Electrolyte and battery

Abstract

The invention relates to the technical field of lithium ion batteries, and provides an electrolyte and a battery. The electrolyte comprises 1, 3, 6-hexane tricarbonitrile and butane tricarbonitrile, and based on the total mass of the electrolyte, the mass ratio of the 1, 3, 6-hexane tricarbonitrile is recorded as a%, and the mass ratio of the butane tricarbonitrile is recorded as b%; a and b satisfy 0.5 < = a < = 4.5, 0.5 < = b < = 4.1, and 0.7 < = a / b < = 7; according to the invention, the fast charging performance and cycle life of the battery under high voltage can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, and in particular to an electrolyte and a battery. BACKGROUND

[0002] Lithium ion batteries have become the mainstream power battery technology due to their long cycle life advantage, and the development of batteries to high-voltage working state is the key path to improve their energy density. Under the premise that the battery capacity is relatively stable, increasing the working voltage can directly improve the overall energy storage capacity of the battery, thereby meeting the core needs of new energy vehicles, energy storage devices and other for longer mileage and higher endurance time. However, under the high-voltage working scenario, the problem of insufficient fast charging performance of the battery is increasingly prominent and gradually becomes an industry bottleneck. The prior art attempts to use dinitrile compounds (such as hexanitrile, butanitrile, and ethylene glycol bis(propionitrile) ether) to improve the electrochemical performance under high voltage. However, the structure of the dinitrile compound is symmetrical and the polarity is weak, and the interaction with lithium ions is insufficient, resulting in poor optimization of the solvation sheath structure of lithium ions and high desolvation energy barrier, which cannot meet the fast charging demand under high voltage. SUMMARY

[0003] The purpose of the present application is to overcome the above-mentioned problems existing in the prior art, and to provide an electrolyte and a battery. By adding 1,3,6-hexanitrile and butanitrile to the electrolyte and controlling the mass fraction of each in the electrolyte and the ratio between the two, the fast charging performance and cycle life of the battery under high voltage can be improved.

[0004] In order to achieve the above-mentioned purpose, the first aspect of the present application provides an electrolyte, which comprises 1,3,6-hexanitrile and butanitrile, and the mass fraction of the 1,3,6-hexanitrile is denoted as a%, and the mass fraction of the butanitrile is denoted as b%, based on the total mass of the electrolyte; a and b satisfy: 0.5≤a≤4.5, 0.5≤b≤4.1, 0.7≤a / b≤7.

[0005] The second aspect of the present application provides a battery, which comprises the electrolyte provided by the first aspect of the present application, a positive electrode sheet, and a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, and the negative electrode active material comprising a silicon-based material.

[0006] The present application has the following beneficial effects by adopting the above technical solution: The electrolyte provided by the application, by adding 1,3,6-hexanetricarbonitrile (HTCN) and butanetricarbonitrile in the electrolyte in a synergistic manner, wherein 1,3,6-hexanetricarbonitrile and butanetricarbonitrile are both tricyanide compounds with stronger polarity (compared with dicyanide compounds), by controlling the mass ratio and proportion of the two, 1,3,6-hexanetricarbonitrile and butanetricarbonitrile in the electrolyte can more effectively combine with lithium ions to optimize the solvation structure, significantly reduce the energy barrier in the desolvation process of lithium ions, and accelerate the transmission rate of lithium ions in the electrolyte and the positive and negative electrode interface. At the same time, the viscosity of butanetricarbonitrile is lower than that of 1,3,6-hexanetricarbonitrile, and the addition of butanetricarbonitrile in the electrolyte can further improve the fluidity of the electrolyte and assist in reducing the lithium ion migration resistance, providing a basis for fast transmission of lithium ions under high-voltage fast charging. Secondly, under high-pressure working conditions, the positive active material is prone to side reactions with the electrolyte and is accompanied by transition metal ion dissolution, and the reduction voltage of butanetricarbonitrile is higher than that of 1,3,6-hexanetricarbonitrile, which will be preferentially adsorbed on the positive electrode surface to form an initial protective layer, inhibiting the initial side reaction and metal ion dissolution in advance. 1,3,6-hexanetricarbonitrile further crosslinks on the basis of the initial protective layer by virtue of the long-chain structure, so that the positive electrode interphase film formed has high compactness and stability, effectively prolonging the protective effect of the interphase film in long-term high-pressure cycling, reducing the continuous decomposition of the electrolyte and the degradation of the positive electrode structure, improving the battery cycle life, and realizing the synergistic improvement of high-voltage fast charging performance and cycle life.

[0007] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges are included in the range unless specifically stated otherwise. Ranges of values are understood to be approximate, including values nearest the stated range limits, unless otherwise indicated. In this context, the data ranges include the endpoints unless specifically stated otherwise. DETAILED DESCRIPTION

[0008] The specific embodiments of the application will be described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and explanatory and are not intended to limit the application.

[0009] Unless otherwise defined, all scientific and technical terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0010] The first aspect of the present application provides an electrolyte, the electrolyte comprising 1,3,6-hexanetricarbonitrile and butanetricarbonitrile, the mass percentage of the 1,3,6-hexanetricarbonitrile in the total mass of the electrolyte is denoted as a%, and the mass percentage of the butanetricarbonitrile in the total mass of the electrolyte is denoted as b%. a and b satisfy: 0.5≤a≤4.5, 0.5≤b≤4.1, 0.7≤a / b≤7. The present application can improve the fast charging performance and cycle life of the battery at high voltage by adding 1,3,6-hexanetricarbonitrile and butanetricarbonitrile to the electrolyte and controlling the mass percentage of each in the electrolyte and the ratio between the two.

[0011] It should be noted that when calculating the value of a / b, neither a nor b is calculated with units.

[0012] Exemplarily, the mass percentage of 1,3,6-hexanetricarbonitrile may be, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or any point value within the range formed by any two of the above point values. If a% is less than 0.5%, the insufficient HTCN content will lead to the following problems: on the one hand, it cannot fully combine with lithium ions to optimize the solvation sheath structure, the desolvation energy barrier is high, the transmission rate of lithium ions at the interface between the electrolyte and the positive and negative electrodes is slow, and the fast charging performance at high voltage is directly weakened; on the other hand, it is difficult to form an interface film with sufficient cross-linking degree on the surface of the positive electrode, the initial side reaction is not sufficiently suppressed, the amount of transition metal ions dissolved increases, the electrolyte decomposition and positive electrode structure degradation are accelerated during the battery cycle process, and the cycle life is shortened. If a% is greater than 4.5%, the excess addition of HTCN will significantly increase the overall viscosity of the electrolyte, increase the lithium ion migration resistance, and reduce the ion transport efficiency during fast charging; at the same time, the interface film formed by the excess HTCN may be too thick or cross-linked too much, leading to an increase in interface impedance, uneven lithium ion deposition during the charging process, and the induction of lithium dendrite growth, which affects the fast charging safety and further shortens the cycle life due to dendrite piercing the separator or consuming the electrolyte.

[0013] Exemplarily, the mass percentage of butanetricarboxylic acid is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.1% or any point value in the range of any two of the above point values. If b% is less than 0.5%, the insufficient content of butanetricarboxylic acid will destroy the synergistic effect with HTCN. On the one hand, the improvement of electrolyte fluidity is limited, the lithium ion migration resistance cannot be effectively reduced, and it is difficult to assist HTCN to improve the fast charging efficiency. On the other hand, the positive electrode surface lacks sufficient initial protective layer formed by butanetricarboxylic acid. Before HTCN directly participates in film formation, the positive electrode has undergone many initial side reactions, and the transition metal ion dissolution occurs in advance. Although the cross-linked film formed by the subsequent HTCN has compactness, it cannot make up for the performance loss caused by the previous side reactions, and the cycle life and fast charging stability are affected. If b% is greater than 4.1%, excessive butanetricarboxylic acid will break the balance of the ratio of HTCN. First, excessive low-viscosity butanetricarboxylic acid may cause the overall polarity of the electrolyte to decrease, thereby weakening the optimization effect on the solvation structure of lithium ions, and partially offsetting the effect of HTCN. Second, the initial protective layer formed by excessive butanetricarboxylic acid may be too thick or have poor uniformity, increasing the interfacial impedance, and excessive butanetricarboxylic acid itself may undergo additional side reactions under high pressure, consuming effective components in the electrolyte, resulting in insignificant improvement in fast charging performance, and instead shortening the cycle life due to the accumulation of side reaction products.

[0014] In some embodiments, the butanetricarboxylic acid comprises at least one of the following structural formulas: Formula I-1, Formula I-2, Formula I-3, Formula I-4.

[0015] Exemplarily, the value of a / b may be, for example, 0.7, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, or any point value in the range consisting of any two of the above point values. If a / b is less than 0.7, the relative content of HTCN is insufficient and the content of butane trinitrile is excessive, the HTCN cannot be fully cross-linked on the basis of the initial protective layer formed by butane trinitrile, the compactness and stability of the interfacial film are reduced, the film is prone to damage in long-term high-pressure cycling, and repeated side reactions and metal ion dissolution occur, accelerating the decline of cycle life. The problems of electrolyte polarity reduction and interfacial impedance increase caused by excessive butane trinitrile are highlighted, the efficiency of lithium ion desolvation and migration is inhibited, and the fast-charging performance is difficult to achieve as expected. If a / b is greater than 7, the relative content of HTCN is excessive and the content of butane trinitrile is insufficient, butane trinitrile cannot form a sufficient initial protective layer, and HTCN is directly exposed to the surface of the positive electrode to participate in film formation. The initial side reaction is insufficiently inhibited, the amount of transition metal ion dissolution increases, and the subsequent HTCN cross-linked film is prone to structural degradation due to metal ion doping. The viscosity problem of excessive HTCN is amplified, the flowability of the electrolyte is significantly reduced, the lithium ion migration resistance increases dramatically, the ion transport rate decreases significantly during fast charging, and the interfacial impedance increase is prone to induce lithium dendrites. At the same time, the risk of side reactions of excessive HTCN also increases, ultimately leading to the deterioration of fast-charging performance and cycle life.

[0016] In some embodiments, the butane trinitrile is selected from a compound represented by formula I-1.

[0017] In some embodiments, the electrolyte comprises a dinitrile compound, the mass percentage of the dinitrile compound in the total mass of the electrolyte is denoted as c%, c satisfies: 0 < c ≤ 2, the mass percentage of the dinitrile compound may be, for example, 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1%, 1.5%, 2%, or any point value in the range between any two of the above point values, and preferably c satisfies: 0 < c ≤ 1.5. The reduction potential of the dinitrile compound in the electrolyte is significantly higher than that of the trinitrile compound, which can preferentially form a protective film on the electrode surface to inhibit the side reaction between the positive electrode material and the electrolyte, and thus the addition of a small amount of dinitrile compound can improve the cycle life performance of the battery. When the content of the dinitrile compound exceeds 2%, the main component of the protective film formed by the dinitrile compound is cyanide (such as LiCN) or poly-nitrile substances, which have weak conductivity, and excessive addition will cause the protective film to be too thick or overly covered, resulting in a sharp increase in the impedance of the positive and negative electrode interface, an increase in the migration resistance of lithium ions at the interface, a direct reduction in the lithium ion transport kinetics, and difficulty in rapid deintercalation of lithium ions during fast charging, which cannot meet the 3C fast charging requirement at 4.53V high voltage. The polarity of the dinitrile compound is weaker than that of the trinitrile, and when excessive, it will occupy the space of 1,3,6-hexanetrinitrile and butanetritrile in the electrolyte, interfere with the effective combination of the two with lithium ions, destroy the optimized lithium ion solvation sheath structure, cause the desolvation energy barrier to rise, and further weaken the fast charging performance. Although a small amount of dinitrile film can inhibit side reactions, when excessive, the thick protective film is prone to poor uniformity, and after the film layer in some areas is broken, it cannot continuously inhibit side reactions, and the effective components are consumed due to additional reactions between the dinitrile itself and the electrolyte, resulting in accelerated electrolyte decomposition, not only the cycle life improvement effect disappears, but also the battery cycle life may be shortened due to the accumulation of side reaction products.

[0018] In some embodiments, the dinitrile compound comprises one or more of adiponitrile (AND), succinonitrile (SN), ethylene glycol bis(propionitrile) ether, ethylene glycol bis(2-cyanoethyl) ether, diethylene glycol bis(2-cyanoethyl) ether, triethylene glycol bis(2-cyanoethyl) ether, tetraethylene glycol bis(2-cyanoethyl) ether, ethylene glycol bis(4-cyanobutyl) ether, and ethylene glycol bis(propionitrile) ether (DENE).

[0019] In some embodiments, the electrolyte comprises a carboxylic acid ester solvent, and the mass percentage of the carboxylic acid ester solvent in the total mass of the electrolyte is denoted as d%, and d satisfies: 18.5≤d≤65, that is, the mass percentage of the carboxylic acid ester solvent may be, for example, 18.5%, 19%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or any value within the range defined by any two of the above values. The carboxylic acid ester solvent has low viscosity and high ion conductivity, which lays a foundation for the rapid transmission of lithium ions in the electrolyte. At the same time, the oxygen atom (electron acceptor) of the ester group in the carboxylic acid ester solvent and the nitrogen atom (electron donor) of the cyano group in the tricyanohydric additive can form a weak coordination through N-O bond, so that the tricyanohydric additive can insert into the solvation sheath of lithium ions to replace part of the ester group molecules to form a mixed solvation layer. This process can significantly reduce the binding energy of lithium ions and solvent molecules, thereby reducing the desolvation energy barrier and further optimizing the lithium ion transmission kinetics required for 3C fast charging at high voltage. When the mass percentage d% of the carboxylic acid ester solvent is greater than 65%, the excessive carboxylic acid ester solvent will occupy the effective content of HTCN and BTCN, which will lead to the failure of the tricyanohydric additive to fully optimize the solvation structure and form a stable interfacial film, thereby intensifying the side reaction between the positive active material and the electrolyte, accelerating the decomposition of the electrolyte during the cycle process, and significantly shortening the cycle life of the battery.

[0020] In some embodiments, the carboxylic acid ester solvent comprises one or more of ethyl propionate, propyl propionate, methyl propionate, ethyl isobutyrate, propyl 2-methylpropionate, ethyl cyclobutanecarboxylate, ethyl 2-methylbutyrate, isopropyl butyrate, isobutyl acetate, ethyl butyrate, methyl butyrate, propyl acetate, ethyl acetate, methyl trimethylacetate, ethyl trimethylacetate, ethyl 2,2-difluoroacetate, ethyl trifluoroacetate, 2,2-difluoroethyl acetate, ethyl monofluoroacetate, monofluoroethyl acetate, trifluoroethyl acetate, propyl difluoroacetate, difluoro propyl acetate.

[0021] In some embodiments, a, b, and d satisfy: 3.5≤d / (a+b)≤40, and the value of d / (a+b) may be, for example, 3.5, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 35, 40, or any value within the range defined by any two of the above values. When the ratio of the carboxylic acid ester solvent to the total amount of HTCN and butane tricyanohydric additive satisfies the above range, a mixed solvation layer can be formed among the three, further improving the deintercalation efficiency of lithium ions at the positive and negative electrode interfaces, and optimizing the fast charging performance and cycle performance at high voltage.

[0022] It should be noted that when calculating the value of d / (a+b), a, b, and d are not calculated with units.

[0023] In some embodiments, the electrolyte comprises propylene carbonate (PC), and the mass percentage of the propylene carbonate in the total mass of the electrolyte is denoted as e%, and e satisfies: e≤8. The electrolyte of the present application also contains PC, which has a much higher dielectric constant than carboxylic acid ester solvents, can more effectively shield the electrostatic attraction between the cations and anions in the lithium salt, and make the lithium salt more easily dissociate into free ions, thereby increasing the solubility of the lithium salt, increasing the concentration of lithium ions in the electrolyte, and further improving the fast charging performance of the battery. However, the content of PC in the electrolyte cannot be too high. If e>8, too much PC will increase the viscosity of the electrolyte, reduce the migration efficiency of lithium ions in the electrolyte, and instead deteriorate the fast charging performance of the battery.

[0024] In some embodiments, the electrolyte comprises lithium salt, and the lithium salt comprises lithium hexafluorophosphate (LiPF6) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and the mass percentage of the lithium bis(trifluoromethylsulfonyl)imide in the total mass of the electrolyte is denoted as f%, and f satisfies: 3.1≤f≤11.7, i.e., the mass percentage of lithium bis(trifluoromethylsulfonyl)imide may be, for example, 3.1%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.7%, or any point value within the range of any two of the above point values. In order to increase the concentration of lithium ions in the electrolyte, it is necessary to increase the content of lithium salt in the electrolyte. The mass percentage of lithium hexafluorophosphate (LiPF6) in the electrolyte is 5%-18%, and LiPF6 is used as the main lithium salt in traditional electrolytes. If the content of LiPF6 in the electrolyte is too high, more HF will be generated by its decomposition, which will increase the risk of corrosion of other components of the battery and easily lead to the attenuation of the cycle life of the battery. The present application further adds LiTFSI to the electrolyte, LiTFSI has good thermal stability, can maintain the stability of the electrolyte system, and reduce the generation of harmful decomposition products; and the anion has a large volume and a low crystallization tendency, so that LiTFSI has good solubility and fluidity in the electrolyte, can more effectively conduct lithium ions, thereby increasing the overall conductivity of the electrolyte, and further improving the charging and discharging efficiency of the battery and the fast charging performance of the battery. However, if f%>11.7, when the content of LiTFSI in the electrolyte is too high, the passivation layer on the surface of the current collector will be destroyed, the metal aluminum will be exposed and react with TFSI - , which will cause continuous corrosion of the aluminum foil and further deteriorate the performance of the battery; and if f%<3.1%, the further improvement effect of LiTFSI on the fast charging performance of the battery is not obvious.

[0025] In some embodiments, the electrolyte comprises one or both of a lithium salt additive and a sulfur-containing additive.

[0026] In some embodiments, the lithium salt additive includes at least one of lithium difluorophosphate, lithium difluoro oxalate phosphate, lithium tetrafluoro oxalate phosphate, and lithium bis-oxalate phosphate.

[0027] In some embodiments, the mass percentage of the lithium salt additive in the total mass of the electrolyte is g%, and g satisfies 0.01≤g≤2, i.e., the mass percentage of the lithium salt additive may be, for example, 0.01%, 0.02%, 0.04%, 0.06%, 0.08%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, or any value within the range of any two of the above values. In the present application, the lithium salt additive may undergo a reduction reaction on the surface of the negative electrode to form a protective layer rich in inorganic components (LiF, Li2CO3, Li2O, Li x PO y F z etc.) on the surface of the negative electrode, significantly improving the chemical stability and mechanical strength of the SEI film, inhibiting the co-intercalation of solvent molecules, and improving the structural integrity of the negative electrode during the cycle process; the SEI film formed by the lithium salt additive can also effectively reduce the impedance of the SEI film and improve the migration rate of lithium ions, thereby improving the charge and discharge performance of the battery. If g%<0.01%, the content of the lithium salt additive is insufficient, the reduction reaction on the surface of the negative electrode is insufficient, and a complete and dense protective layer rich in inorganic components cannot be formed, and the solvent molecules of the electrolyte may co-intercalate into the negative electrode, causing the structural degradation of the negative electrode; at the same time, the interface impedance of the SEI film cannot be further reduced, the migration rate of lithium ions at the negative electrode interface is slow, and the further improvement effect on the cycle life and fast charging performance of the battery is not obvious. If g%>2%, excessive lithium salt additive may undergo excessive reduction reaction on the surface of the negative electrode, and the generated SEI film is too thick, which may cause the interface impedance to increase, the migration resistance of lithium ions at the negative electrode interface to increase, and the charge and discharge efficiency of the battery to decrease, and the fast charging performance to deteriorate. At the same time, the excessive lithium salt additive may have additional side reactions with other components in the electrolyte (such as LiPF6 and carboxylate solvents), and the by-products generated by the side reactions may accumulate at the interface between the positive electrode and the negative electrode, destroy the stability of the interface film, and consume the effective lithium source and functional additives (such as HTCN and butane trinitrile) in the electrolyte, causing the capacity to decay rapidly during the cycle process of the battery and the cycle life to be shortened.

[0028] In some embodiments, the sulfur-containing additive includes: Formula II-1, Formula II-2, Formula II-3, Formula II-4, Formula II-5, Formula II-6, Formula II-7 At least one of Formula II-8.

[0029] In some embodiments, the mass percentage of the sulfur-containing additive, based on the total mass of the electrolyte, is denoted as h%, where h satisfies 0.05 ≤ h ≤ 2.3. That is, the mass percentage of the sulfur-containing additive can be, for example, 0.05%, 0.06%, 0.08%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.3%, or any value within the range of any pairwise values ​​mentioned above. The sulfur-containing additive undergoes a reduction reaction on the negative electrode surface, generating sulfur-containing organic compounds (Li₂SO₄, ROSO₂Li, etc.), which improves the density of the SEI film structure, reduces the migration resistance of lithium ions at the interface, and thus improves the fast-charging performance of the battery. When the electrolyte contains both lithium salt additives and sulfur-containing additives, the SEI film formed on the negative electrode surface will be more dense and stable, significantly improving the battery's charge and discharge efficiency and enhancing its fast-charging performance. If h% < 0.05%, the sulfur-containing additive content is insufficient, resulting in a small amount of sulfur-containing organic compounds generated on the negative electrode surface. This insufficient amount cannot effectively fill the pores of the SEI film, leading to inadequate improvement in the SEI film's density and hindering further enhancement of the battery's fast-charging performance and cycle stability. If h% > 2.3%, excessive sulfur-containing additives will undergo excessive reduction reactions on the negative electrode surface, generating too many sulfur-containing products. On one hand, this may reduce the flexibility and increase the brittleness of the SEI film, making it prone to rupture during battery charging and discharging, thus losing its protective function for the negative electrode and exacerbating side reactions between the electrolyte and the negative electrode. On the other hand, excessive sulfur-containing additives may undergo oxidative decomposition under high pressure, generating sulfur-containing impurities (such as SO2) that corrode the positive electrode active material. They may also react with lithium salts (such as LiPF6) in the electrolyte to generate harmful acidic substances, damaging the stability of the electrolyte system and ultimately leading to a decrease in the battery's fast-charging performance and cycle life.

[0030] A second aspect of the present invention provides a battery comprising an electrolyte, a positive electrode, and a negative electrode provided in the first aspect of the present invention. The negative electrode comprises 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 comprises a negative active material, and the negative active material comprises a silicon-based material.

[0031] In some embodiments, the silicon-based material includes at least one of silicon-carbon materials or silicon-oxygen materials.

[0032] In some embodiments, the negative electrode active material further includes a carbon-based material, which includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, and soft carbon.

[0033] In some embodiments, the particle size Dv50 of the carbon-based material is 2-25 μm, for example, 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm or any value within the range defined by any two of the above values. If the particle size of the carbon-based material is too small, the bulk density is low and the electronic transmission impedance is high. If the particle size is too large, the contact area with the current collector is reduced and the electronic transmission is hindered.

[0034] In some embodiments, the particle size Dv50 of the silicon-based material is 5-15 μm, for example, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm or any value within the range defined by any two of the above values. When the particle size of the silicon-based material is within the above range, the structural stability of the negative electrode active material layer can be improved.

[0035] In the present application, the particle size Dv50 can be tested by conventional testing methods in the art, such as laser particle size testing method. For example, a Malvern particle size tester is used for measurement.

[0036] In some embodiments, the specific surface area of the silicon-based material is i m 2 / g, i satisfies 0.5≤i≤8, i.e., the specific surface area of the silicon-based material can be, for example, 0.5 m 2 / g, 1 m 2 / g, 2 m 2 / g, 3 m 2 / g, 4 m 2 / g, 5 m 2 / g, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g or any value within the range defined by any two of the above values. When the specific surface area of the silicon-based material is within the above range, the lithium ion insertion sites can be increased, the lithium ion migration path can be shortened, the ion insertion efficiency can be improved, the contact between the electrolyte and the silicon-based material can be optimized, the ion transmission rate can be ensured, and the fast charging performance of the battery can be improved. If i<0.5 m 2 / g, the lithium ion insertion sites are insufficient, the lithium ion migration distance is prolonged, the ion insertion efficiency is low, and the fast charging performance cannot be further improved. If i>8 m 2 / g, the contact area with the electrolyte is too large, the side reaction is intensified, the SEI film is easily broken, and the cycle life is attenuated. In addition, a high specific surface area can cause the silicon-based material to agglomerate, the electrode structure is unstable, and lithium dendrites can be induced.

[0037] In the present application, the specific surface area of the silicon-based material can be tested by a specific surface analyzer, which can specifically include the following steps: crushing the silicon-carbon material into powder, adding a sample with a mass of about 1 g in a sample tube, and weighing the mass of the sample and the sample tube; then placing the sample tube into a degassing station for degassing treatment, after degassing is completed, weighing the mass of the sample tube to obtain the mass of the sample after degassing. Then using the specific surface analyzer, inputting the mass data of the sample, starting the instrument to measure the sample, and the analyzer will automatically perform isothermal adsorption and desorption analysis, and the specific surface area and open pore volume are calculated by measuring the adsorption amount of nitrogen on the surface of the sample.

[0038] In some embodiments, the sphericity of the silicon-based material is denoted as j, and j satisfies 0.85≤j≤0.99, that is, the sphericity of the silicon-based material can be, for example, 0.85, 0.87, 0.89, 0.9, 0.91, 0.93, 0.95, 0.97, 0.99, or any point value in the range formed by any two of the above point values. Controlling the sphericity of the silicon-based material in the above range can optimize the particle accumulation structure of the negative electrode sheet, reduce the inter-particle voids, and improve the electrolyte wettability; reduce the transmission resistance of lithium ions between particles, and ensure smooth ion transmission during fast charging.

[0039] In some embodiments, the mass percentage of silicon element is 5%-40% based on the total mass of the negative electrode active material layer, which can be, for example, 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any point value in the range formed by any two of the above point values. If the mass percentage of silicon element is too small, the battery energy density will be limited; if it is too large, the volume expansion of the silicon-based material will be intensified, which can easily damage the SEI film and increase the side reactions.

[0040] In the present application, the mass percentage of silicon in the total mass of the negative electrode active coating can be obtained by conventional methods in the art. For example, after discharging the battery to 0% SOC, the negative electrode sheet is disassembled, soaked in dimethyl carbonate (DMC) solvent for 12 hours, then rinsed with DMC solvent to remove the lithium salt attached to the negative electrode sheet, and then dried. The negative electrode active coating can be peeled off from the negative electrode current collector after high temperature treatment of the negative electrode sheet at 400°C in an inert atmosphere (for example, in a tube furnace, under nitrogen or argon atmosphere) for 2 hours. The negative electrode active coating is collected as a test sample. Using a thermal gravimetric analyzer (for example, TGA 550 thermal gravimetric analyzer), the sample size is 5-15 mg, and the temperature is raised from room temperature (25°C) to 900°C at a rate of 10°C / min in an air or oxygen atmosphere, and held at 900°C for 40 min, so that the non-silicon components in the negative electrode active coating are volatilized while the silicon is fully oxidized to silicon dioxide. The residual material is the ash of the negative electrode active coating, and the mass content of silicon in the negative electrode active material layer can be calculated according to the mass of the ash. The calculation formula is as follows: the mass percentage of silicon in the negative electrode active material layer = 7 x mass of ash / (15 x mass of test sample).

[0041] In the present application, the sphericity of the silicon-based material can be tested by scanning electron microscopy (SEM). The test method can include the following steps: analyzing the images of each silicon-based material particle in the SEM photo under a certain magnification by image processing software (such as Image Pro Plus) to obtain the perimeter and area of each particle, and calculating the perimeter equivalent radius r1 and area equivalent radius r2 of each particle, respectively. The sphericity of each particle S = r2 / r1, and then the sphericity of each particle (for example, 50 particles) is quantitatively averaged to obtain the sphericity of the silicon-based material.

[0042] In some embodiments, the OI value of the negative electrode sheet is denoted as k, and k satisfies 9≤k≤25, i.e. the OI value of the negative electrode sheet can be, for example, 9, 10, 12, 14, 16, 18, 20, 21, 23, 25 or any point value within the range formed by any two of the above point values. The OI value of the negative electrode sheet reflects the order degree of the negative electrode material crystal. When the OI value of the negative electrode sheet is controlled within the above range, the order degree of the crystal is moderate, the lithium ion diffusion path is smooth, the embedding resistance is small, and the fast charging efficiency is improved. At the same time, the negative electrode material has a certain flexibility to cope with the volume expansion during cycling.

[0043] In the present application, the OI value of the negative electrode sheet can be tested by an X-ray diffractometer, which can specifically include the following steps: after discharging the lithium ion secondary battery to 0% SOC, disassembling and taking out the negative electrode sheet, soaking in dimethyl carbonate (DMC) solvent for 12 h, then rinsing with DMC to remove the lithium salt attached to the sheet, drying, and then testing with an X-ray powder diffractometer (such as Shimadzu XRD-6100 type X-ray diffractometer). The diffraction peak appearing at 2θ=54°-55° in the obtained diffraction spectrum is the (004) peak of graphite, and the intensity is denoted as I 004 , the diffraction peak appearing at 2θ=77°-78° is the (110) peak of graphite, and the intensity is denoted as I 110 , and the OI value of the negative electrode sheet is I 004 / I 110 .

[0044] In some embodiments, a plurality of grooves are arranged on the side surface of the negative electrode active material layer away from the negative electrode current collector. In the present application, the grooves arranged on the negative electrode active material layer embed the surface of the active material layer to construct a low-impedance electron transmission channel, effectively improving the electronic conductivity of the silicon-based material and relieving the polarization phenomenon caused by the poor intrinsic conductivity of silicon. At the same time, the grooves can serve as a temporary reservoir for electrolyte, continuously supplying electrolyte to the active material layer during fast charging, avoiding the interruption of lithium ion transmission caused by local electrolyte drying. In addition, the micron-level groove structure accelerates the penetration of electrolyte through capillary action, significantly shortens the infiltration time, and especially improves the poor electrolyte infiltration problem of high-density electrode sheets.

[0045] In the present application, the grooves can be formed by conventional technical means in the art, for example, laser drilling, wire punching process can be used to form the grooves.

[0046] In the present application, the shape of the groove is not specifically limited, for example, it can be a linear groove.

[0047] In some embodiments, the distance between adjacent grooves is 0.5mm-10mm, for example, it can be 0.5mm, 1mm, 2mm, 4mm, 6mm, 8mm, 10mm or any value within the range of two adjacent values. The distance between adjacent grooves can be understood as the shortest straight distance between the two nearest adjacent grooves on the surface of the negative electrode sheet in the length direction of the negative electrode sheet, which is denoted as the distance between adjacent grooves. If the groove distance is less than 0.5mm, the groove density is too high, which will reduce the effective active material carrying area and the battery energy density, and may also cause the mechanical strength of the electrode sheet to decrease due to the high density of the grid structure. If the groove distance is greater than 10mm, the electron transmission channel will be insufficiently covered, which cannot effectively reduce the overall impedance, and the electrolyte storage and penetration path will be reduced, which cannot significantly improve the problem of local electrolyte drying during fast charging.

[0048] In some embodiments, the width of the groove is 50 μm-500 μm, for example, the width of the groove can be 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm or any value within the range consisting of any two of the above-mentioned values. The width of the groove can be understood as the "diameter of the groove", that is, in the direction parallel to the negative electrode sheet, the maximum straight-line distance between the two inner side edges in the groove. If the groove width is less than 50 μm, the amount of electrolyte storage will be limited, and the replenishment capacity will be insufficient during fast charging; if the groove width is greater than 500 μm, it will occupy too much active material space, reduce the energy density, and at the same time, the capillary action will be weakened, the electrolyte penetration speed will be slowed down, and the wettability will be reduced.

[0049] In some embodiments, the depth of the groove is 3 μm-45 μm, for example, it can be 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or any value within the range consisting of any two of the above-mentioned values. The depth of the groove can be understood as the vertical distance from the surface of the negative active material layer to the bottom of the groove, and the groove does not penetrate the negative current collector. If the groove depth is too shallow, the amount of electrolyte storage will be insufficient to meet the fast charging demand, and the embedded depth of the electron transport channel will be insufficient, and the polarization improvement effect will be limited; if the groove depth is too deep, it will weaken the structural stability of the negative active material layer, and the interlayer cracking will be easily caused by the volume expansion of the silicon-based material during the charge and discharge cycle, affecting the integrity of the electrode sheet.

[0050] In the present application, the distance between adjacent grooves, the width of the groove, and the depth of the groove can be observed and tested by conventional methods in the art, for example, by using a scanning electron microscope to test, and after randomly selecting a certain number of grooves (for example, 10) under the scanning electron microscope, the average value is obtained.

[0051] In some embodiments, the positive electrode sheet comprises a positive current collector and a positive active material layer arranged on at least one side surface of the positive current collector, and the positive active material layer comprises a lithium cobalt oxide material.

[0052] In some embodiments, the Dv50 of the lithium cobalt oxide material is 8 μm-25 μm, for example, it can be 8 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 19 μm, 21 μm, 23 μm, 25 μm or any value within the range consisting of any two of the above-mentioned values. The Dv50 of the lithium cobalt oxide material in the above-mentioned range can ensure uniform particle accumulation to optimize the wettability of the electrolyte, shorten the deintercalation path of ions inside the positive electrode, reduce the stress between particles to avoid the cracking of the cycled electrode sheet, and improve the fast charging and cycling performance of the battery.

[0053] In some embodiments, the specific surface area of the lithium cobalt oxide material is 0.075 m 2 / g-0.325 m 2 / g, for example, can be 0.075 m 2 / g, 0.125 m 2 / g, 0.14 m 2 / g, 0.16 m 2 / g, 0.18 m 2 / g, 0.2 m 2 / g, 0.225 m 2 / g, 0.3 m 2 / g, 0.325 m 2 / g, or any value within the range defined by any two of the above values. The specific surface area of the lithium cobalt oxide material within the above range can provide sufficient active sites to ensure fast charging kinetics, while avoiding excessive contact, reducing cobalt ion elution, and maintaining the stability of the positive electrode structure.

[0054] In some embodiments, the lithium cobalt oxide material includes a doping element, the doping element includes an aluminum element, the mass percentage of the doping element in the total mass of the lithium cobalt oxide material is 5000 ppm-15000 ppm, for example, can be 5000 ppm, 7000 ppm, 8000 ppm, 10000 ppm, 11000 ppm, 13000 ppm, 15000 ppm or any value within the range defined by any two of the above values. Aluminum doping can stabilize the layered structure of the positive electrode material, inhibit the occurrence of adverse phase transitions at high voltages (such as ≥4.53V), reduce the change in lattice parameters (such as c-axis contraction), maintain structural integrity, effectively inhibit the precipitation of lattice oxygen, and reduce the risk of thermal runaway. Aluminum doping stabilizes the lattice structure, inhibits phase transition and oxygen precipitation, and butanetricarboxylic acid inhibits metal elution, removes acid and water, and improves interface stability. The synergistic effect of the two can effectively improve the cycle stability and safety of the battery under fast charging conditions. This dual optimization of "structure + interface" can further improve the fast charging cycle life of the battery. If the aluminum content is less than 5000 ppm, the stabilizing effect on the layered structure is weak, and the effect of further improving the thermal safety of the battery is reduced; if the aluminum content is more than 15000 ppm, excess Al 3+ will occupy the lattice sites of Co 3+ , reducing the theoretical capacity of the lithium cobalt oxide material.

[0055] In the present application, the content of aluminum in the total mass of the positive electrode active material can be tested by ICP-MS (inductively coupled plasma mass spectrometry).

[0056] In some embodiments, the charge cut-off voltage of the battery is greater than or equal to 4.53V. The battery described in the present application is suitable for high-voltage charging systems, and can balance high temperature and kinetic performance under high-voltage systems.

[0057] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0058] The materials, reagents and the like used in the following examples can be obtained from commercial channels unless otherwise specified.

[0059] The present application will be described in detail below with reference to specific embodiments, which are used to understand but not to limit the present application.

[0060] Example 1 1) Preparation of positive electrode sheet The positive electrode active material lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), SP (super P) and carbon nanotubes (CNT) are mixed in a mass ratio of 96:2:1.5:0.5, N-methyl pyrrolidone (NMP) is added, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a homogeneous and flowable positive electrode active paste; the positive electrode active paste is uniformly coated on both surfaces of an aluminum foil; the coated aluminum foil is dried, then subjected to rolling and slitting to obtain the required positive electrode sheet.

[0061] 2) Preparation of negative electrode sheet The negative electrode active material artificial graphite, silicon-carbon material, sodium carboxymethyl cellulose (CMC-Na), butadiene rubber, and conductive carbon black (SP) are mixed in a mass ratio of 70:24.5:2.5:1.5:1.5, deionized water is added, and a negative electrode active paste is obtained under the action of a vacuum stirrer; the negative electrode active paste is uniformly coated on both surfaces of a copper foil; the coated copper foil is dried at room temperature, then transferred to a 80°C oven for drying for 10h, then subjected to cold pressing, slitting, cleaning and sheet making to obtain the negative electrode sheet, wherein the content of silicon element in the negative electrode active layer accounts for 10%, and the adjustment of the content of silicon element can be achieved by adjusting the content of silicon-carbon material in the negative electrode active layer or the content of silicon element in the silicon-carbon material.

[0062] 3) Preparation of electrolyte In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), PC, PP, EP, vinyl carbonate (EC), fluoro-vinyl carbonate (FEC) were uniformly mixed, then HTCN, butanetricarboxylic acid (formula I-1) and sulfur-containing additive (formula II-1) were added, then fully dried LiPF6 was added, after stirring uniformly, the obtained electrolyte passed the moisture and free acid detection, and the desired electrolyte was obtained. Among them, the components included the following mass proportions based on the total mass of the electrolyte: 2.5% of HTCN, 1.5% of butanetricarboxylic acid, 37.5% of carboxylic acid ester solvent (wherein PP:EP = 4:1), 5% of PC, 11% of LiPF6, 0.5% of sulfur-containing additive, and 42% of the sum of EC and FEC (wherein EC:FEC = 1:3).

[0063] 4) Preparation of lithium ion battery The positive electrode sheet of step 1), the negative electrode sheet of step 2) and the separator (8 μm thick polyethylene separator, provided by Asahi Kasei) were stacked in the order of positive electrode sheet, separator, negative electrode sheet and separator, and the number of stacked negative electrode sheets was 26, to obtain a battery core; the battery core was placed in an outer packaging aluminum foil; the electrolyte of step 3) was injected into the outer packaging, and after vacuum packaging, standing, formation, shaping, sorting and other processes, a lithium ion battery was obtained.

[0064] The battery of the present application has a charge-discharge range of 3.0V-4.55V.

[0065] 5) Performance test i) 5C rate performance test The batteries obtained in the examples and comparative examples were charged at 0.2C to a voltage of 4.55V at 25℃, then charged at 4.55V to a current of 0.05C, and then discharged at 0.2C to a voltage of 3.0V, which was one charge-discharge cycle, and the discharge capacity of the 3rd cycle was counted as x mAh. Then the batteries obtained in the examples and comparative examples were charged at 0.7C to a voltage of 4.55V at 25℃, then charged at 4.55V to a current of 0.05C, and then discharged at 5C to a voltage of 3.0V, which was one charge-discharge cycle, and the discharge capacity of the 3rd cycle was counted as y mAh. The discharge capacity retention rate of the battery at 5C was represented by y / x.

[0066] ii) 3C cycle life test The batteries obtained in the examples and comparative examples were charged at 25°C at 3C constant current to 4.55V, then charged at 4.55V constant voltage to 0.05C current, rested for 5min, then discharged at 3C constant current to 3.0V, which was one charge-discharge cycle. The discharge capacity of the first week was x mAh, the discharge capacity of the Nth week was y mAh; the capacity of the Nth week divided by the capacity of the first week, the cycle capacity retention rate R of the Nth week was y / x, and the cycle number of the battery when the cycle capacity retention rate was 80% was recorded.

[0067] Examples 2-1, 2-2 and 2-3 were prepared according to Example 1, specifically, in Example 2-1, the mass fraction of 1,3,6-hexanetricarboxylic acid was 0.6%, the mass fraction of butanetricarboxylic acid was 0.8%, and a / b was 0.75; in Example 2-2, the mass fraction of 1,3,6-hexanetricarboxylic acid was 4.5%, the mass fraction of butanetricarboxylic acid was 1.5%, and a / b was 3; in Example 2-3, the mass fraction of 1,3,6-hexanetricarboxylic acid was 4.2%, the mass fraction of butanetricarboxylic acid was 0.6%, and a / b was 7. The mass fraction of the above components was changed by adaptively adjusting the total mass fraction of EC and FEC in the electrolyte.

[0068] Examples 2-4, 2-5 and 2-6 were prepared according to Example 1, and a dinitrile compound (adiponitrile) was further added to the electrolyte, specifically, in Example 2-4, the mass fraction of the dinitrile compound was 2%; in Example 2-5, the mass fraction of the dinitrile compound was 1.5%; in Example 2-6, the mass fraction of the dinitrile compound was 3%. The mass fraction of the above components was changed by adaptively adjusting the total mass fraction of EC and FEC in the electrolyte.

[0069] Examples 2-7 and 2-8 were prepared according to Example 1, specifically, in Example 2-7, the mass fraction of PC was 8%, and butanetricarboxylic acid represented by Formula I-2 was selected; in Example 2-8, butanetricarboxylic acid represented by Formula I-4 was selected. The mass fraction of the above components was changed by adaptively adjusting the total mass fraction of EC and FEC in the electrolyte.

[0070] Example 3-1, Example 3-2, Example 3-3, Example 3-4 are carried out according to Example 1, mainly verifying the range of d / (a+b), specifically, in Example 3-1, the mass ratio of 1,3,6-hexanetricarboxylic acid is 3%, the mass ratio of butane tricarboxylic acid is 3%, the total mass ratio of carboxylic acid ester solvent is 18.5%, and the value of d / (a+b) is 3.08; in Example 3-2, the mass ratio of 1,3,6-hexanetricarboxylic acid is 2.7%, the mass ratio of butane tricarboxylic acid is 2.5%, the total mass ratio of carboxylic acid ester solvent is 18.5%, and the value of d / (a+b) is 3.56; in Example 3-3, the mass ratio of 1,3,6-hexanetricarboxylic acid is 1%, the mass ratio of butane tricarboxylic acid is 0.5%, the total mass ratio of carboxylic acid ester solvent is 60%, and the value of d / (a+b) is 40; in Example 3-4, the mass ratio of 1,3,6-hexanetricarboxylic acid is 0.5%, the mass ratio of butane tricarboxylic acid is 0.5%, the total mass ratio of carboxylic acid ester solvent is 60%, and the value of d / (a+b) is 60. Among them, the mass ratio of the above components is changed by adaptively adjusting the total mass ratio of EC and FEC in the electrolyte.

[0071] Example 3-5 and Example 3-6 are carried out according to Example 1, further adding DFEA in the electrolyte, and no longer adding PP and EP contained in the original electrolyte, specifically, the mass ratio of DFEA in Example 3-5 is 35%; the mass ratio of DFEA in Example 3-6 is 50%. Among them, the mass ratio of the above components is changed by adaptively adjusting the total mass ratio of EC and FEC in the electrolyte.

[0072] Example 4-1, Example 4-2, Example 4-3 are carried out according to Example 1, specifically, the mass ratio of PC in Example 4-1 is 15%; the mass ratio of sulfur-containing additive (DTD) in Example 4-2 is 0.05%; the mass ratio of sulfur-containing additive in Example 4-3 is 2.3%. Among them, the mass ratio of the above components is changed by adaptively adjusting the total mass ratio of EC and FEC in the electrolyte.

[0073] Example 5-1, Example 5-2, Example 5-3 are carried out according to Example 1, further adding LITFSI in the electrolyte, specifically, the mass ratio of LITFSI in Example 5-1 is 8%; the mass ratio of LITFSI in Example 5-2 is 3.1%; the mass ratio of LITFSI in Example 5-3 is 11.7%. Among them, the mass ratio of the above components is changed by adaptively adjusting the total mass ratio of EC and FEC in the electrolyte.

[0074] Example 6-1, Example 6-2, Example 6-3 are performed according to Example 1, further adding LiPO2F2 in electrolyte, specifically, the mass ratio of LiPO2F2 in Example 6-1 is 0.3%; the mass ratio of LiPO2F2 in Example 6-2 is 0.01%; the mass ratio of LiPO2F2 in Example 6-3 is 2%. Example 7 is performed according to Example 1, further adding LITFSI and LiPO2F2 in electrolyte, specifically, the mass ratio of LITFSI in Example 7 is 8%, the mass ratio of LiPO2F2 is 0.3%. The mass ratio of the above components is changed by adaptively adjusting the total mass ratio of EC and FEC in the electrolyte.

[0075] Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4 are performed according to Example 1, specifically, in Comparative Example 1, the mass ratio of 1,3,6-hexanetricarboxylic acid is 1.5%, the mass ratio of butanetricarboxylic acid is 4%, the value of a / b is 0.38; in Comparative Example 2, the mass ratio of 1,3,6-hexanetricarboxylic acid is 4.5%, the mass ratio of butanetricarboxylic acid is 0.5%, the value of a / b is 9; in Comparative Example 3, no butanetricarboxylic acid is added, and an equivalent amount of hexanedinitrile with a mass ratio of 1.5% is used to replace it; in Comparative Example 4, no 1,3,6-hexanetricarboxylic acid and butanetricarboxylic acid is added, and an equivalent amount of hexanedinitrile with a mass ratio of 4% is used to replace it. The mass ratio of the above components is changed by adaptively adjusting the total mass ratio of EC and FEC in the electrolyte.

[0076] Table 1 Example 8 group is performed according to Example 1, the main difference is shown in Table 2. Among them, the Dv50 of the carbon-based material in Example 1 is 18 μm, and the thickness of the negative electrode active material layer is 50 μm.

[0077] Table 2 Example 9 group is performed according to Example 7, and the slitted negative electrode sheet is subjected to laser groove forming, and grooves are arranged on the entire surface of the negative electrode sheet. Here, the grooves are matrix linear grooves, and the main difference is shown in Table 3.

[0078] Table 3 Example 10 group is performed according to Example 9-1, and the positive electrode active material is further doped with aluminum element, and the main difference is shown in Table 4.

[0079] Table 4 From the above, the application can improve the fast charging performance and cycle life of the battery under high voltage by adding 1,3,6-hexanetricarbonitrile and butanetricarbonitrile in the electrolyte and controlling the mass ratio of each in the electrolyte and the proportional relationship between the two.

[0080] It should be noted that in this document, the terms "comprising", "including", or any other variant thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements, but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without more limitations, an element defined by the statement "comprising a" does not exclude the existence of additional identical elements in the process, method, article, or apparatus that includes the element. In addition, it should be pointed out that the scope of the methods and apparatus in the embodiments of the application is not limited to performing functions in the order shown or discussed, but can also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved, for example, the described method can be performed in an order different from that described, and various steps can also be added, omitted, or combined. In addition, the features described with reference to certain examples can be combined in other examples.

[0081] The above only describes the preferred embodiments of the application and is not intended to limit the application. Any modification, equivalent replacement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. An electrolyte, characterized by, The electrolyte comprises 1,3,6-hexanetricarbonitrile and butanetricarbonitrile, the mass percentage of the 1,3,6-hexanetricarbonitrile in the total mass of the electrolyte is denoted as a%, and the mass percentage of the butanetricarbonitrile in the total mass of the electrolyte is denoted as b%; a and b satisfy: 0.5≤a≤4.5, 0.5≤b≤4.1, 0.7≤a / b≤7.

2. The electrolyte according to claim 1, characterized in that, The electrolyte comprises a dinitrile compound, the mass percentage of the dinitrile compound in the total mass of the electrolyte is denoted as c%, and c satisfies: 0 Preferably, c satisfies: 0 Preferably, the dinitrile compound comprises one or more of hexanedinitrile, butanedinitrile, ethylene glycol bis(propionitrile) ether, ethylene glycol bis(2-cyanoethyl) ether, diethylene glycol bis(2-cyanoethyl) ether, triethylene glycol bis(2-cyanoethyl) ether, tetraethylene glycol bis(2-cyanoethyl) ether, ethylene glycol bis(4-cyanobutyl) ether, and ethylene glycol bis(propionitrile) ether; And / or, the butanetricarbonitrile comprises at least one of the following structural formulas: Formula I-1, Formula I-2, Formula I-3, Formula I-4.

3. The electrolyte of claim 1, wherein The electrolyte comprises a carboxylic acid ester solvent, the mass percentage of the carboxylic acid ester solvent in the total mass of the electrolyte is denoted as d%, and d satisfies: 18.5≤d≤65; and / or, the carboxylic acid ester solvent comprises one or more of ethyl propionate, propyl propionate, methyl propionate, ethyl isobutyrate, propyl 2-methylpropionate, ethyl cyclobutanecarboxylate, ethyl 2-methylbutyrate, isopropyl butyrate, isobutyl acetate, ethyl butyrate, methyl butyrate, propyl acetate, ethyl acetate, methyl trimethylacetate, ethyl trimethylacetate, ethyl 2,2-difluoroacetate, ethyl trifluoroacetate, 2,2-difluoroethyl acetate, ethyl monofluoroacetate, monofluoroethyl acetate, trifluoroethyl acetate, propyl difluoroacetate, difluoroethyl propionate.

4. The electrolyte according to claim 3, characterized in that The a, b, and d satisfy: 3.5≤d / (a+b)≤40.

5. The electrolyte of claim 1, wherein The electrolyte comprises propylene carbonate, the mass percentage of the propylene carbonate in the total mass of the electrolyte is denoted as e%; e satisfies: e≤8; And / or, the electrolyte comprises a lithium salt, the lithium salt comprises lithium hexafluorophosphate and lithium bis(trifluoromethylsulfonyl)imide, the mass percentage of the lithium bis(trifluoromethylsulfonyl)imide in the total mass of the electrolyte is denoted as f%, and f satisfies: 3.1≤f≤11.

7.

6. The electrolyte of claim 1, wherein The electrolyte comprises one or both of a lithium salt additive and a sulfur-containing additive, and the electrolyte satisfies at least one of the following conditions: (1) The lithium salt additive comprises at least one of lithium difluorophosphate, lithium difluoro oxalate phosphate, lithium tetrafluoro oxalate phosphate, and lithium bisoxalate phosphate; (2) The mass percentage of the lithium salt additive in the total mass of the electrolyte is denoted as g%, and g satisfies: 0.01≤g≤2, (3) The sulfur-containing additive comprises: Formula II-1, Formula II-2, Formula II-3, Formula II-4, Formula II-5, Formula II-6, at least one of Formula II-7, at least one of Formula II-8; (4) The mass percentage of the sulfur-containing additive in the total mass of the electrolyte is denoted as h%, and h satisfies: 0.05≤h≤2.

3.

7. A battery, characterized by The battery comprises the electrolyte, the positive electrode sheet, and the negative electrode sheet according to any one of claims 1-6, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises a silicon-based material.

8. The battery of claim 7, wherein, The specific surface area of the silicon-based material is denoted by i m 2 / g, i satisfying 0.5≤i≤8; And / or, the sphericity of the silicon-based material is denoted as j, and j satisfies 0.85≤j≤0.99; And / or, the OI value of the negative electrode sheet is denoted as k, and k satisfies 9≤k≤25.

9. The battery according to claim 7 or 8, characterized in that, A plurality of grooves are arranged on the side surface of the negative electrode active material layer away from the negative electrode current collector, and the grooves satisfy at least one of the following conditions: (1) The distance between adjacent grooves is 0.5mm-10mm; (2) The width of the groove is 50μm-500μm; (3) The depth of the groove is 3μm-45μm.

10. The battery of claim 7 or 8, wherein, 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 comprises a lithium cobalt oxide material, and the lithium cobalt oxide material satisfies at least one of the following conditions: (1) The Dv50 of the lithium cobalt oxide material is 8μm-25μm; (2) the specific surface area of the lithium cobaltate material is 0.075 m 2 / g-0.325 m 2 / g; (3) The lithium cobalt oxide material comprises a doping element, the doping element comprises an aluminum element, and the mass fraction of the doping element in the total mass of the lithium cobalt oxide material is 5000ppm-15000ppm.

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