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

Abstract

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

Description

[Technical Field]

[0001] The present application relates to the technical field of batteries, and more particularly to secondary batteries, battery modules, battery packs, and power consuming devices. [Background technology]

[0002] In recent years, secondary batteries have been widely applied in energy storage power systems, such as hydroelectric, thermal, wind, and solar power plants, as well as in various fields, such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. As secondary batteries become more widely used and widespread, the demand for their energy density is increasing. To improve the energy density of secondary batteries, a commonly adopted technical solution is to design secondary batteries with larger and larger battery casings. However, this results in a smaller and smaller remaining space in the secondary battery. As a result, there is insufficient space to accommodate gases generated during chemical formation, charging / discharging, and storage, and the pressure on the battery case continues to increase, seriously affecting the safety performance of the secondary battery. Therefore, there is a need for a secondary battery that combines high energy density with high safety performance. Summary of the Invention

[0003] The 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 can provide 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 housed in the battery case, wherein the non-aqueous electrolyte contains a compound represented by formula I, The mass percent content of the compound represented by formula I is A1%, the group margin of the secondary battery is B relative to the total mass of the non-aqueous electrolyte, and the secondary battery satisfies B in the range of 0.88 to 0.99 and B / A1 in the range of 0.5 to 45. [ka] In Formula I, X and Y each independently represent a hydrogen atom, a halogen atom, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C6-C20 aryl group, a C1-C20 halogenated alkyl group, a C2-C20 halogenated alkenyl group, a C2-C20 halogenated alkynyl group, a C6-C20 halogenated aryl group, a C1-C20 alkoxy group, a C2-C20 alkenyloxy group, a C2-C20 alkynyloxy group, a C6-C20 aryloxy group, a C1-C20 halogenated alkoxy group, a C2-C20 halogenated alkenyloxy group, a C2-C20 halogenated alkynyloxy group, a C6-C20 halogenated aryloxy group, or a combination thereof, and at least one of X and Y represents a fluorine atom or a group containing a fluorine atom.

[0005] The inventors of the present application have discovered through research that when a non-aqueous electrolyte contains a compound represented by Formula I, and the content A1% of the compound and the group margin B of the secondary battery satisfy the ratio B / A1 of 0.5 to 45, the secondary battery can achieve both a high group margin design and high safety performance, and also exhibit good cycle performance and dynamic performance. Meanwhile, the compound represented by Formula I simultaneously forms uniform, dense, and stable interfacial films on the positive and negative electrodes, reducing direct contact between the active materials (positive and negative active materials) and the non-aqueous electrolyte, and reducing damage and regeneration of the positive and negative interfacial films. This process also reduces gas generation and consumption of active lithium ions, reducing gas expansion in the battery and improving the battery's capacity retention. Meanwhile, the compound represented by Formula I stabilizes the crystalline structure of the positive electrode active material, reducing lattice oxygen precipitation and transition metal ion elution, and further reducing a series of side reactions resulting from these, thereby reducing gas expansion in the battery.

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

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

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

[0009] In any embodiment of the present application, the non-aqueous electrolyte further includes a first lithium salt. The first lithium salt is lithium hexafluorophosphate. The mass percent content of the first lithium salt is A2%. A2 is greater than 0 and less than or equal to 14, 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, and more preferably, 60≦A2 / A1≦600, which contributes to improving the capacity retention rate of the secondary battery while reducing gas generation in the secondary battery.

[0011] In any embodiment of the present application, 0<10A1+A2 / 5≦15, preferably 2.6≦10A1+A2 / 5≦5. This reduces gas generation in the secondary battery and contributes to improving the capacity retention rate of the secondary battery.

[0012] In any embodiment of the present application, the non-aqueous electrolyte further includes a second lithium salt. The second lithium salt is a fluorosulfonylimide lithium salt. Preferably, the fluorosulfonylimide lithium salt has a molecular formula of LiN(SO2R1)(SO2R2), where R1 and R2 are each independently F or C. n F 2n+1It is represented by, and n is 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 both higher thermal stability can be achieved, 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 the cycle performance of the secondary battery by fluoroethylene carbonate.

[0017] In any embodiment of the present application, the non-aqueous electrolyte further contains a dehydrating additive including hexamethyldisilazane, tris(trimethylsilyl) phosphate, or a combination thereof. The mass percentage content of the dehydrating 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 including 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 including 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 including 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 plate and a negative electrode plate. The capacity of the positive electrode plate is Q1 Ah, and the capacity of the negative electrode plate is Q2 Ah. The secondary battery satisfies 1 < Q2 / Q1 < 1.05 and A1 < B. Thereby, the secondary battery can achieve 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 thinner positive electrode interfacial films and / or negative electrode interfacial films, thereby contributing to the uniform transport of lithium ions and effectively suppressing the formation of lithium dendrites.

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

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

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

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

[0025] A 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] The battery module, battery pack, and power consumption device of the present application include the secondary battery of the present application, and therefore have at least the same advantages as the secondary battery. [Brief explanation of the drawings]

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

[0028] [Figure 1] 1 is a schematic diagram of one embodiment of a secondary battery of the present application. [Figure 2] FIG. 2 is an exploded schematic view of the embodiment of the secondary battery of FIG. 1. [Figure 3] 1 is a schematic diagram of one embodiment of a battery module of the present application. [Figure 4] 1 is a schematic diagram of one embodiment of a battery pack of the present application. [Figure 5] 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4. [Figure 6] 1 is a schematic diagram of one embodiment of a power consumption device that includes a secondary battery of the present application as a power source. The drawings are not necessarily drawn to scale. 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 secondary battery, 51 battery case, 52 electrode assembly, and 53 cover plate are designated by reference numerals and will be described below. DETAILED DESCRIPTION OF THE INVENTION

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

[0030] The "ranges" disclosed herein are defined in the form of lower and upper limits, where a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits specifically define the boundaries of the range. Ranges defined in this manner may or may not include the endpoints and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a single range. For example, reciting ranges of 60 to 120 and 80 to 110 for a particular parameter is understood to also contemplate ranges of 60 to 110 and 80 to 120. Furthermore, reciting minimum range values of 1 and 2 and maximum range values of 3, 4, and 5 contemplates ranges of 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. Unless otherwise specified, the numerical range "a to b" herein refers to a contraction of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" herein refers to all real numbers between "0 and 5," and "0 to 5" is a contraction of combinations of these numerical values. Furthermore, when a parameter is expressed as an integer ≧2, this 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 stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present application.

[0032] Unless otherwise stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present application.

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

[0034] Unless otherwise specified, the terms "having," "comprising," and "including" referred to in this application may be open-ended or closed-ended. For example, the terms "having," "comprising," and "comprising" indicate that the term may further comprise, include, or contain other components not listed, or may only comprise or contain the listed components.

[0035] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions satisfy the condition "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 A and B are both true (or exist).

[0036]

[0033] At various points in this specification, substituents of compounds are disclosed in groups or ranges. Such descriptions expressly contemplate each of the individual subcombinations of the members of these groups and ranges. For example, the term "C1-C6 alkyl group" is expressly contemplated to separately disclose 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 alkyl groups.

[0037] In this 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 packing rate. There are two methods for calculating the group margin: (1) Group margin = total cross-sectional area of electrode assembly / internal space area of battery case (2) Group clearance = electrode assembly thickness / battery case internal thickness

[0038] As used herein, the terms "plurality" and "multiple types" refer to two or more types.

[0039] A secondary battery typically 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 , a secondary battery 5 having a rectangular structure 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 side plates surround and form a storage cavity. The battery case 51 has an opening communicating with the storage cavity, and the cover plate 53 covers the opening to seal the storage cavity.

[0040] To improve the energy density of secondary batteries, a commonly adopted technical solution is to design the secondary battery with a larger packing margin. The packing margin can reflect the difficulty of inserting the electrode assembly into the battery case, the pressure on the battery case after the electrode assembly expands during charging, and the energy density of the secondary battery. The smaller the packing margin of the secondary battery, the easier it is to insert the electrode assembly into the battery case, but the resulting secondary battery has a relatively low energy density, which may not meet actual usage requirements. The larger the packing margin of the secondary battery, the higher the energy density, but the more difficult it is to insert the electrode assembly into the battery case, which not only increases processing difficulty but also causes damage to the electrode assembly. Furthermore, the larger the packing margin of the secondary battery, the smaller the remaining space inside the battery case, which may not have enough space to accommodate gases generated during chemical formation, charging / discharging, and storage. Furthermore, the pressure on the battery case continues to increase after the electrode assembly expands, seriously affecting the safety performance of the secondary battery.

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

[0042] The inventors of the present application have discovered through their research that by using an appropriate non-aqueous electrolyte, it is possible to significantly reduce the amount of gas generated during the chemical formation, charge / discharge, storage, etc. This reduces the pressure on the battery case, allowing the secondary battery to be designed with high group margin and high safety performance at the same time.

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

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

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

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

[0047] Non-aqueous electrolytes are one of the important factors that affect the performance of secondary batteries. Non-aqueous electrolytes contain an organic solvent and a lithium salt dissolved therein, and are prone to undergo a series of oxidation and reduction reactions during the formation, charge / discharge, and storage processes, resulting in decomposition and the generation of large amounts of gas.

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

[0049] During long-term charge-discharge cycles, the bound water in the electrode pieces of secondary batteries gradually releases into the nonaqueous electrolyte. The increased water content in the nonaqueous electrolyte triggers a series of internal side reactions, resulting in gas expansion in the battery. Currently, the nonaqueous electrolyte system with the widest commercial application is a solution of lithium hexafluorophosphate and mixed carbonate esters. Lithium hexafluorophosphate has poor thermal stability at high temperatures and decomposes to form PF5. PF5 has strong Lewis acidity, which interacts with the lone electron pairs on the oxygen atoms of organic solvent molecules, decomposing the organic solvent and causing gas expansion in the battery. PF5 is also highly sensitive to moisture and generates HF upon contact with water. HF not only induces decomposition of the organic solvent, but also increases the acidity of the nonaqueous electrolyte, which in turn corrodes the positive electrode active material and positive electrode current collector and leads to the leaching of transition metal ions from the positive electrode active material. Transition metal ions in the positive electrode active material dissolve and migrate to the negative electrode, where they are reduced to transition metals. The resulting transition metals act as catalysts, catalyzing the decomposition of the interfacial film on the surface of the negative electrode active material, further increasing gas expansion in the battery and affecting the safety performance of the secondary battery. Furthermore, to replenish the lost interfacial film, nonaqueous electrolyte is constantly consumed, causing a series of oxidation and reduction reactions to occur continuously, further increasing gas expansion in the battery. During this process, active lithium ions in the battery are also constantly consumed, irreversibly affecting the capacity retention rate of the secondary battery.

[0050] During the storage process of a secondary battery, the positive electrode active material is always in a metastable state and is extremely unstable, which causes decomposition reactions and gas expansion. Furthermore, if the stability of the interfacial film on the surface of the negative electrode active material is low, part of the surface in contact with the nonaqueous electrolyte will dissolve as the temperature rises. For example, the organic component (CHOCOLi) in the interfacial film is unstable and prone to decomposition reactions, generating gas and causing gas expansion in the battery.

[0051] The applicants have discovered through their research that when a non-aqueous electrolyte contains a compound represented by formula I, and the content A1% of the compound and the group margin B of the secondary battery satisfy the ratio B / A1 of 0.5 to 45, gas generated during the chemical formation, charge / discharge, storage, etc. can be reduced.

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

[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 reducing direct contact between the positive electrode active material and the non-aqueous electrolyte, reducing side reactions at the interface, reducing the elution of transition metal ions, and reducing a series of side reactions resulting from these, thereby reducing gas expansion in the battery.

[0054] Second, the B atom in the structure of the compound represented by Formula I easily bonds with the O atom in the positive electrode active material. This stabilizes the crystalline structure of the positive electrode active material, reduces the formation of lattice defects such as oxygen vacancies and irreversible intercalation, and reduces lattice oxygen precipitation. At the same time, it reduces the charge transfer resistance of the positive electrode active material and the lithium ion diffusion resistance within the bulk of the positive electrode active material. Furthermore, it allows lithium ions in the bulk of the positive electrode active material to be replenished to the surface in a timely manner, preventing excessive lithium desorption. This results in a more stable crystalline structure of the positive electrode active material, which is less susceptible to lattice oxygen precipitation and transition metal ion desorption, thereby reducing a series of side reactions and gas expansion in the battery.

[0055] Third, the B-O bond in the structure of the compound of formula I is Al 3+ By combining with the above, a layer of passivation film is formed on the surface of the aluminum foil current collector, which can effectively prevent the aluminum foil current collector from being corroded 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 reducing the damage and regeneration of the negative electrode interfacial film, and further reducing gas generation and consumption of active lithium ions during this process, thereby reducing gas expansion in the battery and improving the capacity retention rate of the battery.

[0057] Therefore, when a non-aqueous electrolyte solution contains a compound represented by Formula I, and the content A1% of the compound and the group margin B of the secondary battery satisfy a ratio B / A1 of 0.5 to 45, the compound represented by Formula I simultaneously forms uniform, dense, and stable interfacial films on the positive and negative electrodes, reducing direct contact between the active materials (positive and negative active materials) and the non-aqueous electrolyte, reducing damage and regeneration of the positive and negative interfacial films, further reducing gas generation and consumption of active lithium ions during this process, reducing gas expansion in the battery and improving the battery capacity retention. On the other hand, the compound represented by Formula I stabilizes the crystalline structure of the positive active material, reducing lattice oxygen precipitation and transition metal ion elution, further reducing a series of side reactions resulting from these and reducing gas expansion in the battery. This allows the secondary battery of the present application to achieve both a high group margin design and high safety performance, while also exhibiting 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 the condition that B / A1 is between 0.5 and 45, the compound represented by Formula I can fully exert its effects of reducing gas generation and improving capacity retention. When B / A1 is greater than 45, the content of the compound represented by Formula I is low and the group margin B of the secondary battery is designed to be large. In this case, the compound represented by Formula I is insufficient to form a uniform, dense, and stable positive electrode interfacial film and / or negative electrode interfacial film. As a result, the crystalline structure of the positive electrode active material cannot be effectively stabilized and decomposition of the nonaqueous electrolyte cannot be reduced, resulting in excessive gas generation in the secondary battery, high pressure on the battery case, and a high safety risk for the secondary battery. When B / A1 is less than 0.5, the group margin B of the secondary battery is designed to be small, making it impossible to simultaneously achieve high energy density. Alternatively, if the content of the compound represented by Formula I is high, a thick positive electrode interfacial film and / or a negative electrode interfacial film will be formed, increasing the interfacial resistance of the positive electrode and / or the negative electrode. Furthermore, since the structure of the compound represented by Formula I contains one oxalic acid group, gas will be generated when it decomposes, which will in turn increase gas expansion in the battery. In some embodiments, B / A1 is preferably 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 0.88 to 0.99. Preferably, in some embodiments, B is 0.90 to 0.99, 0.90 to 0.98, 0.90 to 0.97, 0.90 to 0.96, 0.90 to 0.95, 0.92 to 0.99, 0.92 to 0.98, 0.92 to 0.97, 0.92 to 0.96, or 0.92 to 0.95. This allows the secondary battery to have a high energy density 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, such as at least one selected from the group consisting of partially or fully fluorinated C1-C20 alkyl groups, C2-C20 alkenyl groups, C2-C20 alkynyl groups, C6-C20 aryl groups, C1-C20 alkoxy groups, C2-C20 alkenyloxy groups, C2-C20 alkynyloxy groups, and C6-C20 aryloxy groups. The presence of fluorine atoms contributes to the formation of thinner positive and / or negative electrode interfacial films, contributes to uniform lithium ion transport, 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] By way of example, compounds of formula I include at least one of the following compounds: [ka]

[0062] In some embodiments, the content A1% of the compound represented by Formula I satisfies 0.02 or more and less than 2 for A1. 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 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 one oxalic acid group is included in the structure of the compound represented by Formula I, 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 plate is Q1 Ah, the capacity of the negative electrode plate is Q2 Ah, and the secondary battery satisfies 1 < Q2 / Q1 < 1.05 and A1 < B. When the capacity of the negative electrode plate is greater than that of the positive electrode plate, it can ensure that the negative electrode plate has sufficient pores to accommodate lithium ions from the positive electrode and prevent lithium from depositing from the negative electrode. At the same time, when the ratio Q2 / Q1 of the capacity of the negative electrode plate to the capacity of the positive electrode plate is less 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 plate and the capacity of the negative electrode plate have the meanings known in the art and can be measured by devices and methods known in the art. For example, it is measured using a blue electricity meter.

[0066] As an example, as a method for measuring the capacity of the positive electrode plate, after punching a cold-pressed positive electrode plate into a small wafer with an area of S0, it is assembled into a buckle-type battery in a glove box, charged to the charge cut-off voltage at a constant current of 0.1 mA, and discharged to the discharge cut-off voltage at a constant current of 0.1 mA to obtain a discharge capacity CAP1, and the capacity of the positive electrode plate is obtained by the formula CAP1×S1 / S0, where S0 is the area of the small wafer and S1 is the coating area of the positive electrode film layer on the positive electrode plate.

[0067] As an example, as a method for measuring the capacity of the negative electrode plate, after punching a cold-pressed negative electrode plate into a small wafer with an area of S0, it is assembled into a buckle-type battery in a glove box, discharged to the discharge cut-off voltage at a constant current of 0.1 mA, and charged to the charge cut-off voltage at a constant current of 0.1 mA to obtain a discharge capacity CAP2, and the capacity of the negative electrode plate is obtained by the formula CAP1×S2 / S0, where S0 is the area of the small wafer and S2 is the coating area of the negative electrode film layer on the negative electrode plate. [Lithium salt]

[0068] In some embodiments, the non-aqueous electrolyte solution includes a first lithium salt, lithium hexafluorophosphate. The mass percent 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 solution. Preferably, A2 is 4 to 14, 4 to 12, 4 to 10, 6 to 14, 6 to 12, 6 to 10, 8 to 14, 8 to 12, or 8 to 10. Lithium hexafluorophosphate has high ionic conductivity. When its content is within an appropriate range, it contributes to improving the ionic conductivity of the entire non-aqueous electrolyte solution, accelerating lithium ion transport, and improving the capacity retention rate of secondary batteries. However, lithium hexafluorophosphate has poor thermal stability in high-temperature environments and decomposes at high temperatures to produce PF5. PF5 reacts with water to form HF, which corrodes the positive electrode active material and increases gas expansion in batteries. When the non-aqueous electrolyte solution simultaneously contains the compound represented by formula I and lithium hexafluorophosphate, the compound represented by formula I can react with lithium hexafluorophosphate to form the compound LiPF4C2O4, thereby reducing the decomposition of lithium hexafluorophosphate and the formation of HF, and the secondary battery can have high safety, high energy density, and good cycle performance.

[0069] In some embodiments, the content A1% of the compound represented by Formula I and the content A2% of the first lithium salt satisfy 10≦A2 / A1≦600. The rational combination of the content A1% of the compound represented by Formula I and the content A2% of the first lithium salt reduces gas generation in the secondary battery and contributes to improving the capacity retention rate of the secondary battery. Furthermore, when the content of the first lithium salt is high and the content of the compound represented by formula I is low, there is a possibility that a large amount of HF will be present in the non-aqueous electrolyte, which will result in an increased decomposition reaction of the non-aqueous electrolyte, and the interfacial film formed on the positive electrode and / or negative electrode by the compound represented by formula I will not be sufficiently dense, making it impossible to prevent corrosion of the positive electrode active material by HF and a series of side reactions resulting therefrom, which may result in a large amount of gas generation 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, the anion radius of the compound represented by formula I will be small, making it difficult for it to completely dissociate in the non-aqueous electrolyte, and the anion and cation will likely associate, which may result in a decrease in the ionic conductivity of the non-aqueous electrolyte and a deterioration in the capacity retention rate of the secondary battery. This can be effectively avoided. Preferably, A2 / A1 is 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 the relationship 0<10A1+A2 / 5≦15. Rational combination of the content A1% of the compound represented by Formula I and the content A2% of the first lithium salt reduces gas generation in the secondary battery and contributes to improving the capacity retention rate of the secondary battery. Furthermore, if the contents of both lithium hexafluorophosphate and the compound represented by Formula I are high, the non-aqueous electrolyte may contain a large amount of HF, which can reduce the stability of the crystalline structure of the positive electrode active material, increase the decomposition reaction of the non-aqueous electrolyte, and further increase gas generation in the secondary battery, increasing safety risks. At the same time, the small anion radius of the compound represented by Formula I makes it difficult for it to completely dissociate in the non-aqueous electrolyte and prone to association between anions and cations. Therefore, a high content of this compound effectively avoids the following problems: the ionic conductivity of the non-aqueous electrolyte may decrease, and the capacity retention rate of the secondary battery may also decrease. 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 first lithium salt simultaneously satisfy the relationships 10≦A2 / A1≦600 and 0<10A1+A2 / 5≦15. This allows the nonaqueous electrolyte to contain appropriate amounts of the compound represented by Formula I and the first lithium salt, and a secondary battery using the same can achieve 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 the relationships 60≦A2 / A1≦600 and 2.6≦10A1+A2 / 5≦5.

[0072] In some embodiments, the non-aqueous electrolyte further comprises a second lithium salt which is a lithium fluorosulfonylimide salt. Preferably, the molecular formula of the lithium fluorosulfonylimide salt is LiN(SO2R1)(SO2R2), where R1 and R2 are each independently F or C n F 2n+1 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, where 0 ≦ A3 ≦ 2.5. For example, A3 is in the range consisting of any value such as 0, 0.10, 0.20, 0.50, 0.75, 1.0, 1.25, 1.50, 1.75, 2.0, 2.25, 2.50 or more. 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, with a -F or -C having a strong electron-withdrawing property as a conjugate group n F 2n+1The anion charge is highly delocalized, weakening the interaction between the anion and lithium ion. Therefore, fluorosulfonylimide lithium salts have low lattice energy and are easily dissociated. This improves the ionic conductivity of non-aqueous electrolytes, reduces their viscosity, and improves the rate performance of secondary batteries. At the same time, fluorosulfonylimide lithium salts have high thermal stability, a wider electrochemical window, and resistance to hydrolysis, allowing them to 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, and is more thermally stable, reducing side reactions between the negative electrode active material and the non-aqueous electrolyte, reducing gas expansion in the battery, and suppressing the formation of lithium dendrites. Therefore, when a non-aqueous electrolyte contains fluorosulfonylimide lithium salt, it can improve the rate performance of secondary batteries while improving their safety.

[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, 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, 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 a non-aqueous electrolyte contains a fluorosulfonylimide lithium salt, it can improve the rate performance of secondary batteries. However, fluorosulfonylimide lithium salt cannot withstand high pressures, corrodes the positive electrode current collector (e.g., aluminum foil) at high potentials, and has poor film-forming properties on the surface of the positive electrode active material, which can easily affect the cycle performance of secondary batteries. The compound represented by Formula I acts as a stabilizer for the positive electrode active material, forming a high-performance interfacial film on the surface of the positive electrode active material, reducing side reactions between the positive electrode active material and the non-aqueous electrolyte, and stabilizing the crystalline structure of the positive electrode active material. Therefore, using the compound represented by Formula I in combination with a fluorosulfonylimide lithium salt is advantageous in fully utilizing the effect of the fluorosulfonylimide lithium salt in improving the rate performance of secondary batteries. Furthermore, by rationally controlling the relationship between the content A1% of the compound represented by Formula I and the content A3% of the second lithium salt so that 0.25≦A3 / A1≦25 is satisfied, the synergistic effect of the compound represented by Formula I and the fluorosulfonylimide lithium salt can be fully utilized. Not only does this not deteriorate the cycle performance and storage performance of the secondary battery, but it also further reduces the internal resistance of the secondary battery and improves the rate performance of the secondary battery.

[0077] In some embodiments, the nonaqueous electrolyte solution 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 A3 / A2, which satisfies the ratio of 0.5 or less, and more preferably 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. This makes the nonaqueous electrolyte solution less susceptible to hydrolysis and achieves higher thermal stability, contributing to the formation of an interfacial film with lower resistance.

[0078] In some embodiments, the non-aqueous electrolyte may further include a third lithium salt, including at least one of lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium difluorophosphate (LiPOF), lithium difluorodisalophosphate (LiDFOP), and lithium tetrafluorooxalophosphate (LiTFOP). The third lithium salt may serve as an auxiliary lithium salt to further improve the interfacial performance of the positive electrode and / or negative electrode, or to improve the ionic conductivity or thermal stability of the non-aqueous electrolyte. Preferably, the total weight percent content of the third lithium salt in the non-aqueous electrolyte is A4% based on the total weight of the non-aqueous electrolyte, and A4 is 6 or less, more preferably 2 or less.

[0079] In some embodiments, A1+A2+A3+A4 is 10-20, preferably 10-15. [Organic solvents]

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

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

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

[0083] In some embodiments, the organic solvent preferably includes at least a first solvent and a second solvent. A high content of lithium salts, such as lithium hexafluorophosphate, increases the viscosity of the non-aqueous electrolyte, reducing ionic conductivity and adversely affecting lithium ion transport. The first solvent has a high dielectric constant, which can increase the ionic conductivity of the non-aqueous electrolyte, while the second solvent has a low viscosity, which can reduce the viscosity of the non-aqueous electrolyte. Therefore, when the organic solvent includes both the first solvent and the second solvent, the non-aqueous electrolyte has appropriate viscosity and ionic conductivity, which further contributes to the transport of lithium ions.

[0084] In some embodiments, the organic solvent may further include a third solvent. The third solvent is a carboxylic acid ester compound, and may include, for example, 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, and is applied to the non-aqueous electrolyte. This third solvent contributes to the non-aqueous electrolyte having appropriate viscosity and ionic conductivity, and further contributes to improving lithium ion transport and the rate performance of the secondary battery.

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

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

[0087] Although the third solvent can improve the rate performance of the secondary battery, its oxidation resistance is poor and it is prone to decomposition when stored in a highly charged state, so its content should not be too high. In some embodiments, the mass percent 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 include solvents other than the first, second, and third solvents. For example, the other solvents may include sulfone-based solvents such as sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). [Additives]

[0089] In some embodiments, the non-aqueous electrolyte may further contain additives, such as at least one of halogen-substituted cyclic carbonate compounds, nitrile compounds, phosphazene compounds, aromatic hydrocarbons and halogenated aromatic hydrocarbon compounds, isocyanate compounds, acid anhydride compounds, sulfate ester compounds, sulfite ester compounds, sulfonate ester compounds, and disulfonate ester compounds. The types of additives are not particularly limited within the scope of the present invention. Preferably, the total weight percent content of these additives is 10% or less, more preferably 5% or less, based on the total weight 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,​​​When a nonaqueous electrolyte contains fluoroethylene carbonate, it can effectively improve the cycle performance of secondary batteries. However, fluoroethylene carbonate easily decomposes to form HF. HF destroys the positive electrode interfacial film, corrodes the positive electrode active material, and increases the amount of gas generated in secondary batteries. The compound represented by Formula I can be used as a stabilizer for the positive electrode active material. The B atoms in its structure interact with the O atoms on the surface of the positive electrode active material, thereby stabilizing the crystalline structure of the positive electrode active material and reducing the destruction of the crystalline structure of the positive electrode active material by HF. Therefore, using the compound represented by Formula I in combination with fluoroethylene carbonate is advantageous in fully utilizing the fluoroethylene carbonate's effect of further improving the cycle performance of secondary batteries. Furthermore, by rationally controlling the relationship between the content A1% of the compound represented by Formula I and the content C1% of fluoroethylene carbonate so that 5≦C1 / A1≦50 is satisfied, the synergistic effect of the compound represented by Formula I and fluoroethylene carbonate can be fully utilized. Not only does it not significantly increase gas generation in secondary batteries, but it also further improves the cycle performance of secondary batteries. At the same time, fluoroethylene carbonate has a high dielectric constant, and rationally 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 contributes to the formation of free ions by the anions of the compound represented by formula I, thereby reducing the association between anions and cations. As a result, the non-aqueous electrolyte has high ionic conductivity, and the cycle performance of secondary batteries is better.

[0094] In some embodiments, the non-aqueous electrolyte solution 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. Furthermore, the secondary battery simultaneously satisfies 4≦A3 / A1≦20 and 10≦C1 / A1≦30. In this case, the cycle performance and rate performance of the secondary battery can be improved while improving safety performance. 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 serves as a stabilizer for the positive electrode active material, forming a high-performance interfacial film on the surface of the positive electrode active material, improving the lithium ion diffusion rate of the positive electrode active material, reducing side reactions between the positive electrode active material and the non-aqueous electrolyte, stabilizing the crystalline structure of the positive electrode active material, and reducing lattice oxygen precipitation and transition metal ion elution. Therefore, rationally controlling the relationship between the contents of fluoroethylene carbonate, the second lithium salt, and the compound represented by formula I is advantageous in fully utilizing the synergistic effects among the three and fully suppressing the deficiencies of using each component alone.

[0095] In some embodiments, the non-aqueous electrolyte may further include a water-removing additive that reduces the water content of the non-aqueous electrolyte and contributes to reducing a series of side reactions caused by moisture, thereby further improving gas expansion in the secondary battery and enabling the secondary battery to better achieve both high pack margin design and high safety performance.

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

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

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

[0099] In the present application, the components and their contents in the non-aqueous electrolyte solution can be measured by methods known in the art, such as gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), and nuclear magnetic resonance spectroscopy (NMR).

[0100] When testing the nonaqueous electrolyte of the present application, the nonaqueous electrolyte can be obtained from a secondary battery. A specific procedure for one exemplary method for obtaining a nonaqueous electrolyte from a secondary battery involves discharging the secondary battery to a discharge cutoff voltage (for safety reasons, the battery is generally fully discharged), then centrifuging the battery, and then obtaining an appropriate amount of the liquid obtained by the centrifugation to serve as the nonaqueous electrolyte. The nonaqueous electrolyte may also be obtained directly from the inlet of the secondary battery. [Positive pole piece]

[0101] In some embodiments, the positive electrode piece includes a positive electrode current collector and a positive electrode film layer including a positive electrode active material, the positive electrode current collector having two opposing surfaces in the thickness direction of the positive electrode current collector. The positive electrode film layer is provided on one or both of the opposing surfaces of the positive electrode current collector.

[0102] The positive electrode film layer includes a positive electrode active material. The positive electrode active material may be any positive electrode active material for secondary batteries known in the art. For example, the positive electrode active material may include at least one of a lithium transition metal oxide, a lithium-containing phosphate having an olivine structure, and a modified compound thereof. Examples of lithium transition metal oxides include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and a modified compound thereof. Examples of lithium-containing phosphates having an olivine structure include at least one of 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 a modified compound thereof. The present application is not limited to these materials, and other conventionally known materials used as positive electrode active materials for secondary batteries may also 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 has the molecular formula Li a Ni b Co c Mn d Al e M f O g A h where M represents a doping cation at the transition metal site and A represents a doping 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, g+h=2.

[0104] The molecular formula is Li a Ni b Co c Mn d Al e M f Og A h The layered material can be selectively doped and modified 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 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 positive electrode active material. However, cobalt greatly contributes to the diffusion rate of lithium ions in the positive electrode active material, and low-cobalt or cobalt-free reduces the diffusion rate of lithium ions in the positive electrode active material, 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 positive electrode 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 positive electrode active material, reducing the charge transfer resistance of the positive electrode active material, thereby reducing the diffusion resistance of lithium ions within the bulk of the positive electrode active material. Therefore, a low-cobalt or cobalt-free positive electrode active material can have an improved lithium ion diffusion rate, lithium ions within the bulk of the low-cobalt or cobalt-free positive electrode active material can be timely replenished to the surface, and excessive lithium desorption from the surface of the low-cobalt or cobalt-free positive electrode active material can be avoided, thereby stabilizing the crystal structure of the low-cobalt or cobalt-free positive electrode active material. Since the crystal structure of the low-cobalt or cobalt-free positive electrode active material is more stable, the probability of problems such as instability of the structural, chemical or electrochemical properties of the positive electrode active material due to excessive lithium desorption from the surface of the low-cobalt or cobalt-free positive electrode active material can be significantly reduced. For example, the above problems include the problems of irreversible strain and increased lattice defects of the positive electrode active material.

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

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

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

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

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

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

[0118] As an example, the layered material of the chemical 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 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn0.3 O2, LiNi 0.8 Co 0.05 Mn 0.15 O2, LiNi 0.7 Mn 0.3 O2, LiNi 0.69 Co 0.01 Mn 0.3 O2, LiNi 0.68 Co 0.02 Mn 0.3 O2, LiNi 0.65 Co 0.05 Mn 0.3 O2, LiNi 0.63 Co 0.07 Mn 0.3 O2, LiNi 0.61 Co 0.09 Mn 0.3 The present invention is not limited to the above.

[0119] Li a Ni b Co c Mn d Al e M f O g A h can be prepared according to a general method in this field. An exemplary preparation method is to mix a lithium source, a nickel source, a cobalt source, a manganese source, an aluminum source, a precursor of the M element, and a precursor of the A element, followed by sintering. The sintering atmosphere may be an oxygen-containing atmosphere, such as an air atmosphere or an oxygen gas atmosphere. The O2 concentration in the sintering atmosphere is, for example, 70% to 100%. The sintering temperature and sintering time can be adjusted according to the actual situation.

[0120] Examples of lithium sources include, but are not limited to, at least one of lithium oxide (LiO), lithium phosphate (LiPO), lithium dihydrogen phosphate (LiHPO), lithium acetate (CHCOOLi), lithium hydroxide (LiOH), lithium carbonate (LiCO), and lithium nitrate (LiNO). Examples of nickel sources include, but are not limited to, at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. Examples of cobalt sources include, but are not limited to, at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. Examples of manganese sources include, but are not limited to, at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. Examples of aluminum sources include, but are not limited to, at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate. For example, precursors of element M include, but are not limited to, at least one of oxides, nitrates, carbonates, hydroxides, and acetates of element M. For example, precursors of element A include, but are not limited to, at least one of ammonium fluoride, lithium fluoride, hydrogen fluoride, ammonium chloride, lithium chloride, hydrogen chloride, ammonium nitrate, ammonium nitrite, ammonium carbonate, ammonium hydrogen carbonate, ammonium phosphate, phosphoric acid, ammonium sulfate, ammonium hydrogen sulfate, ammonium hydrogen sulfite, ammonium sulfite, ammonium hydrogen sulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur.

[0121] In some embodiments, the total mass of the positive electrode layer is a molecular formula of Li a Ni b Co c Mn d Al e M f O g A h The mass percentage of the layered material is 80% to 99%. For example, a Nib Co c Mn d Al e M f O g A h The mass percentage of the layered material having the molecular formula Li may be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any range therebetween. 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 include a positive electrode conductive agent. The present application does not particularly limit the type of the positive electrode conductive agent, and the positive electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percent content of the positive electrode conductive agent is 5% or less based on the total mass of the positive electrode film layer.

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

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

[0125] In some embodiments, the positive electrode pieces have a pressed density of 2.6 g / cm 3 ~3.7g / cm 3 and preferably 3.4 g / cm 3 ~3.7g / cm 3 The nonaqueous electrolyte of the present invention contributes to matching with a positive electrode that is applied to a large thickness under high pressure, thereby further improving the energy density of the secondary battery.

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

[0127] In some embodiments, the negative electrode piece includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces facing each other in a thickness direction thereof, and the negative electrode film layer is disposed on one or both of the two facing surfaces of the negative electrode current collector.

[0128] The negative electrode active material may be a negative electrode active material known in the art and used in secondary batteries. For example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy material. The present application is not limited to these materials, and other known materials used as negative electrode active materials in secondary batteries may also be used. These negative electrode active materials may be used alone or in combination.

[0129] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present application is not particularly limited to the type of the negative electrode conductive agent, and for example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percent content of the negative electrode conductive agent is 5% or less based on the total mass of the negative electrode film layer.

[0130] In some embodiments, the negative electrode film layer may optionally further include 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 may include at least one of styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid (PAA), polymethacrylic acid (PMAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percent content of the negative electrode adhesive is 5% or less based on the total mass of the negative electrode film layer.

[0131] In some embodiments, the negative electrode membrane layer can further optionally contain other additives. For example, the other additives can include a thickener, such as sodium carboxymethyl cellulose (CMC-Na), a PTC thermistor material, etc. In some embodiments, the mass percent content of the other additives is 2% or less based on the total mass of the negative electrode membrane layer.

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

[0133] In some embodiments, the negative electrode piece has a pressed density of 1.4 g / cm 3 ~2.0g / cm 3 and preferably 1.5 g / cm 3 ~2.0g / cm 3 The nonaqueous electrolyte of the present invention contributes to matching with the negative electrode that is applied to a large thickness under high pressure, thereby further improving the energy density of the secondary battery.

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

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

[0136] In some embodiments, the separator may be made of at least one of glass fiber, nonwoven 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] Methods for fabricating the secondary battery of the present application are well known. In some embodiments, a secondary battery can be formed by assembling a positive electrode piece, a separator, a negative electrode piece, and a non-aqueous electrolyte. For example, the positive electrode piece, the separator, and the negative electrode piece are wound or stacked to form an electrode assembly. The electrode assembly is then placed in a housing, dried, and then a non-aqueous electrolyte is injected. The secondary battery is then obtained through processes such as vacuum sealing, standing, chemical formation, and shaping.

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

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

[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 battery modules can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

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

[0143]

[0006] An embodiment of the present application further provides a power consuming device including at least one of the secondary battery, battery module, or battery pack of the present application. The secondary battery, battery module, or battery pack may be used as a power source for the power consuming device or as an energy storage unit for the power consuming device. The power consuming device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop, etc.), an electric vehicle (e.g., 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.

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

[0145] 6 is a schematic diagram of an example power consuming device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, which may employ a battery pack or battery module to meet the high power and high energy density demands of the power consuming device.

[0146] Other examples of power consuming devices may be mobile phones, tablet computers, laptops, etc. Such power consuming devices are typically required to be thin and may employ secondary batteries as their power source. Example

[0147] The following examples will more specifically illustrate the contents of the present disclosure. These examples are used for illustrative purposes only, and various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. 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. In addition, all equipment 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 positive electrode pole piece

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

[0151] Preparation of negative electrode pole piece

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

[0153] Separator

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

[0155] Preparation of non-aqueous electrolyte

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

[0157] Fabrication of secondary batteries

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

[0159] Testing section

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

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

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

[0163] At 60°C, charge the secondary battery at a constant current of 1C up to 4.3V, then continue charging at a constant voltage until the current drops to 0.05C, at which point measure the volume of the secondary battery using the drainage method and call it V0. Place the secondary battery in a thermostatic box at 60°C and store it for 30 days, then remove it and measure the volume of the secondary battery using the drainage method and call it V1. The volume expansion rate (%) of the secondary battery after storing it at 60°C for 30 days = [(V1-V0) / V0] x 100%.

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

[0165] At 45°C, the secondary battery was charged to 4.3V at a constant current of 1C, and then continued to charge at a constant voltage until the current reached 0.05C. At this point, the secondary battery was fully charged. The charge capacity at this point was recorded and designated the first charge capacity. After allowing the secondary battery to stand for 5 minutes, it was discharged to 2.8V at a constant current of 1C. This constitutes one cycle of charge / discharge. The discharge capacity at this point was recorded and designated the first discharge capacity. The secondary battery was subjected to a cycle charge / 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) Testing the initial DC internal resistance of secondary batteries

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

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

[0169] [Table 1]

[0170] [Table 2]

[0171] As can be seen from the test results summarized in Tables 1 and 2, when a non-aqueous electrolyte contains a compound represented by Formula I, and the content A1% and the secondary battery's group margin B satisfy a ratio B / A1 of 0.5 to 45, the secondary battery can simultaneously achieve high group margin design and high safety performance, as well as low internal resistance and high capacity retention. Meanwhile, the compound represented by Formula I simultaneously forms uniform, dense, and stable interfacial films on the positive and negative electrodes, reducing direct contact between the active material and the non-aqueous electrolyte and reducing the damage and regeneration of the positive and negative interfacial films. This reduces gas generation and the consumption of active lithium ions during this process, reducing gas expansion in the battery and improving the battery's capacity retention. Meanwhile, the compound represented by Formula I stabilizes the crystalline structure of the positive electrode active material, reducing lattice oxygen precipitation and transition metal ion elution, and further reducing a series of side reactions resulting from these, thereby reducing gas expansion in the battery.

[0172] As can be seen from 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 is insufficient to form a uniform, dense, and stable positive electrode interfacial film and / or negative electrode interfacial film. As a result, the crystalline structure of the positive electrode active material cannot be effectively stabilized to reduce decomposition of the non-aqueous electrolyte, resulting in significant gas generation and a high volume expansion rate in the secondary battery. This poses significant safety risks for secondary batteries designed with a high packing margin. At the same time, frequent interfacial side reactions between the non-aqueous electrolyte and the electrodes increase the interfacial resistance of the positive electrode and / or the negative electrode, resulting in high internal resistance and low capacity retention in the secondary battery.

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

[0174] As can be seen from 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 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 coefficient, reduced internal resistance, and increased capacity retention. This is thought to be because the 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 interfacial film with lower resistance and higher thermal stability.

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

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

[0178] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has substantially the same configuration as the technical idea within the scope of the technical solution of the present application and achieves similar effects is included in the technical scope of the present application. Furthermore, within the scope of the present application, various modifications that a person skilled in the art can conceive of to the embodiments and other embodiments constructed by combining some of the components of the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery comprising a battery case, and an electrode assembly and a non-aqueous electrolyte solution housed in the battery case, wherein the non-aqueous electrolyte solution contains 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 nonaqueous electrolyte, the group margin of the secondary battery is B, and the secondary battery satisfies the following requirements: B is 0.88 to 0.99, and A1 is 0.02 or more and less than 2; 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 of the secondary battery to the maximum internal cross-sectional area, i.e., the packing ratio. Secondary battery. 【Chemical 1】 In Formula I, X and Y each independently represent a hydrogen atom, a halogen atom, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C6-C20 aryl group, a C1-C20 halogenated alkyl group, a C2-C20 halogenated alkenyl group, a C2-C20 halogenated alkynyl group, a C6-C20 halogenated aryl group, a C1-C20 alkoxy group, a C2-C20 alkenyloxy group, a C2-C20 alkynyloxy group, a C6-C20 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. 2. The secondary battery according to claim 1, wherein A1 is 0.02 to 1.

3. The non-aqueous electrolyte further comprises a first lithium salt, the first lithium salt being lithium hexafluorophosphate, and the mass percent content of the first lithium salt is A2% based on the total mass of the non-aqueous electrolyte, where A2 is greater than 0 and less than or equal to 14.

2. The secondary battery according to claim 1, wherein 10≦A2 / A1≦600.

4. 2. The secondary battery according to claim 1, wherein the non-aqueous electrolyte further comprises a first lithium salt, the first lithium salt being lithium hexafluorophosphate, the mass percent content of the first lithium salt being A2% based on the total mass of the non-aqueous electrolyte, and 0<10A1+A2 / 5≦15.

5. The non-aqueous electrolyte further comprises a second lithium salt, the second lithium salt being a fluorosulfonylimide lithium salt, and the mass percent content of the second lithium salt is A3% based on the total mass of the non-aqueous electrolyte; 0<A3≦2.5, and / or 4. The secondary battery according to claim 3, wherein 0.25≦A3 / A1≦25.

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

7. The non-aqueous electrolyte further comprises fluoroethylene carbonate, the mass percent content of which is C1% based on the total mass of the non-aqueous electrolyte; 0<C1≦5, and / or The secondary battery according to claim 1 , wherein C1 / A1 satisfies 5≦C1 / A1≦50.

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

9. the nonaqueous electrolyte solution includes an organic solvent, the organic solvent including a first solvent, a second solvent, and a third solvent; The first solvent comprises at least one of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and vinylethylene carbonate, and the mass percent content of the first solvent in the organic solvent is D1% based on the total mass of the organic solvent; The second solvent comprises at least one of ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate, and the mass percent content of the second solvent in the organic solvent is D2% based on the total mass of the organic solvent; the third solvent comprises at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate, and the mass percent content of the third solvent in the organic solvent is D3% based on the total mass of the organic solvent; 2. The secondary battery according to claim 1, wherein the organic solvent satisfies the following conditions: D1 is greater than 0 and not greater than 20; D2 is 50 to 90; and D3 is 0 to 30.

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

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

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

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

14. A battery module comprising the secondary battery according to claim 1 .

15. A battery pack comprising the secondary battery according to claim 1 and one of the battery modules according to claim 14.

16. A power consuming device comprising at least one of the secondary battery according to claim 1, the battery module according to claim 14, and the battery pack according to claim 15.

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