battery

Abstract

Disclosed is a battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte. The positive electrode sheet comprises a positive electrode active material layer, the positive electrode active material layer comprising a positive electrode active material. On the basis of the total mass of the positive electrode active material layer, the mass proportion of the positive electrode active material is B, the specific surface area of the positive electrode active material being C m2 / g. The negative electrode sheet comprises a negative electrode active material, the specific surface area of the negative electrode active material being E. The electrolyte comprises a compound represented by formula 1 and LiBF4. On the basis of the total mass of the electrolyte, the mass proportion of the compound represented by formula 1 is G, which satisfies the following formula: 0.20≤(10×B×G×E2) / C≤3.88. The battery has excellent fast cyclic charging performance at high voltages.

Description

A battery

[0001] Priority information

[0002] The present application claims priority to and the benefit of Chinese Patent Application No. 202411069923.2, filed August 6, 2024, and is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application belongs to the field of batteries, and specifically relates to a battery. BACKGROUND

[0004] Lithium ion batteries are widely used in consumer electronics, electric vehicles and energy storage due to their high energy density and cycle performance. Currently, the discharge capacity of lithium ion batteries is improved by increasing the upper cut-off voltage or the compaction density to meet the high capacity demand of lithium ion batteries by consumers.

[0005] However, during the high-rate charge-discharge cycle of the battery, metal ions in the positive active material are dissolved, further catalyzing the oxidative decomposition of the electrolyte to produce gas, resulting in a decrease in the stability of the SEI (Solid Electrolyte Interface) and CEI (Cathode Electrolyte Interface), a decrease in the deintercalation ability of lithium ions between the positive and negative electrodes, and a rapid decay of the battery capacity, thereby degrading the cycle fast-charging performance of the battery, especially at high voltage, the problem is more prominent.

[0006] Therefore, how to improve the cycle fast-charging performance of high-voltage lithium ion batteries has become a problem to be solved.

[0007] SUMMARY

[0008] The present application aims to at least partially solve one of the technical problems in the related art. To this end, one object of the present application is to provide a battery. The battery has excellent cycle fast-charging performance.

[0009] The first aspect of the present application provides a battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprising a positive active material layer, the positive active material layer comprising a positive active material, the mass fraction of the positive active material being B based on the total mass of the positive active material layer, the specific surface area of the positive active material being C m 2 / g; the negative electrode sheet comprises a negative active material, the specific surface area of the negative active material being E m 2electrolyte, the mass ratio of the compound represented by Formula 1 in the electrolyte is G, and the following formula is satisfied: 0.20≤(10×B×G×E 2 ) / C≤3.88,

[0010] The battery in the present application includes a positive electrode sheet, a negative electrode sheet, and an electrolyte, and the electrolyte includes a compound represented by Formula 1 and LiBF4. Although the compound represented by Formula 1 can form a stable SEI film on the surface of the negative electrode during fast charging of the battery, thereby improving the cycle performance of the battery, there is still a problem of gas generation during long cycle, which affects the safety of the battery. LiBF4 can not only inhibit gas generation, but also participate in the formation of a stable CEI, thereby inhibiting the dissolution of metal ions in the positive active material and improving the stability of the positive electrode side. Therefore, the combination of the two can improve the cycle performance of the battery during fast charging. However, the inventors found that the compound represented by Formula 1 and LiBF4 in the electrolyte have limited effects on the cycle and fast charging performance of the battery, especially the fast charging performance, which is closely related to the mass ratio B of the positive active material in the positive active material layer, the specific surface area C m 2 / g of the positive active material, the specific surface area Em 2 / g of the negative active material in the negative electrode sheet, and the mass ratio G of the compound represented by Formula 1 in the electrolyte. The inventors found that when the above parameters satisfy the following formula: 0.20≤(10×B×G×E 2 ) / C≤3.88, the matching of the positive electrode, the negative electrode, and the electrolyte of the battery is optimal, which can minimize the negative effects of the positive active material and the negative active material on the fast charging performance and the cycle performance of the battery, so that the battery has excellent cycle and fast charging performance at high voltage. This is because the comprehensive performance of the battery is determined by the electrolyte, the positive electrode, the negative electrode, and the separator parameters. In the present application, only when the amount of the positive active material satisfies the above formula, the adhesion between the positive active material and the electrode sheet can be ensured, thereby improving the cycle performance of the battery. On the other hand, only when the specific surface area of the positive electrode and the negative electrode satisfies the above formula, lithium ions can quickly deintercalate on the formed SEI and CEI interface film, thereby showing excellent kinetic performance and improving the fast charging performance of the battery. Therefore, when the above parameters satisfy the given formula, the battery has excellent cycle and fast charging performance at high voltage.

[0011] In some embodiments, 95%≤B≤99%.

[0012] In some embodiments, 0.2≤C≤2.

[0013] In some embodiments, 0.2≤E≤3.5.

[0014] In some embodiments, 0.5%≤G≤3%.

[0015] In some embodiments, the mass ratio of the compound represented by Formula 1 and LiBF4 is (0.5-3):(0.1-1).

[0016] In some embodiments, the mass percentage of LiBF4 is 0.1%-1% based on the total mass of the electrolyte.

[0017] In some embodiments, the electrolyte further comprises a nitrile compound.

[0018] In some embodiments, the nitrile compound comprises at least one of succinonitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2,3-tris(2-cyanato)propane, 1,3,6-hexanetricarbonitrile, and tetracyanoethylene.

[0019] In some embodiments, the mass percentage of the nitrile compound is 0.2%-3% based on the total mass of the electrolyte.

[0020] In some embodiments, the mass ratio of the compound represented by Formula 1, LiBF4, and the nitrile compound is (0.5-3):(0.1-1):(0.2-3).

[0021] In some embodiments, the positive electrode active material comprises at least one of lithium cobaltate, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium-rich manganese material, lithium nickel-manganese oxide material, lithium manganese iron phosphate, and lithium manganate.

[0022] In some embodiments, the negative electrode active material comprises at least one of graphite and silicon-carbon material.

[0023] Additional aspects and advantages of the present application will be in part apparent and in part expressly stated in the description that follows. DETAILED DESCRIPTION

[0024] The embodiments of the present application are described in detail below with the aim of explaining the present application and cannot be understood as limiting the present application.

[0025] During the high-rate charging and discharging cycle of the battery, metal ions in the positive electrode active material are dissolved out, further catalyzing the oxidation and decomposition of the electrolyte to produce gas, resulting in a decrease in the stability of SEI and CEI, a decrease in the deintercalation ability of lithium ions between the positive and negative electrodes, a rapid capacity decay of the battery, and a deterioration of the fast charging cycle performance of the battery, especially at high voltage, the problem is more prominent.

[0026] The first aspect of the application provides a battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprises a positive electrode active material layer, the positive electrode active material layer comprises a positive electrode active material, the mass fraction of the positive electrode active material is B based on the total mass of the positive electrode active material layer, the specific surface area of the positive electrode active material is C m 2 / g; the negative electrode sheet comprises a negative electrode active material, the specific surface area of the negative electrode active material is E m 2 / g; the electrolyte comprises a compound represented by Formula 1 and LiBF4, the mass fraction of the compound represented by Formula 1 is G based on the total mass of the electrolyte, and the following formula is satisfied: 0.20≤(10×B×G×E 2 ) / C≤3.88,

[0027] As an example, the value of (10×B×G×E 2 ) / C can be 0.20, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 3.88, etc.

[0028] The battery in the application comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, the electrolyte comprises a compound represented by Formula 1 and LiBF4, although the compound represented by Formula 1 can form a stable SEI film on the negative electrode surface during the fast charging process of the battery, improving the cycle performance of the battery, but there is still a problem of gas production during long cycle, affecting the safety of the battery, and LiBF4 not only can inhibit gas production, but also can participate in the formation of stable CEI, inhibit the dissolution of metal ions in the positive electrode active material, and improve the stability of the positive electrode side. Therefore, the combination of the two can improve the cycle performance of the battery during fast charging. However, the inventors found that the compound represented by Formula 1 and LiBF4 in the electrolyte have limited influence on the cycle and fast charging performance of the battery, especially the fast charging performance, during the actual cycle of the battery. The cycle and fast charging performance of the battery is closely related to the mass ratio B of the positive electrode active material in the positive electrode active material layer, the specific surface area C m 2 / g of the positive electrode active material, the specific surface area E m 2 / g of the negative electrode active material in the negative electrode sheet, and the mass fraction G of the compound represented by Formula 1 in the electrolyte. The inventors found that when the above parameters satisfy the following formula: 0.20≤(10×B×G×E 2 ) / C≤3.88, the matching of the positive electrode, the negative electrode and the electrolyte of the battery is best, which can minimize the negative influence of the positive electrode active material and the negative electrode active material on the fast charging performance and cycle performance of the battery, so that the battery has excellent cycle and fast charging performance at high voltage.

[0029] It can be understood that in the present application, the unit of the specific surface area of the positive active material and the negative active material is m 2 / g, but the present application does not limit the unit of the specific surface area of the positive active material and the negative active material, for example, the unit of the specific surface area can also be m 2 / g, cm 2 / g, etc., when the unit of the specific surface area is other than m 2 / g, the unit is converted into m 2 / g, and the obtained formula value is between 0.20-3.88, which is also within the protection scope of the present application.

[0030] In some embodiments, 95%≤B≤99%, for example, B can be 95%, 96%, 96.5%, 97%, 98%, 98.5%, 99%, etc. The higher the amount of the positive active material, the higher the theoretical capacity can be provided, but when exceeding a certain range, the adhesion between the positive active material and the binder is poor, which greatly reduces the conductivity, thereby affecting the cycle performance of the battery. By controlling the positive active material within the above range, the present application ensures the conductivity stability of the battery, and is conducive to controlling (10×B×G×E 2 ) / C within the range of 0.20-3.88, thereby improving the cycle fast-charging performance of the battery at high voltage.

[0031] In some embodiments, 0.2≤C≤2, for example, C can be 0.2, 0.3, 0.6, 0.9, 1.3, 1.5, 2, etc. There are active sites on the surface of the positive active material, the larger the specific surface area of the positive active material, the more active sites, and LiBF4 can combine with the active sites on the surface of the positive active material to form CEI. When the specific surface area is too small, it is difficult for LiBF4 to form a complete CEI on the surface of the positive electrode, and when the specific surface area is too large, a relatively thick CEI is formed, which is not conducive to the extraction of lithium ions. By controlling the specific surface area of the positive active material within the range of 0.2m 2 / g-2m 2 / g, a CEI film with low impedance and high stability can be formed, the kinetic performance is improved, and it is conducive to controlling (10×B×G×E 2 ) / C within the range of 0.20-3.88, thereby improving the cycle fast-charging performance of the battery at high voltage.

[0032] In some embodiments, 0.2≤E≤3.5, for example, E can be 0.2, 0.8, 1.2, 1.6, 2, 2.8, 3.5, etc. There are also active sites on the surface of the negative active material, but when the specific surface area of the positive and negative active materials is too different, the kinetics of the positive and negative electrodes of the battery will also be mismatched. By controlling the specific surface area of the negative active material within the range of 0.2m 2 / g-3.5m2 / g range, the specific surface area of the positive active material matches the specific surface area of the negative active material, which can improve the kinetic performance of the battery and is conducive to controlling (10 x B x G x E 2 ) / C in the range of 0.20-3.88, thereby improving the cycle fast-charging performance of the battery at high voltage.

[0033] In some embodiments, 0.5%≤G≤3%, for example, G is 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, etc. When G is in this range, the content of the compound of formula 1 in the electrolyte is moderate, which can ensure the formation of an effective CEI and SEI film with low impedance and high stability on the positive and negative electrode surfaces, and is conducive to controlling (10 x B x G x E 2 ) / C in the range of 0.20-3.88, thereby improving the cycle fast-charging performance of the battery at high voltage.

[0034] Since the cycle performance and fast-charging performance of the lithium ion battery are jointly determined by the positive electrode sheet, the negative electrode sheet and the electrolyte, the inventors found that by adjusting the values of B, G, E and C, the cycle performance and fast-charging performance of the battery can be optimized when the compound of formula 1 and LiBF4 are added to the electrolyte: a higher positive active material mass ratio B means that more positive active material participates in the reaction, which can provide more lithium ions, thereby increasing the capacity of the battery; a larger specific surface area C of the positive active material means more lithium ion intercalation / deintercalation sites, which can increase the charge and discharge rate of the battery; the specific surface area E of the negative active material is similar to C, which affects the diffusion and reaction rate of lithium ions in the negative electrode, and experiments have shown that the specific surface area of the negative active material has a square effect on the performance of the battery; the mass fraction G of the compound of formula 1 in the electrolyte affects the quality of the SEI film of the electrolyte, and in turn affects the cycle performance.

[0035] That is, based on experience and experimental findings, within a certain range, each parameter is positively correlated with the cycle and fast-charging effect, and the product (10 x B x G x E 2 ) divided by the specific surface area C of the positive active material is to normalize, so that the formula is applicable to positive active materials with different specific surface areas. That is, if B, E and G increase, the performance of the battery may improve, but a larger C is needed to maintain the charge and discharge rate and cycle stability.

[0036] The specific physical meaning of the formula (10 x B x G x E 2 ) / C is actually the matching degree of the positive electrode, the negative electrode and the electrolyte in the battery. Experiments have shown that (10 x B x G x E 2When the value of (I) / (C) is between 0.20 and 3.88, the matching of the positive electrode, the negative electrode and the electrolyte of the battery is optimal, which can minimize the negative influence of the positive active material and the negative active material on the fast charging performance and the cycle performance of the battery, so that the battery has excellent cycle fast charging performance at high voltage. If the value is too large or too small, the matching of the negative electrode and the positive electrode will be unreasonable, which will affect the ion transmission of lithium ions in the positive electrode and the negative electrode, and further affect the cycle performance and the rate performance of the battery.

[0037] In some embodiments, the mass percentage of LiBF4 is 0.1% to 1%, for example, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1%, etc., based on the total mass of the electrolyte. In this way, the mass percentage of LiBF4 is controlled within the above range, which is sufficient to inhibit gas production and also participate in the formation of stable CEI, inhibits the dissolution of metal ions in the positive active material, and can improve the cycle fast charging performance of the battery at high voltage.

[0038] In some embodiments, the mass ratio of the compound represented by Formula 1 to LiBF4 is (0.5-3):(0.1-1). For example, it can be 2:0.5, 2:0.1, 2:1, 0.5:0.5, 3:0.5, etc. Controlling the mass ratio of the compound represented by Formula 1 to LiBF4 in the electrolyte within the above range can fully exert the synergistic effect of the two, inhibit the dissolution of metal ions in the positive active material, improve the stability of the positive electrode and the negative electrode, and further improve the cycle performance of the battery during fast charging.

[0039] In some embodiments, the electrolyte further comprises a nitrile compound. When the battery charging cutoff voltage is above 4.5V, metal ions in the positive active material will still be dissolved at high voltage and catalyze the decomposition of the electrolyte to produce gas. On this basis, the introduction of nitriles into the electrolyte can further improve the cycle fast charging performance at high voltage. This is mainly due to the strong complexation of the cyano group with metal ions, which not only inhibits the dissolution of metal ions in the positive active material and avoids excessive oxidation and decomposition of the electrolyte during the cycle process, but also improves the CEI film and improves the stability of the battery. Therefore, the combination of the compound represented by Formula 1, LiBF4 and the nitrile compound in the electrolyte can further improve the cycle fast charging performance of the battery at high voltage.

[0040] In some embodiments, the mass ratio of the compound represented by Formula 1, LiBF4 and the nitrile compound is (0.5-3):(0.1-1):(0.2-3). For example, it can be 1:0.5:2, 0.5:0.5:2, 3:0.5:2, 1:0.1:2, 1:1:2, 1:0.5:0.2, 1:0.5:3, etc. Thus, by controlling the mass ratio of the compound represented by Formula 1, LiBF4 and the nitrile compound within the above range, the synergistic effect of the three can be fully exerted, and the cycle fast-charging performance of the battery at high voltage of 4.5 V or above can be further improved.

[0041] In some embodiments, the nitrile compound includes at least one of succinonitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2,3-tris(2-cyanato)propane, 1,3,6-hexanetricarbonitrile and tetracyanoethylene. The above nitrile compound as an electrolyte additive can further improve the cycle fast-charging performance of the battery at high voltage of 4.5 V or above.

[0042] In some embodiments, the mass fraction of the nitrile compound is 0.2%-3% based on the total mass of the electrolyte. For example, it can be 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc. Thus, by controlling the content of the nitrile compound in the electrolyte within the above range, the insufficient inhibition of metal ion dissolution caused by too little nitrile compound can be reduced, and the impedance increase caused by too much nitrile compound can be reduced, and the cycle fast-charging performance of the battery at high voltage of 4.5 V or above can be further improved.

[0043] In some embodiments, the positive electrode active material includes at least one of lithium cobaltate, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium-rich manganese material, lithium nickel-manganese oxide material, lithium manganese iron phosphate and lithium manganate. The above positive electrode active material has high energy density and excellent cycle performance, thereby improving the cycle stability of the battery at high voltage.

[0044] In some embodiments, the battery is a lithium ion battery, and the positive electrode active material includes lithium cobaltate, which has excellent cycle performance and high energy density, has a low probability of side reactions with the compound represented by Formula 1, LiBF4 and the nitrile compound in the electrolyte of the present application, and has high high-pressure resistance, thereby improving the cycle fast-charging performance of the battery at high voltage.

[0045] In some embodiments, the electrolyte further comprises a non-aqueous organic solvent, the non-aqueous organic solvent comprising at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone, phenyl acetate, 1,4-butyrolactone, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl formate, ethyl acetate, methyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, ethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl trifluoroethyl carbonate, (2,2,2)-trifluoroethyl carbonate, 2,2-difluoroethyl acetate, 2,2-difluoroethyl propionate, and 2,2-difluoroethyl methyl carbonate. The mass percentage of the non-aqueous organic solvent in the electrolyte is 60-80%. For example, it can be 60%, 65%, 70%, 75%, 80%, etc. The solvent in the above range can ensure that the battery has stable electrochemical properties.

[0046] In some embodiments of the present application, the electrolyte further comprises a lithium salt, the lithium salt comprising at least one of LiPF6, LiAsF6, LiClO4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2, and LiPF4C2O4; the mass percentage of the lithium salt in the electrolyte is 10-18%. For example, it can be 10%, 12%, 14%, 15%, 18%, etc. The electrolyte salt is controlled in the above range, which can ensure that the battery has stable electrochemical properties.

[0047] Generally, the battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuiting of the positive and negative electrodes, while allowing ions to pass through.

[0048] The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode current collector, the positive electrode active material layer comprising the above-mentioned positive electrode active material.

[0049] In some embodiments of the present application, the positive current collector can include a metal foil or a composite positive current collector. For example, the metal foil can employ an aluminum foil. The composite positive current collector can include a polymer material base layer and a metal layer formed on at least one side surface of the polymer material base layer. For example, the composite positive current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material base material (e.g., a polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0050] In some embodiments of the present application, the positive active material layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0051] In some embodiments of the present application, the positive active material layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic resin.

[0052] In some embodiments of the present application, the positive electrode sheet can be prepared by dispersing the above-described components for preparing the positive electrode sheet, e.g., the positive active material, the conductive agent, the binder, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive current collector, and then performing drying, cold pressing, etc. to obtain the positive electrode sheet.

[0053] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, the negative active material layer including a negative active material.

[0054] In some embodiments of the present application, the negative current collector can employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material base material (e.g., a polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0055] In some embodiments of the present application, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of the following materials: natural graphite, artificial graphite, soft carbon, hard carbon, mesocarbon microbeads, nanocarbon, elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon alloys, elemental tin, tin oxide compounds, tin-carbon composites, tin alloys, at least one of lithium titanate.

[0056] In some embodiments of the present application, the negative active material includes at least one of graphite and silicon-carbon material. The above-mentioned negative active material can better match the positive active material and the electrolyte, adapt to the high-voltage and high-rate scenarios of the battery, and enable the battery to have excellent fast-charging performance at high voltage.

[0057] In some embodiments of the present application, the negative active material layer can also optionally include a binder. The binder can include at least one 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).

[0058] In some embodiments of the present application, the negative active material layer can also optionally include a conductive agent. The conductive agent can include at least one of super-conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0059] In some embodiments of the present application, the negative active material layer can also optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0060] In some embodiments of the present application, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained.

[0061] The present application does not have a particular limitation on the type of the separator film, and any known porous structure separator film with good chemical stability and mechanical stability can be selected.

[0062] In some embodiments of the present application, the material of the separator film can include at least one of glass fiber, non-woven fabric, polyolefin film, aromatic polyamide film, polytetrafluoroethylene film, and polyether sulfone film.

[0063] In some embodiments of the present application, the thickness of the separator film can be 10-12 μm, for example, 10 μm, 11 μm, 12 μm, and the like.

[0064] The embodiments of the present application are described in detail below, it should be noted that the embodiments described below are exemplary, only for explaining the present application, and can not be understood as limiting the present application. In addition, if not specifically stated, all reagents used in the following examples are commercially available, or can be synthesized according to the methods described herein or known methods, and the reaction conditions not listed are also readily available to those skilled in the art.

[0065] Example 1

[0066] 1. Preparation of positive electrode sheet

[0067] The positive electrode active material (lithium cobaltate), the binder polyvinylidene fluoride PVDF, the conductive carbon black, and the conductive carbon nanotube were mixed uniformly according to the weight ratio of 95:2.3:2:0.7, N-methyl pyrrolidone NMP was added, and stirring was carried out under the action of a vacuum stirrer until the mixed system became a uniform flowable positive electrode slurry; the positive electrode slurry was uniformly coated on the positive electrode current collector aluminum foil, and the coating amount was 35 g / m 2 , and after drying at 85°C, cold pressing was carried out, edge cutting, sheet cutting, and striping were carried out, and after striping, drying was carried out at 85°C under vacuum conditions for 4 hours, and the tab was welded to obtain the positive electrode sheet, the specific surface area C of the lithium cobaltate was 0.6 m 2 / g.

[0068] 2. Preparation of negative electrode sheet

[0069] The negative electrode active material graphite, the conductive agent carbon black, the thickening agent sodium carboxymethyl cellulose (CMC-Na), and the binder styrene-butadiene rubber were mixed according to the weight ratio of 95:1.5:1:2.5, deionized water was added, and the negative electrode slurry was obtained under the action of a vacuum stirrer; the negative electrode slurry was uniformly coated on the negative electrode current collector copper foil, and the coating amount was 20 g / m 2 , and after drying at 85°C, cold pressing was carried out, edge cutting, sheet cutting, and striping were carried out, and after striping, drying was carried out at 85°C under vacuum conditions for 4 hours, and the tab was welded to obtain the negative electrode sheet, the specific surface area E of the graphite was 1.6 m 2 / g.

[0070] 3. Preparation of electrolyte

[0071] In an argon-filled glove box (moisture < 10 ppm, oxygen < 1 ppm), solvent vinyl carbonate, propylene carbonate, diethyl carbonate, propyl propionate were mixed uniformly in a mass ratio of 1:1:1:2, and fully dried lithium hexafluorophosphate was quickly added to the mixed solvent, the molar concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L, and then compound 1, LiBF4, and succinonitrile were sequentially added, and the electrolyte was obtained after fully mixing. Among them, the mass ratio of compound 1 in the electrolyte is 2%, the mass ratio of LiBF4 in the electrolyte is 0.2%, and the mass ratio of succinonitrile in the electrolyte is 2%.

[0072] 4. Isolation film

[0073] An isolation film of polyethylene with a thickness of 8 μm was selected.

[0074] 5. Preparation of lithium ion battery

[0075] The positive electrode sheet, the negative electrode sheet and the isolation film prepared according to the above process were subjected to a winding process to form a lithium ion battery with a thickness of 4.7 mm, a width of 55 mm and a length of 60 mm. The battery was vacuum baked at 85°C for 10 hours, and then the electrolyte prepared above was injected. After standing for 24 hours, the battery was placed in an environment at 45°C, and a pressure of 3 kg was applied. After charging to 4.5V at 0.1C (195mA), the battery was allowed to stand under the same temperature and pressure conditions for more than 24 hours (to fully activate the battery) to obtain the battery.

[0076] wherein (10 x B x G x E 2 ) / C = 0.81.

[0077] The preparation method of the lithium ion battery of Examples 2-27 and Comparative Examples 1-8 was basically the same as that of Example 1, but the electrolyte composition, the positive active material and the negative active material were different, as shown in Table 1.

[0078] wherein, Comparative Example 1 contains two additives (compound 1 and LiBF4), but the value of formula (10 x B x G x E 2 ) / C is too low; Comparative Example 2 contains three additives (compound 1, LiBF4 and nitrile compound), but the value of formula (10 x B x G x E 2 ) / C is too low; Comparative Example 3 contains two additives (compound 1 and LiBF4), but the value of formula (10 x B x G x E 2 ) / C is too high; Comparative Example 4 contains three additives (compound 1, LiBF4 and nitrile compound), but the value of formula (10 x B x G x E 2 ) / C is too high; no LiBF4 is added in the electrolyte of Comparative Examples 5 and 7, and no compound 1 is added in the electrolyte of Comparative Examples 6 and 8.

[0079] Table 1

[0080] The batteries prepared in Examples 1-27 and Comparative Examples 1-8 were subjected to normal temperature cycle fast charging test at 25°C, and the capacity retention rate and expansion rate of the batteries at cycle 800 were recorded, and the performance test results are shown in Table 2.

[0081] At 25°C, the lithium ion battery was left for 5 minutes, charged to 4.50V at 2C rate, left for 5 minutes, then charged to current less than or equal to 0.05C at constant current and constant voltage, then left for 5 minutes, discharged to 3.0V at 1C rate, and the cycle charging and discharging test was repeated for 800 cycles in this way, the maximum discharge capacity of the first 5 cycles was recorded as Q, and the discharge capacity at cycle 800 was recorded as Q1, and the calculation method of the capacity retention rate at cycle 800 was as follows:

[0082] Capacity retention rate (%) after cycle 800 = Q1 / Q x 100.

[0083] The thickness of the fresh battery was measured by a thickness tester, and was recorded as P1, and the thickness of the battery after cycle 800 was recorded as P2, and the calculation formula of the expansion rate of the battery after cycle 800 was as follows:

[0084] Expansion rate of the battery after cycle 800 (%) = P2 / P1 x 100

[0085] Table 2

[0086] From the data in Table 2, the capacity retention rates of the batteries in Examples 1-27 were significantly higher than those in Comparative Examples 5-8, and the expansion rates were lower, indicating that the synergistic effect of LiBF4 and the compound represented by Formula 1 could ensure the cycle fast charging performance of the battery at high voltage. As can be seen from Examples 1, 9-27 and Examples 2-8, the nitrile compound can further improve the cycle fast charging performance of the battery at high voltage. In addition, Comparative Examples 2 and 4 added the compound represented by Formula 1 and LiBF4 in a suitable ratio, and Comparative Examples 1 and 3 added the compound represented by Formula 1, LiBF4 and the nitrile compound in a suitable ratio, but the value calculated by the formula (10xBxGxE 2 ) / C in Comparative Examples 1-4 was not between 0.2 and 3.88, and the capacity retention rate of the battery was much lower than that of Examples 1-27, indicating that the addition of the compound represented by Formula 1 and LiBF4 in the electrolyte and the formula value satisfying between 0.2 and 3.88, or the addition of the compound represented by Formula 1, LiBF4 and the nitrile compound in the electrolyte and the formula value satisfying between 0.2 and 3.88, can achieve excellent cycle fast charging performance at high voltage.

[0087] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are contained in at least one embodiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0088] Although the embodiments of the present application have been shown and described above, it is understood that the above embodiments are exemplary and are not to be construed as limiting the present application, and the person skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A battery, wherein, Comprising: A positive electrode tab, the positive electrode tab comprising a positive electrode active material layer, the positive electrode active material layer comprising a positive electrode active material, a mass fraction of the positive electrode active material based on a total mass of the positive electrode active material layer being B, a specific surface area of the positive electrode active material being Cm 2 / g; A negative electrode sheet including a negative electrode active material, the specific surface area of the negative electrode active material being E m 2 / g; an electrolyte, the electrolyte comprising a compound shown in Formula 1 and LiBF4, the mass percentage of the compound shown in Formula 1 based on the total mass of the electrolyte being G, satisfies the following equation: 0.20 < (10 x B x G x E) / C < 3.88, 2 ​ 2. The battery of claim 1, wherein, 95％≤B≤99％。 3. The battery of claim 1, wherein, 0.2≤C≤2。 4. The battery of claim 1, wherein, 0.2≤E≤3.5。 5. The battery of claim 1, wherein, 0.5％≤G≤3％。 6. The battery of any one of claims 1-5, wherein, the mass ratio of the compound shown in Formula 1 and the LiBF4 being (0.5-3):(0.1-1).

7. The battery of any one of claims 1-5, wherein, The mass percentage of the LiBF4 based on the total mass of the electrolyte is 0.1%-1%.

8. The battery of any one of claims 1-5, wherein, The electrolyte further comprises a nitrile compound.

9. The battery of claim 8, wherein, The mass ratio of the compound shown in Formula 1, the LiBF4 and the nitrile compound is (0.5-3):(0.1-1):(0.2-3); and / or, The mass percentage of the nitrile compound based on the total mass of the electrolyte is 0.2%-3%; and / or, The nitrile compound comprises at least one of succinonitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2,3-tris(2-cyanato)propane, 1,3,6-hexanetricarbonitrile and tetracyanoethylene.

10. The battery of any one of claims 1-5, wherein, The positive electrode active material comprises at least one of lithium cobaltate, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium-rich manganese material, lithium nickel-manganese oxide material, lithium manganese iron phosphate and lithium manganate; and / or, The negative electrode active material comprises at least one of graphite and silicon-carbon material.

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