Secondary batteries, battery modules, battery packs, and power consumption devices

Abstract

To provide a secondary battery, a battery module, a battery pack, and a power consumption device that can provide both a design with high group tolerance and high safety performance to a secondary battery and also can provide good cycle performance and dynamic performance to a secondary battery.SOLUTION: The secondary battery includes: a battery case; and an electrode assembly and a nonaqueous electrolyte accommodated in the battery case. The nonaqueous electrolyte includes a compound represented by Formula I. The mass percentage content of the compound represented by Formula I is A1% based on the total mass of the nonaqueous electrolyte. The group tolerance of the secondary battery is B, and the secondary battery satisfies the relation that B is 0.88 to 0.99, and B / A1 is 0.5 to 45.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application belongs to the field of battery technology and specifically relates to secondary batteries, battery modules, battery packs, and power consumption devices. [Background technology]

[0002] In recent years, secondary batteries have been widely applied in various fields, including energy storage and power systems such as hydroelectric, thermal, wind, and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. With the increasing application and proliferation of secondary batteries, the demand for higher energy density is constantly rising. A commonly adopted technique to improve the energy density of secondary batteries is to design them with increasingly larger group margins. However, this results in increasingly smaller residual space within the battery. Consequently, there is insufficient space to accommodate gases generated during processes such as chemical conversion, charging / discharging, and storage, leading to continuously increasing pressure on the battery case and seriously impacting the safety performance of the secondary battery. Therefore, there is a need for secondary batteries that achieve both high energy density and high safety performance. [Overview of the project]

[0003] The objective of this invention is to provide a secondary battery, battery module, battery pack, and power consumption device that can achieve both a high group margin design and high safety performance in a secondary battery, while also providing the secondary battery with good cycle performance and dynamic performance.

[0004] A first aspect of the present application is a secondary battery comprising a battery case, an electrode assembly and a non-aqueous electrolyte housed within the battery case, wherein the non-aqueous electrolyte comprises a compound represented by formula I. The present invention provides a secondary battery in which the mass percentage content of the compound represented by formula I is A1%, the group margin of the secondary battery is B relative to the total mass of the non-aqueous electrolyte, and the secondary battery satisfies the conditions that B is 0.88 to 0.99 and B / A1 is 0.5 to 45. [ka] In Formula I, X and Y independently represent a hydrogen atom, a halogen atom, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C6-C20 aryl group, a C1-C20 halogenated alkyl group, a C2-C20 halogenated alkenyl group, a C2-C20 halogenated alkynyl group, a C6-C20 halogenated aryl group, a C1-C20 alkoxy group, a C2-C20 alkenyloxy group, a C2-C20 alkynyloxy group, a C6-C20 halogenated aryloxy group, a C1-C20 halogenated alkoxy group, a C2-C20 halogenated alkenyloxy group, a C2-C20 halogenated alkynyloxy group, a C6-C20 halogenated aryloxy group, or a combination thereof, and at least one of X and Y represents a fluorine atom or a group containing a fluorine atom.

[0005] As a result of research conducted by the inventors of this invention, when a non-aqueous electrolyte contains a compound represented by formula I, and the content A1% of the compound and the group margin B of the secondary battery satisfy the condition that B / A1 is between 0.5 and 45, the secondary battery can achieve both a high group margin design and high safety performance, as well as good cycle performance and dynamic performance. On the other hand, the compound represented by formula I simultaneously forms a uniform, dense, and stable interfacial film on the positive and negative electrodes, reducing direct contact between the active material (positive electrode active material and negative electrode active material) and the non-aqueous electrolyte, reducing damage and regeneration of the positive electrode interfacial film and negative electrode interfacial film, further reducing gas generation and consumption of active lithium ions in this process, reducing gas expansion of the battery, and improving the battery's capacity retention rate. On the other hand, the compound represented by formula I stabilizes the crystal structure of the positive electrode active material, reducing the deposition of lattice oxygen and the elution of transition metal ions, further reducing a series of side reactions resulting therefrom, and reducing gas expansion of the battery.

[0006] In any embodiment of the present invention, B is 0.90 to 0.95. This allows the secondary battery to have a high energy density without affecting the safety performance of the secondary battery.

[0007] In any embodiment of the present application, B / A1 is 4 to 20, preferably 10 to 20. This allows the compound represented by formula I to fully exert its effect of reducing gas generation and improving the volume retention rate.

[0008] In any embodiment of the present application, A1 is 0.02 or more and less than 2, preferably 0.02 to 1. This contributes to better reducing gas generation and active lithium ion consumption, thereby reducing gas expansion of the battery and improving capacity retention.

[0009] In any embodiment of the present application, the non-aqueous electrolyte further comprises a first lithium salt, the first lithium salt being lithium hexafluorophosphate. The mass percentage content of the first lithium salt is A2%, where A2 is greater than 0 and less than or equal to 14, and preferably between 6 and 14, according to the total mass of the non-aqueous electrolyte.

[0010] In any embodiment of the present application, preferably 10 ≤ A2 / A1 ≤ 600, and more preferably 60 ≤ A2 / A1 ≤ 600. This contributes to improving the capacity retention rate of the secondary battery while reducing gas generation in the secondary battery.

[0011] In any embodiment of the present application, 0 < 10A1 + A2 / 5 ≤ 15, preferably 2.6 ≤ 10A1 + A2 / 5 ≤ 5. This reduces gas generation in the secondary battery while contributing to an improvement in the capacity retention rate of the secondary battery.

[0012] In any embodiment of the present application, the non-aqueous electrolyte further comprises a second lithium salt. The second lithium salt is a lithium fluorosulfonylimide salt. Preferably, the molecular formula of the lithium fluorosulfonylimide salt is LiN(SO2R1)(SO2R2), where R1 and R2 are independently F or C. n F 2n+1represents, and n is an integer from 1 to 10. Based on the total mass of the non-aqueous electrolyte, the mass percentage content of the second lithium salt is A3%. Preferably, 0 < A3 ≦ 2.5, more preferably 0.5 ≦ A3 ≦ 2.0. Thereby, the rate performance of the secondary battery can be improved while improving the safety of the secondary battery.

[0013] In any embodiment of the present application, preferably 0.25 ≦ A3 / A1 ≦ 25, more preferably 4 ≦ A3 / A1 ≦ 20. Thereby, the rate performance of the secondary battery can be improved by further reducing the internal resistance of the secondary battery without degrading the cycle performance and storage performance of the secondary battery.

[0014] In any embodiment of the present application, A3 / A2 is 0.5 or less, preferably 0.02 to 0.2. Thereby, the non-aqueous electrolyte is less prone to hydrolysis, can achieve both higher thermal stability, and contributes to the formation of an interfacial film with lower resistance.

[0015] In any embodiment of the present application, the non-aqueous electrolyte further comprises fluoroethylene carbonate having a mass percentage content of C1% based on the total mass of the non-aqueous electrolyte. Preferably, 0 < C1 ≦ 5, more preferably 0.5 ≦ C1 ≦ 3. Thereby, the cycle performance of the secondary battery can be effectively improved.

[0016] In any embodiment of the present application, preferably 5 ≦ C1 / A1 ≦ 50, more preferably 10 ≦ C1 / A1 ≦ 30. This is advantageous for fully exerting the further improvement effect of fluoroethylene carbonate on the cycle performance of the secondary battery.

[0017] In any embodiment of the present application, the non-aqueous electrolyte further comprises a water-removing additive including hexamethyldisilazane, tris(trimethylsilyl) phosphate, or a combination thereof. The mass percent content of the water-removing additive, based on the total mass of the non-aqueous electrolyte, is C2%. Preferably, C2 is greater than 0 and equal to or less than 2, more preferably from 0.01 to 2. Thereby, gas swelling of the secondary battery can be further improved, and the secondary battery can better achieve both a high group margin design and high safety performance.

[0018] In any embodiment of the present application, the non-aqueous electrolyte comprises an organic solvent. Based on the total mass of the organic solvent, the organic solvent comprises: a first solvent comprising at least one selected from ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate and vinylethylene carbonate, wherein the mass percent content of the first solvent in the organic solvent is D1%; a second solvent comprising at least one selected from ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate and ethyl propyl carbonate, wherein the mass percent content of the second solvent in the organic solvent is D2% based on the total mass of the organic solvent; and a third solvent comprising at least one selected from methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate and ethyl butyrate, wherein the mass percent content of the third solvent in the organic solvent is D3% based on the total mass of the organic solvent, wherein for the organic solvent, D1 is greater than 0 and equal to or less than 20, D2 is from 50 to 90, and D3 is from 0 to 30. Preferably, D1 is from 0.5 to 20, more preferably from 10 to 20.

[0019] In any embodiment of the present application, the electrode assembly comprises a positive electrode plate and a negative electrode plate. The capacity of the positive electrode plate is Q1 Ah, and the capacity of the negative electrode plate is Q2 Ah. The secondary battery satisfies 1 < Q2 / Q1 < 1.05 and A1 < B. Thereby, the secondary battery can achieve both high energy density, high safety performance and good dynamic performance.

[0020] In any embodiment of the present application, at least one of X and Y represents a fluorine atom. Preferably, both X and Y represent fluorine atoms. The presence of fluorine atoms contributes to the formation of thinner positive and / or negative electrode interface films, thereby contributing to the uniform transport of lithium ions and effectively suppressing the formation of lithium dendrites.

[0021] In any embodiment of the present application, the compound represented by formula I includes at least one of the following compounds. [ka]

[0022] In any embodiment of the present application, the material of the battery case includes at least one of a hard plastic case, aluminum, and stainless steel.

[0023] A second aspect of the present application provides a battery module including the secondary battery of the first aspect of the present application.

[0024] A third aspect of the present application provides a battery pack including one of the secondary battery of the first aspect of the present application and one of the battery module of the second aspect of the present application.

[0025] A fourth aspect of the present application provides a power consumption device comprising at least one of the secondary battery of the first aspect of the present application, the battery module of the second aspect, and the battery pack of the third aspect.

[0026] The battery module, battery pack, and power consumption device of this application include a secondary battery according to this application, and therefore have at least the same advantages as the aforementioned secondary battery. [Brief explanation of the drawing]

[0027] To more clearly illustrate the technical concept of the embodiments of this application, the drawings that need to be used in the embodiments of this application are briefly described below. Obviously, the drawings described below represent only a few embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0028] [Figure 1] This is a schematic diagram of one embodiment of the secondary battery of the present invention. [Figure 2] Figure 1 is a schematic diagram of an exploded view of an embodiment of a secondary battery. [Figure 3] This is a schematic diagram of one embodiment of the battery module of the present invention. [Figure 4] This is a schematic diagram of one embodiment of the battery pack of the present invention. [Figure 5] Figure 4 is an exploded schematic diagram of an embodiment of the battery pack shown. [Figure 6] This is a schematic diagram of one embodiment of a power consumption device that includes a secondary battery of the present invention as a power source. The drawing is not necessarily drawn to the actual scale. Reference numerals indicate the following components: 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 secondary battery, 51 battery case, 52 electrode assembly, and 53 cover plate. [Modes for carrying out the invention]

[0029] Hereinafter, embodiments specifically disclosing the secondary battery, battery module, battery pack, and power consumption device of the present application will be described in detail with reference to the drawings as appropriate. However, unnecessary details may be omitted. For example, detailed explanations of already well-known matters and redundant explanations of the same actual structure may be omitted. This is to avoid the following explanation becoming unnecessarily verbose and to facilitate understanding for those skilled in the art. Furthermore, the drawings and the following explanation are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0030] The “range” disclosed herein is limited in the form of a lower limit and an upper limit, and a given range is limited by selecting one lower limit and one upper limit, which in particular define the boundaries of the range. Ranges limited in this manner may or may not include endpoints and can be combined in any way, that is, any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also expected. Similarly, if the minimum range values ​​1 and 2, and the maximum range values ​​3, 4 and 5 are listed, the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all expected. In this application, unless otherwise stated, the numerical range “a-b” represents a contracted representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" in this specification refers to all real numbers between "0 to 5", and "0 to 5" is a contracted representation of combinations of these numbers. Also, when a parameter is described as being an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0031] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions, and such technical solutions should be considered to be included in the disclosures of this application.

[0032] Unless otherwise specified, all technical features and selectable technical features of this application can be combined to form new technical solutions, and such technical solutions should be considered to be included in the disclosures of this application.

[0033] Unless otherwise specified, all steps of this invention may be performed sequentially or randomly, but preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, if the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or it may further include steps (c), (a), and (b), and so on.

[0034] Unless otherwise specified, the terms “have,” “equip,” and “include” as used in this application may be open or closed. For example, “have,” “equip,” and “include” may further have, equip, or include other components not listed, or may equip or include only the listed components.

[0035] Unless otherwise specified, the term “or” is inclusive in this application. For example, the phrase “A or B” means “A, B, or both A and B.” More specifically, any of the following conditions satisfy the “A or B” condition: A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or both A and B are true (or exist).

[0036] Throughout this specification, substituents of compounds are disclosed in groups or ranges. Such descriptions are clearly expected to be that each member of these groups and ranges is a separate subcombination. For example, the term “C1-C6 alkyl group” is clearly expected to be disclosing alkyl groups of C1, C2, C3, C4, C5, C6, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C6, C2-C5, C2-C4, C2-C3, C3-C6, C3-C5, C3-C4, C4-C6, C4-C5 and C5-C6 individually.

[0037] In this application, group margin refers to the ratio of the actual internal cross-sectional area of ​​a secondary battery to its maximum internal cross-sectional area, i.e., the packing efficiency. There are two methods for calculating group margin, as follows: (1) Group margin = Total cross-sectional area of ​​electrode assembly / Internal space area of ​​battery case (2) Group margin = Thickness of electrode assembly / Inner thickness of battery case

[0038] In this application, the terms "multiple" and "multiple types" refer to two or more types.

[0039] A secondary battery typically includes an electrode assembly, a non-aqueous electrolyte, and an outer casing for sealing the electrode assembly and the non-aqueous electrolyte. As shown in Figure 1, an example of a secondary battery 5 with a rectangular structure is shown in Figure 1. In some embodiments, as shown in Figure 2, the outer casing includes a battery case 51 and a cover plate 53. The battery case 51 includes a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates surround and form a housing cavity. The battery case 51 has an opening that communicates with the housing cavity, and the cover plate 53 covers the opening and seals the housing cavity.

[0040] Currently, a commonly adopted technique to improve the energy density of secondary batteries is to design them with increasingly larger group margins. Group margins can reflect factors such as the difficulty of inserting electrode assemblies into the case, the pressure on the battery case after the electrode assemblies expand during charging, and the energy density of the secondary battery. A smaller group margin makes it easier to insert electrode assemblies into the case, but the resulting energy density of the secondary battery is relatively lower, which may not meet the requirements of actual use. A larger group margin results in higher energy density, but it makes it more difficult to insert electrode assemblies into the case, increasing process complexity and potentially causing damage to the electrode assemblies. Furthermore, a larger group margin reduces the residual space inside the battery case, which may leave insufficient space to contain gases generated during processes such as chemical conversion, charging / discharging, and storage. After the electrode assemblies expand, the pressure on the battery case continues to increase, seriously impacting the safety performance of the secondary battery.

[0041] Therefore, currently, it is not possible to achieve both a high group margin design and high safety performance for secondary batteries.

[0042] The inventors of this invention have discovered through their research that by employing an appropriate non-aqueous electrolyte, the gases generated during processes such as chemical conversion, charging / discharging, and storage can be significantly reduced. This lowers the pressure on the battery case, enabling secondary batteries to achieve both a high group margin design and high safety performance.

[0043] Specifically, the secondary battery of the present application comprises a battery case, an electrode assembly and a non-aqueous electrolyte housed within the battery case, the non-aqueous electrolyte comprises a compound represented by formula I, [ka] In Formula I, X and Y independently represent a hydrogen atom, a halogen atom, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C6-C20 aryl group, a C1-C20 halogenated alkyl group, a C2-C20 halogenated alkenyl group, a C2-C20 halogenated alkynyl group, a C6-C20 halogenated aryl group, a C1-C20 alkoxy group, a C2-C20 alkenyloxy group, a C2-C20 alkynyloxy group, a C6-C20 halogenated aryloxy group, a C1-C20 halogenated alkoxy group, a C2-C20 halogenated alkenyloxy group, a C2-C20 halogenated alkynyloxy group, a C6-C20 halogenated aryloxy group, or a combination thereof, and at least one of X and Y represents a fluorine atom or a group containing a fluorine atom.

[0044] The mass percentage content of the compound represented by formula I is A1%, the group margin of the secondary battery is B relative to the total mass of the non-aqueous electrolyte, and the secondary battery satisfies the conditions that B is 0.88 to 0.99 and B / A1 is 0.5 to 45.

[0045] The secondary battery of this application may be a lithium secondary battery, and in particular a lithium-ion secondary battery.

[0046] An electrode assembly typically includes a positive electrode piece, a negative electrode piece, and a separator. The separator is placed between the positive and negative electrode pieces and primarily serves to prevent short circuits between the positive and negative electrodes while allowing lithium ions to pass through. The positive electrode piece, negative electrode piece, and separator can be formed into an electrode assembly by a winding process and / or a lamination process. The electrode assembly is sealed in a housing cavity formed by the bottom plate of the battery case and side plates connected to the bottom plate, and a non-aqueous electrolyte is impregnated into the electrode assembly. The number of electrode assemblies included in a secondary battery may be one or more and can be adjusted as needed. In this application, the material of the battery case and the cover plate may include at least one of hard plastic, aluminum, and stainless steel.

[0047] Non-aqueous electrolytes are one of the important factors that affect the performance of secondary batteries. Non-aqueous electrolytes contain organic solvents and lithium salts dissolved therein, and a series of oxidation and reduction reactions readily occur during processes such as chemical conversion, charging and discharging, and storage, causing decomposition and the generation of large amounts of gas.

[0048] During the chemical formation process of a secondary battery (i.e., initial charging), the non-aqueous electrolyte undergoes a series of oxidation and reduction reactions on the surface of the negative electrode active material, forming a solid electrolyte interphase (SEI) film, which is accompanied by gas generation.

[0049] During long-term charge-discharge cycles, bound water in the electrode pieces of a secondary battery is gradually released and enters the non-aqueous electrolyte. As the water content in the non-aqueous electrolyte increases, a series of internal side reactions occur, causing the battery to expand due to gas. Currently, the most widely used non-aqueous electrolyte system is a mixed carbonate solution of lithium hexafluorophosphate. Lithium hexafluorophosphate has poor thermal stability in high-temperature environments and decomposes at high temperatures to produce PF5. PF5 is a strong Lewis acid and reacts with lone pairs of electrons on oxygen atoms in organic solvent molecules to decompose the organic solvent, causing the battery to expand due to gas. Furthermore, PF5 is highly sensitive to water and produces HF upon contact with water. HF not only induces the decomposition of organic solvents but also increases the acidity of the non-aqueous electrolyte, further corrodes the positive electrode active material and positive electrode current collector, and causes the elution of transition metal ions in the positive electrode active material. After transition metal ions dissolve from the positive electrode active material and move to the negative electrode, they are reduced back to the transition metal. This generated transition metal acts as a "catalyst," catalyzing the decomposition of the interfacial film on the surface of the negative electrode active material, further increasing the gas expansion of the battery and affecting the safety performance of the secondary battery. In addition, to replenish the lost interfacial film, the non-aqueous electrolyte is constantly consumed, and a series of oxidation and reduction reactions occur continuously, further increasing the gas expansion of the battery. During this process, active lithium ions inside the battery are also constantly consumed, further irreversibly affecting the capacity retention rate of the secondary battery.

[0050] During the storage process of secondary batteries, the positive electrode active material is always in a metastable state and is extremely unstable, leading to decomposition reactions and gas expansion. Furthermore, if the interfacial film on the negative electrode active material surface is unstable, a portion of the surface in contact with the non-aqueous electrolyte will dissolve as the temperature rises. For example, the organic component (CH2OCO2Li)2 in the interfacial film is unstable and prone to decomposition reactions, generating gas and causing gas expansion in the battery.

[0051] As a result of our research, we have found that if a non-aqueous electrolyte contains a compound represented by formula I, and the ratio of its content A1% to the group margin B of the secondary battery satisfies B / A1 of 0.5 to 45, then the amount of gas generated during processes such as chemical conversion, charging / discharging, and storage can be reduced.

[0052] The reason is unknown, but it is thought to be due to the following reasons.

[0053] Firstly, the compound represented by formula I can form a uniform, dense, and stable interfacial film on the surface of the positive electrode active material. This reduces direct contact between the positive electrode active material and the non-aqueous electrolyte, reduces interfacial side reactions, reduces the elution of transition metal ions, and reduces a series of side reactions resulting from this, thereby reducing the gas expansion of the battery.

[0054] Secondly, the B atom in the structure of the compound represented by formula I readily bonds with the O atom in the positive electrode active material. This stabilizes the crystal structure of the positive electrode active material, reduces the formation of lattice defects such as oxygen vacancies and irreversible interlayer migration, and reduces the deposition of lattice oxygen. At the same time, it can lower the resistance of charge transfer in the positive electrode active material and reduce the diffusion resistance of lithium ions within the bulk of the positive electrode active material. Furthermore, it can replenish lithium ions within the bulk of the positive electrode active material to the surface in a timely manner, thus avoiding excessive lithium desorption. As a result, the crystal structure of the positive electrode active material is more stable, lattice oxygen deposition is less likely, transition metal ions are less likely to desorb, a series of side reactions resulting from these are reduced, and gas expansion of the battery is reduced.

[0055] Thirdly, the BO bond in the structure of the compound represented by formula I is Al 3+ By combining with this, a passivation film is formed on the surface of the aluminum foil current collector, effectively improving corrosion of the aluminum foil current collector due to HF.

[0056] Fourth, the compound represented by formula I can also form a uniform, dense, and stable interfacial film on the surface of the negative electrode active material. This reduces damage and regeneration of the negative electrode interfacial film, further reduces gas generation and active lithium ion consumption in this process, reduces gas expansion of the battery, and improves the battery's capacity retention rate.

[0057] Therefore, when the non-aqueous electrolyte contains a compound represented by formula I, and its content A is 1%, and the group margin B of the secondary battery satisfies B / A1 = 0.5 to 45, on the one hand, the compound represented by formula I simultaneously forms a uniform, dense, and stable interfacial film on the positive and negative electrodes, reducing direct contact between the active material (positive electrode active material and negative electrode active material) and the non-aqueous electrolyte, reducing damage and regeneration of the positive electrode interfacial film and negative electrode interfacial film, further reducing gas generation and consumption of active lithium ions in this process, reducing gas expansion of the battery and improving the battery's capacity retention rate. On the other hand, the compound represented by formula I stabilizes the crystal structure of the positive electrode active material, reducing the deposition of lattice-like oxygen and the elution of transition metal ions, further reducing a series of side reactions resulting therefrom, and reducing gas expansion of the battery. As a result, the secondary battery of this application can achieve both a high group margin design and high safety performance, as well as good cycle performance and dynamic performance.

[0058] In this application, when the content A of the compound represented by formula I (1%) and the group margin B of the secondary battery satisfy the condition that B / A1 is between 0.5 and 45, the effect of reducing gas generation and improving capacity retention of the compound represented by formula I can be fully exerted. When B / A1 is greater than 45, the content of the compound represented by formula I is low, and the group margin of the secondary battery is designed to be large. In this case, there is insufficient amount of the compound represented by formula I to form a uniform, dense, and stable positive electrode interface film and / or negative electrode interface film. As a result, the crystal structure of the positive electrode active material cannot be effectively stabilized, the decomposition of the non-aqueous electrolyte cannot be reduced, gas generation in the secondary battery is high, the pressure on the battery case is high, and the safety risk of the secondary battery is high. When B / A1 is less than 0.5, the group margin of the secondary battery is designed to be small, and as a result, it is not possible to simultaneously achieve high energy density. Alternatively, a high content of the compound represented by formula I results in the formation of an excessively thick positive and / or negative electrode interface film, increasing the interfacial resistance of the positive and / or negative electrode. Furthermore, because the structure of the compound represented by formula I contains one oxalic acid group, when it decomposes, it generates gas, conversely increasing the gas expansion of the battery. Preferably, in some embodiments, B / A1 is 1-45, 1-30, 1-20, 1-18, 1-16, 1-14, 1-12, 1-10, 4-45, 4-30, 4-20, 4-18, 4-16, 4-14, 4-12, 4-10, 10-45, 10-30, 10-20, 10-18, or 10-16.

[0059] In this application, the group margin B of the secondary battery satisfies the range B = 0.88 to 0.99. Preferably, in some embodiments, B is 0.90 to 0.99, 0.90 to 0.98, 0.90 to 0.97, 0.90 to 0.96, 0.90 to 0.95, 0.92 to 0.99, 0.92 to 0.98, 0.92 to 0.97, 0.92 to 0.96, or 0.92 to 0.95. This makes it possible to give the secondary battery a high energy density without affecting the safety performance of the secondary battery.

[0060] In this application, at least one of X and Y represents a fluorine atom or a group containing a fluorine atom, for example, at least one selected from the group consisting of partially fluorinated or totally fluorinated C1-C20 alkyl groups, C2-C20 alkenyl groups, C2-C20 alkynyl groups, C6-C20 aryl groups, C1-C20 alkoxy groups, C2-C20 alkenyloxy groups, C2-C20 alkynyloxy groups, and C6-C20 aryloxy groups. The presence of a fluorine atom contributes to the formation of a thinner positive electrode interface film and / or negative electrode interface film, contributes to the uniform transport of lithium ions, and can also effectively suppress the formation of lithium dendrites. In some embodiments, at least one of X and Y represents a fluorine atom. Preferably, both X and Y represent a fluorine atom.

[0061] For example, the compound represented by formula I includes at least one of the following compounds. [ka]

[0062] In some examples, the content A1% of the compound represented by Formula I satisfies 0.02 ≤ A1 < 2. Preferably, A1 ranges from 0.02 to 1.8, 0.02 to 1.6, 0.02 to 1.4, 0.02 to 1.2, 0.02 to 1, 0.02 to 0.8, 0.02 to 0.6, 0.02 to 0.4, 0.02 to 0.3, 0.02 to 0.2, 0.02 to 0.1, 0.05 to 1.8, 0.05 to 1.6, 0.05 to 1.4, 0.05 to 1.2, 0.05 to 1, 0.05 to 0.8, 0.05 to 0.6, 0.05 to 0.4, 0.05 to 0.3, 0.05 to 0.2, or 0.05 to 0.1. When the content of the compound represented by Formula I is within an appropriate range, it contributes to better reducing gas generation and consumption of active lithium ions, reduces gas expansion of the battery, and improves the capacity retention rate. In addition, when the content of the compound represented by Formula I is low, an insufficient amount of the compound represented by Formula I to form a uniform, dense and stable positive electrode interface film and / or negative electrode interface film results in failure to effectively stabilize the crystal structure of the positive electrode active material and reduce decomposition of the non-aqueous electrolyte, leading to large amounts of gas generation in the secondary battery, high pressure applied to the battery case, and high safety risk of the secondary battery. When the content of the compound represented by Formula I is high, the interface resistance of the positive electrode and / or the interface resistance of the negative electrode increases, and since the structure of the compound represented by Formula I contains one oxalic acid group, gas is also generated when the compound itself decomposes, which can effectively avoid the situation where gas expansion of the battery is increased conversely.

[0063] In some embodiments, the content A1% of the compound represented by Formula I and the group margin B of the secondary battery satisfy A1 < B. When the content of the compound represented by Formula I is high, the interface resistance of the positive electrode and / or the interface resistance of the negative electrode increases, which affects the dynamic performance of the secondary battery. Therefore, when the secondary battery satisfies A1 < B, the secondary battery can achieve both a high group margin design, high safety performance and good dynamic performance.

[0064] In some embodiments, the capacity of the positive electrode plate is Q1 Ah, the capacity of the negative electrode plate is Q2 Ah, and the secondary battery satisfies 1<Q2 / Q1<1.05 and A1<B. When the capacity of the negative electrode plate is greater than the capacity of the positive electrode plate, it can be ensured that the negative electrode plate has sufficient voids to accommodate lithium ions from the positive electrode, thereby preventing lithium precipitation from the negative electrode. Meanwhile, when the ratio of the capacity of the negative electrode plate to the capacity of the positive electrode plate Q2 / Q1 is less than 1.05, it is advantageous for further improving the energy density of the secondary battery. Therefore, when the secondary battery satisfies both 1<Q2 / Q1<1.05 and A1<B, it can achieve both high energy density, high safety performance and good dynamic performance.

[0065] In the present application, the capacity of the positive electrode plate and the capacity of the negative electrode plate have meanings well-known in the art, and can be measured by instruments and methods well-known in the art. For example, the measurement is performed using a LAND battery tester.

[0066] As an example, a method for measuring the capacity of a positive electrode plate comprises: punching a cold-pressed positive electrode plate into a small wafer with an area of S0, assembling the wafer into a button-type battery in a glove box, charging the battery at a constant current of 0.1 mA to a charge cut-off voltage, discharging the battery at a constant current of 0.1 mA to a discharge cut-off voltage to obtain a discharge capacity CAP1, and calculating the capacity of the positive electrode plate according to the formula CAP1×S1 / S0, wherein S0 is the area of the small wafer, and S1 is the coating area of the positive electrode film layer on the positive electrode plate.

[0067] As an example, a method for measuring the capacity of a negative electrode plate comprises: punching a cold-pressed negative electrode plate into a small wafer with an area of S0, assembling the wafer into a button-type battery in a glove box, discharging the battery at a constant current of 0.1 mA to a discharge cut-off voltage, charging the battery at a constant current of 0.1 mA to a charge cut-off voltage to obtain a discharge capacity CAP2, and calculating the capacity of the negative electrode plate according to the formula CAP2×S2 / S0, wherein S0 is the area of the small wafer, and S2 is the coating area of the negative electrode film layer on the negative electrode plate. [Lithium salt]

[0068] In some embodiments, the non-aqueous electrolyte contains a first lithium salt, which is lithium hexafluorophosphate. The mass percentage content of the first lithium salt is A2%. A2 is greater than 0 and less than or equal to 14, according to the total mass of the non-aqueous electrolyte. Preferably, A2 is 4-14, 4-12, 4-10, 6-14, 6-12, 6-10, 8-14, 8-12, or 8-10. Because lithium hexafluorophosphate has the characteristic of high ionic conductivity, when its content is within an appropriate range, it contributes to improving the overall ionic conductivity of the non-aqueous electrolyte, accelerating lithium ion transport, and improving the capacity retention rate of the secondary battery. However, lithium hexafluorophosphate has poor thermal stability in high-temperature environments and decomposes at high temperatures to produce PF5. PF5 reacts with water to form HF, which corrodes the positive electrode active material and tends to increase the gas expansion of the battery. When a non-aqueous electrolyte contains both the compound represented by formula I and lithium hexafluorophosphate, the compound represented by formula I can react with lithium hexafluorophosphate to form the compound LiPF4C2O4. This reduces the decomposition of lithium hexafluorophosphate and the formation of HF, and the secondary battery can have high safety, high energy density, and good cycle performance.

[0069] In some embodiments, the content of the compound represented by formula I (A1%) and the content of the first lithium salt (A2%) satisfy the condition 10 ≤ A2 / A1 ≤ 600. After rationally combining the content of the compound represented by formula I (A1%) and the content of the first lithium salt (A2%), gas generation in the secondary battery is reduced, and the capacity retention rate of the secondary battery is improved. Furthermore, if the content of the first lithium salt is high and the content of the compound represented by formula I is low, there is a possibility that a large amount of HF is present in the non-aqueous electrolyte, which may lead to an increase in the decomposition reaction of the non-aqueous electrolyte. Additionally, the interfacial film formed on the positive and / or negative electrodes of the compound represented by formula I may not be sufficiently dense, failing to prevent corrosion of the positive electrode active material by HF and a series of resulting side reactions, which may lead to increased gas generation in the secondary battery. Conversely, if the content of the first lithium salt is low and the content of the compound represented by formula I is high, the anionic radius of the compound represented by formula I is small, making it difficult for it to completely dissociate in the non-aqueous electrolyte, and making it easy for anions and cations to associate. This can effectively avoid situations where the ionic conductivity of the non-aqueous electrolyte decreases, potentially worsening the capacity retention rate of the secondary battery. Preferably, the ranges are 15≦A2 / A1≦600, 20≦A2 / A1≦600, 40≦A2 / A1≦600, 60≦A2 / A1≦600, 80≦A2 / A1≦600, 100≦A2 / A1≦600, 120≦A2 / A1≦600, 150≦A2 / A1≦600, 10≦A2 / A1≦300, 20≦A2 / A1≦300, 40≦A2 / A1≦300, 60≦A2 / A1≦300, 80≦A2 / A1≦300, 100≦A2 / A1≦300, 120≦A2 / A1≦300, or 150≦A2 / A1≦300.

[0070] In some examples, the content of the compound represented by formula I (A1%) and the content of the first lithium salt (A2%) satisfy 0 < 10A1 + A2 / 5 ≤ 15. By rationally combining the content of the compound represented by formula I (A1%) and the content of the first lithium salt (A2%), gas generation in the secondary battery is reduced, and the capacity retention rate of the secondary battery is improved. Furthermore, when the content of both lithium hexafluorophosphate and the compound represented by formula I is high, there is a possibility that a large amount of HF is present in the non-aqueous electrolyte, which worsens the stability of the crystal structure of the positive electrode active material, leading to more decomposition reactions in the non-aqueous electrolyte and increased gas generation in the secondary battery, thus increasing safety risks. At the same time, because the anionic radius of the compound represented by formula I is small, it is difficult for it to completely dissociate in the non-aqueous electrolyte, and anions and cations tend to associate easily. Therefore, when its content is high, the ionic conductivity of the non-aqueous electrolyte decreases, and the capacity retention rate of the secondary battery also deteriorates. This situation can be effectively avoided. Preferably, 2.6 ≤ 10A1 + A2 / 5 ≤ 15, 2.6 ≤ 10A1 + A2 / 5 ≤ 12, 2.6 ≤ 10A1 + A2 / 5 ≤ 10, 2.6 ≤ 10A1 + A2 / 5 ≤ 8, 2.6 ≤ 10A1 + A2 / 5 ≤ 7, 2.6 ≤ 10A1 + A2 / 5 ≤ 6, 2.6 ≤ 10A1 + A2 / 5 ≤ 5, or 2.6 ≤ 10A1 + A2 / 5 ≤ 4.

[0071] In some embodiments, preferably, the content of the compound represented by formula I (A1%) and the content of the first lithium salt (A2%) simultaneously satisfy 10 ≤ A2 / A1 ≤ 600 and 0 < 10A1 + A2 / 5 ≤ 15. This ensures that the non-aqueous electrolyte contains appropriate content of the compound represented by formula I and the first lithium salt, and that the secondary battery using this electrolyte can achieve both a high group margin design, high safety performance, and good cycle performance. More preferably, the content of the compound represented by formula I (A1%) and the content of the first lithium salt (A2%) simultaneously satisfy 60 ≤ A2 / A1 ≤ 600 and 2.6 ≤ 10A1 + A2 / 5 ≤ 5.

[0072] In some embodiments, the non-aqueous electrolyte further comprises a second lithium salt which is a lithium fluorosulfonylimide salt. Preferably, the molecular formula of the lithium fluorosulfonylimide salt is LiN(SO₂R¹)(SO₂R²), wherein R¹ and R² are each independently F or C n F 2n+1 , and n is an integer from 1 to 10. By way of example, the lithium fluorosulfonylimide salt comprises lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or a combination thereof. Preferably, the lithium fluorosulfonylimide salt comprises lithium bis(fluorosulfonyl)imide (LiFSI).

[0073] Preferably, in some embodiments, the mass percentage content of the second lithium salt is A3% based on the total mass of the non-aqueous electrolyte, wherein 0 ≤ A3 ≤ 2.5. For example, A3 is in a range consisting of any value of 0, 0.10, 0.20, 0.50, 0.75, 1.0, 1.25, 1.50, 1.75, 2.0, 2.25, 2.50 or any higher value. More preferably, 0 < A3 ≤ 2.5, 0 < A3 ≤ 2.25, 0 < A3 ≤ 2.0, 0 < A3 ≤ 1.75, 0 < A3 ≤ 1.50, 0 < A3 ≤ 1.25, 0 < A3 ≤ 1.0, 0.5 ≤ A3 ≤ 2.5, 0.5 ≤ A3 ≤ 2.25, 0.5 ≤ A3 ≤ 2.0, 0.5 ≤ A3 ≤ 1.75, 0.5 ≤ A3 ≤ 1.50, 0.5 ≤ A3 ≤ 1.25 or 0.5 ≤ A3 ≤ 1.0.

[0074] The fluorosulfonylimide anion is a weakly coordinating anion centered on N, and has -F or -C with a conjugated group and strong electron-withdrawing property n F 2n+1It contains fluorosulfonylimide lithium salt, which has highly delocalized anionic charge and weakens the interaction between anions and lithium ions. Therefore, fluorosulfonylimide lithium salt has low lattice energy and is easily dissociated. This can improve the ionic conductivity of the non-aqueous electrolyte, reduce its viscosity, and improve the rate performance of the secondary battery. At the same time, fluorosulfonylimide lithium salt has high thermal stability, a wider electrochemical window, and resistance to hydrolysis, and can form a LiF-rich interfacial film on the surface of the negative electrode active material. This LiF-rich interfacial film is thinner, has lower resistance, higher thermal stability, reduces side reactions between the negative electrode active material and the non-aqueous electrolyte, reduces gas expansion of the battery, and suppresses the formation of lithium dendrites. Therefore, when the non-aqueous electrolyte contains fluorosulfonylimide lithium salt, the rate performance of the secondary battery can be improved while improving the safety of the secondary battery.

[0075] In some embodiments, the content A1% of the compound represented by formula I and the content A3% of the second lithium salt further satisfy 0.25 ≤ A3 / A1 ≤ 25. Preferably, 1 ≤ A3 / A1 ≤ 25, 1 ≤ A3 / A1 ≤ 20, 1 ≤ A3 / A1 ≤ 15, 1 ≤ A3 / A1 ≤ 12.5, 1 ≤ A3 / A1 ≤ 10, 1 ≤ A3 / A1 ≤ 7.5, 2 ≤ A3 / A1 ≤ 25, 2 ≤ A3 / A1 ≤ 20, 2 ≤ A3 / A1 ≤ 15, 2 ≤ A3 / A1 ≤ 12.5, 2 ≤ A3 / A1 ≤ 10, 2 ≤ A3 / A1 ≤ 7.5, 4 ≤ A3 / A1 ≤ 25, 4 ≤ A3 / A1 ≤ 20, 4 ≤ A3 / A1 ≤ 15, 4 ≤ A3 / A1 ≤ 12.5, or 4 ≤ A3 / A1 ≤ 10.

[0076] When the non-aqueous electrolyte contains lithium fluorosulfonylimide salt, the rate performance of the secondary battery can be improved. However, lithium fluorosulfonylimide salt cannot withstand high pressure, corrodes the positive electrode current collector (e.g., aluminum foil) at high potential, and has poor film formation effect on the surface of the positive electrode active material, which easily affects the cycle performance of the secondary battery. The compound represented by formula I can act as a stabilizer for the positive electrode active material, forming a high-performance interfacial film on the surface of the positive electrode active material, reducing side reactions between the positive electrode active material and the non-aqueous electrolyte, and stabilizing the crystal structure of the positive electrode active material. Therefore, using the compound represented by formula I in combination with lithium fluorosulfonylimide salt is advantageous in fully utilizing the rate performance improvement effect of lithium fluorosulfonylimide salt in the secondary battery. Furthermore, by rationally controlling the relationship between the content A1% of the compound represented by formula I and the content A3% of the second lithium salt so that 0.25 ≤ A3 / A1 ≤ 25, the synergistic effect between the compound represented by formula I and lithium fluorosulfonylimide salt can be fully utilized. This not only avoids degrading the cycle performance and storage performance of secondary batteries, but also further reduces the internal resistance of secondary batteries, thereby improving their rate performance.

[0077] In some embodiments, the non-aqueous electrolyte contains both a first lithium salt and a second lithium salt. Preferably, the content of the first lithium salt (A2%) and the content of the second lithium salt (A3%) satisfy the condition that A3 / A2 is 0.5 or less, and more preferably 0.005-0.5, 0.005-0.4, 0.005-0.3, 0.005-0.2, 0.02-0.5, 0.02-0.4, 0.04-0.3, 0.02-0.2, 0.04-0.5, 0.04-0.4, 0.04-0.3, or 0.04-0.2. This makes the non-aqueous electrolyte less susceptible to hydrolysis and also achieves higher thermal stability, while contributing to the formation of a lower-resistance interfacial film.

[0078] In some embodiments, the non-aqueous electrolyte may further contain a third lithium salt comprising at least one of lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium difluorophosphate (LiPO2F2), lithium difluorodisoxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The third lithium salt can serve as an auxiliary lithium salt to further improve the interfacial performance of the positive and / or negative electrodes, or to improve the ionic conductivity or thermal stability of the non-aqueous electrolyte. Preferably, the total mass percentage content of the third lithium salt in the non-aqueous electrolyte is A4% based on the total mass of the non-aqueous electrolyte, where A4 is 6 or less, and more preferably 2 or less.

[0079] In some embodiments, A1+A2+A3+A4 is 10 to 20, preferably 10 to 15. [organic solvent]

[0080] In some embodiments, the organic solvent comprises at least one of the first solvent, the second solvent, and the third solvent.

[0081] The first solvent is a cyclic carbonate compound, and may include, for example, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), and vinylethylene carbonate (VEC).

[0082] The second solvent is a chain-like carbonate compound, which may include, for example, at least one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0083] In some embodiments, the organic solvent preferably comprises at least a first solvent and a second solvent. A high content of lithium salts, such as lithium hexafluorophosphate, increases the viscosity of the non-aqueous electrolyte, decreases its ionic conductivity, and is unfavorable for lithium ion transport. The first solvent has a high dielectric constant, which can increase the ionic conductivity of the non-aqueous electrolyte, and the second solvent has a low viscosity, which can decrease the viscosity of the non-aqueous electrolyte. Therefore, when the organic solvent comprises both the first and second solvents, it contributes to the non-aqueous electrolyte having appropriate viscosity and ionic conductivity, and further contributes to lithium ion transport.

[0084] In some embodiments, the organic solvent may further comprise a third solvent. The third solvent is a carboxylic acid ester compound and may comprise at least one of the following: methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), and ethyl butyrate (EB). The third solvent has the advantages of low viscosity and high dielectric constant, and is applied to non-aqueous electrolytes, contributing to the non-aqueous electrolyte having appropriate viscosity and ionic conductivity, and further contributing to the transport of lithium ions and the improvement of the rate performance of secondary batteries.

[0085] The first solvent can increase the ionic conductivity of the non-aqueous electrolyte, but it is prone to decomposition reactions and affects the safety performance of the secondary battery; therefore, its content needs to be controlled within an appropriate range. In some examples, the mass percentage content of the first solvent in the organic solvent is D1% according to the total mass of the organic solvent, and D1 is greater than 0 and less than or equal to 20. Preferably, D1 is 0.5-20, 5-20, 10-20, 12-20, or 15-20.

[0086] In some examples, the mass percentage content of the second solvent in the organic solvent is D2% according to the total mass of the organic solvent, where D2 is 50 to 90. Preferably, D2 is 55 to 90, 60 to 90, 65 to 90, or 70 to 90.

[0087] The third solvent can improve the rate performance of the secondary battery, but its oxidation resistance is poor and it is prone to decomposition when stored in a highly charged state, so its content should not be too high. In some examples, the mass percentage content of the third solvent in the organic solvent is D3% according to the total mass of the organic solvent, and D3 is 0 to 30. Preferably, D3 is 2 to 20, 2 to 15, 2 to 10, 2 to 8, 2 to 6, or 2 to 5.

[0088] The organic solvent of this application may include solvents other than the first, second, and third solvents described above. For example, the other solvents may include sulfone-based solvents such as sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). [Additives]

[0089] In some embodiments, the non-aqueous electrolyte may further contain additives, such as at least one of halogen-substituted cyclic carbonate compounds, nitrile compounds, phosphazene compounds, aromatic hydrocarbons and halogenated aromatic hydrocarbon compounds, isocyanate compounds, acid anhydride compounds, sulfate ester compounds, sulfite ester compounds, sulfonic acid ester compounds, and disulfonic acid ester compounds. The types of these additives are not particularly limited in this application, as long as they do not impair the spirit of this application. Preferably, the total mass percentage content of these additives is 10% or less, more preferably 5% or less, based on the total mass of the non-aqueous electrolyte.

[0090] In some embodiments, based on the total mass of the non-aqueous electrolyte, the non-aqueous electrolyte further comprises fluoroethylene carbonate (FEC), the mass percentage content thereof is C1%, and 0≦C1≦5. For example, C1 is in a range consisting of any value selected from 0, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 and the above values. Preferably, it is 0<C1≦5, 0<C1≦4, 0<C1≦3, 0<C1≦2.5, 0<C1≦2, 0.5≦C1≦5, 0.5≦C1≦4, 0.5≦C1≦3, 0.5≦C1≦2.5 or 0.5≦C1≦2.

[0091] In a secondary battery, fluoroethylene carbonate undergoes a reductive decomposition reaction at a high potential, forms an interface film with certain toughness on the surface of the negative electrode active material, and can suppress the reductive decomposition of an organic solvent at a low potential, and suppress the insertion of the organic solvent into the negative electrode active material. Therefore, when the non-aqueous electrolyte contains fluoroethylene carbonate, the cycle performance of the secondary battery can be effectively improved. In addition, fluoroethylene carbonate can resist high-voltage oxidation, which is beneficial for matching with high-voltage positive electrode active materials, and is further beneficial for improving the energy density of the secondary battery.

[0092] In some embodiments, the content A1% of the compound represented by formula I and the content C1% of fluoroethylene carbonate further satisfy 5≦C1 / A1≦50. Preferably, it is 5≦C1 / A1≦45, 5≦C1 / A1≦40, 5≦C1 / A1≦35, 5≦C1 / A1≦30, 5≦C1 / A1≦25, 5≦C1 / A1≦20, 10≦C1 / A1≦45, 10≦C1 / A1≦40, 10≦C1 / A1≦35, 10≦C1 / A1≦30, 10≦C1 / A1≦25 or 10≦C1 / A1≦20.

[0093] When a non-aqueous electrolyte contains fluoroethylene carbonate, the cycle performance of a secondary battery can be effectively improved. However, fluoroethylene carbonate readily decomposes to form HF. HF destroys the positive electrode interface film, corrodes the positive electrode active material, and increases the amount of gas generated in the secondary battery. The compound represented by formula I can be used as a stabilizer for the positive electrode active material. The B atoms in its structure interact with the O atoms on the surface of the positive electrode active material, thereby stabilizing the crystal structure of the positive electrode active material and reducing the destruction of the crystal structure of the positive electrode active material by HF. Therefore, using the compound represented by formula I in combination with fluoroethylene carbonate is advantageous in fully utilizing the further improvement effect of fluoroethylene carbonate on the cycle performance of the secondary battery. Furthermore, by rationally controlling the relationship between the content A1% of the compound represented by formula I and the content C1% of fluoroethylene carbonate so that 5 ≤ C1 / A1 ≤ 50, the synergistic effect between the compound represented by formula I and fluoroethylene carbonate can be fully utilized. This not only significantly reduces gas generation in secondary batteries but also further improves their cycle performance. Simultaneously, fluoroethylene carbonate has a high dielectric constant. By rationally controlling the relationship between the content A1% of the compound represented by formula I and the content C1% of fluoroethylene carbonate, satisfying 5 ≤ C1 / A1 ≤ 50, the anions of the compound represented by formula I contribute to the formation of free ions, reducing the association of anions and cations. As a result, the non-aqueous electrolyte has high ionic conductivity, leading to better cycle performance in secondary batteries.

[0094] In some embodiments, the non-aqueous electrolyte contains both a second lithium salt and fluoroethylene carbonate. Preferably, the secondary battery satisfies both 0.25 ≤ A3 / A1 ≤ 25 and 5 ≤ C1 / A1 ≤ 50 simultaneously. Furthermore, the secondary battery satisfies both 4 ≤ A3 / A1 ≤ 20 and 10 ≤ C1 / A1 ≤ 30 simultaneously. In this case, the cycle performance and rate performance can be improved while improving the safety performance of the secondary battery. Fluoroethylene carbonate can effectively improve the cycle performance of the secondary battery. The second lithium salt can improve the rate performance of the secondary battery. The compound represented by formula I can act as a stabilizer for the positive electrode active material, forming a high-performance interfacial film on the surface of the positive electrode active material, improving the lithium ion diffusion rate of the positive electrode active material, reducing side reactions between the positive electrode active material and the non-aqueous electrolyte, stabilizing the crystal structure of the positive electrode active material, and reducing the deposition of lattice oxygen and the elution of transition metal ions. Therefore, rationally controlling the relationship between the content of fluoroethylene carbonate, the second lithium salt, and the compound represented by formula I is advantageous in fully maximizing the synergistic effect among the three and effectively suppressing the drawbacks of using each component individually.

[0095] In some embodiments, the non-aqueous electrolyte may further contain a water-removing additive that reduces the water content of the non-aqueous electrolyte and helps to reduce a series of side reactions caused by moisture. This further improves the gas expansion of the secondary battery and allows the secondary battery to better achieve both a high group margin design and high safety performance.

[0096] Preferably, in some embodiments, the water-removing additive includes hexamethyldisilazane (HMDS), tris(trimethylsilyl) phosphate (TMSP), or a combination thereof. These two water-removing additives can effectively reduce the water content of the non-aqueous electrolyte and can also react with lithium hexafluorophosphate to form lithium difluorophosphate. This reduces the decomposition of lithium hexafluorophosphate and the formation of HF, while also further stabilizing the positive electrode interface film and / or negative electrode interface film, contributing to a reduction in the interfacial resistance of the positive electrode and / or negative electrode. This further improves the safety performance of the secondary battery and enhances its cycle performance and rate performance.

[0097] In some embodiments, the mass percentage content of the water-removing additive is C2% based on the total mass of the non-aqueous electrolyte. C2 is greater than 0 and less than or equal to 2, preferably 0.01 to 2, and more preferably 0.1 to 1.

[0098] The non-aqueous electrolyte of this application can be prepared according to conventional methods in the art. For example, the non-aqueous electrolyte can be obtained by uniformly mixing the organic solvent, the lithium salt, etc. The order in which the materials are added is not particularly limited; for example, the lithium salt, etc. can be added to the organic solvent and uniformly mixed to obtain the non-aqueous electrolyte.

[0099] In this application, each component in the non-aqueous electrolyte and its content can be measured according to methods known in the art. For example, they can be measured by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), etc.

[0100] Furthermore, when testing the non-aqueous electrolyte of this application, the non-aqueous electrolyte can be obtained from a secondary battery. One example of a specific procedure for obtaining the non-aqueous electrolyte from a secondary battery is to discharge the secondary battery to its discharge cutoff voltage (generally, the battery is completely discharged for safety reasons), then perform centrifugation, and then obtain an appropriate amount of the liquid obtained by centrifugation as the non-aqueous electrolyte. The non-aqueous electrolyte may also be obtained directly from the filling port of the secondary battery. [Positive electrode piece]

[0101] In some embodiments, the positive electrode piece includes a positive electrode current collector and a positive electrode film layer comprising a positive electrode active material, provided on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two opposing surfaces in the direction of its own thickness. The positive electrode film layer is provided on one or both of the two opposing surfaces of the positive electrode current collector.

[0102] Said positive electrode membrane layer comprises a positive electrode active material. A positive electrode active material for secondary batteries known in the art can be employed as said positive electrode active material. For example, the positive electrode active material may comprise at least one selected from the group consisting of lithium transition metal oxides, lithium-containing phosphates having an olivine structure, and modified compounds thereof. Examples of the lithium transition metal oxide include, for example, at least one selected from the group consisting of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. Examples of the lithium-containing phosphate having an olivine structure include, for example, at least one selected from the group consisting of lithium iron phosphate, composite materials of lithium iron phosphate and carbon, lithium manganese phosphate, composite materials of lithium manganese phosphate and carbon, lithium manganese iron phosphate, composite materials of lithium manganese iron phosphate and carbon, and modified compounds thereof. The present application is not limited to these materials, and other conventionally known materials that can be used as a positive electrode active material for secondary batteries may be used. Only one of these positive electrode active materials may be used alone, or two or more of them may be used in combination.

[0103] In some embodiments, the positive electrode active material has a molecular formula of Li a Ni b Co c Mn d Al e M f O g A h comprises a layered material of, wherein M represents a doped cation at a transition metal site, A represents a doped anion at an oxygen site, and 0.8≦a≦1.2, 0≦b≦1, 0≦c≦1, 0≦d≦1, 0≦e≦1, 0≦f≦0.2, 0≦g≦2, 0≦h≦2, b+c+d+e+f=1, g+h=2.

[0104] The molecular formula is Li a Ni b Co c Mn d Al e M f Og A h The layered material can be selectively doped and modified with M cations, A anions, or both M cations and A anions. The crystal structure of the layered material obtained after doping is more stable, lattice oxygen is less prone to precipitation, transition metal ions are less prone to detachment, and a series of side reactions caused thereby are reduced. Thereby, the safety performance and electrochemical performance of the secondary battery, such as cycle performance and dynamic performance, are further improved.

[0105] In some embodiments, M is at least one selected from the group consisting of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te, and W.

[0106] In some embodiments, A is at least one selected from the group consisting of F, N, P and S. Preferably, A is selected from F. After being doped and modified by F, Li a Ni b Co c Mn d Al e M f O g A h has a more stable crystal structure, lattice oxygen is less prone to precipitation, and transition metal ions are less prone to detachment, whereby the secondary battery can have better safety performance, cycle performance and dynamic performance.

[0107] The values of a, b, c, d, e, f, g, h satisfy the condition for maintaining electrical neutrality of Li a Ni b Co c Mn d Al e M f O g A h .

[0108] In some embodiments, 0<b<0.98. Preferably, 0.50≦b<0.98, 0.55≦b<0.98, 0.60≦b<0.98, 0.65≦b<0.98, 0.70≦b<0.98, 0.75≦b<0.98 or 0.80≦b<0.98.

[0109] In some embodiments, c=0.

[0110] In some embodiments, 0 < c ≦ 0.20. Preferably, 0 < c ≦ 0.15, 0 < c ≦ 0.10, 0 < c ≦ 0.09, 0 < c ≦ 0.08, 0 < c ≦ 0.07, 0 < c ≦ 0.06, 0 < c ≦ 0.05, 0 < c ≦ 0.04, 0 < c ≦ 0.03, 0 < c ≦ 0.02, or 0 < c ≦ 0.01. Cobalt has low content in the crust, is difficult to mine and is expensive, so low-cobalt or cobalt-free is an inevitable development trend for positive electrode active materials. However, cobalt greatly contributes to the diffusion rate of lithium ions in the positive electrode active material, and low-cobalt or cobalt-free reduces the diffusion rate of lithium ions in the positive electrode active material, which affects the cycle performance of secondary batteries. Researchers have been studying to improve the diffusion rate of lithium ions in low-cobalt or cobalt-free positive electrode active materials, but there is still no good solution at present.

[0111] As an unexpected finding obtained through further research by the inventors of the present application, in the structure of the compound represented by formula I, B atoms are prone to bonding with O atoms in the positive electrode active material, which can reduce the charge transfer resistance of the positive electrode active material, thereby reducing the diffusion resistance of lithium ions in the bulk of the positive electrode active material. Therefore, the low-cobalt or cobalt-free positive electrode active material can have an improved lithium ion diffusion rate, lithium ions in the bulk of the low-cobalt or cobalt-free positive electrode active material can be replenished to the surface in a timely manner, and excessive lithium desorption on the surface of the low-cobalt or cobalt-free positive electrode active material can be avoided, thereby stabilizing the crystal structure of the low-cobalt or cobalt-free positive electrode active material. Since the crystal structure of the low-cobalt or cobalt-free positive electrode active material is more stable, the probability of problems such as instability of the structural, chemical or electrochemical properties of the positive electrode active material caused by excessive lithium desorption on the surface of the low-cobalt or cobalt-free positive electrode active material can be greatly reduced. For example, the above problem includes irreversible strain and increased lattice defects of the positive electrode active material.

[0112] In some embodiments, d=0 and 0<e<0.50. Preferably, d=0 and 0<e≦0.45, d=0 and 0<e≦0.40, d=0 and 0<e≦0.35, d=0 and 0<e≦0.30, d=0 and 0<e≦0.25, d=0 and 0<e≦0.20, d=0 and 0<e≦0.15, or d=0 and 0<e≦0.10.

[0113] In some embodiments, e=0 and 0<d<0.50. Preferably, e=0 and 0<d≦0.45, e=0 and 0<d≦0.40, e=0 and 0<d≦0.35, e=0 and 0<d≦0.30, e=0 and 0<d≦0.25, e=0 and 0<d≦0.20, e=0 and 0<d≦0.15, or e=0 and 0<d≦0.10.

[0114] In some embodiments, 0<d<0.50 and 0<e<0.50. Preferably, 0<d≦0.30 and 0<e≦0.10.

[0115] In some embodiments, g=2 and h=0.

[0116] In some embodiments, g=0 and h=2.

[0117] In some embodiments, 0<g<2, 0<h<2, and g+h=2.

[0118] As an example, the molecular formula is Li a Ni b Co c Mn d Al e M f O g A h layered material is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn0.3 O2, LiLiLi 0.8 Co 0.05 Mn 0.15 O2, LiLiLi 0.7 Mn 0.3 O2, LiLiLi 0.69 Co 0.01 Mn 0.3 O2, LiLiLi 0.68 Co 0.02 Mn 0.3 O2, LiLiLi 0.65 Co 0.05 Mn 0.3 O2, LiLiLi 0.63 Co 0.07 Mn 0.3 O2, LiLiLi 0.61 Co 0.09 Mn 0.3 It contains, but is not limited to, at least one type of O2.

[0119] Li a Ni b Co c Mn d Al e M f O g A h This material can be produced according to general methods in this field. An exemplary method involves mixing a lithium source, a nickel source, a cobalt source, a manganese source, an aluminum source, a precursor of element M, and a precursor of element A, and then sintering the mixture. The sintering atmosphere may be an oxygen-containing atmosphere, for example, an air atmosphere or an oxygen gas atmosphere. The O2 concentration of the sintering atmosphere is, for example, 70% to 100%. The sintering temperature and sintering time can be adjusted according to the actual conditions.

[0120] By way of example, the lithium source includes, but is not limited to, at least one selected from the group consisting of lithium oxide (Li₂O), lithium phosphate (Li₃PO₄), lithium dihydrogen phosphate (LiH₂PO₄), lithium acetate (CH₃COOLi), lithium hydroxide (LiOH), lithium carbonate (Li₂CO₃) and lithium nitrate (LiNO₃). By way of example, the nickel source includes, but is not limited to, at least one selected from the group consisting of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate and nickel acetate. By way of example, the cobalt source includes, but is not limited to, at least one selected from the group consisting of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate and cobalt acetate. By way of example, the manganese source includes, but is not limited to, at least one selected from the group consisting of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate and manganese acetate. By way of example, the aluminum source includes, but is not limited to, at least one selected from the group consisting of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate and aluminum acetate. By way of example, the precursor of the element M includes, but is not limited to, at least one selected from the group consisting of oxides, nitrate compounds, carbonate compounds, hydroxides and acetate compounds of the element M. By way of example, the precursor of the element A includes, but is not limited to, at least one selected from the group consisting of ammonium fluoride, lithium fluoride, hydrogen fluoride, ammonium chloride, lithium chloride, hydrogen chloride, ammonium nitrate, ammonium nitrite, ammonium carbonate, ammonium bicarbonate, ammonium phosphate, phosphoric acid, ammonium sulfate, ammonium bisulfate, ammonium bisulfite, ammonium sulfite, ammonium hydrosulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide and elemental sulfur.

[0121] In some embodiments, based on the total mass of the positive electrode film layer, the molecular formula is Li a Ni b Co c Mn d Al e M f O g A h the mass percentage of the layered material is 80% to 99%. For example, the molecular formula is Li a Nib Co c Mn d Al e M f O g A h The mass percentage of the layered material may be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or a range formed by any of the foregoing values. Preferably, the molecular formula is Li a Ni b Co c Mn d Al e M f O g A h The mass percentage of the layered material is 85%~99%, 90%~99%, 95%~99%, 80%~98%, 85%~98%, 90%~98%, 95%~98%, 80%~97%, 85%~97%, 90%~97%, or 95%~97%.

[0122] In some embodiments, the positive electrode membrane layer may optionally further comprise a positive electrode conductive agent. The present application does not particularly limit the type of the positive electrode conductive agent. For example, the positive electrode conductive agent comprises at least one selected from the group consisting of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. In some embodiments, based on the total mass of the positive electrode membrane layer, the mass percentage content of the positive electrode conductive agent is 5% or less.

[0123] In some embodiments, the positive electrode film layer may further optionally contain a positive electrode adhesive. The present application does not particularly limit the type of positive electrode adhesive, and as an example, the positive electrode adhesive may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a ternary copolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a ternary copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, or a fluorine-containing acrylate resin. In some embodiments, the mass percentage content of the positive electrode adhesive is 5% or less, based on the total mass of the positive electrode film layer.

[0124] In some embodiments, the positive electrode current collector can be a metal foil sheet or a composite current collector. As an example of a metal foil sheet, aluminum foil can be used. The composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. As an example, the metal material is at least one selected from aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material substrate is selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0125] In some embodiments, the compressed density of the positive electrode piece is 2.6 g / cm³. 3 ~3.7g / cm 3 Preferably 3.4 g / cm³ 3 ~3.7g / cm 3 The non-aqueous electrolyte of this invention contributes to matching with the positive electrode, which is coated to the actual thickness under high pressure, thereby further improving the energy density of the secondary battery.

[0126] The positive electrode film layer is typically formed by applying a positive electrode slurry to a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing a positive electrode active material, a selectable conductive agent, a selectable adhesive, and any other components in a solvent and stirring uniformly. The solvent may, but is not limited to, N-methylpyrrolidone (NMP). [Negative pole piece]

[0127] In some embodiments, the negative electrode piece includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector and containing a negative electrode active material. For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode film layer is provided on one or both of the two opposing surfaces of the negative electrode current collector.

[0128] The anode active material can be anode active material used in secondary batteries known in the art. For example, the anode active material includes, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy material. This application is not limited to these materials, and other conventionally known materials used as anode active materials in secondary batteries may be used. These anode active materials may be used individually or in combination of two or more types.

[0129] In some embodiments, the negative electrode film layer may further selectively contain a negative electrode conductive agent. The present application is not particularly limited to the type of negative electrode conductive agent, and as an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage content of the negative electrode conductive agent is 5% or less, according to the total mass of the negative electrode film layer.

[0130] In some embodiments, the negative electrode film layer may further optionally include a negative electrode adhesive. The present application is not particularly limited to the type of negative electrode adhesive, and as an example, the negative electrode adhesive may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylate PAA, polymethacrylate PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage content of the negative electrode adhesive is 5% or less according to the total mass of the negative electrode film layer.

[0131] In some embodiments, the negative electrode film layer may further optionally contain other additives. For example, the other additives may include thickeners such as sodium carboxymethylcellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass percentage content of the other additives is 2% or less, according to the total mass of the negative electrode film layer.

[0132] In some embodiments, the negative electrode current collector can be a metal foil sheet or a composite current collector. Copper foil can be used as an example of a metal foil sheet. The composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. For example, the metal material is at least one selected from copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer material substrate is selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0133] In some embodiments, the compressed density of the negative electrode piece is 1.4 g / cm³. 3 ~2.0g / cm 3 Preferably, 1.5 g / cm³ 3 ~2.0g / cm 3 The non-aqueous electrolyte of this invention contributes to matching with the negative electrode, which is coated to the actual thickness under high pressure, thereby further improving the energy density of the secondary battery.

[0134] The negative electrode film layer is typically formed by applying a negative electrode slurry to a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, a selectable conductive agent, a selectable adhesive, and other selectable auxiliary agents in a solvent and stirring uniformly. The solvent may, but is not limited to, N-methylpyrrolidone (NMP) or deionized water. [Separator]

[0135] The separator is placed between the positive electrode piece and the negative electrode piece and primarily serves to prevent short circuits between the positive and negative electrodes, while simultaneously allowing lithium ions to pass through. The present application does not particularly limit the type of separator, and any known porous structure separator having good chemical and mechanical stability can be selected.

[0136] In some embodiments, the material of the separator may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film. If the separator is a multilayer composite film, the materials of each layer may be the same or different.

[0137] The method for manufacturing the secondary battery of the present invention is known. In some embodiments, a secondary battery can be formed by assembling a positive electrode, a separator, a negative electrode, and a non-aqueous electrolyte. For example, an electrode assembly is formed by winding or laminating the positive electrode, separator, and negative electrode by a winding or laminating process, the electrode assembly is placed in an outer casing, dried, and then a non-aqueous electrolyte is injected. A secondary battery is then obtained through processes such as vacuum sealing, standing, chemical formation, and shaping.

[0138] In some embodiments of the present invention, the secondary battery according to the present invention can be assembled into a battery module. The number of secondary batteries included in the battery module may be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0139] Figure 3 is a schematic diagram of an example battery module 4. As shown in Figure 3, in the battery module 4, the multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, they can be arranged in any other manner. The multiple secondary batteries 5 may be further fixed by fasteners.

[0140] Preferably, the battery module 4 further includes a housing having a housing space, and a plurality of secondary batteries 5 are housed in the housing space.

[0141] In some embodiments, the battery modules can be further assembled into a battery pack. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0142] Figures 4 and 5 are schematic diagrams of an example battery pack 1. As shown in Figures 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 installed in the battery box. The battery box includes an upper housing 2 and a lower housing 3, with the upper housing 2 covering the lower housing 3 and being used to form a sealed space for housing the battery modules 4. The plurality of battery modules 4 can be arranged arbitrarily within the battery box.

[0143] Embodiments of the present invention further provide a power consumption device comprising at least one of the secondary battery, battery module, or battery pack of the present invention. The secondary battery, battery module, or battery pack may be used as a power source for the power consumption device, or as an energy storage unit for the power consumption device. The power consumption device may be, but is not limited to, mobile devices (e.g., mobile phones, laptop computers, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0144] The aforementioned power consumption device can select a secondary battery, battery module, or battery pack depending on its usage needs.

[0145] Figure 6 is a schematic diagram of an example power consumption device. This power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this power consumption device, a battery pack or battery module can be used.

[0146] Other examples of power-consuming devices may include mobile phones, tablet computers, and laptop computers. These power-consuming devices are typically required to be thin and can use rechargeable batteries as their power source. Examples

[0147] The following examples illustrate the disclosures of this application in more detail, and these examples are used solely for illustrative purposes. It will be apparent to those skilled in the art that various modifications and changes can be made within the scope of the disclosures. Unless otherwise specified, all parts, percentages, and ratios described in the following examples are based on mass. Furthermore, all reagents used in the examples can be obtained by purchase or synthesis according to conventional methods and are ready for direct use without further processing. Furthermore, all equipment used in the examples can be obtained by purchase.

[0148] The secondary batteries in Examples 1-36 and Comparative Examples 1-3 were all manufactured using the following method.

[0149] Fabrication of positive electrode segments

[0150] LiNi 0.6 Co 0.2 Mn 0.2 O2, carbon black (a conductive agent), and polyvinylidene fluoride (PVDF) (an adhesive) are thoroughly mixed in an appropriate amount of solvent NMP in a weight ratio of 97.5:1.4:1.1 to form a uniform positive electrode slurry. The positive electrode slurry is uniformly applied to the surface of aluminum foil, which is the positive electrode current collector, and then dried and cold-pressed to obtain a positive electrode piece.

[0151] Fabrication of negative electrode piece

[0152] The negative electrode active material, graphite, the adhesive, styrene-butadiene rubber (SBR), the thickener, sodium carboxymethylcellulose (CMC-Na), and the conductive agent, carbon black (Super P), are mixed thoroughly with an appropriate amount of deionized water as a solvent in a weight ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry is uniformly applied to the surface of the copper foil, which is the negative electrode current collector, and then dried and cold-pressed to obtain a negative electrode piece.

[0153] Separator

[0154] A porous polyethylene (PE) film is used as the separator.

[0155] Preparation of non-aqueous electrolyte

[0156] After uniformly mixing the first, second, and third solvents in the compositions shown in Table 1 to obtain an organic solvent, the compound represented by formula I, the first lithium salt, the second lithium salt, the third lithium salt, fluoroethylene carbonate (FEC), and a water-removing additive were added to the organic solvent in the compositions shown in Table 1 and uniformly mixed to obtain a non-aqueous electrolyte. In Table 1, the content A1% of the compound represented by formula I, A2% of the first lithium salt, A3% of the second lithium salt, A4% of the third lithium salt, C1% of the FEC, and C2% of the water-removing additive are all based on the total mass of the non-aqueous electrolyte, while the content D1% of the first solvent, D2% of the second solvent, and D3% of the third solvent are all based on the total mass of the organic solvent. " / " indicates that the corresponding component was not added.

[0157] Manufacturing of secondary batteries

[0158] The positive electrode piece, separator, and negative electrode piece are stacked and wound in order to obtain an electrode assembly. The electrode assembly is placed in a battery case, a cover plate is welded on, and then the above-mentioned non-aqueous electrolyte is injected. After further processes such as packaging, standing, chemical conversion, and aging, a rectangular hard-case secondary battery is obtained. The group margin B of the secondary battery is as shown in Table 1, and is obtained by a test method in which the group margin B of the secondary battery = L2 / L1, where L1 is the thickness of the inside of the battery case and L2 is the thickness of the electrode assembly.

[0159] Test section

[0160] (1) Test of the mass energy density of secondary batteries

[0161] At 25°C, the secondary battery was charged to 4.3V with a constant current of 0.33C, and charging was continued at a constant voltage until the current reached 0.05C. After the secondary battery was left standing for 5 minutes, it was discharged to 2.8V with a constant current of 0.33C to obtain the discharge energy Q. The mass energy density of a secondary battery (Wh / Kg) = discharge energy Q / mass m of the secondary battery

[0162] (2) Testing of the storage performance of secondary batteries

[0163] At 60°C, a secondary battery is charged to 4.3V with a constant current of 1C, and then continued charging with a constant voltage until the current drops to 0.05C. At this time, the volume of the secondary battery is measured by the drainage method and defined as V0. The secondary battery is placed in a constant temperature chamber at 60°C and stored for 30 days. After removing it, the volume of the secondary battery is measured by the drainage method and defined as V1. The volume expansion rate (%) of the secondary battery after 30 days of storage at 60°C = [(V1-V0) / V0] × 100%.

[0164] (3) Testing of the cycle performance of secondary batteries

[0165] At 45°C, the secondary battery is charged to 4.3V with a constant current of 1C, and then continued charging with a constant voltage until the current drops to 0.05C. At this point, the secondary battery is fully charged, and the charge capacity at this time is recorded and recorded as the first charge capacity. After the secondary battery is left to stand for 5 minutes, it is discharged to 2.8V with a constant current of 1C. This is one charge-discharge cycle, and the discharge capacity at this time is recorded and recorded as the first discharge capacity. The secondary battery is subjected to a charge-discharge cycle test according to the above method, and the discharge capacity after each cycle is recorded. The capacity retention rate (%) of the secondary battery after 600 cycles at 45°C = Discharge capacity after 600 cycles / First discharge capacity × 100%.

[0166] (4) Test of the initial DC internal resistance of a secondary battery

[0167] At 25°C, the secondary battery is charged to 4.3V with a constant current of 1C, and then continued charging with a constant voltage until the current drops to 0.05C, at which point the secondary battery is fully charged. The secondary battery is discharged with a constant current of 0.5C and adjusted to 50% SOC, and the voltage of the secondary battery at this point is denoted as U1. The secondary battery is discharged with a constant current of 4C I1 for 30 seconds, and a sampling point of 0.1 seconds is adopted, and the discharge end voltage is denoted as U2. The DC internal resistance of the secondary battery at 50% SOC represents the initial DC internal resistance of the secondary battery, and the initial DC internal resistance of the secondary battery (mΩ) = (U1 - U2) / I1.

[0168] Table 1 shows the manufacturing parameters for Examples 1-36 and Comparative Examples 1-3, and Table 2 shows the test results obtained for Examples 1-36 and Comparative Examples 1-3 according to the performance test method described above.

[0169] [Table 1]

[0170] [Table 2]

[0171] As can be seen from the summary of the test results in Tables 1 and 2, when the non-aqueous electrolyte contains the compound represented by formula I, and its content A is 1%, and the group margin B of the secondary battery satisfies B / A1 of 0.5 to 45, the secondary battery can simultaneously achieve a high group margin design and high safety performance, as well as low internal resistance and a high capacity retention rate. On the other hand, the compound represented by formula I simultaneously forms a uniform, dense, and stable interfacial film on the positive and negative electrodes, reducing direct contact between the active material and the non-aqueous electrolyte, reducing damage and regeneration of the positive and negative electrode interfacial films, further reducing gas generation and consumption of active lithium ions in this process, reducing gas expansion of the battery, and improving the battery's capacity retention rate. On the other hand, the compound represented by formula I stabilizes the crystal structure of the positive electrode active material, reduces the deposition of lattice oxygen and the elution of transition metal ions, further reducing a series of side reactions resulting therefrom, and reducing gas expansion of the battery.

[0172] As can be seen from the combined test results of Examples 1-9 and Comparative Example 2, when B / A1 is greater than 45, there is insufficient compound represented by formula I that forms a uniform, dense, and stable positive electrode interface film and / or negative electrode interface film. Consequently, the crystal structure of the positive electrode active material cannot be effectively stabilized and the decomposition of the non-aqueous electrolyte cannot be reduced, resulting in high gas generation in the secondary battery, a high coefficient of volume expansion, and a high safety risk still faced by secondary batteries with a high group margin design. At the same time, due to the frequent interfacial side reactions between the non-aqueous electrolyte and the electrodes, the interfacial resistance of the positive electrode and / or negative electrode increases, resulting in high internal resistance and low capacity retention of the secondary battery.

[0173] As can be seen from the combined test results of Examples 1-9 and Comparative Example 3, when B / A1 is less than 0.5, an excessively thick positive electrode interface film and / or negative electrode interface film are formed, resulting in high interfacial resistance of the positive electrode and / or negative electrode. Consequently, the secondary battery has high internal resistance and low capacity retention. At the same time, because the structure of the compound represented by formula I contains one oxalic acid group, a high content of this group increases the amount of gas generated by its decomposition, causing the volume expansion coefficient of the secondary battery to increase without decreasing.

[0174] As can be seen from summarizing the test results of Examples 1 to 9, the overall performance of the secondary battery is better when the content A1% of the compound represented by formula I and the content A2% of the first lithium salt satisfy 0 < 10A1 + A2 / 5 ≤ 15 and / or 10 ≤ A2 / A1 ≤ 600.

[0175] As can be seen from summarizing the test results of Examples 4, 10-14, when the non-aqueous electrolyte further contains a second lithium salt, and the content of the second lithium salt (A3%) and the content of the compound represented by formula I (A1%) satisfy 0.25 ≤ A3 / A1 ≤ 25, preferably 4 ≤ A3 / A1 ≤ 20, the secondary battery has a reduced volume expansion rate, reduced internal resistance, and increased capacity retention rate. This is thought to be because the possible second lithium salt can improve the ionic conductivity of the non-aqueous electrolyte, reduce the viscosity of the non-aqueous electrolyte, and contribute to the formation of a negative electrode interface film with lower resistance and higher thermal stability.

[0176] As can be seen from summarizing the test results of Examples 4, 15-19, when the non-aqueous electrolyte further contains the additive FEC, and the content of FEC (C1%) and the content of the compound represented by formula I (A1%) satisfy 5 ≤ C1 / A1 ≤ 50, preferably 10 ≤ C1 / A1 ≤ 30, it contributes to improving the capacity retention rate of the secondary battery.

[0177] As can be seen from the summary of the test results in Examples 17 and 20-21, when the non-aqueous electrolyte further contains a water-removing additive, it contributes to a decrease in the volume expansion rate of the secondary battery and an improvement in the capacity retention rate of the secondary battery.

[0178] Furthermore, this application is not limited to the embodiments described above. The embodiments described above are merely illustrative, and any embodiment that has a configuration substantially identical to the technical idea and produces similar effects within the scope of the technical proposal of this application is included in the scope of this application. In addition, forms that add various modifications to the embodiments that can be conceived by a person skilled in the art, without departing from the spirit of this application, and other forms that are constructed by combining some of the components of the embodiments are also included in the scope of this application.

Claims

1. A secondary battery comprising a battery case, an electrode assembly housed within the battery case, and a non-aqueous electrolyte, Here, the non-aqueous electrolyte contains a compound represented by formula I, The mass percentage content of the compound represented by formula I is A1% according to the total mass of the non-aqueous electrolyte, the group margin of the secondary battery is B, and the secondary battery satisfies the conditions that B is 0.88 to 0.99 and A1 is 0.05 or more and less than 2. The group margin = Thickness of electrode assembly / Inner thickness of battery case The aforementioned group margin is the ratio of the actual internal cross-sectional area of ​​the secondary battery to the maximum internal cross-sectional area, i.e., the filling rate. Secondary battery. 【Chemistry 1】 In formula I, X and Y each independently represent a hydrogen atom, a halogen atom, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C6-C20 aryl group, a C1-C20 halogenated alkyl group, a C2-C20 halogenated alkenyl group, a C2-C20 halogenated alkynyl group, a C6-C20 halogenated aryl group, a C1-C20 alkoxy group, a C2-C20 alkenyloxy group, a C2-C20 alkynyloxy group, a C6-C20 halogenated aryloxy group, a C1-C20 halogenated alkoxy group, a C2-C20 halogenated alkenyloxy group, a C2-C20 halogenated alkynyloxy group, a C6-C20 halogenated aryloxy group, or a combination thereof, and at least one of X and Y represents a fluorine atom or a group containing a fluorine atom.

2. The secondary battery according to claim 1, wherein A1 is 0.05 to 1.

3. The non-aqueous electrolyte further contains a first lithium salt, the first lithium salt being lithium hexafluorophosphate, and the mass percentage content of the first lithium salt is A2% according to the total mass of the non-aqueous electrolyte, where A2 is greater than 0 and less than or equal to 14. The secondary battery according to claim 1, wherein 10 ≤ A2 / A1 ≤ 280.

4. The secondary battery according to claim 1, wherein the non-aqueous electrolyte further comprises a first lithium salt, the first lithium salt being lithium hexafluorophosphate, and the mass percentage content of the first lithium salt is A2% according to the total mass of the non-aqueous electrolyte, and 0.5 < 10A1 + A2 / 5 ≤ 15.

5. The non-aqueous electrolyte further contains a second lithium salt, the second lithium salt being a lithium fluorosulfonylimide salt, and the mass percentage content of the second lithium salt is 3% according to the total mass of the non-aqueous electrolyte. 0 < A3 ≤ 2.5 and / or, The secondary battery according to claim 3, wherein 0.25 ≤ A3 / A1 ≤ 25.

6. The secondary battery according to claim 5, wherein A3 / A2 is 0.5 or less.

7. The non-aqueous electrolyte further contains fluoroethylene carbonate, and its mass percentage content is 1% of the total mass of the non-aqueous electrolyte. 0 < C1 ≤ 5 and / or, The secondary battery according to claim 1, wherein 5 ≤ C1 / A1 ≤ 50.

8. The non-aqueous electrolyte further comprises a water-removing additive containing hexamethyldisilazane, tris(trimethylsilyl) phosphate, or a combination thereof, wherein the mass percentage content of the water-removing additive is 2% of the total mass of the non-aqueous electrolyte. The secondary battery according to claim 1, wherein C2 is greater than 0 and less than or equal to 2.

9. The non-aqueous electrolyte comprises an organic solvent, and the organic solvent comprises a first solvent, a second solvent, and a third solvent. The first solvent comprises at least one of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and vinylethylene carbonate, and the mass percentage content of the first solvent in the organic solvent is D1% according to the total mass of the organic solvent. The second solvent comprises at least one of ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate, and the mass percentage content of the second solvent in the organic solvent is D2% according to the total mass of the organic solvent. The third solvent comprises at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate, and the mass percentage content of the third solvent in the organic solvent is D3% according to the total mass of the organic solvent. The secondary battery according to claim 1, wherein the organic solvent satisfies the following conditions: D1 is greater than 0 and 20 or less, D2 is between 50 and 90, and D3 is between 0 and 30.

10. The secondary battery according to claim 1, wherein the electrode assembly includes a positive electrode piece and a negative electrode piece, the capacity of the positive electrode piece is Q1 Ah, the capacity of the negative electrode piece is Q2 Ah, and the secondary battery satisfies 1 < Q2 / Q1 < 1.05 and A1 < B.

11. The secondary battery according to claim 1, wherein at least one of X and Y represents a fluorine atom.

12. The secondary battery according to claim 1, wherein the compound represented by formula I includes at least one of the following compounds. 【Chemistry 2】

13. The secondary battery according to claim 1, wherein the material of the battery case includes at least one of a hard plastic case, aluminum, and stainless steel.

14. A battery module comprising the secondary battery described in claim 1.

15. A battery pack comprising one of the secondary battery described in claim 1 and one of the battery modules described in claim 14.

16. A power consumption device comprising at least one of the secondary battery described in claim 1, the battery module described in claim 14, and the battery pack described in claim 15.

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