Secondary battery, battery module, battery pack, and power consumption device

Abstract

The present application provides a secondary battery, a battery module, a battery pack, and a power consumption device. The secondary battery includes a battery case, and an electrode assembly and a non-aqueous electrolyte contained in the battery case, the non-aqueous electrolyte includes a compound represented by formula I, the mass percent content of the compound represented by formula I is A1% based on the total mass of the non-aqueous electrolyte, the group margin of the secondary battery is B, and the secondary battery satisfies B is 0.88 to 0.99 and B / A1 is 0.5 to 45. The present application allows the secondary battery to have both a high group margin design and high safety performance, and also provides the secondary battery with good cycle performance and dynamic performance. [Formula 1] TIFF2024527211000010.tif42123Figure 1

Description

Technical Field

[0001] The present application belongs to the technical field of batteries, and specifically relates to secondary batteries, battery modules, battery packs, and power consumption devices.

Background Art

[0002] In recent years, secondary batteries have been widely applied in multiple fields such as energy storage power systems such as hydraulic, thermal, wind, and solar power plants, and electric tools, electric bicycles, electric motorcycles, electric vehicles, military devices, aerospace, etc. With the application and popularization of secondary batteries, the requirements for their energy density are becoming increasingly high. In order to improve the energy density of secondary batteries, the commonly adopted technical solution is to design the group margin of secondary batteries to be increasingly large. However, in this way, the remaining space of secondary batteries is becoming increasingly small. As a result, there is not enough space to accommodate the gas generated during processes such as formation, charge and discharge, and storage, the pressure on the battery case continues to increase, and it has a serious impact on the safety performance of secondary batteries. Therefore, there is a demand for providing secondary batteries that can achieve both energy density and safety performance.

Summary of the Invention

[0003] An object of the present application is to provide a secondary battery, a battery module, a battery pack, and a power consumption device that can achieve both a high group margin design and high safety performance in the secondary battery, and endow the secondary battery with good cycle performance and dynamic performance.

[0004] A first aspect of the present application is a secondary battery including a battery case, and an electrode assembly and a non-aqueous electrolyte accommodated in the battery case, where the non-aqueous electrolyte contains a compound represented by Formula I, The mass percentage content of the compound represented by Formula I is A1%, the group margin of the secondary battery is B with respect to the total mass of the non-aqueous electrolyte, and the secondary battery satisfies that B is 0.88 to 0.99 and B / A1 is 0.5 to 45. A secondary battery is provided.

Chemical Formula

[0005] As a discovery made by the inventors of the present application, when the non-aqueous electrolyte contains a compound represented by Formula I and the content A1% thereof and the group margin B of the secondary battery satisfy that B / A1 is 0.5 to 45, the secondary battery can achieve both a high group margin design and high safety performance, and can have good cycle performance and dynamic performance. On the other hand, the compound represented by Formula I can simultaneously form a uniform, dense and stable interfacial film on the positive electrode and the negative electrode, reduce the direct contact between the active materials (positive electrode active material and negative electrode active material) and the non-aqueous electrolyte, reduce the breakage and regeneration of the positive electrode interfacial film and the negative electrode interfacial film, further reduce the gas generation and the consumption of active lithium ions in this process, reduce the gas expansion of the battery, and improve the capacity retention rate of the battery. On the other hand, the compound represented by Formula I can stabilize the crystal structure of the positive electrode active material, reduce the precipitation of lattice oxygen and the elution of transition metal ions, and further reduce a series of side reactions caused thereby, and reduce the gas expansion of the battery.

[0006] In any embodiment of the present application, B is 0.90 to 0.95. Thereby, without affecting the safety performance of the secondary battery, the secondary battery can be provided with a high energy density.

[0007] In any embodiment of the present application, B / A1 is 4 to 20, preferably 10 to 20. Thereby, the compound represented by Formula I can sufficiently exhibit the effect of reducing gas generation and improving the capacity 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. Thereby, it contributes to better reducing gas generation and consumption of active lithium ions, reducing gas expansion of the battery, and improving the capacity retention rate.

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

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

[0011] In any embodiment of the present application, 0 < 10A1 + A2 / 5 ≤ 15, preferably, 2.6 ≤ 10A1 + A2 / 5 ≤ 5. Thereby, while reducing gas generation in the secondary battery, it contributes to improving the capacity retention rate of the secondary battery.

[0012] In any embodiment of the present application, the non-aqueous electrolyte further contains a second lithium salt. The second lithium salt is a lithium fluorosulfonylimide salt. Preferably, the molecular formula of the lithium fluorosulfonylimide salt is LiN(SO 2 R 1 )(SO 2 R 2 ), where R 1 , R 2 are each independently F or C n F2n+1 which is represented by n being an integer from 1 to 10. The mass percentage content of the second lithium salt is A3% based on the total mass of the non-aqueous electrolyte. Preferably, 0 < A3 ≤ 2.5, and more preferably, 0.5 ≤ A3 ≤ 2.0. Thereby, while improving the safety of the secondary battery, the rate performance of the secondary battery can be improved.

[0013] In any embodiment of the present application, preferably, 0.25 ≤ A3 / A1 ≤ 25, and more preferably, 4 ≤ A3 / A1 ≤ 20. Thereby, without degrading the cycle performance and storage performance of the secondary battery, the internal resistance of the secondary battery can be further reduced to improve the rate 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 likely to hydrolyze, and high thermal stability can be achieved at the same time, and it contributes to the formation of an interfacial film with lower resistance.

[0015] In any embodiment of the present application, the non-aqueous electrolyte further contains fluoroethylene carbonate with a mass percentage content of C1% based on the total mass of the non-aqueous electrolyte. Preferably, 0 < C1 ≤ 5, and 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, and more preferably, 10 ≤ C1 / A1 ≤ 30. Thereby, it is advantageous to fully exert 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 includes a water removal additive containing hexamethyldisilazane, tris(trimethylsilyl) phosphate, or a combination thereof. The mass percentage content of the water removal additive is C2% based on the total mass of the non-aqueous electrolyte. Preferably, C2 is greater than 0 and less than or equal to 2, and more preferably, it is 0.01 to 2. Thereby, the gas expansion of the secondary battery can be further improved, and a high group margin design and high safety performance of the secondary battery can be better balanced.

[0018] In any embodiment of the present application, the non-aqueous electrolyte contains an organic solvent. The organic solvent includes a first solvent containing at least one of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and vinyl ethylene carbonate, with a mass percentage content in the organic solvent of D1% based on the total mass of the organic solvent, a second solvent containing at least one of ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate, with a mass percentage content in the organic solvent of D2% based on the total mass of the organic solvent, and a third solvent containing at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate, with a mass percentage content in the organic solvent of D3% based on the total mass of the organic solvent. For the organic solvent, D1 is greater than 0 and less than or equal to 20, D2 is 50 to 90, and D3 is 0 to 30. Preferably, D1 is 0.5 to 20, and more preferably, it is 10 to 20.

[0019] In any embodiment of the present application, the electrode assembly includes a positive electrode tab and a negative electrode tab. The capacity of the positive electrode tab is Q1 Ah, and the capacity of the negative electrode tab is Q2 Ah. The secondary battery satisfies 1 < Q2 / Q1 < 1.05 and A1 < B. Thereby, the secondary battery can achieve a 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 a thinner positive electrode interface film and / or negative electrode interface film, thus 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 the formula I includes at least one of the following compounds.

Chemical formula

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

[0024] The 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 the battery module of the second aspect.

[0025] The fourth aspect of the present application provides a power consumption device including 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] Since the battery module, battery pack, and power consumption device of the present application include the secondary battery according to the present application, they have at least the same advantages as the secondary battery.

Brief Description of the Drawings

[0027] To more clearly explain the technical solutions of the embodiments of this application, the drawings that need to be used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application, and those skilled in the art can also obtain other drawings based on these drawings without creative efforts.

[0028]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0029] Hereinafter, embodiments specifically disclosing the secondary battery, battery module, battery pack, and power consumption device of this application will be described in detail with appropriate reference to the drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and duplicate descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily redundant and to facilitate the understanding of those skilled in the art. Also, the drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter recited in the claims.

[0030] The "range" disclosed in this application is limited in the form of a lower limit and an upper limit. A predetermined range is limited by selecting one lower limit and one upper limit, and the selected lower limit and upper limit particularly limit the boundaries of the range. The range limited in such a manner may or may not include the endpoints and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are enumerated for a specific parameter, ranges of 60 - 110 and 80 - 120 are also understood to be expected. Also, if the minimum range values 1 and 2, and the maximum range values 3, 4, and 5 are enumerated, ranges of 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5 are all expected. In this application, unless otherwise explained, the numerical range "a - b" represents a reduced expression of any real number combination between a and b, where both a and b are real numbers. For example, the numerical range "0 - 5" represents all real numbers between 0 and 5 in this specification, and "0 - 5" is a reduced expression of the combination of these numerical values. Also, when a certain parameter is expressed as 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 selectable embodiments of this application can be combined with each other to form a new technical solution, and such a technical solution should be considered to be included in the disclosure content of this application.

[0032] Unless otherwise specified, all technical features and selectable technical features of this application can be combined with each other to form a new technical solution, and such a technical solution should be considered to be included in the disclosure content of this application.

[0033] Unless otherwise specified, all steps of the present application may be performed in sequence or randomly, but preferably in sequence. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, when it is said that the method can 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), and it is also possible to include steps (c), (a) and (b), etc.

[0034] Unless otherwise specified, the terms "having", "comprising" and "including" referred to in the present application are open-ended and may also be closed-ended. For example, the above "having", "comprising" and "including" can further have, comprise or include other components not listed, or can comprise or include only the listed components.

[0035] Unless otherwise specified, in the present application, the term "or" is inclusive. For example, the phrase "A or B" represents "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition of "A or B". 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 clearly contemplate that each of the members included in these groups and ranges is an individual sub-combination. For example, the term "alkyl group of C1-C6" clearly contemplates the disclosure of the 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 the present application, the group margin is the ratio of the actual internal cross-sectional area of the secondary battery to the maximum internal cross-sectional area, that is, the filling rate. There are two calculation methods for the group margin as follows. (1) Group margin = Total cross-sectional area of the electrode assembly / Internal space area of the battery case (2) Group margin = Thickness of the electrode assembly / Internal thickness of the battery case

[0038] In the present application, the terms "a plurality" and "a plurality of types" refer to two or more than two.

[0039] A secondary battery generally includes an electrode assembly, a non-aqueous electrolyte, and an exterior for sealing the electrode assembly and the non-aqueous electrolyte. As shown in FIG. 1, it is a rectangular-structured secondary battery 5 which is an example of the present application. In some embodiments, as shown in FIG. 2, the exterior 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 the side plates surround to form an accommodation cavity. The battery case 51 has an opening communicating with the accommodation cavity, and the cover plate 53 covers the opening to seal the accommodation cavity.

[0040] Currently, in order to improve the energy density of secondary batteries, a commonly adopted technical solution is to design the group margin of secondary batteries to be increasingly large. The group margin can reflect factors such as the difficulty of inserting the electrode assembly into the case, the pressure of the electrode assembly on the battery case after charging expansion, and the energy density of the secondary battery. The smaller the group margin of the secondary battery, the easier it is for the electrode assembly to enter the case. However, correspondingly, the energy density of the obtained secondary battery is relatively low, so there is a possibility that the actual usage requirements cannot be met. The larger the group margin of the secondary battery, the higher the energy density. However, it becomes difficult for the electrode assembly to enter the case, which not only increases the difficulty of the process but also causes damage to the electrode assembly. Also, the larger the group margin of the secondary battery, the smaller the remaining space inside the battery case, and thus there may not be enough space to accommodate the gas generated during processes such as formation, charge-discharge, and storage. And after the electrode assembly expands, the pressure received by the battery case continues to increase, seriously affecting the safety performance of the secondary battery.

[0041] Therefore, currently, it is impossible to achieve both a high group margin design and high safety performance for secondary batteries.

[0042] As a discovery made by the inventors of the present application, by adopting an appropriate non-aqueous electrolyte, the gas generated during processes such as formation, charge-discharge, and storage can be significantly reduced. Thereby, the pressure received by the battery case is reduced, enabling the secondary battery to achieve both a high group margin design and high safety performance.

[0043] Specifically, the secondary battery of the present application includes a battery case, an electrode assembly and a non-aqueous electrolyte accommodated in the battery case, and the non-aqueous electrolyte contains a compound represented by Formula I.

Chemical formula

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

[0045] The secondary battery of the present application can be a lithium secondary battery, particularly a lithium ion secondary battery.

[0046] The electrode assembly usually includes a positive electrode plate, a negative electrode plate and a separator. The separator is provided between the positive electrode plate and the negative electrode plate, mainly plays a role in preventing short circuit between the positive electrode and the negative electrode, and can allow lithium ions to pass through. The positive electrode plate, the negative electrode plate and the separator can form an electrode assembly by a winding process and / or a lamination process. The electrode assembly is enclosed in a housing cavity formed by being surrounded by the bottom plate of the battery case and the side plate connected to the bottom plate, and the non-aqueous electrolyte is impregnated into the electrode assembly. The number of electrode assemblies included in the secondary battery may be one or more and can be adjusted as needed. In the present application, the materials of the battery case and the cover plate may include at least one of a hard plastic case, aluminum, and stainless steel.

[0047] The non-aqueous electrolyte is one of the important factors affecting the performance of secondary batteries. The non-aqueous electrolyte contains an organic solvent and a lithium salt dissolved therein, and in processes such as formation, charge-discharge, and storage, a series of oxidation and reduction reactions are likely to occur, and decomposition occurs to generate a large amount of gas.

[0048] In the process of forming (i.e., the first charge) of a secondary battery, a series of oxidation and reduction reactions occur on the surface of the negative electrode active material, and gas generation accompanies the formation of a solid electrolyte interphase (SEI).

[0049] In the process of long-term charge-discharge cycles of a secondary battery, the bound water in the electrode tab is gradually released into the non-aqueous electrolyte. When the water content in the non-aqueous electrolyte increases, a series of side reactions inside are caused, leading to gas expansion of the battery. Currently, the non-aqueous electrolyte system with the widest commercial application is a mixed carbonate ester solution of lithium hexafluorophosphate. Lithium hexafluorophosphate has poor thermal stability in a high-temperature environment and decomposes at high temperatures to generate PF 5 to produce. PF 5 has strong Lewis acidity and acts on the lone pair of electrons on the oxygen atom in the organic solvent molecule to decompose the organic solvent, causing gas expansion of the battery. Also, PF 5has high sensitivity to moisture and generates HF upon contact with water. HF not only induces the decomposition of organic solvents, but also causes an increase in the acidity of non-aqueous electrolytes, and further easily corrodes the cathode active material and the cathode current collector, causing the elution of transition metal ions in the cathode active material. After the transition metal ions in the cathode active material elute and move to the anode, they are reduced to transition metals, and the thus generated transition metals correspond to "catalysts", which catalyze the decomposition of the interfacial film on the surface of the anode active material, further increasing the gas expansion of the battery and affecting the safety performance of the secondary battery. Also, in order to replenish the lost interfacial film, the non-aqueous electrolyte is continuously consumed and a series of oxidation and reduction reactions continuously occur, thereby further increasing the gas expansion of the battery. In this process, the active lithium ions inside the battery are also continuously consumed, further irreversibly affecting the capacity retention rate of the secondary battery.

[0050] During the storage process of the secondary battery, the cathode active material is always in a metastable state and is extremely unstable, so decomposition reactions occur and cause gas expansion. Also, if the stability of the interfacial film on the surface of the anode active material is low, a part of the surface in contact with the non-aqueous electrolyte is dissolved as the temperature rises. For example, the organic component (CH 2 OCO 2 Li) 2 in the interfacial film is unstable and prone to decomposition reactions, generating gas and causing gas expansion of the battery.

[0051] As a discovery made by the applicant's research, it has been found that by containing a compound represented by Formula I in the non-aqueous electrolyte and satisfying 0.5 ≤ B / A1 ≤ 45 for the content A1% thereof and the group margin B of the secondary battery, the gas generated during processes such as formation, charge and discharge, and storage can be reduced.

[0052] The reason is unknown, but it is considered to be due to the reasons shown below.

[0053] First, the compound represented by Formula I can form a uniform, dense, and stable interfacial film on the surface of the positive electrode active material. Thereby, the direct contact between the positive electrode active material and the non-aqueous electrolyte can be reduced, side reactions at the interface can be reduced, the elution of transition metal ions can be reduced, and a series of side reactions caused thereby can be reduced to reduce the gas expansion of the battery.

[0054] Second, the B atom in the structure of the compound represented by Formula I is likely to bond with the O atom in the positive electrode active material. Thereby, the crystal structure of the positive electrode active material can be stabilized, the formation of lattice defects such as oxygen vacancies and irreversible interlayer movement can be reduced, and the precipitation of lattice oxygen can be reduced. At the same time, the resistance of charge transfer of the positive electrode active material can be decreased, the diffusion resistance of lithium ions within the positive electrode active material bulk can be decreased, and furthermore, lithium ions within the positive electrode active material bulk can be timely replenished to the surface to avoid over-detachment and over-insertion of lithium. Thereby, the crystal structure of the positive electrode active material has higher stability, lattice oxygen is less likely to precipitate, transition metal ions are less likely to desorb, a series of side reactions caused thereby are reduced, and the gas expansion of the battery is reduced.

[0055] Third, the B-O bond in the structure of the compound represented by Formula I binds to Al 3+ to form a layer of passivation film on the surface of the aluminum foil current collector, and can effectively improve the corrosion of the aluminum foil current collector by 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. Thereby, the breakage and regeneration of the negative electrode interfacial film can be reduced, and furthermore, the gas generation and the consumption of active lithium ions in this process can be reduced, the gas expansion of the battery can be reduced, and the capacity retention rate of the battery can be improved.

[0057] Therefore, when the non-aqueous electrolyte contains the compound represented by Formula I and the content A1% thereof and the group margin B of the secondary battery satisfy 0.5 ≤ B / A1 ≤ 45, on the one hand, the compound represented by Formula I can simultaneously form a uniform, dense and stable interfacial film on both the positive electrode and the negative electrode, reduce the direct contact between the active materials (positive electrode active material and negative electrode active material) and the non-aqueous electrolyte, reduce the breakage and regeneration of the positive electrode interfacial film and the negative electrode interfacial film, further reduce the gas generation and the consumption of active lithium ions in this process, reduce the gas expansion of the battery and improve the capacity retention rate of the battery. On the other hand, the compound represented by Formula I can stabilize the crystal structure of the positive electrode active material, reduce the precipitation of lattice oxygen and the elution of transition metal ions, and further reduce a series of side reactions caused thereby, reducing the gas expansion of the battery. Thereby, the secondary battery of the present application can achieve both a high group margin design and high safety performance, and can have good cycle performance and dynamic performance.

[0058] In the present application, when the content A1% of the compound represented by Formula I and the group margin B of the secondary battery satisfy that B / A1 is between 0.5 and 45, the effects of reducing the gas generation of the compound represented by Formula I and improving the capacity retention rate 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, the compound represented by Formula I that forms a uniform, dense, and stable positive electrode interface film and / or negative electrode interface film is insufficient. 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, the gas generation of the secondary battery is large, the pressure received by the battery case is large, and the safety risk of the secondary battery is high. When B / A1 is less than 0.5, the design of the group margin of the secondary battery is small, and thus a high energy density cannot be achieved simultaneously. Alternatively, the content of the compound represented by Formula I is high, a too thick positive electrode interface film and / or negative electrode interface film is formed, the interface resistance of the positive electrode and / or the interface resistance of the negative electrode increase, and since the structure of the compound represented by Formula I contains one oxalic acid group, gas is generated when it decomposes itself, which instead increases the gas expansion of the battery. Preferably, in some embodiments, B / A1 is 1 to 45, 1 to 30, 1 to 20, 1 to 18, 1 to 16, 1 to 14, 1 to 12, 1 to 10, 4 to 45, 4 to 30, 4 to 20, 4 to 18, 4 to 16, 4 to 14, 4 to 12, 4 to 10, 10 to 45, 10 to 30, 10 to 20, 10 to 18 or 10 to 16.

[0059] In the present application, the group margin B of the secondary battery satisfies that B is 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. Thereby, a high energy density can be given to the secondary battery without affecting the safety performance of the secondary battery.

[0060] In the present application, at least one of X and Y represents a fluorine atom or a group containing a fluorine atom. For example, it represents at least one selected from the group consisting of a partially fluorinated or fully fluorinated C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C6-C20 aryl group, a C1-C20 alkoxy group, a C2-C20 alkenyloxy group, a C2-C20 alkynyloxy group, and a C6-C20 aryloxy group. The presence of the 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 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 fluorine atoms.

[0061] As an example, the compound represented by the formula I contains at least one of the following compounds.

Chemical formula

[0062] In some embodiments, the content A1% of the compound represented by Formula I satisfies that A1 is not less than 0.02 and less than 2. Preferably, A1 is 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 the generation of gas and the consumption of active lithium ions, reducing the gas expansion of the battery, and improving the capacity retention rate. Also, when the content of the compound represented by Formula I is low, due to the 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, the crystal structure of the positive electrode active material cannot be effectively stabilized and the decomposition of the non-aqueous electrolyte cannot be reduced. Therefore, there is a large amount of gas generation in the secondary battery, the pressure received by the battery case is large, and the safety risk of the secondary battery is high. 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 it decomposes itself, and conversely, the situation of increasing the gas expansion of the battery can be effectively avoided.

[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, affecting 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 tab is Q1 Ah, the capacity of the negative electrode tab is Q2 Ah, and the secondary battery satisfies 1 < Q2 / Q1 < 1.05 and A1 < B. When the capacity of the negative electrode tab is larger than that of the positive electrode tab, it can ensure that the negative electrode tab has sufficient pores to accommodate lithium ions from the positive electrode, and prevent lithium from precipitating from the negative electrode. At the same time, when the ratio Q2 / Q1 of the capacity of the negative electrode tab to the capacity of the positive electrode tab is smaller than 1.05, it is beneficial to further improve 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 tab and the capacity of the negative electrode tab have the meanings known in the art and can be measured by devices and methods known in the art. For example, it can be measured using a blue battery measuring instrument.

[0066] As an example, as a method for measuring the capacity of the positive electrode tab, after punching out the cold-pressed positive electrode tab into a small wafer with an area of S 0 , assembling it into a buckle-type battery in a glove box, charging it to the charge cut-off voltage at a constant current of 0.1 mA, and discharging it to the discharge cut-off voltage at a constant current of 0.1 mA to obtain a discharge capacity CAP1, and obtaining the capacity of the positive electrode tab by the formula CAP1×S 1 / S 0 , where S 0 is the area of the small wafer, and S 1 is the coating area of the positive electrode film layer on the positive electrode tab.

[0067] As an example, as a method for measuring the capacity of the negative electrode tab, after punching out the cold-pressed negative electrode tab into a small wafer with an area of S 0 , assembling it into a buckle-type battery in a glove box, discharging it to the discharge cut-off voltage at a constant current of 0.1 mA, and charging it to the charge cut-off voltage at a constant current of 0.1 mA to obtain a discharge capacity CAP2, and obtaining the capacity of the negative electrode tab by the formula CAP1×S 2 / S 0 , where S0 is the area of the small wafer, S 2 is the coating area of the negative electrode film layer on the negative electrode tab. [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 based on 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. Since lithium hexafluorophosphate has the property of high ionic conductivity, when its content is within an appropriate range, it contributes to the improvement of the ionic conductivity of the whole non-aqueous electrolyte, the acceleration of lithium ion transport, and the improvement of the capacity retention rate of the secondary battery. However, lithium hexafluorophosphate has poor thermal stability in a high-temperature environment and decomposes at a high temperature to produce PF 5 to generate. PF 5 reacts with water to form HF, which easily corrodes the positive electrode active material and increases the gas expansion of the battery. When the non-aqueous electrolyte contains the compound represented by Formula I and lithium hexafluorophosphate at the same time, the compound represented by Formula I reacts with lithium hexafluorophosphate to form the compound LiPF 4 C 2 O 4 can be formed, so the decomposition of lithium hexafluorophosphate and the formation of HF are reduced, and the secondary battery can have high safety, high energy density and good cycle performance.

[0069] In some embodiments, the content A1% of the compound represented by formula I and the content A2% of the first lithium salt satisfy 10 ≤ A2 / A1 ≤ 600. After reasonably combining the content A1% of the compound represented by formula I and the content A2% of the first lithium salt, it reduces the generation of gas in the secondary battery and contributes to the improvement of the capacity retention rate of the secondary battery. Also, when the content of the first lithium salt is high and the content of the compound represented by formula I is low, there may be a large amount of HF in the non-aqueous electrolyte, which increases the decomposition reaction of the non-aqueous electrolyte and the interfacial film formed on the positive electrode and / or negative electrode of the compound represented by formula I is not sufficiently dense, and it cannot prevent the corrosion of the positive electrode active material by HF and a series of side reactions resulting therefrom, which may increase the generation of gas in the secondary battery. When the content of the first lithium salt is low and the content of the compound represented by formula I is high, since the anion radius of the compound represented by formula I is small, it is difficult for it to completely dissociate in the non-aqueous electrolyte and the anions and cations are likely to associate, thereby reducing the ionic conductivity of the non-aqueous electrolyte and possibly deteriorating the capacity retention rate of the secondary battery. Preferably, 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 embodiments, 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. After reasonably combining the content A1% of the compound represented by Formula I and the content A2% of the first lithium salt, it can reduce the generation of gas in the secondary battery and contribute to the improvement of the capacity retention rate of the secondary battery. Further, when both the content of lithium hexafluorophosphate and the content of the compound represented by Formula I are high, there may be a large amount of HF in the non-aqueous electrolyte, so the stability of the crystal structure of the positive electrode active material deteriorates, there are many decomposition reactions of the non-aqueous electrolyte, and further, there is a large amount of gas generation in the secondary battery, increasing the safety risk. At the same time, because the anion radius of the compound represented by Formula I is small, it is difficult to completely dissociate in the non-aqueous electrolyte, and the anion and cation are likely to associate. 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 A1% of the compound represented by Formula I and the content A2% of the content of the first lithium salt simultaneously satisfy 10 ≤ A2 / A1 ≤ 600 and 0 < 10A1 + A2 / 5 ≤ 15. Thereby, the non-aqueous electrolyte contains an appropriate content of the compound represented by Formula I and the first lithium salt, and the secondary battery using the same can achieve both a high group margin design, high safety performance and good cycle performance. More preferably, the content A1% of the compound represented by Formula I and the content A2% of the first lithium salt simultaneously satisfy 60 ≤ A2 / A1 ≤ 600 and 2.6 ≤ 10A1 + A2 / 5 ≤ 5.

[0072] In some embodiments, the non-aqueous electrolyte further contains a second lithium salt which is lithium fluorosulfonyl imide salt. Preferably, the molecular formula of the lithium fluorosulfonyl imide salt is LiN(SO2 R 1 )(SO 2 R 2 ) and R 1 、R 2 are each independently F or C n F 2n+1 represents, and n is an integer from 1 to 10. As an example, the lithium fluorosulfonylimide salt includes lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or a combination thereof. Preferably, the lithium fluorosulfonylimide salt includes 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, and 0 ≦ A3 ≦ 2.5. For example, A3 is in the range consisting 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 value above. 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 a -F or -C with a strong electron-withdrawing property as a conjugate group n F 2n+1It contains, and its anion charge is highly delocalized, weakening the interaction force between the anion and lithium ions. Therefore, lithium fluorosulfonylimide salt has a low lattice energy and is easy to dissociate. Thereby, the ionic conductivity of the non-aqueous electrolyte can be improved, the viscosity of the non-aqueous electrolyte can be reduced, and the rate performance of the secondary battery can be improved. At the same time, lithium fluorosulfonylimide salt has high thermal stability, a wider electrochemical window and is difficult to hydrolyze, and can form a LiF-rich interfacial film on the surface of the negative electrode active material. The LiF-rich interfacial film is thinner, has lower resistance, higher thermal stability, can reduce the side reaction between the negative electrode active material and the non-aqueous electrolyte, reduce the gas expansion of the battery, and suppress the formation of lithium dendrites. Therefore, when the non-aqueous electrolyte contains lithium fluorosulfonylimide salt, the safety of the secondary battery can be improved while improving the rate performance 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 fluorosulfonyl imide salt, the rate performance of the secondary battery can be improved. However, lithium fluorosulfonyl imide salt cannot withstand high voltages, corrodes the positive electrode current collector (for example, aluminum foil) at high potentials, and has a poor film-forming effect on the surface of the positive electrode active material, and is likely to affect the cycle performance of the secondary battery. The compound represented by Formula I, as a stabilizer for the positive electrode active material, can form an interfacial film with excellent performance on the surface of the positive electrode active material, reduce the side reaction between the positive electrode active material and the non-aqueous electrolyte, and stabilize the crystal structure of the positive electrode active material. Therefore, using the compound represented by Formula I in combination with lithium fluorosulfonyl imide salt is advantageous for fully exerting the improvement effect of the rate performance of the secondary battery by lithium fluorosulfonyl imide salt. Further, by reasonably controlling the relationship between the content A1% of the compound represented by Formula I and the content A3% of the second lithium salt so as to satisfy 0.25 ≦ A3 / A1 ≦ 25, the synergistic effect between the compound represented by Formula I and lithium fluorosulfonyl imide salt can be fully exerted. It can not only prevent the cycle performance and storage performance of the secondary battery from deteriorating, but also further reduce the internal resistance of the secondary battery and improve the rate performance of the secondary battery.

[0077] In some embodiments, the non-aqueous electrolyte contains both a first lithium salt and a second lithium salt. Preferably, the content A2% of the first lithium salt and the content A3% of the second lithium salt satisfy that A3 / A2 is 0.5 or less, and more preferably, it is 0.005 to 0.5, 0.005 to 0.4, 0.005 to 0.3, 0.005 to 0.2, 0.02 to 0.5, 0.02 to 0.4, 0.04 to 0.3, 0.02 to 0.2, 0.04 to 0.5, 0.04 to 0.4, 0.04 to 0.3, or 0.04 to 0.2. Thereby, the non-aqueous electrolyte is less likely to hydrolyze, can achieve higher thermal stability, and contributes to the formation of an interfacial film with lower resistance.

[0078] In some embodiments, the non-aqueous electrolyte is lithium tetrafluoroborate (LiBF 4 ) and lithium perchlorate (LiClO 4) Lithium hexafluoroarsenate (LiAsF 6 ) Lithium difluorophosphate (LiPO 2 F 2 ) It may further contain a third lithium salt including at least one of lithium difluorodioxalate phosphate (LiDFOP) and lithium tetrafluoroborate phosphate (LiTFOP). The third lithium salt, as an auxiliary lithium salt, can play a role in further improving the interfacial performance of the positive electrode and / or the negative electrode, or improving 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, 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 includes at least one of a first solvent, a second solvent, and a third solvent.

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

[0082] The second solvent is a chain carbonate compound, for example, it may include 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, preferably, the organic solvent comprises at least a first solvent and a second solvent. When the content of a lithium salt such as lithium hexafluorophosphate is high, the viscosity of the non-aqueous electrolyte increases, the ionic conductivity decreases, which is disadvantageous for the transport of lithium ions. Since the first solvent has a high dielectric constant, it can increase the ionic conductivity of the non-aqueous electrolyte. Since the second solvent has a low viscosity, it can decrease the viscosity of the non-aqueous electrolyte. Therefore, when the organic solvent contains both the first solvent and the second solvent, it contributes to the non-aqueous electrolyte having an appropriate viscosity and ionic conductivity, and further contributes to the transport of lithium ions.

[0084] In some embodiments, the organic solvent may further comprise a third solvent. The third solvent is a carboxylic acid ester compound, and for example, may contain at least one of 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, is applied to the non-aqueous electrolyte, contributes to the non-aqueous electrolyte having an appropriate viscosity and ionic conductivity, and further contributes to the transport of lithium ions and the improvement of the rate performance of the secondary battery.

[0085] Although the first solvent can increase the ionic conductivity of the non-aqueous electrolyte, it is likely to cause a decomposition reaction and affect the safety performance of the secondary battery. Therefore, it is necessary to control its content within an appropriate range. In some embodiments, the mass percentage content of the first solvent in the organic solvent is D1% based on the total mass of the organic solvent, where 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 embodiments, the mass percentage content of the second solvent in the organic solvent is D2% based on the total mass of the organic solvent, and 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. Therefore, it is not preferable that its content is too high. In some embodiments, the mass percentage content of the third solvent in the organic solvent is D3% based on 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 the present application may further include other solvents other than the above first solvent, second solvent, and third solvent. As an example, the other solvents may include sulfone solvents such as sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). [Additive]

[0089] In some embodiments, the non-aqueous electrolyte may further include an additive. For example, it may include at least one of a halogen-substituted cyclic carbonate compound, a nitrile compound, a phosphazene compound, an aromatic hydrocarbon and a halogenated aromatic hydrocarbon compound, an isocyanate compound, an acid anhydride compound, a sulfate ester compound, a sulfite ester compound, a sulfonic acid ester compound, and a disulfonic acid ester compound. As long as the gist of the present application is not impaired, the types of these additives are not particularly limited in the present 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, according to the total mass of the non-aqueous electrolyte, the non-aqueous electrolyte further contains fluoroethylene carbonate (FEC), and the mass percentage content thereof is C1%, where 0 ≦ C1 ≦ 5. For example, C1 is in the range consisting of any numerical value such as 0, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or more. Preferably, 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 reduction decomposition reaction at a high potential, forms an interfacial film with certain flexibility on the surface of the negative electrode active material, suppresses the reduction decomposition of the organic solvent at a low potential, and can 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 withstand high-voltage oxidation, is advantageous for matching with a high-voltage positive electrode active material, and is advantageous for further 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, 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 the non-aqueous electrolyte contains fluoroethylene carbonate, the cycle performance of the secondary battery can be effectively improved. However, fluoroethylene carbonate is likely to decompose to form HF. HF destroys the cathode interface film, corrodes the cathode active material, and increases the gas generation amount of the secondary battery. The compound represented by Formula I can be used as a stabilizer for the cathode active material. The B atom in its structure has the function of interacting with the O atom on the surface of the cathode active material, thereby stabilizing the crystal structure of the cathode active material and reducing the destruction of the crystal structure of the cathode active material by HF. Therefore, using the compound represented by Formula I in combination with fluoroethylene carbonate is advantageous for fully exerting the further improvement effect of the cycle performance of the secondary battery by fluoroethylene carbonate. Further, by reasonably controlling the relationship between the content A1% of the compound represented by Formula I and the content C1% of fluoroethylene carbonate to satisfy 5 ≦ C1 / A1 ≦ 50, the synergistic effect between the compound represented by Formula I and fluoroethylene carbonate can be fully exerted. It can not only significantly increase the gas generation of the secondary battery but also further improve the cycle performance of the secondary battery. At the same time, fluoroethylene carbonate has a high dielectric constant. By reasonably controlling the relationship between the content A1% of the compound represented by Formula I and the content C1% of fluoroethylene carbonate to satisfy 5 ≦ C1 / A1 ≦ 50, the anions of the compound represented by Formula I contribute to the formation of free ions, and the association between anions and cations can be reduced. Thereby, the non-aqueous electrolyte has a high ionic conductivity, and the cycle performance of the secondary battery is better.

[0094] In some embodiments, the non-aqueous electrolyte contains both a second lithium salt and fluoroethylene carbonate. Preferably, the secondary battery simultaneously satisfies 0.25 ≦ A3 / A1 ≦ 25 and 5 ≦ C1 / A1 ≦ 50. Further, the secondary battery simultaneously satisfies 4 ≦ A3 / A1 ≦ 20 and 10 ≦ C1 / A1 ≦ 30. In this case, while improving the safety performance of the secondary battery, the cycle performance and rate performance can be improved. 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, as a stabilizer for the positive electrode active material, forms an interfacial film with excellent performance on the surface of the positive electrode active material, improves the lithium ion diffusion rate of the positive electrode active material, reduces the side reaction between the positive electrode active material and the non-aqueous electrolyte, stabilizes the crystal structure of the positive electrode active material, and can reduce the precipitation of lattice oxygen and the elution of transition metal ions. Therefore, reasonably controlling the relationship between the contents of fluoroethylene carbonate, the second lithium salt, and the compound represented by Formula I is advantageous for fully exerting the synergistic effect among the three and sufficiently suppressing the defects of each component used alone.

[0095] In some embodiments, the non-aqueous electrolyte may further contain a water removal additive that contributes to reducing the water content of the non-aqueous electrolyte and reducing a series of side reactions caused by moisture. Thereby, the gas expansion of the secondary battery is further improved, and the secondary battery better achieves both a high group margin design and high safety performance.

[0096] Preferably, in some embodiments, the water removal additive includes hexamethyldisilazane (HMDS), tris(trimethylsilyl) phosphate (TMSP), or a combination thereof. These two water removal additives can effectively reduce the water content of the non-aqueous electrolyte and can also react with lithium hexafluorophosphate to form lithium difluorophosphate. While reducing the decomposition of lithium hexafluorophosphate and the formation of HF, it also further stabilizes the positive electrode interface film and / or the negative electrode interface film, contributing to reducing the interface resistance of the positive electrode and / or the interface resistance of the negative electrode. Thereby, the safety performance of the secondary battery can be further improved, and the cycle performance and rate performance of the secondary battery can be enhanced.

[0097] In some embodiments, the mass percentage content of the water removal 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 - 2, and more preferably 0.1 - 1.

[0098] The non-aqueous electrolyte of the present application can be prepared according to the conventional methods in the art. For example, the organic solvent, the lithium salt, etc. can be uniformly mixed to obtain a non-aqueous electrolyte. The addition order of each material is not particularly limited. For example, the lithium salt, etc. can be added to the organic solvent and uniformly mixed to obtain a non-aqueous electrolyte.

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

[0100] When testing the non-aqueous electrolyte of the present application, the non-aqueous electrolyte can be obtained from the secondary battery. As a specific procedure of one exemplary method for obtaining the non-aqueous electrolyte from the secondary battery, after discharging the secondary battery to the discharge cut-off voltage (generally, the battery is fully discharged for safety), centrifugation is performed, and then an appropriate amount of the liquid obtained by the centrifugation is used as the non-aqueous electrolyte. The non-aqueous electrolyte may also be directly obtained from the liquid injection port of the secondary battery. [Positive electrode tab]

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

[0102] The positive electrode film layer contains a positive electrode active material. The positive electrode active material can adopt a positive electrode active material for a secondary battery known in the art. For example, the positive electrode active material may include at least one of lithium transition metal oxides, lithium-containing phosphates having an olivine structure, and modified compounds thereof. Examples of lithium transition metal oxides include, for example, 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 at least one of modified compounds thereof. Examples of lithium-containing phosphates having an olivine structure include, for example, lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and at least one of modified compounds thereof. The present application is not limited to these materials, and other conventionally known materials used as positive electrode active materials for secondary batteries can be used. These positive electrode active materials may be used alone or in combination of two or more.

[0103] In some embodiments, the positive electrode active material includes a layered material having the molecular formula Li a Ni b Co c Mn d Al e M f O g A h where M represents a doped cation at the transition metal site and A represents a doped anion at the oxygen site, where 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, and 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 of h can be selectively doped and modified by M cations, A anions, or both M cations and A anions. After doping, the crystal structure of the obtained layered material is more stable, lattice oxygen is less likely to precipitate, transition metal ions are less likely to desorb, 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, dynamic performance, etc. are further improved.

[0105] In some embodiments, M is at least one selected from 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 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 The crystal structure of h is more stable, lattice oxygen is less likely to precipitate, transition metal ions are less likely to desorb, and thereby 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 of keeping Li a Ni b Co c Mn d Al e M f O g A h electrically neutral.

[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. Since cobalt has a low content in the earth's crust, is difficult to extract and is expensive, low-cobalt or cobalt-free is an inevitable development trend of the cathode active material. However, cobalt greatly contributes to the diffusion rate of lithium ions in the cathode active material, and low-cobalt or cobalt-free reduces the diffusion rate of lithium ions in the cathode active material, affecting the cycle performance of the secondary battery. Researchers are studying to improve the diffusion rate of lithium ions in low-cobalt or cobalt-free cathode active materials, but there is still no good solution at present.

[0111] As an unexpected discovery further studied by the inventors of the present application, the B atom in the structure of the compound represented by Formula I is likely to bond with the O atom in the cathode active material, reducing the charge transfer resistance of the cathode active material, thereby reducing the diffusion resistance of lithium ions within the bulk of the cathode active material. Therefore, a low-cobalt or cobalt-free cathode active material can have an improved lithium ion diffusion rate, lithium ions within the bulk of the low-cobalt or cobalt-free cathode active material can be timely replenished to the surface, and excessive lithium desorption from the surface of the low-cobalt or cobalt-free cathode active material can be avoided, thereby stabilizing the crystal structure of the low-cobalt or cobalt-free cathode active material. Since the crystal structure of the low-cobalt or cobalt-free cathode active material is more stable, the probability of problems such as instability of the structural, chemical or electrochemical properties of the cathode active material due to excessive lithium desorption from the surface of the low-cobalt or cobalt-free cathode active material can be significantly reduced. For example, the above problems include the problems of irreversible strain and increased lattice defects of the cathode 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] By way of example, a layered material of the formula Li a Ni b Co c Mn d Al e M f O g A h is LiNi 0.8 Co 0.1 Mn 0.1 O 2 、LiNi 0.6 Co 0.2 Mn 0.2 O 2 、LiNi 0.5 Co0.2 Mn 0.3 O 2 、 LiNi 0.8 Co 0.05 Mn 0.15 O 2 、 LiNi 0.7 Mn 0.3 O 2 、 LiNi 0.69 Co 0.01 Mn 0.3 O 2 、 LiNi 0.68 Co 0.02 Mn 0.3 O 2 、 LiNi 0.65 Co 0.05 Mn 0.3 O 2 、 LiNi 0.63 Co 0.07 Mn 0.3 O 2 、 LiNi 0.61 Co 0.09 Mn 0.3 O 2 includes at least one of these, but is not limited thereto.

[0119] Li a Ni b Co c Mn d Al e M f O g A h A can be prepared according to the general methods in this field. An exemplary preparation method is a method obtained by 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 sintering atmosphere may be an oxygen-containing atmosphere, for example, an air atmosphere or an oxygen gas atmosphere. The O 2 concentration in the sintering atmosphere is, for example, 70% - 100%. The sintering temperature and sintering time can be adjusted according to the actual situation.

[0120] As an example, the lithium source is lithium oxide (Li 2 O), lithium phosphate (Li 3 PO 4) Lithium dihydrogen phosphate (LiH 2 PO 4 ), lithium acetate (CH 3 COOLi), lithium hydroxide (LiOH), lithium carbonate (Li 2 CO 3 ), and lithium nitrate (LiNO 3 ), and includes at least one of these, but is not limited thereto. As an example, the nickel source includes at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate, but is not limited thereto. As an example, the cobalt source includes at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate, but is not limited thereto. As an example, the manganese source includes at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate, but is not limited thereto. As an example, the aluminum source includes at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate, but is not limited thereto. As an example, the precursor of element M includes at least one of an oxide of element M, a nitrate compound, a carbonate compound, a hydroxide, and an acetate compound, but is not limited thereto. As an example, the precursor of element A includes at least one 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 hydrogen sulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur, but is not limited thereto.

[0121] In some embodiments, according to 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 hThe mass percentage of the layered material is 80% to 99%. For example, 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 may be in the range composed of any value of 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more. 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% to 99%, 90% to 99%, 95% to 99%, 80% to 98%, 85% to 98%, 90% to 98%, 95% to 98%, 80% to 97%, 85% to 97%, 90% to 97%, or 95% to 97%.

[0122] In some embodiments, the positive electrode film layer may further optionally contain a positive electrode conductive agent. The present application is not particularly limited to the type of the positive electrode conductive agent. For example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber. In some embodiments, according to the total mass of the positive electrode film 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 places no particular restrictions on the type of the positive electrode adhesive. By way of example, the positive electrode adhesive may contain at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of vinylidene fluoride - tetrafluoroethylene - propylene, a terpolymer of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, a copolymer of tetrafluoroethylene - hexafluoropropylene, and a fluorine - containing acrylate - based resin. In some embodiments, based on the total mass of the positive electrode film layer, the mass percentage content of the positive electrode adhesive is 5% or less.

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

[0125] In some embodiments, the compression density of the positive electrode tab is 2.6 g / cm 3 ~3.7 g / cm 3 and preferably 3.4 g / cm 3 ~3.7 g / cm 3 This is the case. The non - aqueous electrolyte of the present application contributes to the matching with the positive electrode coated with a practical thickness at high voltage, thereby further improving the energy density of the secondary battery.

[0126] The positive electrode film layer is usually formed by applying a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional adhesive, and any other components in a solvent and stirring them uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP). [Negative electrode tab]

[0127] In some embodiments, the negative electrode tab includes a negative electrode current collector and a negative electrode film layer disposed 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 either one or both of the two opposing surfaces of the negative electrode current collector.

[0128] The negative electrode active material can adopt a negative electrode active material used in secondary batteries known in the art. By way of example, the negative electrode active material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, but is not limited thereto. The silicon-based materials can include at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloy materials. The tin-based materials can include at least one of elemental tin, tin oxides, and tin alloy materials. The present application is not limited to these materials, and other conventionally known materials used as negative electrode active materials for secondary batteries can be used. These negative electrode active materials may be used alone or in combination of two or more kinds.

[0129] In some embodiments, the negative electrode film layer can optionally further contain a negative electrode conductive agent. The present application is not particularly limited to the type of the negative electrode conductive agent. For example, the negative electrode conductive agent can 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, based on the total mass of the negative electrode film layer, the mass percentage content of the negative electrode conductive agent is 5% or less.

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

[0131] In some embodiments, the negative electrode film layer can optionally further contain other auxiliaries. For example, the other auxiliaries can include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, and the like. In some embodiments, based on the total mass of the negative electrode film layer, the mass percentage content of the other auxiliaries is 2% or less.

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

[0133] In some embodiments, the compression density of the negative electrode tab is 1.4 g / cm 3 ~2.0 g / cm 3 and preferably 1.5 g / cm 3 ~2.0 g / cm 3 This contributes to the matching with the negative electrode coated with the actual thickness at high voltage, thereby further improving the energy density of the secondary battery.

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

[0135] The separator is disposed between the positive electrode tab and the negative electrode tab, mainly functions to prevent short circuit between the positive electrode and the negative electrode, and at the same time can allow lithium ions to pass through. The present application does not particularly limit the type of the separator, and any known porous structure separator having good chemical stability and mechanical stability can be selected.

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

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

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

[0139] FIG. 3 is a schematic diagram of a battery module 4 as an example. As shown in FIG. 3, in the battery module 4, a plurality of secondary batteries 5 may be arranged and installed in sequence along the length direction of the battery module 4. Of course, they can be arranged in any other manner. The plurality of secondary batteries 5 may be further fixed by a fastener.

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

[0141] In some embodiments, the above battery module can be further assembled into a battery pack. The quantity 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 a battery pack 1 as an example. As shown in FIGS. 4 and 5, the battery pack 1 can 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. The upper housing 2 covers the lower housing 3 and is used to form a sealed space for accommodating the battery module 4. The plurality of battery modules 4 can be arbitrarily arranged in the battery box.

[0143] Embodiments of the present application further provide a power consumption device including at least one of a secondary battery, a battery module, or a battery pack of the present application. The secondary battery, battery module, or battery pack may be used as a power source of the power consumption device or as an energy storage unit of the power consumption device. The power consumption device may be a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc., but is not limited thereto.

[0144] The power consumption device can select a secondary battery, a battery module, or a battery pack according to its usage demand.

[0145] Figure 6 is a schematic diagram of a power consumption device as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the demand for high power and high energy density of the power consumption device, a battery pack or a battery module can be adopted.

[0146] Another example of the power consumption device may be a mobile phone, a tablet computer, a notebook computer, etc. The power consumption device is usually required to be thin and can adopt a secondary battery as a power source. Example

[0147] The following examples illustrate the disclosure of the present application in more detail. These examples are for illustrative purposes only, and it is obvious to those skilled in the art that various modifications and changes can be made within the scope of the disclosure of the present application. Unless otherwise specified, all parts, percentages, and ratios described in the following examples are based on mass. In addition, all reagents used in the examples can be purchased or synthesized according to conventional methods, and can be used directly without further treatment. Also, all the devices used in the examples can be purchased.

[0148] The secondary batteries of Examples 1 to 36 and Comparative Examples 1 to 3 were all fabricated by the following method.

[0149] Fabrication of the positive electrode plate

[0150] LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O 2 , carbon black as the conductive agent, and polyvinylidene fluoride (PVDF) as the adhesive are sufficiently stirred and mixed in an appropriate amount of solvent NMP at a weight ratio of 97.5:1.4:1.1 to form a uniform positive electrode slurry. The positive electrode slurry is uniformly coated on the surface of the aluminum foil, which is the positive electrode current collector, and after drying and cold pressing, a positive electrode plate is obtained.

[0151] Fabrication of the negative electrode plate

[0152] Graphite as the negative electrode active material, styrene-butadiene rubber (SBR) as the adhesive, sodium carboxymethyl cellulose (CMC-Na) as the thickener, and carbon black (Super P) as the conductive agent are sufficiently stirred and mixed in an appropriate amount of deionized water, which is the solvent, at 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 coated on the surface of the copper foil, which is the negative electrode current collector, and after drying and cold pressing, a negative electrode plate is obtained.

[0153] Separator

[0154] As the separator, a porous polyethylene (PE) film is used.

[0155] Fabrication of the non-aqueous electrolyte

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

[0157] Fabrication of the secondary battery

[0158] The positive electrode plate, the separator, and the negative electrode plate were stacked and wound in order to obtain an electrode assembly. The electrode assembly was placed in a battery case, and after welding the cover plate, the above non-aqueous electrolyte was injected. After further undergoing processes such as packaging, standing, formation, and aging, a rectangular hard case secondary battery was 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 internal thickness of the battery case is L1, the thickness of the electrode assembly is L2, and the group margin B of the secondary battery is B = L2 / L1.

[0159] Test section

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

[0161] At 25°C, the secondary battery was charged at a constant current of 0.33C until 4.3V, and then the 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 at a constant current of 0.33C until 2.8V, and the discharge energy Q was obtained. The mass energy density of the secondary battery (Wh / Kg) = discharge energy Q / mass m of the secondary battery

[0162] (2) Test on the storage performance of the secondary battery

[0163] At 60°C, the secondary battery was charged at a constant current of 1C until 4.3V, and the charging was continued at a constant voltage until the current reached 0.05C. At this time, the volume of the secondary battery was measured by the drainage method and denoted as V 0 Let it be so. The secondary battery was placed in an incubator at 60°C and stored for 30 days and then taken out. At this time, the volume of the secondary battery was measured by the drainage method and denoted as V 1 Let it be so. The volume expansion rate (%) of the secondary battery after being stored at 60°C for 30 days = [(V 1 - V 0 ) / V 0 × 100%.

[0164] (3) Test on the cycle performance of the secondary battery

[0165] At 45°C, the secondary battery was charged at a constant current of 1C until 4.3V, and the charging was continued at a constant voltage until the current reached 0.05C. At this time, the secondary battery was in a fully charged state, and the charging capacity at this time was recorded and taken as the first charging capacity. After the secondary battery was left standing for 5 minutes, it was discharged at a constant current of 1C until 2.8V. This is a process of one cycle of charge and discharge. The discharge capacity at this time was recorded and taken as the first discharge capacity. The secondary battery was subjected to a cycle of charge and discharge test according to the above method, and the discharge capacity after each cycle was 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 on the initial DC internal resistance of the secondary battery

[0167] At 25°C, the secondary battery is charged at a constant current of 1C up to 4.3V, and then charged at a constant voltage until the current reaches 0.05C. At this time, the secondary battery is in a fully charged state. The secondary battery is discharged at a constant current of 0.5C and the secondary battery is adjusted to 50% SOC. At this time, the voltage of the secondary battery is U 1 is set as. The secondary battery is discharged at a constant current of 4C with current I 1 for 30 seconds. An sampling point of 0.1 second is adopted, and the terminal discharge voltage is U 2 is set as. The discharge DC internal resistance at 50% SOC of the secondary battery indicates the initial DC internal resistance of the secondary battery. The initial DC internal resistance (mΩ) of the secondary battery = (U 1 -U 2 ) / I 1 .

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

[0169]

Table 1

[0170]

Table 2

[0171] As can be seen from summarizing the test results in Table 1 and Table 2, when the non-aqueous electrolyte contains the compound represented by Formula I and the content A1% thereof and the group margin B of the secondary battery satisfy 0.5 ≤ B / A1 ≤ 45, the secondary battery can simultaneously achieve a high group margin design and high safety performance, and has a low internal resistance and a high capacity retention rate. On the other hand, the compound represented by Formula I can simultaneously form a uniform, dense, and stable interfacial film on both the positive electrode and the negative electrode, reduce the direct contact between the active material and the non-aqueous electrolyte, reduce the damage and regeneration of the positive electrode interfacial film and the negative electrode interfacial film, further reduce the generation of gas and the consumption of active lithium ions in this process, reduce the gas expansion of the battery, and improve the capacity retention rate of the battery. On the other hand, the compound represented by Formula I can stabilize the crystal structure of the positive electrode active material, reduce the precipitation of lattice oxygen and the elution of transition metal ions, and further reduce a series of side reactions caused thereby, and reduce the gas expansion of the battery.

[0172] As can be seen from summarizing the test results of Examples 1 to 9 and Comparative Example 2, when B / A1 is greater than 45, the compound represented by Formula I that forms a uniform, dense, and stable positive electrode interfacial film and / or negative electrode interfacial film is insufficient. As a result, the crystal structure of the positive electrode active material cannot be effectively stabilized to reduce the decomposition of the non-aqueous electrolyte, so the secondary battery generates a large amount of gas, has a high volume expansion rate, and the safety risk faced by the secondary battery with a high group margin design is still high. At the same time, since there are many interfacial side reactions between the non-aqueous electrolyte and the electrode, the interfacial resistance of the positive electrode and / or the interfacial resistance of the negative electrode increase, the internal resistance of the secondary battery is high, and the capacity retention rate is low.

[0173] As can be seen from summarizing the test results of Examples 1 to 9 and Comparative Example 3, when B / A1 is less than 0.5, a too thick positive electrode interfacial film and / or negative electrode interfacial film is formed, so the interfacial resistance of the positive electrode and / or the interfacial resistance of the negative electrode become high. And the secondary battery has a high internal resistance and a low capacity retention rate. At the same time, since the structure of the compound represented by Formula I contains one oxalic acid group, when its content is high, the gas generated by its own decomposition increases, and the volume expansion rate of the secondary battery increases without decreasing.

[0174] As can be seen from summarizing the test results of Examples 1 to 9, 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, the overall performance of the secondary battery is better.

[0175] As can be seen from summarizing the test results of Examples 4, 10 to 14, when the non-aqueous electrolyte further contains a second lithium salt, and the content A3% of the second lithium salt and the content A1% of the compound represented by Formula I satisfy 0.25 ≦ A3 / A1 ≦ 25, preferably 4 ≦ A3 / A1 ≦ 20, the secondary battery has a reduced volume expansion rate, a reduced internal resistance, and an increased capacity retention rate. It is considered that 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 to 19, when the non-aqueous electrolyte further contains the additive FEC, and the content C1% thereof and the content A1% of the compound represented by Formula I satisfy 5 ≦ C1 / A1 ≦ 50, preferably 10 ≦ C1 / A1 ≦ 30, it contributes to the improvement of the capacity retention rate of the secondary battery.

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

[0178] Note that the present application is not limited to the above embodiments. The above embodiments are merely examples, and embodiments having a configuration substantially the same as the technical idea within the scope of the technical solution of the present application and exhibiting the same operational effects are all included in the technical scope of the present application. Also, within the scope not departing from the gist of the present application, forms in which various modifications conceivable by those skilled in the art are added to the embodiments, and other forms constructed by combining some components in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery comprising a battery case, an electrode assembly accommodated in the battery case, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte contains 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 non-aqueous electrolyte, the group margin of the secondary battery is B, and the secondary battery satisfies that B is 0.88 to 0.99 and B / A1 is 0.5 to 45, wherein the group margin = thickness of the electrode assembly / internal thickness of the battery case the group margin is the ratio of the actual internal cross-sectional area to the maximum internal cross-sectional area of the secondary battery, i.e., the filling rate, a secondary battery. 【Chemical 1】 In Formula I, X and Y are each independently 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 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. B is 0.90 to 0.95, and / or B / A1 is 4 to 20, the secondary battery according to Claim 1.

3. The secondary battery according to Claim 2, wherein B / A1 is 10 to 20.

4. A1 is 0.02 or more and less than 2, the secondary battery according to any one of Claims 1 to 3.

5. The secondary battery according to Claim 4, wherein A1 is 0.02 to 1.

6. the non-aqueous electrolyte further contains a first lithium salt, the first lithium salt is lithium hexafluorophosphate, the mass percentage content of the first lithium salt is A2% based on the total mass of the non-aqueous electrolyte, and A2 is greater than 0 and 14 or less, 10 ≤ A2 / A1 ≤ 600, the secondary battery according to any one of Claims 1 to 3.

7. The non-aqueous electrolyte further contains a first lithium salt, the first lithium salt is lithium hexafluorophosphate, the mass percentage content of the first lithium salt is A2% based on the total mass of the non-aqueous electrolyte, and 0 < 10A1 + A2 / 5 ≦ 15. The secondary battery according to any one of claims 1 to 3.

8. The non-aqueous electrolyte further contains a second lithium salt, the second lithium salt is lithium fluorosulfonylimide salt, and the mass percentage content of the second lithium salt is A3% based on the total mass of the non-aqueous electrolyte. 0 < A3 ≦ 2.5, and / or 0.25 ≦ A3 / A1 ≦ 25. The secondary battery according to claim 6.

9. A3 / A2 is 0.5 or less. The secondary battery according to claim 8.

10. The non-aqueous electrolyte further contains fluoroethylene carbonate, and its mass percentage content is C1% based on the total mass of the non-aqueous electrolyte. 0 < C1 ≦ 5, and / or 5 ≦ C1 / A1 ≦ 50. The secondary battery according to any one of claims 1 to 3.

11. The non-aqueous electrolyte further contains a water removal additive containing hexamethyldisilazane, tris(trimethylsilyl) phosphate, or a combination thereof, and the mass percentage content of the water removal additive is C2% based on the total mass of the non-aqueous electrolyte. C2 is greater than 0 and 2 or less. The secondary battery according to any one of claims 1 to 3.

12. The non-aqueous electrolyte contains an organic solvent, and the organic solvent contains a first solvent, a second solvent, and a third solvent. The first solvent contains at least one of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and vinyl ethylene carbonate, and the mass percentage content of the first solvent in the organic solvent is D1% based on the total mass of the organic solvent. The second solvent contains 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% based on the total mass of the organic solvent. The third solvent includes at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate. The mass percentage content of the third solvent in the organic solvent is D3% based on the total mass of the organic solvent. The organic solvent satisfies that D1 is greater than 0 and less than or equal to 20, D2 is 50 to 90, and D3 is 0 to 30. The secondary battery according to any one of claims 1 to 3.

13. The electrode assembly includes 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. Moreover, the secondary battery satisfies 1 < Q2 / Q1 < 1.05 and A1 < B. The secondary battery according to any one of claims 1 to 3.

14. The secondary battery according to any one of claims 1 to 3, wherein at least one of X and Y represents a fluorine atom.

15. The compound represented by the formula I includes at least one of the following compounds. The secondary battery according to any one of claims 1 to 3. 【Chemical Formula 2】

16. The material of the battery case includes at least one of a hard plastic case, aluminum, and stainless steel. The secondary battery according to any one of claims 1 to 3.

17. A battery module including the secondary battery according to any one of claims 1 to 3.

18. A battery pack including one of the secondary battery according to any one of claims 1 to 3 and the battery module according to claim 17.

19. A power consumption device including at least one of the secondary battery according to any one of claims 1 to 3, the battery module according to claim 17, and the battery pack according to claim 18.

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