge cycle of the battery, and the discharge capacity of this cycle is recorded as the discharge capacity (C1) of the battery in the first cycle. The above steps are repeated for the same battery. The process capacity (Cn) of the battery after the nth cycle is recorded. The capacity retention rate after n cycles is calculated as Cn / C1 × 100%. The number of cycles in which the capacity retention rate is 80% is recorded (see Table 3) or the capacity retention rate after 600 cycles is recorded (see Table 4).

[0565] The test results can be found in Table 3, “Number of cycles from 60℃ capacity decay to 80% SOC”, and Table 4, “Capacity retention rate after 600 cycles at 45℃”.

[0566] A higher cycle count or capacity retention rate indicates a better cycle life.

[0567] 5. Cycling performance at room temperature (25℃)

[0568] At 25°C, the battery under test was charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V to a cutoff current of 0.05C, and left to rest for 10 minutes. Then, it was discharged at a constant current of 1C to 2.1V (Examples 1-18 and Comparative Examples 1-5) or 2.5V (Example 19 and Comparative Example 6), and left to rest for 5 minutes. This constitutes one charge-discharge cycle. The discharge capacity at this point is recorded as C0. This charge-discharge cycle is repeated for the same battery, and the discharge capacity C0 of the first, second, ..., nth cycles is recorded. n The number of cycles must be at least 300.

[0569] Record the battery's cycle capacity retention rate P300 = C after 300 cycles. 300 / C0×100%.

[0570] The test results can be found in Table 4, "Capacity Retention Rate After 300 Cycles at Room Temperature". The higher the test value, the better the cycle life at room temperature.

[0571] III. Test Analysis Results

[0572] Table 1.

[0573] In Table 1, “F” I "This represents the initial mass percentage of solvent I in the non-aqueous solvent."

[0574] “F A"" indicates the initial mass percentage of the first additive in the electrolyte.

[0575] In Table 1, the additive content expressed as a percentage is the mass percentage in the electrolyte.

[0576] Table 2. Mass percentage of the first additive in the electrolyte before and after formation.

[0577] Table 3.

[0578] Table 4.

[0579] The conductivity of the electrolytes in Examples 1-19 was in the range of 9 mS / cm to 25 mS / cm at 25°C, while that in Examples 1-3, 4-17, and 19 was in the range of 10 mS / cm to 18 mS / cm.

[0580] In the lithium-ion secondary batteries prepared by formation, the electrolyte composition was tested by disassembling the cells: the mass percentage of the first additive in the electrolytes of Examples 1-19 was in the range of 0.01% to 3.2%; the mass percentage of the first additive in the electrolytes of Examples 1-7 and 10-19 was in the range of 0.05% to 1.6%; the mass percentage of various second additives in the electrolytes of Examples 1-19 decreased to varying degrees and all still had residues.

[0581] The lithium-ion secondary batteries prepared in Examples 1-19 all exhibit good fast-charging performance, while extending battery cycle life and improving fast-charging performance (extending the cycle life of fast-charging batteries). See Tables 3-4 for details.

[0582] Comparative Example 1 is relative to Example 1, Comparative Example 2 is relative to Example 16, Comparative Example 3 is relative to Example 17, and Comparative Example 6 is relative to Example 19. Comparative Examples 1-3 and 6 omitted the first additive, resulting in a deterioration in the cycle life of the fast-charging battery.

[0583] Compared to Example 1, in Comparative Example 4, the ethyl acetate solvent of Formula I in the electrolyte was replaced with propyl propionate, resulting in a significant increase in battery internal resistance and a severe deterioration in fast charging capability and cycle life.

[0584] Compared to Example 1, Comparative Example 3 omitted ethyl acetate, a non-aqueous solvent, from the electrolyte, resulting in a significant increase in battery internal resistance and a severe deterioration in fast-charging capability and cycle life.

[0585] The descriptions of the various implementation methods and embodiments above tend to emphasize the differences between them. Similarities or resemblances can be referenced interchangeably, and for the sake of brevity, they will not be repeated here. The technical features of the implementation methods and embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combinations of these technical features do not contradict each other, they should be considered within the scope of this specification.

[0586] It should be noted that this application is not limited to the above-described embodiments and examples. The above-described embodiments and examples are merely examples, and any embodiments and examples that have the same structure and achieve the same effect as the technical concept within the scope of this application are included in the technical scope of this application. The embodiments and examples described above only illustrate several embodiments and examples of this application, and although the descriptions are relatively detailed, they should not be construed as limiting the scope of the patent. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments or examples, and other ways of constructing embodiments or examples by combining some of the constituent elements of the embodiments or examples, are also included in the scope of this application without departing from the spirit of this application.

Claims

A lithium-ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte, wherein a separator is disposed between the positive electrode and the negative electrode; the electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent includes a chain-like carboxylic acid ester compound, wherein the chain-like carboxylic acid ester compound includes a solvent of formula I, the structure of which is shown in formula (I): In equation (I), R 11 and R 12 Each can be independently methyl or ethyl; The additives include a first additive and a second additive. The first additive is a nonionic organic additive containing carbon-carbon triple bonds, and the second additive is a negative electrode film-forming additive that is different from the first additive. According to claim 1, the lithium-ion secondary battery, wherein, The chain-like carboxylic acid ester compounds include one or more of methyl formate, ethyl formate, methyl acetate, and ethyl acetate. The lithium-ion secondary battery according to claim 1 or 2, wherein, The negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material, and the average particle size of the primary particles in the negative electrode active material is denoted as D1, where D1 is 0.1μm to 2μm. The lithium-ion secondary battery according to claim 3, wherein, The D1 of the negative electrode active material is 0.5 μm to 1.2 μm. The lithium-ion secondary battery according to any one of claims 1 to 4, wherein, The negative electrode active material D v 50 has a diameter of 5μm to 18μm, and optionally, the negative electrode active material is D. v 50 is 6μm to 15μm. The lithium-ion secondary battery according to any one of claims 1 to 5, wherein, The negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material, and the average particle size of the primary particles in the negative electrode active material is denoted as D1. The negative electrode active material D v The ratio of 50 to D1 is 5 to 50, and can be selected as 8 to 30. The lithium-ion secondary battery according to any one of claims 1 to 6, wherein, The negative electrode active material includes a coated negative electrode material, which includes a negative electrode active body and a carbon coating layer located on the negative electrode active body, comprising at least a portion thereof. The lithium-ion secondary battery according to claim 7, wherein, The negative electrode sheet satisfies one or more of the following characteristics: (a1) The mass percentage of the coated negative electrode material in the negative electrode active material is 80% to 100%; (a2) The coated negative electrode material includes coated graphite, and the negative electrode active body in the coated graphite includes graphite body, and the mass percentage of the coated graphite in the negative electrode active material is 80% to 100%. The lithium-ion secondary battery according to any one of claims 1 to 8, wherein, The positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material; the positive electrode active material includes one or more of lithium phosphate-based positive electrode materials and lithium transition metal oxide-based positive electrode materials; Optionally, the positive electrode sheet satisfies one or more of the following characteristics: (b1) The positive electrode active material includes a lithium phosphate-containing positive electrode material, wherein the lithium phosphate-containing positive electrode material has a D... v 50 is 0.3μm to 2μm; (b2) The positive electrode active material includes a lithium transition metal oxide positive electrode material, wherein the lithium transition metal oxide positive electrode material has a D v 50 is 2μm to 10μm. The lithium-ion secondary battery according to any one of claims 1 to 9, wherein, The negative electrode sheet includes a negative electrode active layer, and the negative electrode active layer includes a negative electrode active material; the positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material. (c1) The D of the negative electrode active material v 1 is greater than or equal to 1.5 μm; (c2) The positive electrode active material includes a lithium transition metal oxide positive electrode material, wherein the lithium transition metal oxide positive electrode material has a D v 10 is greater than or equal to 1 μm; (c3) The positive electrode active material includes a lithium phosphate-containing positive electrode material, wherein the lithium phosphate-containing positive electrode material has a D... v 10 is greater than or equal to 0.2 μm. The lithium-ion secondary battery according to any one of claims 1 to 10, wherein, The negative electrode sheet includes a negative electrode active layer, and the negative electrode active layer includes a negative electrode active material; the negative electrode active material includes at least one of carbon-based materials and silicon-based materials; Optionally, the silicon-based material accounts for 0% to 40% of the mass of the negative electrode active material. The lithium-ion secondary battery according to claim 11, wherein, The negative electrode sheet satisfies one or more of the following characteristics: (d1) The silicon-based material accounts for 0-25% of the mass of the negative electrode active material; (d2) The silicon-based material includes a silicon-carbon composite material, which includes a porous carbon matrix and elemental silicon located in the pores of the porous carbon matrix; optionally, the silicon-carbon composite material accounts for 80% to 100% of the mass of the silicon-based material. The lithium-ion secondary battery according to any one of claims 1 to 12, wherein, The electrolyte satisfies one or more of the following characteristics: (e1) The first additive in the electrolyte has a mass percentage of 0.01% to 3.2%; (e2) The mass ratio of the second additive to the first additive is 0.01 to 50. The lithium-ion secondary battery according to any one of claims 1 to 13, wherein, The electrolyte satisfies one or more of the following characteristics: (e1') The first additive is present in the electrolyte at a mass percentage of 0.05% to 1.6%; (e2') The mass ratio of the second additive to the first additive is 0.1 to 30. The lithium-ion secondary battery according to any one of claims 1 to 14, wherein, The second additive includes one or more of lithium salt additives, phosphate ester additives, vinylene carbonate, fluorocarbonate additives, saturated sulpholactones, and cyclic sulfates; Optionally, the electrolyte satisfies one or more of the following characteristics: (f1) The lithium salt additive includes one or more of oxalate lithium salts, lithium tetrafluoroborate, lithium difluorophosphate, and fluorosulfonic acid lithium salts; the oxalate lithium salt includes one or more of lithium difluorooxalateborate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate; the fluorosulfonic acid lithium salt includes one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide. (f2) The phosphate ester additives include silicon-based phosphate ester additives; the silicon-based phosphate ester additives include one or more of tris(trimethylsilane) phosphate and tris(trimethylsilyl) phosphite; (f3) The second additive includes fluorocarbonate additives, wherein the fluorocarbonate additives include fluoroethylene carbonate; (f4) The cyclic sulfates include one or more of monocyclic sulfates and polycyclic sulfates. The lithium-ion secondary battery according to claim 15, wherein, The electrolyte satisfies one or more of the following characteristics: (g1) The lithium salt additive in the electrolyte has a mass percentage of 0-3%; (g2) The lithium salt additive includes lithium difluorooxalate borate, wherein the mass percentage of lithium difluorooxalate borate in the electrolyte is 0-3%; (g3) The lithium salt additive includes lithium bis(fluorosulfonyl)imide; (g4) The phosphate ester additives in the electrolyte have a mass percentage of 0-2%; (g5) The mass percentage of the vinylene carbonate in the electrolyte is 0-3%; (g6) The fluorocarbonate additives in the electrolyte are 0-10% by mass; (g7) The fluorocarbonate additives include fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate in the electrolyte is 0 to 10%. (g8) The mass percentage of the saturated sulfonyl lactone in the electrolyte is 0-3%; (g9) The cyclic sulfate ester in the electrolyte has a mass percentage of 0-3%; (g10) The cyclic sulfate esters include polycyclic sulfate esters, wherein the mass percentage of the polycyclic sulfate esters in the electrolyte is 0 to 3%. The lithium-ion secondary battery according to any one of claims 1 to 16, wherein, The electrolyte comprises lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; Optionally, the molar volume concentration of the lithium bis(fluorosulfonyl)imide in the electrolyte is 0.01 mol / L to 0.5 mol / L. The lithium-ion secondary battery according to any one of claims 1 to 17, wherein, The electrolyte satisfies one or more of the following characteristics: (h1) The molecular weight of the first additive is less than or equal to 500 Da; (h2) The molecule of the first additive contains 1 to 4 carbon-carbon triple bonds; (h3) The carbon-carbon triple bond in the first additive is CH≡C-; (h4) The first additive comprises one or more of a first alkynyl compound and a second alkynyl compound; wherein the first alkynyl compound contains a carbon-carbon triple bond and a Lewis base nitrogen heterocycle, and the carbon-carbon triple bond and the Lewis base nitrogen heterocycle in the first alkynyl compound are linked by a linker L1, wherein the linker L1 contains a C-type carbon bond covalently bonded to the carbon-carbon triple bond. 1-3 Alkylene; the second alkynyl compound contains a carbon-carbon triple bond and an alkyl carbonate group, wherein the alkyl carbonate group has the structure R2-OC(=O)-O-*, where * is the bonding site attached to a carbon atom, and R2 is C 1-3 Alkyl group; the carbon-carbon triple bond and alkyl carbonate group in the second alkynyl compound are linked by a linker L2, wherein the linker L2 contains a C- group covalently bonded to the carbon-carbon triple bond. 1-3 Alkylene. The lithium-ion secondary battery according to claim 18, wherein, The electrolyte satisfies one or more of the following characteristics: (i1) The molecular weight of the first additive is less than or equal to 300 Da; (i2) The molecule of the first additive contains 1 to 4 Lewis base nitrogen heterocycles; (i3) The Lewis base nitrogen heterocycle comprises a substituted or unsubstituted imidazole group, wherein the imidazole ring in the substituted or unsubstituted imidazole group is substituted by 0, 1 or more substituents Q2, and each substituent Q2 in the substituted imidazole group is independently C. 1-3 Alkyl, cyano, or fluorine atom; (i4) The first alkynyl compound consists of a carbon-carbon triple bond, C, and C bonds connected in sequence. 1-3 Alkylene and -OC(=O)-R 10 Composition, R 10 It is a Lewis base nitrogen heterocycle; the second alkynyl compound consists of a carbon-carbon triple bond, C, and C bonds connected in sequence. 1-3 Alkylene and -OC(=O)-OR 20 Composition, R 20 C 1-3 alkyl. The lithium-ion secondary battery according to any one of claims 1 to 19, wherein, The first additive includes one or more of compound II and compound III; The structure of compound II is as follows: Among them, L 11 C 1-3 Alkylene, Q2 is independently C 1-3 Alkyl, cyano, or fluorine atom, p2 is 0, 1, 2, or 3; The structure of compound III is as follows: Among them, L 21 C 1-3 Alkylene, R 22 C 1- 3-alkyl group. The lithium-ion secondary battery according to any one of claims 1 to 20, wherein, The electrolyte satisfies one or more of the following characteristics: (j1) The first additive includes compound II, wherein the mass percentage of compound II in the first additive is 80% to 100%; (j2) The first additive comprises the structure as follows The compound IIa, wherein the mass percentage of compound IIa in the first additive is 80% to 100%. The lithium-ion secondary battery according to any one of claims 1 to 21, wherein, The electrolyte satisfies one or more of the following characteristics: (k1) The solvent of Formula I in the chain carboxylic acid ester compound accounts for 75% to 100% by mass; (k2) The chain carboxylic acid ester compound accounts for 5% to 80% of the mass in the non-aqueous solvent; (k3) The conductivity of the electrolyte at 25°C is 9mS / cm~25mS / cm. The lithium-ion secondary battery according to any one of claims 1 to 22, wherein, The electrolyte satisfies one or more of the following characteristics: (k1') The solvent of Formula I accounts for 90% to 100% of the mass of the chain carboxylic acid ester compound; (k2') The chain carboxylic acid ester compound in the non-aqueous solvent accounts for 10% to 60% by mass; (k3') The conductivity of the electrolyte at 25°C is 10 mS / cm to 18 mS / cm. A method for preparing a lithium-ion secondary battery includes the following steps: An electrode assembly, including a positive electrode, a separator, and a negative electrode, is placed inside the battery casing; wherein, The separator is provided between the positive electrode and the negative electrode; An electrolyte is injected into the battery casing, and the battery is allowed to stand to allow the electrolyte to wet the positive and negative electrode plates, thus forming the battery. The electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives. The non-aqueous solvent comprises a chain-like carboxylic acid ester compound, which includes a solvent of formula I, the structure of which is shown in formula (I). In equation (I), R 11 and R 12 Each is independently methyl or ethyl; the additives are a first additive and a second additive, wherein the first additive is a nonionic organic additive containing a carbon-carbon triple bond, and the second additive is a negative electrode film-forming additive different from the first additive. The method for preparing a lithium-ion secondary battery according to claim 24, wherein, In the step of injecting electrolyte into the battery casing, the initial mass percentage of the first additive in the electrolyte is 0.1% to 5%. The method for preparing a lithium-ion secondary battery according to claim 24, wherein, In the step of injecting electrolyte into the battery casing, the initial mass percentage of the first additive in the electrolyte is 0.1% to 3%. The method for preparing a lithium-ion secondary battery according to any one of claims 24 to 26, wherein, The lithium-ion secondary battery according to any one of claims 2 to 23 is prepared. An electrical device comprising at least one of the lithium-ion secondary batteries according to any one of claims 1 to 23 and the lithium-ion secondary batteries prepared by the preparation method of any one of claims 24 to 26.

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