Non-aqueous electrolytes and secondary batteries, battery modules, battery packs and electrical devices containing them.

Abstract

A non-aqueous electrolyte and a secondary battery, battery module, battery pack, and electrical device comprising the non-aqueous electrolyte are disclosed. The non-aqueous electrolyte comprises an electrolyte salt, a non-aqueous solvent, and a first additive. The electrolyte salt includes lithium difluorosulfonylimide, lithium tetrafluoroborate, and lithium difluorooxalate borate. The first additive includes fluoroethylene carbonate. Based on the total mass of the non-aqueous electrolyte, the contents of lithium difluorosulfonylimide (A1), lithium tetrafluoroborate (A2), lithium difluorooxalate borate (A3), and fluoroethylene carbonate (B1) satisfy the following: A1 is 9% to 15%, A1 / A2 is 30 to 1500, A1 / B1 is 3.6 to 15, and A2 / A3 is 0.02 to 30. The secondary battery comprising the non-aqueous electrolyte simultaneously exhibits good cycle performance, storage performance, safety performance, and kinetic performance.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a non-aqueous electrolyte and a secondary battery, battery module, battery pack and power-consuming device containing the electrolyte. Background Technology

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the application and promotion of secondary batteries, their comprehensive performance has received increasing attention. For example, secondary batteries need to simultaneously meet requirements such as high energy density, long cycle life, high safety performance, and good rate performance. Non-aqueous electrolytes play a role in conducting ions between the positive and negative electrodes, and are one of the key factors affecting the performance of secondary batteries. Therefore, there is an urgent need to provide a non-aqueous electrolyte with excellent comprehensive performance. Summary of the Invention

[0003] The purpose of this application is to provide a non-aqueous electrolyte and a secondary battery, battery module, battery pack and electrical device containing the electrolyte, which enables the secondary battery to simultaneously achieve good cycle performance, storage performance, thermal safety performance and kinetic performance.

[0004] This application provides a non-aqueous electrolyte comprising an electrolyte salt, a non-aqueous solvent, and a first additive. The electrolyte salt comprises: lithium difluorosulfonylimide, with a mass content of A1 in the non-aqueous electrolyte, based on the total mass of the non-aqueous electrolyte; lithium tetrafluoroborate, with a mass content of A2 in the non-aqueous electrolyte, based on the total mass of the non-aqueous electrolyte; and lithium difluorooxalateborate, with a mass content of A3 in the non-aqueous electrolyte, based on the total mass of the non-aqueous electrolyte. The first additive comprises: fluoroethylene carbonate, with a mass content of B1 in the non-aqueous electrolyte, based on the total mass of the non-aqueous electrolyte. The non-aqueous electrolyte satisfies the following conditions: A1 is 9% to 15%, A1 / A2 is 30 to 1500, A1 / B1 is 3.6 to 15, and A2 / A3 is 0.02 to 30.

[0005] The inventors of this application, through extensive research, discovered that by using lithium tetrafluoroborate, lithium difluorooxalate borate, and fluoroethylene carbonate in a non-aqueous electrolyte with lithium difluorosulfonylimide as the main lithium salt, and by rationally adjusting the contents of lithium difluorosulfonylimide (A1), lithium tetrafluoroborate (A2), lithium difluorooxalate borate (A3), and fluoroethylene carbonate (B1) to satisfy A1 / A2 of 30 to 1500, A1 / B1 of 3.6 to 15, and A2 / A3 of 0.02 to 30, the non-aqueous electrolyte can simultaneously possess high thermal stability, high conductivity, and a wide electrochemical window. Furthermore, the non-aqueous electrolyte can passivate the aluminum foil current collector and form a dense, stable, and low-resistance interface film on the surface of the negative electrode active material. Thus, secondary batteries using the non-aqueous electrolyte of this application can simultaneously achieve good cycle performance, storage performance, thermal box safety performance, and kinetic performance.

[0006] In any embodiment of this application, A1 / A2 is 50 to 250, optionally 50 to 150. When A1 / A2 is within a suitable range, it is beneficial to fully utilize the synergistic effect between lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate, thereby making the non-aqueous electrolyte less prone to corroding the aluminum foil current collector, thus further improving the cycle performance and storage performance of the secondary battery.

[0007] In any embodiment of this application, A1 / B1 is 4 to 9, and optionally 4 to 7. When A1 / B1 is within a suitable range, it is beneficial to fully utilize the synergistic effect between lithium bis(fluorosulfonyl)imide and fluoroethylene carbonate, and the non-aqueous electrolyte can simultaneously maintain high thermal stability and electrical conductivity, thereby further improving the cycle performance and thermal box safety performance of the secondary battery.

[0008] In any embodiment of this application, A2 / A3 is 0.5 to 13.5, and optionally 1 to 10. When A2 / A3 is within a suitable range, it is beneficial to fully utilize the synergistic effect between lithium tetrafluoroborate and lithium difluorooxalate borate, which not only better protects the aluminum foil current collector, but also forms a low-resistance organic-inorganic composite interface film on the surface of the negative electrode active material, thereby further improving the cycle performance and kinetic performance of the secondary battery.

[0009] In any embodiment of this application, the non-aqueous electrolyte further satisfies that (A2+A3) / B1 is 0.008 to 0.8, and optionally, (A2+A3) / B1 is 0.026 to 0.2. This ensures the presence of BF4 in the non-aqueous electrolyte. - and DFOB - The formation of free ions reduces the association between cations and anions, thereby maximizing the utilization of BF4. - and DFOB - Improvement effect on the dynamic performance of secondary batteries.

[0010] In any embodiment of this application, A1 is 10% to 15%, and optionally 10% to 13%.

[0011] In any embodiment of this application, A2 is 0.01% to 0.3%, and optionally 0.05% to 0.2%.

[0012] In any embodiment of this application, A3 is 0.01% to 0.5%, and optionally 0.015% to 0.1%.

[0013] In any embodiment of this application, B1 is 1.0% to 2.5%, optionally 1.5% to 2.5%.

[0014] In any embodiment of this application, the non-aqueous solvent comprises: a first solvent, including at least one of ethylene carbonate, propylene carbonate, and butylene carbonate, wherein the mass content of the first solvent in the non-aqueous solvent is C1, based on the total mass of the non-aqueous solvent; a second solvent, including at least one of methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate, wherein the mass content of the second solvent in the non-aqueous solvent is C2, based on the total mass of the non-aqueous 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, wherein the mass content of the third solvent in the non-aqueous solvent is C3, based on the total mass of the non-aqueous solvent, wherein the non-aqueous solvent satisfies: C1 is 10% to 30%, C2 is 50% to 90%, and C3 is 0% to 20%.

[0015] In any embodiment of this application, C1 / (C2+C3) is 0.1 to 0.45, and optionally 0.2 to 0.3.

[0016] In any embodiment of this application, the non-aqueous electrolyte further includes a second additive, comprising at least one of vinylene carbonate, vinyl sulfate, and 1,3-propanesulfonic acid lactone, wherein the additive comprises a mass content of B2 in the non-aqueous electrolyte, and B2 is 0.05% to 2% based on the total mass of the non-aqueous electrolyte, optionally 0.5% to 2%. The second additive helps to further improve the interfacial properties of the positive and / or negative electrodes, thereby further improving at least one of the cycle performance, storage performance, thermal safety performance, and kinetic performance of the secondary battery.

[0017] In any embodiment of this application, (A1+B2) / C1 is 0.4 to 1.3, optionally 0.4 to 0.8. This allows the secondary battery to have excellent cycle performance while avoiding deterioration in kinetic and power performance.

[0018] In any embodiment of this application, the non-aqueous electrolyte further includes a third additive, comprising at least one of aminosulfonic acid and its salts, wherein the mass content of the additive in the non-aqueous electrolyte is B3, and the mass content of B3 is 0.005% to 0.1%, optionally 0.005% to 0.05%, based on the total mass of the non-aqueous electrolyte. This helps to improve the cycle performance and kinetic performance of the secondary battery.

[0019] The second aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is the same as that of the first aspect of this application. Thus, the secondary battery of this application can simultaneously achieve good cycle performance, storage performance, thermal safety performance, and kinetic performance.

[0020] In any embodiment of this application, the room temperature conductivity of the non-aqueous electrolyte is x mS / cm, the thickness of the negative electrode is L μm, and the secondary battery satisfies:

[0021] In any embodiment of this application, the positive electrode comprises a material with the molecular formula Li. a Ni b Co c Mn d Al e M f O g A h The layered material, M represents the transition metal site doped cation, A represents the oxygen site doped anion, 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.

[0022] In some embodiments of this application, M is selected from at least one of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te and W.

[0023] In some embodiments of this application, A is selected from at least one of F, N, P and S, and optionally, A is selected from F.

[0024] In some embodiments of this application, 0 < b < 0.98, and optionally, 0.50 ≤ b < 0.98.

[0025] In some embodiments of this application, c = 0.

[0026] In some embodiments of this application, 0 < c ≤ 0.20, and optionally, 0 < c ≤ 0.10.

[0027] In some embodiments of this application, d = 0 and 0 < e < 0.50, and optionally, d = 0 and 0 < e ≤ 0.10.

[0028] In some embodiments of this application, e = 0 and 0 < d < 0.50, and optionally, e = 0 and 0 < d ≤ 0.10.

[0029] In some embodiments of this application, 0 < d < 0.50 and 0 < e < 0.50, and optionally, 0 < d ≤ 0.30 and 0 < e ≤ 0.10.

[0030] A third aspect of this application provides a battery module, including the secondary battery of the second aspect of this application.

[0031] The fourth aspect of this application provides a battery pack, including one of the secondary battery of the second aspect of this application and the battery module of the third aspect.

[0032] The fifth aspect of this application provides an electrical device, including at least one of the secondary battery of the second aspect of this application, the battery module of the third aspect, and the battery pack of the fourth aspect.

[0033] The secondary battery of this application can simultaneously achieve good cycle performance, storage performance, thermal box safety performance and dynamic performance. The battery module, battery pack and power device of this application include the secondary battery provided in this application, and therefore have at least the same advantages as the secondary battery. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0036] Figure 2 yes Figure 1 An exploded view of the implementation method of the secondary battery.

[0037] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0038] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0039] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0040] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0041] The accompanying drawings are not necessarily drawn to scale. The reference numerals are as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0042] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the non-aqueous electrolyte of this application, as well as secondary batteries, battery modules, battery packs, and electrical devices comprising the electrolyte. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0043] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0044] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0045] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0046] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0047] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0048] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0049] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0050] With the application and promotion of secondary batteries, their comprehensive performance has received increasing attention. Non-aqueous electrolytes are one of the key factors affecting the performance of secondary batteries. Currently, the most widely used commercial non-aqueous electrolyte system is a mixed carbonate solution of lithium hexafluorophosphate. However, lithium hexafluorophosphate has poor thermal stability at high temperatures, and it decomposes to form PF5 at higher temperatures. PF5 has strong Lewis acidity and interacts with the lone pair electrons on the oxygen atoms in the solvent molecules, causing solvent decomposition. Furthermore, PF5 is highly sensitive to trace amounts of water in the non-aqueous electrolyte, producing HF upon contact with water, thus increasing the acidity of the non-aqueous electrolyte. This easily corrodes the positive electrode active material and the positive electrode current collector, causing the dissolution of transition metal ions from the positive electrode active material. In addition, after the transition metal ions dissolve from the positive electrode active material and migrate to the negative electrode, they are reduced to transition metals. These transition metals act as "catalysts," catalyzing the decomposition of the solid electrolyte interphase (SEI) film on the surface of the negative electrode active material, producing byproducts. One part of the byproducts is gas, which causes the secondary battery to expand and affects its safety performance. Another part of the byproducts is deposited on the surface of the negative electrode active material, which hinders the lithium-ion transport channel, causing an increase in the impedance of the secondary battery and thus affecting its kinetic performance. In addition, in order to replenish the lost interface film, the non-aqueous electrolyte and the active lithium ions inside the battery are continuously consumed, which will have an irreversible impact on the capacity retention rate of the secondary battery.

[0051] The inventors of this application unexpectedly discovered after conducting extensive research that when the non-aqueous electrolyte contains appropriate amounts of lithium difluorosulfonylimide, lithium tetrafluoroborate, lithium difluorooxalate borate, and fluoroethylene carbonate, the secondary battery can simultaneously achieve good cycle performance, storage performance, thermal safety performance, and kinetic performance.

[0052] Non-aqueous electrolyte

[0053] Specifically, a first aspect of this application provides a non-aqueous electrolyte comprising an electrolyte salt, a non-aqueous solvent, and a first additive. The electrolyte salt comprises: lithium bis(fluorosulfonyl)imide (LiFSI), with a mass content of A1 in the non-aqueous electrolyte, based on the total mass of the non-aqueous electrolyte; lithium tetrafluoroborate (LiBF4), with a mass content of A2 in the non-aqueous electrolyte, based on the total mass of the non-aqueous electrolyte; and lithium difluorooxalate borate (LiDFOB), with a mass content of A3 in the non-aqueous electrolyte, based on the total mass of the non-aqueous electrolyte. The first additive comprises: fluoroethylene carbonate (FEC), with a mass content of B1 in the non-aqueous electrolyte, based on the total mass of the non-aqueous electrolyte. The non-aqueous electrolyte satisfies the following conditions: A1 is 9% to 15%, A1 / A2 is 30 to 1500, A1 / B1 is 3.6 to 15, and A2 / A3 is 0.02 to 30.

[0054] The non-aqueous electrolyte of this application uses lithium bis(fluorosulfonyl)imide as the main lithium salt, with a mass content of 9% to 15% in the non-aqueous electrolyte. Lithium bis(fluorosulfonyl)imide has the chemical formula F₂NO₄S₂.Li, where the N atom is bonded to two electron-withdrawing sulfonyl groups. This allows for sufficient delocalization of the charge on the N atom, resulting in lithium bis(fluorosulfonyl)imide having a low lattice energy and easy dissociation, thereby improving the conductivity and reducing the viscosity of the non-aqueous electrolyte. Furthermore, lithium bis(fluorosulfonyl)imide exhibits good high-temperature resistance and is not easily hydrolyzed, enabling the formation of a thinner, lower-impedance, and more thermally stable interfacial film on the surface of the negative electrode active material, thus reducing side reactions between the negative electrode active material and the non-aqueous electrolyte. Therefore, lithium bis(fluorosulfonyl)imide is expected to become one of the next-generation main lithium salts to replace lithium hexafluorophosphate.

[0055] However, one of the drawbacks of using lithium bis(fluorosulfonyl)imide as the main lithium salt is the effect on aluminum foil current collectors at approximately 3.7 V vs. Li / Li. + The corrosion of aluminum foil current collectors is exacerbated by high temperatures and voltages. This corrosion significantly impacts the performance of secondary batteries, increasing polarization and irreversible capacity loss, and even affecting safety. The main effects are as follows: some insoluble solid corrosion products increase the internal resistance of the secondary battery; some soluble corrosion products contaminate and accelerate the decomposition of non-aqueous electrolytes, increasing self-discharge; and the Al produced during corrosion... 3+ It may migrate to the negative electrode through diffusion and be reduced to aluminum dendrites. During the research process, the inventors also unexpectedly discovered that another drawback of using lithium bisfluorosulfonylimide as the main lithium salt is that lithium bisfluorosulfonylimide reacts with LiC6 at the negative electrode and releases a large amount of gas (such as SO2, NO2) and heat, which affects the safety performance of the secondary battery, especially the thermal box safety performance.

[0056] Therefore, secondary batteries using lithium bisfluorosulfonylimide as the main lithium salt are currently difficult to commercialize.

[0057] The inventors of this application, through extensive research, discovered that by using lithium tetrafluoroborate, lithium difluorooxalate borate, and fluoroethylene carbonate in a non-aqueous electrolyte with lithium difluorosulfonylimide as the main lithium salt, and by rationally adjusting the contents of lithium difluorosulfonylimide (A1), lithium tetrafluoroborate (A2), lithium difluorooxalate borate (A3), and fluoroethylene carbonate (B1) to satisfy A1 / A2 of 30 to 1500, A1 / B1 of 3.6 to 15, and A2 / A3 of 0.02 to 30, the non-aqueous electrolyte can simultaneously possess high thermal stability, high conductivity, and a wide electrochemical window. Furthermore, the non-aqueous electrolyte can passivate the aluminum foil current collector and form a dense, stable, and low-resistance interface film on the surface of the negative electrode active material. Thus, secondary batteries using the non-aqueous electrolyte of this application can simultaneously achieve good cycle performance, storage performance, thermal box safety performance, and kinetic performance.

[0058] Although the mechanism is not yet clear, the inventors speculate that the possible reasons include the following.

[0059] First, lithium tetrafluoroborate has a passivating effect on aluminum foil current collectors. It can preferentially be oxidized and decomposed on the surface of the aluminum foil current collector to form a passivation film, thereby effectively improving the corrosion of aluminum foil current collectors by lithium bis(fluorosulfonyl)imide; at the same time, due to BF4 - The ionic radius of lithium tetrafluoroborate is small, making it easy to associate. Therefore, if its content is too high, it will reduce the conductivity of the non-aqueous electrolyte. Through extensive research, the inventors further discovered that when the content of lithium difluorosulfonylimide (A1) and lithium tetrafluoroborate (A2) is reasonably adjusted to meet the A1 / A2 ratio of 30 to 1500, the synergistic effect between the two can be fully utilized. Thus, the non-aqueous electrolyte simultaneously possesses high thermal stability and high conductivity, and it is less prone to corroding the aluminum foil current collector. When A1 / A2 is greater than 1500, the passivation effect of lithium tetrafluoroborate on the aluminum foil cannot prevent the corrosion of the aluminum foil current collector by lithium difluorosulfonylimide, resulting in poor cycle performance of the secondary battery. When A1 / A2 is less than 30, excessive lithium tetrafluoroborate leads to a significant decrease in the conductivity of the non-aqueous electrolyte, deteriorating the kinetic performance of the secondary battery.

[0060] Secondly, FEC can undergo reduction decomposition at higher potentials and form a flexible, LiF-rich interfacial film on the surface of the negative electrode active material. This inhibits the reduction decomposition of non-aqueous solvents at lower potentials and suppresses their intercalation into the negative electrode active material. Simultaneously, because the formed interfacial film contains a relatively stable LiF component, it effectively reduces the reaction between LiFSI and LiC6, improving the thermal safety performance of the secondary battery. Furthermore, FEC is resistant to high-voltage oxidation, which is beneficial for matching high-voltage positive electrode active materials, thus contributing to increased energy density in the secondary battery. Extensive research further revealed that when the content of lithium bis(fluorosulfonyl)imide (A1) and the content of fluoroethylene carbonate (B1) are appropriately adjusted to achieve an A1 / B1 ratio of 3.6 to 15, the improvement effect of FEC on the thermal safety performance, cycle performance, and energy density of the secondary battery is fully realized. When A1 / B1 is greater than 15, the FEC cannot protect the negative electrode from the reaction between LiFSI and LiC6, resulting in poor thermal safety performance of the secondary battery. When A1 / B1 is less than 3.6, there is too much LiF component in the interface film on the surface of the negative electrode active material, which significantly increases the internal resistance of the secondary battery and deteriorates its kinetic performance.

[0061] Third, the anionic radius of lithium difluorooxalate borate (DFOB) - The smaller charge transfer resistance results in a lower charge transfer resistance for the non-aqueous electrolyte, leading to relatively high conductivity at both high and low temperatures and broadening the electrochemical window of the non-aqueous electrolyte; the BO bond in the lithium difluorooxalate borate structure can interact with Al... 3+ The bonding and deposition of lithium difluorosulfonylimide onto the surface of the aluminum foil current collector forms a passivation film, effectively improving the corrosion of the aluminum foil current collector by lithium difluorosulfonylimide. Lithium difluorooxalate borate can also form a low-resistance interface film on the surface of the negative electrode active material. However, because lithium difluorooxalate borate contains an oxalate group in its molecular structure, its thermal stability is lower than that of lithium tetrafluoroborate. When heated, it is oxidized to form carbon dioxide gas. Therefore, if its content is too high, it will reduce the thermal stability of the non-aqueous electrolyte and increase the gas production of the secondary battery. Through extensive research, the inventors further discovered that when the content of lithium tetrafluoroborate (A2) and lithium difluorooxalate borate (A3) is reasonably adjusted to meet the A2 / A3 ratio of 0.02 to 30, it can not only better protect the aluminum foil current collector but also form a low-resistance organic-inorganic composite interface film on the surface of the negative electrode active material, thereby further improving the cycle performance and kinetic performance of the secondary battery. When A2 / A3 is greater than 30, lithium difluorooxalate borate has a weak effect on reducing the interface impedance of the negative electrode, which is insufficient to compensate for the deterioration of the kinetic performance of the secondary battery caused by lithium tetrafluoroborate. When A2 / A3 is less than 0.02, excessive lithium difluorooxalate borate leads to a decrease in the thermal stability of the non-aqueous electrolyte, resulting in a deterioration in the storage performance and thermal box safety performance of the secondary battery.

[0062] Therefore, the reason why the secondary battery using the non-aqueous electrolyte of this application can simultaneously achieve good cycle performance, storage performance, thermal safety performance, and kinetic performance may be due to the synergistic effect formed among the above-mentioned components. Lithium tetrafluoroborate and lithium difluorooxalate borate can effectively improve the corrosion of aluminum foil current collectors by lithium difluorosulfonylimide, reduce battery polarization, reduce irreversible capacity loss, and improve the cycle performance and storage performance of the secondary battery; ethylene fluoride carbonate can effectively reduce the reaction between lithium difluorosulfonylimide and LiC6, improving the thermal safety performance of the secondary battery; and lithium tetrafluoroborate, lithium difluorooxalate borate, and ethylene fluoride carbonate can form an organic-inorganic composite interface film containing F and B atoms on the surface of the negative electrode active material, reducing the internal resistance of the secondary battery and improving its kinetic performance.

[0063] In some embodiments, A1 / A2 can be 30 to 1000, 30 to 750, 30 to 500, 30 to 400, 30 to 300, 30 to 250, 30 to 200, 30 to 150, 30 to 100, 30 to 80, 50 to 1000, 50 to 750, 50 to 500, 50 to 400, 50 to 300, 50 to 250, 50 to 200, 50 to 150, 50 to 120, 50 to 100, or 50 to 80.

[0064] In some embodiments, A1 / B1 can be 4 to 15, 4 to 14, 4 to 13, 4 to 12, 4 to 11, 4 to 10, 4 to 9, 4 to 8, 4 to 7, 5 to 15, 5 to 14, 5 to 13, 5 to 12, 5 to 11, 5 to 10, 5 to 9, 5 to 8, or 5 to 7.

[0065] In some embodiments, A2 / A3 is 0.1 to 30, 0.1 to 25, 0.1 to 20, 0.1 to 18, 0.1 to 15, 0.1 to 13.5, 0.1 to 12, 0.1 to 11, 0.1 to 10, 0.1 to 9, 0.1 to 8, 0.1 to 7, 0.1 to 6, 0.1 to 5, 0.5 to 30, 0.5 to 25, 0.5 to 20, 0.5 to 1 8, 0.5 to 15, 0.5 to 13.5, 0.5 to 12, 0.5 to 11, 0.5 to 10, 0.5 to 9, 0.5 to 8, 0.5 to 7, 0.5 to 6, 0.5 to 5, 1 to 30, 1 to 25, 1 to 20, 1 to 18, 1 to 15, 1 to 13.5, 1 to 12, 1 to 11, 1 to 10, 1 to 9, 1 to 8, 1 to 7, 1 to 6 or 1 to 5.

[0066] When A1 / A2 is within a suitable range, it is beneficial to fully utilize the synergistic effect between lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate. As a result, the non-aqueous electrolyte is less likely to corrode the aluminum foil current collector, thereby further improving the cycle performance and storage performance of the secondary battery.

[0067] When A1 / B1 is within a suitable range, it is beneficial to fully leverage the synergistic effect between lithium bis(fluorosulfonyl)imide and fluoroethylene carbonate. The non-aqueous electrolyte can simultaneously maintain high thermal stability and conductivity, thereby further improving the cycle performance and thermal box safety performance of the secondary battery.

[0068] When A2 / A3 is within a suitable range, it is beneficial to give full play to the synergistic effect between lithium tetrafluoroborate and lithium difluorooxalate borate. This not only better protects the aluminum foil current collector, but also forms a low-resistance organic-inorganic composite interface film on the surface of the negative electrode active material, thereby further improving the cycle performance and kinetic performance of the secondary battery.

[0069] Lithium tetrafluoroborate and lithium difluorooxalate borate have small anionic radii, making them difficult to completely dissociate in non-aqueous electrolytes, and their cations and anions readily associate. Through extensive research, the inventors further discovered that when the contents of lithium tetrafluoroborate (A2), lithium difluorooxalate borate (A3), and fluoroethylene carbonate (B1) are appropriately adjusted to satisfy (A2+A3) / B1 of 0.008 to 0.8, the non-aqueous electrolyte exhibits moderate viscosity and maintains high conductivity. This may be because FEC has a high dielectric constant, thereby ensuring the presence of BF4 in the non-aqueous electrolyte. - and DFOB - The formation of free ions reduces the association between cations and anions, thereby maximizing the utilization of BF4. - and DFOB - It improves the kinetic performance of secondary batteries and effectively avoids the following situation: when (A2+A3) / B1 is greater than 0.8, BF4 in the non-aqueous electrolyte... - It readily associates with DFOB-, which may increase the viscosity and decrease the conductivity of the non-aqueous electrolyte. When (A2+A3) / B1 is less than 0.008, the high viscosity of FEC itself may also lead to a decrease in the conductivity of the non-aqueous electrolyte. Optionally, in some embodiments, (A2+A3) / B1 is 0.01 to 0.8, 0.01 to 0.7, 0.01 to 0.6, 0.01 to 0.5, 0.01 to 0.4, 0.01 to 0.3, 0.01 to 0.2, 0.026 to 0.8, 0.026 to 0.7, 0.026 to 0.6, 0.026 to 0.5, 0.026 to 0.4, 0.026 to 0.3, 0.026 to 0.2, 0.1 to 0.8, 0.1 to 0.7, 0.1 to 0.6, 0.1 to 0.5, 0.1 to 0.4, 0.1 to 0.3, or 0.1 to 0.2.

[0070] The non-aqueous electrolyte of this application uses lithium bis(fluorosulfonyl)imide as the main lithium salt, which has a high mass content in the non-aqueous electrolyte. In some embodiments, A1 can be 10% to 15%, 11% to 15%, 12% to 15%, 13% to 15%, 9% to 14%, 10% to 14%, 11% to 14%, 12% to 14%, 13% to 14%, 9% to 13%, 10% to 13%, 11% to 13%, or 12% to 13%.

[0071] As the LiBF4 content increases, the conductivity of the non-aqueous electrolyte decreases, which is detrimental to the formation of a stable interfacial film on the surface of the negative electrode active material. In some embodiments, A2 can be 0.01% to 0.3%. Optionally, A2 can be 0.02% to 0.3%, 0.02% to 0.26%, 0.02% to 0.22%, 0.02% to 0.2%, 0.02% to 0.18%, 0.02% to 0.16%, 0.02% to 0.14%, 0.02% to 0.12%, 0.02% to 0.1%, 0.05% to 0.3%, 0.05% to 0.26%, 0.05% to 0.22%, 0.05% to 0.2%, 0.05% to 0.18%, 0.05% to 0.16%, 0.05% to 0.14%, 0.05% to 0.12%, or 0.05% to 0.1%.

[0072] The LiDFOB molecule contains an oxalate group, which is oxidized upon heating to form carbon dioxide gas, reducing the thermal stability of the non-aqueous electrolyte. In some embodiments, A3 can be 0.01% to 0.5%. Optionally, A3 can be 0.01% to 0.45%, 0.01% to 0.4%, 0.01% to 0.35%, 0.01% to 0.3%, 0.01% to 0.25%, 0.01% to 0.2%, 0.01% to 0.15%, 0.01% to 0.1%, 0.015% to 0.45%, 0.015% to 0.4%, 0.015% to 0.35%, 0.015% to 0.3%, 0.015% to 0.25%, 0.015% to 0.2%, 0.015% to 0.15%, or 0.015% to 0.1%.

[0073] When the FEC content increases, the viscosity of the non-aqueous electrolyte increases and the conductivity decreases. Simultaneously, FEC easily decomposes at high temperatures to form HF, which disrupts the structural stability of the positive electrode active material, increases gas production in the secondary battery, and affects the battery's storage performance and thermal safety. In some embodiments, B1 can be 1.0% to 2.5%. For example, B1 can be 1.1% to 2.5%, 1.2% to 2.5%, 1.3% to 2.5%, 1.4% to 2.5%, 1.5% to 2.5%, 1.6% to 2.5%, 1.7% to 2.5%, 1.8% to 2.5%, 1.9% to 2.5%, or 2% to 2.5%.

[0074] In some embodiments, the non-aqueous solvent includes at least one of a first solvent, a second solvent, and a third solvent.

[0075] The first solvent is a cyclic carbonate compound, which may include at least one of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Optionally, the first solvent includes ethylene carbonate.

[0076] The second solvent is a chain carbonate compound, which may include at least one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). Optionally, the second solvent includes at least one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC).

[0077] In some embodiments, the non-aqueous solvent includes at least a first solvent and a second solvent. When the contents of the electrolyte salt and the first additive are high, the viscosity of the non-aqueous electrolyte increases and its conductivity decreases, which is detrimental to the formation of a uniform, dense, stable, and low-resistivity interfacial film on the surface of the negative electrode active material. The first solvent, due to its high dielectric constant, can increase the conductivity of the non-aqueous electrolyte, while the second solvent, due to its lower viscosity, can reduce the viscosity of the non-aqueous electrolyte. Therefore, when the non-aqueous solvent includes both the first and second solvents, it helps the non-aqueous electrolyte to have suitable viscosity and conductivity, thereby facilitating lithium-ion transport and the formation of a uniform, dense, stable, and low-resistivity interfacial film on the surface of the negative electrode active material.

[0078] In some embodiments, the non-aqueous solvent may further include a third solvent. The third solvent is a carboxylic acid ester compound, and may include, for example, at least one selected from 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 helps the non-aqueous electrolyte to have suitable viscosity and conductivity, thereby facilitating lithium-ion transport; furthermore, the third solvent also helps to ensure the presence of BF4 in the non-aqueous electrolyte. - and DFOB - The formation of free ions reduces the association between cations and anions, thereby enabling BF4 to fully exert its potential. - and DFOB - It improves the capacity retention and kinetic performance of secondary batteries.

[0079] The non-aqueous solvents of this application may also include solvents other than the first solvent, second solvent, and third solvent described above. As an example, the other solvents may include sulfone solvents, such as sulfolane (SF), dimethyl sulfone (MSM), ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0080] In some embodiments, the mass content of the first solvent in the non-aqueous solvent is C1, the mass content of the second solvent in the non-aqueous solvent is C2, and the mass content of the third solvent in the non-aqueous solvent is C3, all based on the total mass of the non-aqueous solvent, and the non-aqueous solvent satisfies: C1 is 10% to 30%, C2 is 50% to 90%, and C3 is 0% to 20%.

[0081] In some embodiments, C1 / (C2+C3) is 0.1 to 0.45, optionally 0.2 to 0.3. When the non-aqueous solvent contains a suitable amount of the first solvent, particularly a suitable amount of ethylene carbonate, the free radicals formed by the decomposition of lithium difluorooxalate borate can induce ring-opening and polymerization of ethylene carbonate, making the interfacial film formed on the surface of the negative electrode active material more dense and smooth, thereby effectively inhibiting dendrite growth.

[0082] In some embodiments, the non-aqueous electrolyte further includes a second additive, comprising at least one of vinylene carbonate (VC), vinyl sulfate (DTD), and 1,3-propanesulfonate lactone (PS). These second additives contribute to further improving the interfacial properties of the positive and / or negative electrodes, thereby further improving at least one of the cycle performance, storage performance, thermal safety performance, and kinetic performance of the secondary battery.

[0083] In some embodiments, the second additive has a mass content of B2 in the non-aqueous electrolyte, which can be 0.05% to 2% based on the total mass of the non-aqueous electrolyte. Optionally, B2 can be 0.1% to 2%, 0.2% to 2%, 0.3% to 2%, 0.4% to 2%, 0.5% to 2%, 0.6% to 2%, 0.7% to 2%, 0.8% to 2%, 0.9% to 2%, 1% to 2%, 0.1% to 1%, 0.2% to 1%, 0.3% to 1%, 0.4% to 1%, 0.5% to 1%, 0.6% to 1%, 0.7% to 1%, 0.8% to 1%, 0.9% to 1%, or 1% to 1%.

[0084] In some embodiments, the content of lithium difluorosulfonylimide (A1), the content of the second additive (B2), and the content of the first solvent (C1) satisfy (A1+B2) / C1 as 0.4 to 1.3, optionally 0.4 to 0.8. The second additive helps form films on the positive and negative electrode surfaces to reduce persistent side reactions, thereby improving at least one of the cycle performance, storage performance, thermal safety performance, and kinetic performance of the secondary battery. However, a higher content of the second additive increases the positive and / or negative electrode interfacial impedance, affecting the power performance of the secondary battery. Lithium difluorosulfonylimide can improve the conductivity and thermal stability of non-aqueous electrolytes and reduce the positive and / or negative electrode interfacial impedance, but it has a certain corrosive effect on the aluminum foil current collector, and a higher content of it can affect the cycle performance of the secondary battery. The first solvent has a high dielectric constant, which facilitates the dissociation of lithium salts and thus improves the conductivity of the non-aqueous electrolyte to some extent. However, a high content of this solvent increases the viscosity of the non-aqueous electrolyte and affects its thermal stability, impacting the storage performance of the secondary battery. Further research by the inventors revealed that controlling the (A1+B2) / C1 ratio between 0.4 and 1.3, optionally between 0.4 and 0.8, helps to fully leverage the synergistic effect between the components and effectively reduces the defects of using each component individually. This allows the secondary battery to exhibit excellent cycle performance while avoiding deterioration in kinetic and power performance.

[0085] In some embodiments, the non-aqueous electrolyte further includes a third additive, comprising at least one of aminosulfonic acid and its salts. The molecular formula of aminosulfonic acid is H3NO3S, and aminosulfonates include at least one of ammonium salts, alkali metal salts, alkaline earth metal salts, and alkaline earth-like metal salts. For example, aminosulfonates may include at least one of ammonium aminosulfonate, lithium aminosulfonate, sodium aminosulfonate, and zinc aminosulfonate. Optionally, the third additive comprises aminosulfonic acid, lithium aminosulfonate, or a combination thereof.

[0086] Aminosulfonic acid is a strong acid and is commonly used to prepare lithium bis(fluorosulfonyl)imide. Currently, its application in non-aqueous electrolytes has not been found. In further research, the inventors of this application have surprisingly discovered that when the non-aqueous electrolyte contains an appropriate amount of aminosulfonic acid and its salts, it helps improve the cycle performance and kinetic performance of the secondary battery. Although the mechanism is not yet clear, the inventors speculate that the possible reasons are that aminosulfonic acid and its salts help increase the conductivity and reduce the viscosity of the non-aqueous electrolyte, while also playing a role in slowly dissolving lithium dendrites and other metals to a certain extent. This reduces the reduction and deposition of elemental lithium, elemental aluminum, and transition metals on the surface of the negative electrode active material, thereby improving the cycle performance and kinetic performance of the secondary battery.

[0087] Aminosulfonic acid and its salts are readily soluble in water and are highly acidic. When present in high concentrations, they can corrode the positive electrode active material and disrupt the stability of the positive and negative electrode interfacial films. In some embodiments, the third additive in the non-aqueous electrolyte contains B3 by mass, which is optionally 0.005% to 0.1% based on the total mass of the non-aqueous electrolyte, and more preferably 0.005% to 0.05%.

[0088] In some embodiments, the non-aqueous electrolyte may also include the second and third additives described above.

[0089] In some embodiments, the non-aqueous electrolyte may further comprise other electrolyte salts, such as at least one selected from lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). These other electrolyte salts can further improve the interfacial properties of the positive and / or negative electrodes, or improve the conductivity or thermal stability of the non-aqueous electrolyte. Optionally, the total mass content of these other electrolyte salts in the non-aqueous electrolyte is less than 1%, more preferably less than 0.5%, based on the total mass of the non-aqueous electrolyte.

[0090] The non-aqueous electrolyte of this application can be prepared using methods conventional in the art. For example, the additives, the non-aqueous solvent, and the electrolyte salt can be mixed evenly to obtain the non-aqueous electrolyte. There are no particular restrictions on the order of addition of the materials; for example, the additives and the electrolyte salt can be added to the non-aqueous solvent and mixed evenly to obtain the non-aqueous electrolyte.

[0091] In this application, the components and their contents in the non-aqueous electrolyte can be determined according to methods known in the art. For example, they can be determined by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), etc.

[0092] It should be noted that during the non-aqueous electrolyte testing of this application, freshly prepared non-aqueous electrolyte can be used directly, or it can be obtained from a secondary battery. An exemplary method for obtaining non-aqueous electrolyte from a secondary battery includes the following steps: discharging the secondary battery to the discharge cutoff voltage (for safety, the battery is generally left fully discharged), followed by centrifugation. A suitable amount of the centrifuged liquid is then taken as the non-aqueous electrolyte. Alternatively, the non-aqueous electrolyte can be obtained directly from the secondary battery's filling port.

[0093] Secondary batteries

[0094] The second aspect of this application provides a secondary battery, which includes an electrode assembly and a non-aqueous electrolyte. The non-aqueous electrolyte is the same as that of the first aspect of this application. Thus, the secondary battery of this application can simultaneously achieve good cycle performance, storage performance, thermal safety performance, and kinetic performance.

[0095] The secondary battery of this application may be a lithium secondary battery, and more particularly a lithium-ion secondary battery.

[0096] Electrode assemblies typically include a positive electrode, a negative electrode, and a separator. The separator is placed between the positive and negative electrodes and mainly serves to prevent short circuits between the positive and negative electrodes, while allowing lithium ions to pass through.

[0097] [Positive electrode plate]

[0098] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0099] The positive electrode film layer includes a positive electrode active material, which may be a positive electrode active material known in the art for use in secondary batteries. For example, the positive electrode active material may include at least one of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may 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 their respective modified compounds. Examples of lithium-containing phosphates with an olivine structure may include at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. This application is not limited to these materials, and other conventionally known materials that can be 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.

[0100] In some embodiments, the positive electrode active material includes materials with the molecular formula Li. a Ni b Co c Mn d Al e M f O g A h The layered material, M represents the transition metal site doped cation, A represents the oxygen site doped anion, 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.

[0101] The molecular formula is Li a Ni b Co c Mn d Al e M f O g A h The layered material can be selectively modified by M cation doping, A anion doping, or by simultaneous doping with M cation and A anion. The resulting layered material has a more stable crystal structure, which can further improve the electrochemical performance of the secondary battery, such as cycle performance and kinetic performance.

[0102] In some embodiments, M is selected from at least one of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te, and W.

[0103] In some embodiments, A is selected from at least one of F, N, P, and S. Optionally, A is selected from F. After F doping modification, Li a Ni b Co c Mn d Al e M f O g A h The crystal structure is more stable, which enables secondary batteries to have better cycle performance and kinetic performance.

[0104] The values ​​of a, b, c, d, e, f, g, and h satisfy the following condition: that makes Li a Ni b Co c Mn d Al e M f O g A h Maintain electrical neutrality.

[0105] In some embodiments, 0 < b < 0.98. Optionally, 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.

[0106] In some embodiments, c = 0.

[0107] In some embodiments, 0 < c ≤ 0.20. Optionally, 0 < c ≤ 0.15, 0 < c ≤ 0.10, 0 < c ≤ 0.09, 0 < c ≤ 0.08, 0 < c ≤ 0.07, 0 < c ≤ 0.06, 0 < c ≤ 0.05, 0 < c ≤ 0.04, 0 < c ≤ 0.03, 0 < c ≤ 0.02, or 0 < c ≤ 0.01. Cobalt is scarce in the Earth's crust, difficult to mine, and expensive; therefore, low-cobalt or cobalt-free materials have become an inevitable development trend for cathode active materials. However, cobalt contributes significantly to the lithium-ion diffusion rate of cathode active materials; low-cobalt or cobalt-free materials will reduce the lithium-ion diffusion rate of cathode active materials, affecting the cycle performance of secondary batteries. Researchers have been working to improve the lithium-ion diffusion rate of low-cobalt or cobalt-free cathode active materials, but a good solution has not yet been found.

[0108] During their research, the inventors of this application unexpectedly discovered that when the content of lithium tetrafluoroborate (A2) and lithium difluorooxalate borate (A3) is reasonably adjusted to satisfy an A2 / A3 ratio of 0.02 to 30, a low-resistance interfacial film can be formed on the surface of the positive electrode active material. Furthermore, the boron atoms in the structures of lithium tetrafluoroborate and lithium difluorooxalate borate readily combine with the oxygen atoms in the positive electrode active material, thereby reducing the charge transfer resistance of the positive electrode active material and decreasing the diffusion resistance of lithium ions within the bulk phase of the positive electrode active material. Therefore, when the non-aqueous electrolyte contains appropriate amounts of lithium tetrafluoroborate and lithium difluorooxalate borate, the low-cobalt or cobalt-free positive electrode active material exhibits a significantly improved lithium-ion diffusion rate. Lithium ions within the bulk phase of the low-cobalt or cobalt-free positive electrode active material can be promptly replenished to the surface, preventing excessive delithiation from the surface and thus stabilizing the crystal structure of the low-cobalt or cobalt-free positive electrode active material. Because low-cobalt or cobalt-free cathode active materials have a more stable crystal structure, they can greatly reduce the probability of problems such as unstable structural, chemical, or electrochemical properties of cathode active materials due to over-delithiation on the surface of low-cobalt or cobalt-free cathode active materials. For example, the problem of irreversible distortion and increased lattice defects in cathode active materials.

[0109] In some embodiments, d = 0 and 0 < e < 0.50. Alternatively, 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.

[0110] In some embodiments, e = 0 and 0 < d < 0.50. Optionally, 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.

[0111] In some embodiments, 0 < d < 0.50 and 0 < e < 0.50. Alternatively, 0 < d ≤ 0.30 and 0 < e ≤ 0.10.

[0112] In some embodiments, g = 2, h = 0.

[0113] In some embodiments, g = 0, h = 2.

[0114] In some embodiments, 0 < g < 2, 0 < h < 2, and g + h = 2.

[0115] As an example, the molecular formula is Li a Nib Co c Mn d Al e M f O g A h Layered materials including but not limited to 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 Mn 0.3 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 At least one of O2.

[0116] Li a Ni b Co c Mn d Al e M f O g A h It can be prepared according to conventional methods in the art. An exemplary preparation method is as follows: a lithium source, a nickel source, a cobalt source, a manganese source, an aluminum source, an M-element precursor, and an A-element precursor are mixed and then sintered. The sintering atmosphere can be an oxygen-containing atmosphere, such as an air atmosphere or an oxygen atmosphere. The O2 concentration of the sintering atmosphere is, for example, 70% to 100%. The sintering temperature and sintering time can be adjusted according to actual conditions.

[0117] As examples, lithium sources include, but are not limited to, at least one of lithium oxide (Li₂O), lithium phosphate (Li₃PO₄), lithium dihydrogen phosphate (LiH₂PO₄), lithium acetate (CH₃COOLi), lithium hydroxide (LiOH), lithium carbonate (Li₂CO₃), and lithium nitrate (LiNO₃). As examples, nickel sources include, but are not limited to, at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. As examples, cobalt sources include, but are not limited to, at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. As examples, manganese sources include, but are not limited to, at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. As examples, aluminum sources include, but are not limited to, at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate. As examples, precursors of element M include, but are not limited to, at least one of oxides, nitrate compounds, carbonate compounds, hydroxides, and acetate compounds of element M. As an example, the 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 bicarbonate, ammonium phosphate, phosphoric acid, ammonium sulfate, ammonium bisulfate, ammonium bisulfite, ammonium sulfite, ammonium hydrogen sulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur.

[0118] In some embodiments, based on the total mass of the positive electrode film, the molecular formula is Li a Ni b Co c Mn d Al e M f O g A h The layered material has a mass percentage content of 80% to 99%. For example, the molecular formula is Li. a Ni b Co c Mn d Al e M f O g A h The mass percentage of the layered material can be any range consisting of 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or higher. Optionally, the molecular formula is Li. a Ni b Co c Mn d Al e M f O g A hThe mass percentage of the layered material is 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%.

[0119] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent is less than 5% based on the total mass of the positive electrode film layer.

[0120] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. In some embodiments, the mass percentage of the positive electrode binder is less than 5% based on the total mass of the positive electrode film layer.

[0121] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. An example of a metal material may be selected from at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. An example of a polymer substrate may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0122] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this.

[0123] [Negative electrode plate]

[0124] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0125] The negative electrode active material may be any negative electrode active material known in the art for use in secondary batteries. As an example, the negative electrode active material includes, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0126] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent is less than 5% based on the total mass of the negative electrode film layer.

[0127] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (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 percentage of the negative electrode binder is less than 5% based on the total mass of the negative electrode film layer.

[0128] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass percentage of the other additives is less than 2% based on the total mass of the negative electrode film.

[0129] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer substrate and a metal material layer formed on at least one surface of the polymer substrate. As an example, the metal material may be selected from at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0130] In some embodiments, the room temperature conductivity of the non-aqueous electrolyte is x mS / cm, the thickness of the negative electrode is L μm, and the secondary battery satisfies:

[0131] The inventors of this application also discovered during their research that when the room temperature conductivity x mS / cm of the non-aqueous electrolyte and the thickness Lμm of the negative electrode sheet satisfy... In this case, non-aqueous electrolytes help to form a uniform, dense, stable and low-resistance organic-inorganic composite interface film on the surface of the negative electrode active material, thereby enabling the secondary battery to have excellent electrochemical performance, and in particular, excellent kinetic performance.

[0132] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0133] [Isolation membrane]

[0134] The separator is disposed between the positive electrode and the negative electrode, mainly to prevent short circuits between the positive and negative electrodes, while allowing lithium ions to pass through. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0135] In some embodiments, the material of the separator may include at least one selected from 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.

[0136] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process or a stacking process.

[0137] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and the non-aqueous electrolyte.

[0138] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0139] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1 This is an example of a square-structured secondary battery 5.

[0140] In some embodiments, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. A non-aqueous electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0141] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and a non-aqueous electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer packaging, dried, and injected with a non-aqueous electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0142] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0143] Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0144] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0145] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0146] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0147] Electrical appliances

[0148] This application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0149] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0150] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0151] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0152] Example

[0153] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0154] The secondary batteries of Examples 1 to 43 and Comparative Examples 1 to 9 were all prepared according to the following method.

[0155] Preparation of positive electrode sheet

[0156] LiNi, the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are mixed in an appropriate amount of solvent NMP at a weight ratio of 97.5:1.4:1.1 to form a uniform positive electrode slurry. The positive electrode slurry is uniformly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode sheet is obtained.

[0157] Preparation of negative electrode sheet

[0158] The negative electrode active material graphite, the binder styrene-butadiene rubber (SBR), the thickener sodium carboxymethyl cellulose (CMC-Na), and the conductive agent carbon black (Super P) are mixed thoroughly in an appropriate amount of deionized water at a weight ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0159] Separating membrane

[0160] Porous polyethylene (PE) membrane is used as the separator.

[0161] Preparation of non-aqueous electrolyte

[0162] Electrolyte salts and additives were added to a non-aqueous solvent and mixed thoroughly to obtain a non-aqueous electrolyte. The composition and content of each component are shown in Table 1. In Table 1, the content of each electrolyte salt component and each additive component is based on the total mass of the non-aqueous electrolyte, and the content of the first solvent, second solvent, and third solvent is based on the total mass of the non-aqueous solvent. " / " indicates that the corresponding component was not added.

[0163] Preparation of secondary batteries

[0164] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, and the above-mentioned non-aqueous electrolyte is added. After processes such as encapsulation, standing, formation, and aging, a secondary battery is obtained.

[0165] Test section

[0166] (1) Cyclic performance test of secondary batteries at room temperature

[0167] At 25℃, the secondary battery was charged at a constant current of 1C to 4.3V, and then charged at a constant voltage until the current reached 0.05C. At this point, the secondary battery was fully charged, and the charging capacity was recorded, which is the first charge capacity. After the secondary battery was left to stand for 5 minutes, it was discharged at a constant current of 1C to 2.8V. This completes one charge-discharge cycle, and the discharge capacity was recorded, which is the first discharge capacity. The secondary battery was subjected to cyclic charge-discharge tests using the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the secondary battery after 600 cycles at 25℃ = discharge capacity after 600 cycles / discharge capacity of the first cycle × 100%.

[0168] (2) High-temperature cycle performance test of secondary batteries

[0169] At 45℃, the secondary battery was charged at a constant current of 1C to 4.3V, and then charged at a constant voltage until the current reached 0.05C. At this point, the secondary battery was fully charged, and the charging capacity was recorded, which is the first charge capacity. After the secondary battery was left to stand for 5 minutes, it was discharged at a constant current of 1C to 2.8V. This completes one charge-discharge cycle, and the discharge capacity was recorded, which is the first discharge capacity. The secondary battery was subjected to cyclic charge-discharge tests using 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℃ = discharge capacity after 600 cycles / discharge capacity of the first cycle × 100%.

[0170] (3) High-temperature storage performance test of secondary batteries

[0171] At 60℃, the secondary battery is charged at a constant current of 1C to 4.3V, and then charged at a constant voltage until the current reaches 0.05C. The volume of the secondary battery at this point is measured using the water displacement method and recorded as V0. The secondary battery is then placed in a 60℃ constant temperature chamber and stored for 30 days. After storage, its volume is measured again using the water displacement method and recorded as V1. The volume expansion rate (%) of the secondary battery after 30 days of storage at 60℃ is calculated as [(V1-V0) / V0]×100%.

[0172] (4) Initial DC internal resistance test of secondary battery

[0173] At 25℃, the secondary battery is charged at a constant current of 1C to 4.3V, and then charged at a constant voltage until the current is 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, and the voltage of the secondary battery at this point is recorded as U1. The secondary battery is then discharged at a constant current of 4C I1 for 30 seconds, and the voltage at the end of the discharge is recorded as U2, using a 0.1-second sampling time. The initial DC internal resistance of the secondary battery is expressed as the DC internal resistance at 50% SOC, and the initial DC internal resistance (mΩ) of the secondary battery is given by (U1-U2) / I1.

[0174] (5) Safety performance test of the thermal chamber for secondary batteries

[0175] At 25℃, the secondary battery was charged at a constant current of 1C to 4.3V, and then charged at a constant voltage until the current reached 0.05C, at which point the secondary battery was fully charged. The fully charged secondary battery was placed in a well-sealed high-temperature chamber, and the temperature was increased to 100℃ at a rate of 5℃ / min and held for 1 hour. Then, the temperature was increased to 105℃ at a rate of 5℃ / min and held for 30 minutes. After that, the temperature was increased by 5℃ at a rate of 5℃ / min and held for 30 minutes each time, until the secondary battery failed. The highest temperature T before the secondary battery failed was recorded. max T max The higher the value, the better the thermal safety performance of the secondary battery.

[0176] To ensure the reliability of the test results, each of the above tests can be conducted using at least three parallel samples, and the average value should be taken as the test result.

[0177] Table 1 shows the preparation parameters of the non-aqueous electrolytes for Examples 1 to 43 and Comparative Examples 1 to 9, and Table 2 shows the test results obtained by Examples 1 to 43 and Comparative Examples 1 to 9 according to the above performance test methods.

[0178]

[0179]

[0180]

[0181]

[0182] Based on the test results of Comparative Examples 1 to 9 and Examples 1 to 43, it can be seen that by using lithium tetrafluoroborate, lithium difluorooxalate borate, and fluoroethylene carbonate in a non-aqueous electrolyte with lithium difluorosulfonylimide as the main lithium salt, and by reasonably adjusting the contents of lithium difluorosulfonylimide (A1), lithium tetrafluoroborate (A2), lithium difluorooxalate borate (A3), and fluoroethylene carbonate (B1) to satisfy A1 / A2 of 30 to 1500, A1 / B1 of 3.6 to 15, and A2 / A3 of 0.02 to 30, the secondary battery can simultaneously achieve high capacity retention, low internal resistance, low volume expansion rate, and high thermal safety performance.

[0183] The test results of Examples 37 to 41 show that when the non-aqueous electrolyte further contains a second additive and / or a third additive, it helps to further improve the overall performance of the secondary battery.

[0184] The inventors further investigated the effect of the thickness of the negative electrode sheet on the performance of the secondary battery. The preparation of the positive electrode sheet, the negative electrode sheet, the non-aqueous electrolyte, and the secondary battery in Examples 44 to 47 were the same as in Example 5, except that the thickness of the negative electrode sheet was different.

[0185] Table 3

[0186]

[0187] As shown in Table 3, the room temperature conductivity x mS / cm of the non-aqueous electrolyte and the thickness L μm of the negative electrode sheet satisfy the following conditions: This will help to further improve the overall performance of secondary batteries.

[0188] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A non-aqueous electrolyte comprising an electrolyte salt, a non-aqueous solvent, and a first additive, wherein, The electrolyte salt includes: Lithium difluorosulfonylimide, the mass content of which in the non-aqueous electrolyte is A1, based on the total mass of the non-aqueous electrolyte; Lithium tetrafluoroborate, whose mass content in the non-aqueous electrolyte is A2, is based on the total mass of the non-aqueous electrolyte; Lithium difluorooxalate borate, the mass content of which in the non-aqueous electrolyte is A3, based on the total mass of the non-aqueous electrolyte; The first additive includes: fluoroethylene carbonate, the mass content of which in the non-aqueous electrolyte is B1, based on the total mass of the non-aqueous electrolyte; The non-aqueous electrolyte meets the following requirements: A1 is 9% to 15%, A1 / A2 is 30 to 1500, A1 / B1 is 3.6 to 15, A2 / A3 is 0.02 to 30, A2 is 0.01% to 0.3%, A3 is 0.01% to 0.5%, and B1 is 1.0% to 2.5%. The non-aqueous electrolyte further includes a third additive, comprising at least one of aminosulfonic acid and its salt, wherein the mass content of the non-aqueous electrolyte is B3, and the mass content of B3 is 0.005% to 0.1% based on the total mass of the non-aqueous electrolyte.

2. The non-aqueous electrolyte according to claim 1, wherein, A1 / A2 is between 50 and 250; and / or, A1 / B1 is 4 to 9; and / or The A2 / A3 ratio ranges from 0.5 to 13.

5.

3. The non-aqueous electrolyte according to claim 2, wherein, A1 / A2 ranges from 50 to 150.

4. The non-aqueous electrolyte according to claim 2, wherein, A1 / B1 is between 4 and 7.

5. The non-aqueous electrolyte according to claim 2, wherein, A2 / A3 ranges from 1 to 10.

6. The non-aqueous electrolyte according to claim 1, wherein, The non-aqueous electrolyte also satisfies that (A2+A3) / B1 is 0.008 to 0.

8.

7. The non-aqueous electrolyte according to claim 6, wherein, The non-aqueous electrolyte also satisfies that (A2+A3) / B1 is 0.026 to 0.

2.

8. The non-aqueous electrolyte according to claim 1, wherein, The non-aqueous electrolyte satisfies at least one of the following conditions (1) to (2): (1) A1 is 10% to 15%; (2) A3 is 0.015% to 0.1%.

9. The non-aqueous electrolyte according to claim 8, wherein, A1 is 10% to 13%.

10. The non-aqueous electrolyte according to claim 8, wherein, A2 ranges from 0.05% to 0.2%.

11. The non-aqueous electrolyte according to claim 8, wherein, B1 is 1.5% to 2.5%.

12. The non-aqueous electrolyte according to claim 1, wherein, The non-aqueous solvent includes: The first solvent includes at least one of ethylene carbonate, propylene carbonate, and butylene carbonate, wherein the mass content of the first solvent in the non-aqueous solvent is C1, based on the total mass of the non-aqueous solvent. The second solvent includes at least one of methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate, wherein the mass content of the second solvent in the non-aqueous solvent is C2, based on the total mass of the non-aqueous solvent. The third solvent includes at least one selected from methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, and ethyl butyrate, wherein its mass content in the non-aqueous solvent is C3, based on the total mass of the non-aqueous solvent. The non-aqueous solvent satisfies the following conditions: C1 is 10% to 30%, C2 is 50% to 90%, and C3 is 0% to 20%.

13. The non-aqueous electrolyte according to claim 12, wherein, C1 / (C2+C3) ranges from 0.1 to 0.

45.

14. The non-aqueous electrolyte according to claim 13, wherein, C1 / (C2+C3) is between 0.2 and 0.

3.

15. The non-aqueous electrolyte according to claim 1, wherein, The non-aqueous electrolyte further includes a second additive, comprising at least one of vinylene carbonate, vinyl sulfate, and 1,3-propanesulfonic acid lactone, wherein the mass content of the additive in the non-aqueous electrolyte is B2, and the mass content of B2 is 0.05% to 2% based on the total mass of the non-aqueous electrolyte.

16. The non-aqueous electrolyte according to claim 15, wherein, B2 is 0.5% to 2%.

17. The non-aqueous electrolyte according to claim 15, wherein, (A1+B2) / C1 ranges from 0.4 to 1.

3.

18. The non-aqueous electrolyte according to claim 17, wherein, (A1+B2) / C1 ranges from 0.4 to 0.

8.

19. The non-aqueous electrolyte according to claim 1, wherein, Aminosulfonates include at least one of ammonium salts, alkali metal salts, alkaline earth metal salts, and alkaline earth-like metal salts.

20. The non-aqueous electrolyte according to claim 1, wherein, B3 is 0.005% to 0.05%.

21. A secondary battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein, The non-aqueous electrolyte is the non-aqueous electrolyte according to any one of claims 1-20.

22. The secondary battery according to claim 21, wherein, The non-aqueous electrolyte has a room temperature conductivity of x mS / cm, the negative electrode has a thickness of L μm, and the secondary battery satisfies the following:

23. The secondary battery according to claim 21 or 22, wherein, The positive electrode sheet comprises Li a Ni b Co c Mn d Al e M f O g A h The layered material, M represents the transition metal site doped cation, A represents the oxygen site doped anion, 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.

24. The secondary battery according to claim 23, wherein, Li a Ni b Co c Mn d Al e M f O g A h At least one of the following conditions (1) to (8) must be met: (1) M is selected from at least one of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te and W; (2) A is selected from at least one of F, N, P and S; (3)0＜b＜0.98； (4)c＝0； (5)0＜c≤0.20； (6) d = 0 and 0 < e < 0.50; (7) e = 0 and 0 < d < 0.50; (8) 0 < d < 0.50 and 0 < e < 0.

50.

25. The secondary battery according to claim 24, wherein, A is selected from F.

26. The secondary battery according to claim 24, wherein, 0.50≤b＜0.98。 27. The secondary battery according to claim 24, wherein, 0＜c≤0.10。 28. The secondary battery according to claim 24, wherein, d = 0 and 0 < e ≤ 0.

10.

29. The secondary battery according to claim 24, wherein, e = 0 and 0 < d ≤ 0.

10.

30. The secondary battery according to claim 24, wherein, 0 < d ≤ 0.30 and 0 < e ≤ 0.

10.

31. A battery module comprising a secondary battery according to any one of claims 21-30.

32. A battery pack comprising a secondary battery according to any one of claims 21-30 and a battery module according to claim 31.

33. An electrical device comprising at least one of the following: a secondary battery according to any one of claims 21-30, a battery module according to claim 31, and a battery pack according to claim 32.

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