Nonaqueous electrolyte solution and secondary battery, battery module, battery

Abstract

The invention provides a non-aqueous electrolyte, and a secondary battery, a battery module, a battery pack and an electric device comprising the same. The secondary battery comprises an electrode assembly, a non-aqueous electrolyte and an outer package, the non-aqueous electrolyte comprises an electrolyte salt and a non-aqueous solvent, and the electrolyte salt comprises a first lithium salt, a second lithium salt and a third lithium salt; the content of A1 is 0.005% to 0.2%; a2 is from 0.005% to 0.3%; and A3 is from 0.01% to 0.5%. According to the present invention, the secondary battery can simultaneously give consideration to good cycle performance, good storage performance and good dynamic performance.

Description

[0001] This application is a divisional application based on the invention patent application with application number 202280012714.7, application date May 20, 2022, filed by CATL (Contemporary Amperex Technology Co., Ltd.), entitled "Non-aqueous electrolyte and secondary battery, battery module, battery pack and power device containing the same". Technical Field

[0002] 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

[0003] 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

[0004] The purpose of this application is to provide a non-aqueous electrolyte and a secondary battery, battery module, battery pack and power device containing the electrolyte, which enables the secondary battery to simultaneously achieve good cycle performance, storage performance and kinetic performance.

[0005] The first aspect of this application provides a secondary battery comprising an electrode assembly, a non-aqueous electrolyte, and an outer packaging. The non-aqueous electrolyte comprises an electrolyte salt and a non-aqueous solvent. The electrolyte salt comprises: a first lithium salt having the structure shown in Formula 1, where R1 represents a fluorine atom or a partially or fully fluorinated C1-C10 alkyl group, and its mass content in the non-aqueous electrolyte is A1, based on the total mass of the non-aqueous electrolyte; and a second lithium salt having the structure shown in Formula 2, where R2 and R3 independently represent fluorine atoms or partially or fully fluorinated alkyl groups. The electrolyte comprises at least one of the following groups: C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C8 aryl, C1-C10 alkoxy, C2-C10 alkenyloxy, C2-C10 alkynyloxy, and C6-C8 aryloxy, with a mass content of A2 based on the total mass of the non-aqueous electrolyte; and a third lithium salt selected from lithium tetrafluoroborate, with a mass content of A3 based on the total mass of the non-aqueous electrolyte. Formula 1 Formula 2 A1 is 0.005% to 0.2%; A2 is 0.005% to 0.3%; A3 is 0.01% to 0.5%.

[0006] In any embodiment of this application, the non-aqueous electrolyte satisfies the following conditions: A1+A2+A3 is less than 1%, A1 / A2 is 0.016 to 40, and A1 / (A2+A3) is 0.006 to 13.5.

[0007] Through extensive research, the inventors discovered that by using the aforementioned first, second, and third lithium salts as auxiliary lithium salts in a non-aqueous electrolyte to control their total content to below 1%, and by reasonably adjusting the contents of the first lithium salt (A1), the second lithium salt (A2), and the third lithium salt (A3) to satisfy A1 / A2 being 0.016 to 40, and A1 / (A2+A3) being 0.006 to 13.5, the resulting non-aqueous electrolyte can simultaneously possess high thermal stability, high ionic conductivity, and a wide electrochemical window. Furthermore, the non-aqueous electrolyte can passivate the aluminum foil current collector and form a dense, stable, low-resistance, and highly ionicly conductive interface film on both the positive and negative electrode active materials. Thus, secondary batteries using the non-aqueous electrolyte of this application can simultaneously achieve good cycle performance, storage performance, and kinetic performance.

[0008] In any embodiment of this application, A1 / A2 is 0.03 to 10, and optionally 0.1 to 5. This is beneficial for fully utilizing the synergistic effect between the first lithium salt and the second lithium salt, thereby enabling the formation of a denser, more stable, and more ion-conducting interface film on the surface of the negative electrode active material.

[0009] In any embodiment of this application, A1 / (A2+A3) is from 0.02 to 3.5, and optionally from 0.1 to 2. This is beneficial for fully utilizing the synergistic effect between the first lithium salt, the second lithium salt, and the third lithium salt, thereby enabling the formation of a denser, more stable, and more ion-conducting interface film on the surface of the positive electrode active material.

[0010] In any embodiment of this application, the non-aqueous electrolyte further satisfies that A3 / A2 is 0.04 to 30, optionally 1 to 10. This facilitates the full utilization of the synergistic effect between the second and third lithium salts, thereby further improving the cycle performance, storage performance, and kinetic performance of the secondary battery.

[0011] In any embodiment of this application, A1 is 0.005% to 0.2%, optionally 0.01% to 0.1%, and optionally 0.02% to 0.1%.

[0012] In any embodiment of this application, A2 is 0.005% to 0.3%, optionally 0.01% to 0.3%, and optionally 0.02% to 0.2%.

[0013] In any embodiment of this application, A3 is 0.01% to 0.5%, optionally 0.02% to 0.2%, and optionally 0.05% to 0.2%.

[0014] In any embodiment of this application, the first lithium salt comprises at least one of the following compounds: .

[0015] In any embodiment of this application, the second lithium salt comprises at least one of the following compounds:

[0016]

[0017] .

[0018] In any embodiment of this application, the electrolyte salt further includes at least one of a fourth lithium salt and a fifth lithium salt, wherein the fourth lithium salt is lithium hexafluorophosphate, and its mass content in the non-aqueous electrolyte is A4, based on the total mass of the non-aqueous electrolyte; the fifth lithium salt is lithium difluorosulfonamide, and its mass content in the non-aqueous electrolyte is A5, based on the total mass of the non-aqueous electrolyte; and the non-aqueous electrolyte satisfies that A4+A5 is 10% to 20%, optionally 10% to 18%.

[0019] In any embodiment of this application, A4 / A5 is 0.09 to 3, optionally 0.2 to 3, and optionally 0.5 to 1.5. Therefore, the non-aqueous electrolyte is less prone to hydrolysis and also achieves higher thermal stability, while simultaneously contributing to the formation of an interface film with lower impedance.

[0020] In any embodiment of this application, (A4+A5) / (A1+A2+A3) is 10 to 200, optionally 20 to 120, and more preferably 40 to 100. This helps the non-aqueous electrolyte to simultaneously possess high thermal stability, high ionic conductivity, and a wide electrochemical window. Furthermore, the non-aqueous electrolyte can passivate the aluminum foil current collector and form a dense, stable, low-resistance, and highly ionicly conductive interfacial film on both the positive and negative electrode active materials.

[0021] 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 B1, 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 B2, 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 B3, based on the total mass of the non-aqueous solvent. The non-aqueous electrolyte satisfies the following: B1 is 10% to 30%, B2 is 50% to 90%, and B3 is 0% to 20%, optionally B1 is 10% to 30%, B2 is 70% to 90%, and B3 is 0% to 5%.

[0022] In any embodiment of this application, B1 / (B2+B3) is 0.1 to 0.45, optionally 0.2 to 0.3. This helps to make the interface film formed on the surface of the negative electrode active material more dense and smooth, thereby effectively suppressing dendrite growth.

[0023] In any embodiment of this application, the non-aqueous electrolyte further includes: a first additive, comprising at least one selected from fluoroethylene carbonate, vinylene carbonate, ethylene sulfate, and 1,3-propanesulfonic acid lactone, wherein the additive has a mass content of C1 in the non-aqueous electrolyte, and C1 is 0.05% to 2% based on the total mass of the non-aqueous electrolyte, optionally 0.1% to 1%. The first 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, and kinetic performance of the secondary battery.

[0024] In any embodiment of this application, the non-aqueous electrolyte further satisfies that (C1+A5) / B1 is 0.23 to 0.8, optionally 0.3 to 0.8, or optionally 0.3 to 0.6. This helps to fully utilize the synergistic effect between the above components and effectively reduce the defects of using each component alone, enabling the secondary battery to have excellent cycle performance and avoiding deterioration in kinetic and power performance.

[0025] In any embodiment of this application, the non-aqueous electrolyte further includes a second additive, comprising at least one of aminosulfonic acid and its salts, wherein the mass content of the additive in the non-aqueous electrolyte is C2, and the mass content of C2 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.

[0026] In any embodiment of this application, the electrode assembly includes a positive electrode and a negative electrode. The charge transfer resistance of the positive electrode is Rct1, and the charge transfer resistance of the negative electrode is Rct2, with Rct1 / Rct2 being 0.5 to 2, optionally 1.25 to 2. This results in a smaller difference in charge transfer resistance between the positive and negative electrodes, which can better improve the performance of the secondary battery.

[0027] The charge transfer resistance of the positive electrode is obtained by the following test method: the positive electrode is assembled into a symmetrical battery, and its electrochemical impedance spectroscopy is measured using the electrochemical AC impedance method of an electrochemical workstation. A Nyquist plot is plotted, and the obtained Nyquist plot is analyzed using the equivalent circuit curve fitting method. The semicircle diameter is taken as the charge transfer resistance of the positive electrode, Rct1. The charge transfer resistance of the negative electrode is obtained by the following test method: the negative electrode is assembled into a symmetrical battery, and its electrochemical impedance spectroscopy is measured using the electrochemical AC impedance method of an electrochemical workstation. A Nyquist plot is plotted, and the obtained Nyquist plot is analyzed using the equivalent circuit curve fitting method. The semicircle diameter is taken as the charge transfer resistance of the negative electrode, Rct2.

[0028] In any embodiment of this application, the non-aqueous electrolyte includes a first electrolyte that wets the electrode assembly and a second electrolyte located between the electrode assembly and the outer packaging. The sum of the mass contents of the first lithium salt, second lithium salt, third lithium salt, first additive, and second additive in the first electrolyte is X1, based on the total mass of the first electrolyte. The sum of the mass contents of the first lithium salt, second lithium salt, third lithium salt, first additive, and second additive in the second electrolyte is X2, based on the total mass of the second electrolyte, and 0.5 ≤ X1 / X2 < 1. The first electrolyte is obtained by the following test method: after discharging the secondary battery to the discharge cutoff voltage, the electrode assembly is disassembled and centrifuged. The liquid obtained after centrifugation is the first electrolyte.

[0029] 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 hThe 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.

[0030] 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.

[0031] 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.

[0032] In some embodiments of this application, 0 < b < 0.98, and optionally, 0.50 ≤ b < 0.98.

[0033] In some embodiments of this application, c = 0.

[0034] In some embodiments of this application, 0 < c ≤ 0.20, and optionally, 0 < c ≤ 0.10.

[0035] In some embodiments of this application, d = 0 and 0 < e < 0.50, and optionally, d = 0 and 0 < e ≤ 0.10.

[0036] In some embodiments of this application, e = 0 and 0 < d < 0.50, and optionally, e = 0 and 0 < d ≤ 0.10.

[0037] 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.

[0038] A second aspect of this application provides a non-aqueous electrolyte, the non-aqueous electrolyte comprising an electrolyte salt and a non-aqueous solvent, the electrolyte salt comprising: The first lithium salt has the structure shown in Formula 1, where R1 represents a fluorine atom or a partially or fully fluorinated C1-C10 alkyl group, and its mass content in the non-aqueous electrolyte is A1, based on the total mass of the non-aqueous electrolyte. The second lithium salt has the structure shown in Formula 2, where R2 and R3 each independently represent a fluorine atom or at least one of the following groups that are partially or fully fluorinated: C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C8 aryl, C1-C10 alkoxy, C2-C10 alkenyloxy, C2-C10 alkynyloxy, and C6-C8 aryloxy, and its mass content in the non-aqueous electrolyte is A2, based on the total mass of the non-aqueous electrolyte; The third lithium salt, selected from lithium tetrafluoroborate, has a mass content of A3 in the non-aqueous electrolyte, based on the total mass of the non-aqueous electrolyte. Formula 1 Formula 2 A1 is 0.005% to 0.2%; A2 is 0.005% to 0.3%; A3 is 0.01% to 0.5%.

[0039] In some embodiments of this application, the non-aqueous electrolyte further includes: a first additive, including at least one of fluoroethylene carbonate, vinylene carbonate, ethylene sulfate, and 1,3-propanesulfonic acid lactone, wherein the mass content of the additive in the non-aqueous electrolyte is C1, and C1 is 0.05% to 2% based on the total mass of the non-aqueous electrolyte.

[0040] In some embodiments of this application, the non-aqueous electrolyte further includes a second additive, comprising at least one of aminosulfonic acid and its salt, wherein the mass content of the additive in the non-aqueous electrolyte is C2, and the mass content of C2 is 0.005% to 0.1% based on the total mass of the non-aqueous electrolyte.

[0041] In some embodiments of this application, the electrolyte salt further includes at least one of a fourth lithium salt and a fifth lithium salt. The fourth lithium salt is lithium hexafluorophosphate, and its mass content in the non-aqueous electrolyte is A4, based on the total mass of the non-aqueous electrolyte. The fifth lithium salt is lithium bis(fluorosulfonyl)imide, and its mass content in the non-aqueous electrolyte is A5, based on the total mass of the non-aqueous electrolyte. The non-aqueous electrolyte meets the following requirements: A4+A5 is 10% to 20%.

[0042] A third aspect of this application provides a battery module, including the secondary battery of the first aspect of this application.

[0043] The fourth aspect of this application provides a battery pack, including one of the secondary battery of the first aspect of this application and the battery module of the third aspect.

[0044] The fifth aspect of this application provides an electrical device, including at least one of the secondary battery of the first aspect of this application, the battery module of the third aspect, and the battery pack of the fourth aspect.

[0045] The secondary battery of this application can simultaneously achieve good cycle performance, storage 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

[0046] 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.

[0047] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0048] Figure 2 yes Figure 1 An exploded view of the implementation method of the secondary battery.

[0049] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0050] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0051] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0052] 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.

[0053] 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

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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 method may also include step (c), indicating 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.

[0059] 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.

[0060] 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).

[0061] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0062] In this document, the term "alkyl" refers to a saturated hydrocarbon group, including both straight-chain and branched structures. Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl (e.g., n-propyl, isopropyl), butyl (e.g., n-butyl, isobutyl, sec-butyl, tert-butyl), and pentyl (e.g., n-pentyl, isopentyl, neopentyl). In various embodiments, C1-C10 alkyl groups, i.e., alkyl groups, may contain 1 to 10 carbon atoms.

[0063] The term "alkenyl" refers to an unsaturated hydrocarbon group containing carbon-carbon double bonds, including both straight-chain and branched structures, and the number of carbon-carbon double bonds can be one or more. Examples of alkenyl groups include, but are not limited to, vinyl, propenyl, allyl, and butadienyl. In various embodiments, C2-C10 alkenyl groups, i.e., alkenyl groups, can contain 2 to 10 carbon atoms.

[0064] The term "alkynyl" refers to an unsaturated hydrocarbon group containing a carbon-carbon triple bond, including both straight-chain and branched structures, and the number of carbon-carbon triple bonds can be one or more. Examples of alkynyl groups include, but are not limited to, ethynyl, propynyl, butynyl, and butadiynyl. In various embodiments, the C2-C10 alkynyl group, i.e., the alkynyl group, can contain 2 to 10 carbon atoms.

[0065] The term "aryl" refers to a carbocyclic system with aromatic properties, whose structure can be monocyclic, polycyclic, or fused-ring. Examples of aryl groups include, but are not limited to, phenyl. In various embodiments, C6-C8 aryl groups, i.e., aryl groups, can contain 6 to 8 carbon atoms.

[0066] In this document, the term "alkoxy" refers to an alkyl group containing an oxygen atom (-O-), the term "alkenoxy" refers to an alkenyl group containing an oxygen atom (-O-), the term "alkynoxy" refers to an alkyl group containing an oxygen atom (-O-), and the term "aryloxy" refers to an alkyl group containing an oxygen atom (-O-).

[0067] Throughout this specification, substituents of compounds are disclosed by groups or ranges. It is expressly intended that such description include each individual sub-combination of members of these groups and ranges. For example, it is expressly intended that the term "C1-C6 alkyl" individually discloses alkyl groups of C1, C2, C3, C4, C5, C6, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C6, C2-C5, C2-C4, C2-C3, C3-C6, C3-C5, C3-C4, C4-C6, C4-C5, and C5-C6.

[0068] 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, decomposing to form LiF and PF5 at higher temperatures. LiF increases interfacial impedance; PF5 has strong Lewis acidity and interacts with the lone pair electrons on the oxygen atoms in solvent molecules, causing solvent decomposition. Furthermore, PF5 is highly sensitive to trace amounts of water in the non-aqueous electrolyte, generating 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. Additionally, 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.

[0069] Therefore, it is necessary to provide a non-aqueous electrolyte with good overall performance.

[0070] After extensive research, the inventors of this application made a surprising discovery: when the non-aqueous electrolyte contains an appropriate amount of auxiliary lithium salt, the secondary battery can simultaneously achieve good cycle performance, storage performance, and kinetic performance.

[0071] Non-aqueous electrolyte Specifically, the first aspect of this application provides a non-aqueous electrolyte comprising an electrolyte salt and a non-aqueous solvent.

[0072] The electrolyte salt comprises: a first lithium salt having the structure shown in Formula 1, wherein R1 represents a fluorine atom or a partially or fully fluorinated C1-C10 alkyl group, and its mass content in the non-aqueous electrolyte is A1, based on the total mass of the non-aqueous electrolyte; a second lithium salt having the structure shown in Formula 2, wherein R2 and R3 each independently represent a fluorine atom or at least one of the following groups that are partially or fully fluorinated: C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C8 aryl, C1-C10 alkoxy, C2-C10 alkenoxy, C2-C10 alkynoxy, C6-C8 aryloxy, and its mass content in the non-aqueous electrolyte is A2, based on the total mass of the non-aqueous electrolyte; and a third lithium salt selected from lithium tetrafluoroborate, and its mass content in the non-aqueous electrolyte is A3, based on the total mass of the non-aqueous electrolyte.

[0073] Formula 1 Formula 2 In this application, the non-aqueous electrolyte satisfies the following conditions: A1+A2+A3 is less than 1%, A1 / A2 is 0.016 to 40, and A1 / (A2+A3) is 0.006 to 13.5.

[0074] Through extensive research, the inventors discovered that by using the aforementioned first, second, and third lithium salts as auxiliary lithium salts in a non-aqueous electrolyte to control their total content to below 1%, and by reasonably adjusting the contents of the first lithium salt (A1), the second lithium salt (A2), and the third lithium salt (A3) to satisfy A1 / A2 being 0.016 to 40, and A1 / (A2+A3) being 0.006 to 13.5, the resulting non-aqueous electrolyte can simultaneously possess high thermal stability, high ionic conductivity, and a wide electrochemical window. Furthermore, the non-aqueous electrolyte can passivate the aluminum foil current collector and form a dense, stable, low-resistance, and highly ionicly conductive interface film on both the positive and negative electrode active materials. Thus, secondary batteries using the non-aqueous electrolyte of this application can simultaneously achieve good cycle performance, storage performance, and kinetic performance.

[0075] Although the mechanism is not yet clear, the inventors speculate that the possible reasons include the following.

[0076] First, by rationally adjusting the content of the first lithium salt (A1) and the second lithium salt (A2) to ensure that A1 / A2 is between 0.016 and 40, it helps to form a dense, stable, and highly ionicly conductive interfacial film on the surface of the negative electrode active material. The first lithium salt contains sulfonate anions, which can be reduced to form highly ionicly conductive compounds such as Li2SO4, thereby improving the ion transport characteristics of the negative electrode interfacial film. The second lithium salt contains an oxalate group in its molecular structure, and its reduction product can further react with organic components such as (LiOCO2CH2)2 in the interfacial film to form complex and stable oligomers, which fully coat the surface of the negative electrode active material, preventing direct contact between the non-aqueous electrolyte and the negative electrode active material, and reducing the embedding of non-aqueous solvents into the negative electrode active material. When A1 / A2 is greater than 40, the negative electrode interface film cannot fully cover the surface of the negative electrode active material, thereby increasing the irreversible consumption of lithium ions and reducing the capacity retention rate of the secondary battery. When A1 / A2 is less than 0.016, the ion transport characteristics of the negative electrode interface film are poor, which leads to an increase in the internal resistance of the secondary battery and a deterioration in its kinetic performance.

[0077] Secondly, by reasonably adjusting the contents of the first lithium salt (A1), the second lithium salt (A2), and the third lithium salt (A3) to ensure that A1 / (A2+A3) is between 0.006 and 13.5, it helps to form a dense, stable interface film containing a small amount of LiF on the surface of the positive electrode active material. This increases the lithium-ion transport channels in the positive electrode interface film and reduces the lithium-ion transport resistance. Simultaneously, it suppresses the irreversible phase transition of the positive electrode active material, maintaining its structural stability, thereby resulting in better capacity utilization of the secondary battery. Furthermore, the B atoms in the second lithium salt molecule readily combine with the O atoms in the positive electrode active material, which can also reduce the charge transfer impedance of the positive electrode active material and decrease the diffusion resistance of lithium ions within the bulk phase of the positive electrode active material. When A1 / (A2+A3) is greater than 13.5, the second and third lithium salts cannot effectively compensate for the deterioration of the battery's internal resistance caused by the excessive first lithium salt, resulting in poor kinetic performance of the secondary battery. At the same time, the positive electrode interface film cannot fully cover the surface of the positive electrode active material, thereby increasing the irreversible consumption of lithium ions and reducing the capacity retention rate of the secondary battery. When A1 / (A2+A3) is less than 0.006, the LiF content in the positive electrode interface film is excessive, thereby increasing the positive electrode interface impedance and affecting the kinetic performance of the secondary battery.

[0078] Third, the first lithium salt can form an interfacial film not only at the negative electrode but also at the positive electrode, thereby improving the capacity utilization and kinetic performance of the secondary battery. However, the fluorosulfonic acid groups in the first lithium salt easily corrode the aluminum foil current collector, affecting the performance of the secondary battery. For example, it can increase battery polarization and irreversible capacity loss, and even affect the safety performance of the secondary battery. The main surface corrosion issues are as follows: some solid insoluble corrosion products increase the internal resistance of the secondary battery; some soluble corrosion products contaminate and exacerbate the decomposition of non-aqueous electrolytes, increasing the self-discharge of the secondary battery; and Al generated during the corrosion process... 3+ It may migrate to the negative electrode via diffusion and be reduced to aluminum dendrites. The BO bond in the second lithium salt molecule can bind with Al. 3+ The bonding is formed on the surface of the aluminum foil current collector to form a passivation film. The third lithium salt can be preferentially oxidized and decomposed on the surface of the aluminum foil current collector to form a passivation film. Therefore, the non-aqueous electrolyte of this application can passivate the aluminum foil current collector, effectively improve the corrosion of the aluminum foil current collector by the first lithium salt, and reduce the irreversible capacity loss of the secondary battery.

[0079] Therefore, the reason why the secondary battery using the non-aqueous electrolyte of this application can simultaneously achieve good cycle performance, storage performance, and kinetic performance may be due to the synergistic effect formed among the above-mentioned components. The first lithium salt forms an interfacial film on both the positive and negative electrodes. The synergistic effect between the second, third, and first lithium salts improves the ionic conductivity of the non-aqueous electrolyte, thereby compensating for the low degree of dissociation and low ionic conductivity of the first lithium salt. The synergistic effect between the first and second lithium salts forms a dense, stable, low-impedance, and highly ionicly conductive interfacial film on the surface of the negative electrode active material. The synergistic effect between the first, second, and third lithium salts forms a dense, stable interfacial film containing a small amount of LiF on the surface of the positive electrode active material. As a result, interfacial side reactions between the non-aqueous electrolyte and the electrodes are reduced, irreversible consumption of active lithium ions is reduced, the capacity utilization of the secondary battery is increased, and gas production is reduced. In addition, the interfacial films formed on the surfaces of the positive and negative electrode active materials have low impedance and high ionic conductivity, reducing the internal resistance of the secondary battery.

[0080] In some embodiments, A1 / A2 can be 0.03 to 40, 0.03 to 30, 0.03 to 20, 0.03 to 15, 0.03 to 10, 0.03 to 8, 0.03 to 6, 0.05 to 40, 0.05 to 30, 0.05 to 20, 0.05 to 15, 0.05 to 10, 0.05 to 8, 0.05 to 6, 0.05 to 5, 0.1 to 40, 0.1 to 30, 0.1 to 20, 0.1 to 15, 0.1 to 10, 0.1 to 8, 0.1 to 6, 0.1 to 5, 0.2 to 40, 0.2 to 30, 0.2 to 20, 0.2 to 15, 0.2 to 10, 0.2 to 8, 0.2 to 6, 0.2 to 5, or 0.2 to 2.5. When A1 / A2 is within a suitable range, it is beneficial to give full play to the synergistic effect between the first lithium salt and the second lithium salt, thereby forming a denser, more stable and more ion-conducting interface film on the surface of the negative electrode active material.

[0081] In some embodiments, A1 / (A2+A3) can be 0.01 to 13.5, 0.01 to 10, 0.01 to 8, 0.01 to 6, 0.01 to 5, 0.01 to 4, 0.01 to 3.5, 0.01 to 3, 0.01 to 2.5, 0.01 to 2, 0.02 to 13.5, 0.02 to 10, 0.02 to 8, 0.02 to 6, 0.02 to 5, 0.02 to 4, 0.02 to 3.5, 0.02 to 3, 0.02 to 2.5, 0.02 to 2, 0.1 to 13.5, 0.1 to 10, 0.1 to 8, 0.1 to 6, 0.1 to 5, 0.1 to 4, 0.1 to 3.5, 0.1 to 3, 0.1 to 2.5, 0.1 to 2, or 0.1 to 1. When A1 / (A2+A3) is within a suitable range, it is beneficial to give full play to the synergistic effect between the first lithium salt, the second lithium salt and the third lithium salt, thereby forming a denser, more stable and more ion-conducting interface film on the surface of the positive electrode active material.

[0082] Because the second lithium salt contains an oxalate group in its molecular structure, its thermal stability is lower than that of the third lithium salt. It is oxidized upon heating to form carbon dioxide gas. Therefore, a higher content of BF4 may reduce the thermal stability of the non-aqueous electrolyte and increase the gas production of the secondary battery. - The ionic radius of lithium is small, making it easy to associate. Therefore, a high content of the third lithium salt may reduce the ionic conductivity of the non-aqueous electrolyte. Through extensive research, the inventors further discovered that when the content of the second lithium salt (A2) and the third lithium salt (A3) are reasonably adjusted to satisfy an A3 / A2 ratio of 0.04 to 30, the non-aqueous electrolyte can simultaneously possess high thermal stability and high ionic conductivity. This not only forms a low-resistance, highly ionicly conductive interfacial film at both the positive and negative electrodes but also better protects the aluminum foil current collector, thereby further improving the cycle performance, storage performance, and kinetic performance of the secondary battery. When A3 / A2 is greater than 30, the effect of the second lithium salt in reducing the negative electrode interfacial impedance is weak and may not be sufficient to compensate for the deterioration of the secondary battery's kinetic performance caused by the third lithium salt. When A3 / A2 is less than 0.04, a higher content of the second lithium salt may lead to a decrease in the thermal stability of the non-aqueous electrolyte and a deterioration in the storage performance of the secondary battery.

[0083] In some embodiments, optionally, A3 / A2 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 The ranges are: 18, 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. When A3 / A2 is within a suitable range, it is beneficial to fully utilize the synergistic effect between the second and third lithium salts, thereby further improving the cycle performance, storage performance, and kinetic performance of the secondary battery.

[0084] The first lithium salt readily forms associated ion pairs in non-aqueous solvents, reducing the ionic conductivity of the non-aqueous electrolyte. In some embodiments, Al is 0.005% to 0.2%. Optionally, A1 can be 0.005% to 0.18%, 0.005% to 0.16%, 0.005% to 0.14%, 0.005% to 0.12%, 0.005% to 0.1%, 0.005% to 0.08%, 0.008% to 0.18%, 0.008% to 0.16%, 0.008% to 0.14%, 0.008% to 0.12%, 0.008% to 0.1%, 0.008% to 0.08%, 0.01% to 0.18%, 0.01% to 0.16%, 0.01% to 0.14%, 0.01% to 0.12%, 0.01% to 0.1%, or 0.01% to 0.08%.

[0085] The second lithium salt 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, A2 is 0.005% to 0.3%. Optionally, A2 is 0.01% to 0.3%, 0.01% to 0.26%, 0.01% to 0.22%, 0.01% to 0.2%, 0.01% to 0.18%, 0.01% to 0.16%, 0.01% to 0.14%, 0.01% to 0.12%, 0.01% to 0.1%, 0.02% to 0.3%, 0.02% to 0.26%, 0.02% to 0.22%, 0.02% to 0.2%, 0.0 2% 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%.

[0086] When the content of the third lithium salt increases, the ionic 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, A3 is 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%, 0.02% to 0.45%, 0.02% to 0.4%, 0.02% to 0.35%, 0.02% to 0.3%, 0.02% to 0.25%, 0.02% to 0.2%, 0.02% to 0.15%, or 0.02% to 0.1%.

[0087] In some embodiments, R1 represents a fluorine atom or a partially or fully fluorinated C1-C6 alkyl group. Optionally, R1 represents a fluorine atom or a partially or fully fluorinated methyl, ethyl, or propyl group. More preferably, R1 represents a fluorine atom, trifluoromethyl, difluoromethyl, or monofluoromethyl group.

[0088] As an example, the first lithium salt includes at least one of the following compounds: .

[0089] R2 and R3 represent fluorine atoms or fluorine-containing groups. The presence of fluorine atoms or fluorine-containing groups helps to form thinner positive and / or negative electrode interface films, thereby facilitating uniform lithium-ion transport and effectively suppressing lithium dendrite formation. In some embodiments, R2 and R3 independently represent fluorine atoms or at least one of the following groups that are partially or fully fluorinated: C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, C6-C8 aryl, C1-C6 alkoxy, C2-C6 alkenyloxy, C2-C6 alkynyloxy, and C6-C8 aryloxy. Optionally, R2 and R3 independently represent fluorine atoms or at least one of the following groups that are partially or fully fluorinated: methyl, ethyl, propyl, phenyl, methoxy, ethoxy, propoxy, and phenoxy. More preferably, both R2 and R3 represent fluorine atoms.

[0090] As an example, the second lithium salt includes at least one of the following compounds:

[0091]

[0092] .

[0093] In some embodiments, the electrolyte salt further includes at least one of a fourth lithium salt and a fifth lithium salt. The fourth lithium salt is lithium hexafluorophosphate, with a mass content of A4 in the non-aqueous electrolyte, based on the total mass of the non-aqueous electrolyte. The fifth lithium salt is lithium difluorosulfonylimide, with a mass content of A5 in the non-aqueous electrolyte, based on the total mass of the non-aqueous electrolyte. The non-aqueous electrolyte satisfies the following conditions: A4 + A5 is 10% to 20%, optionally 10% to 18%, 10% to 17%, 10% to 16%, 10% to 15%, 12% to 18%, 12% to 17%, 12% to 16%, or 12% to 15%.

[0094] The non-aqueous electrolyte of this application uses lithium hexafluorophosphate and / or lithium bis(fluorosulfonyl)imide as the main lithium salt. Lithium hexafluorophosphate has the characteristics of high ionic conductivity and non-corrosion of aluminum foil current collectors. As the main lithium salt, it can improve the overall ionic conductivity and thermal stability of the non-aqueous electrolyte. The chemical formula of lithium bis(fluorosulfonyl)imide is F2NO4S2·Li, in which the N atom is bonded to two electron-withdrawing sulfonyl groups, thereby fully delocalizing the charge on the N atom. As a result, lithium bis(fluorosulfonyl)imide has a low lattice energy and is easy to dissociate, which can improve the ionic conductivity and reduce the viscosity of the non-aqueous electrolyte. In addition, lithium bis(fluorosulfonyl)imide also has the characteristics of good high temperature resistance and non-hydrolysis resistance, which can form a thinner interface film with lower impedance and higher thermal stability on the surface of the negative electrode active material, thereby reducing the side reactions between the negative electrode active material and the non-aqueous electrolyte.

[0095] In some embodiments, the non-aqueous electrolyte uses lithium hexafluorophosphate as the main lithium salt, i.e., A5 is 0%, A4 is 10% to 20%, and optionally 10% to 18%, 10% to 17%, 10% to 16%, 10% to 15%, 12% to 18%, 12% to 17%, 12% to 16%, or 12% to 15%.

[0096] In some embodiments, the non-aqueous electrolyte uses lithium difluorosulfonylimide as the main lithium salt, with A4 being 0% and A5 being 10% to 20%, optionally 10% to 18%, 10% to 17%, 10% to 16%, 10% to 15%, 12% to 18%, 12% to 17%, 12% to 16%, or 12% to 15%.

[0097] In some embodiments, the electrolyte salt may simultaneously include a fourth lithium salt and a fifth lithium salt. Optionally, A4 / A5 is 0.2 to 3, more preferably 0.3 to 2, 0.4 to 1.8, or 0.5 to 1.5. Thus, the non-aqueous electrolyte is less prone to hydrolysis and also achieves higher thermal stability, while simultaneously contributing to the formation of an interface film with lower impedance.

[0098] In some embodiments, the non-aqueous electrolyte satisfies a (A4+A5) / (A1+A2+A3) ratio of 10 to 200. Optionally, (A4+A5) / (A1+A2+A3) is 15 to 250, 20 to 120, 40 to 100, or 40 to 80. When the mass ratio of the main lithium salt to the auxiliary lithium salt is within a suitable range, it helps the non-aqueous electrolyte to simultaneously possess high thermal stability, high ionic conductivity, and a wide electrochemical window. Furthermore, the non-aqueous electrolyte can passivate the aluminum foil current collector and form a dense, stable, low-resistance, and highly ionicly conductive interfacial film on both the positive and negative electrode active materials.

[0099] In some embodiments, the non-aqueous electrolyte may further comprise other electrolyte salts, such as at least one selected from lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). These other electrolyte salts can serve as auxiliary lithium salts, further improving the interfacial properties of the positive and / or negative electrodes, or improving the ionic 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.

[0100] In some embodiments, the non-aqueous solvent may include at least one of a first solvent, a second solvent, and a third solvent.

[0101] The first solvent is a cyclic carbonate compound, such as at least one selected from ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Optionally, the first solvent includes ethylene carbonate (EC).

[0102] 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). More preferably, the second solvent includes ethyl methyl carbonate (EMC), diethyl carbonate (DEC), or a combination thereof.

[0103] In some embodiments, the non-aqueous solvent may optionally include at least a first solvent and a second solvent. When the content of the electrolyte salt is high, the viscosity of the non-aqueous electrolyte increases and the ionic conductivity decreases, which is detrimental to the formation of a dense, stable, and low-resistivity interfacial film. The first solvent, due to its higher 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 a first solvent and a second solvent, it helps the non-aqueous electrolyte to have suitable viscosity and ionic conductivity, thereby facilitating lithium-ion transport.

[0104] In some embodiments, the non-aqueous solvent may further include a third solvent. The third solvent is a carboxylic acid ester compound, such as 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 has the advantages of low viscosity and high dielectric constant; its application in non-aqueous electrolytes helps the non-aqueous electrolyte to have suitable viscosity and ionic conductivity, thereby facilitating lithium-ion transport.

[0105] In some embodiments, the mass content of the first solvent in the non-aqueous solvent is B1, the mass content of the second solvent in the non-aqueous solvent is B2, and the mass content of the third solvent in the non-aqueous solvent is B3, all based on the total mass of the non-aqueous solvent, and the non-aqueous solvent satisfies: B1 is 10% to 30%, B2 is 50% to 90%, and B3 is 0% to 20%.

[0106] The third solvent has poor oxidation resistance and is prone to oxidative decomposition when stored under a high-charge state; therefore, its content should not be too high. In some embodiments, B3 is 0%. In some embodiments, B3 is 2% to 20%, optionally 5% to 10%.

[0107] In some embodiments, B1 / (B2+B3) 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 the second lithium salt 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.

[0108] 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).

[0109] In some embodiments, the non-aqueous electrolyte further includes: a first additive, comprising at least one selected from fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl sulfate (DTD), and 1,3-propanesulfonic acid lactone (PS), wherein the additive comprises a mass content of C1 in the non-aqueous electrolyte, and C1 is 0.05% to 2% based on the total mass of the non-aqueous electrolyte. Optionally, C1 is 0.1% to 2%, 0.1% to 1.5%, 0.1% to 1.2%, 0.1% to 1%, 0.1% to 0.8%, 0.1% to 0.6%, or 0.1% to 0.5%. The first 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, and kinetic performance of the secondary battery.

[0110] In some embodiments, the non-aqueous electrolyte further includes: a first additive, comprising at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), ethylene sulfate (DTD), and 1,3-propanesulfonyl lactone (PS), wherein the first additive is present in a mass fraction C1 of the non-aqueous electrolyte based on the total mass of the non-aqueous electrolyte, and the content of the first additive C1, the content of lithium bis(fluorosulfonyl)imide A5, and the content of the first solvent B1 satisfy (C1+A5) / B1 of 0.3 to 0.8, optionally 0.3 to 0.6. The first additive helps to form a film on the positive and negative electrode surfaces to reduce persistent side reactions, thereby improving at least one of the cycle performance, storage performance, and kinetic performance of the secondary battery. However, when the content of the first additive is high, the positive electrode interfacial impedance and / or the negative electrode interfacial impedance increase, affecting the power performance of the secondary battery. Lithium difluorosulfonylimide can improve the ionic conductivity and thermal stability of non-aqueous electrolytes, and reduce the positive and / or negative electrode interface impedances. However, it has a certain corrosive effect on the aluminum foil current collector, and its high content can affect the cycle performance of the secondary battery. The first solvent has a high dielectric constant, which helps the dissociation of lithium salts and thus can improve the ionic conductivity of the non-aqueous electrolyte to a certain extent. However, its high content will increase the viscosity of the non-aqueous electrolyte and affect its thermal stability, thus affecting the storage performance of the secondary battery. In further research, the inventors found that by controlling the (C1+A5) / B1 ratio between 0.3 and 0.8, it is helpful to give full play to the synergistic effect between the above components and effectively reduce the defects of each component when used alone. This can enable the secondary battery to have excellent cycle performance and avoid the degradation of kinetic and power performance.

[0111] In some embodiments, the non-aqueous electrolyte further includes a second 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 second additive comprises aminosulfonic acid, lithium aminosulfonate, or a combination thereof.

[0112] 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 a non-aqueous electrolyte containing the aforementioned auxiliary lithium salts (first lithium salt, second lithium salt, and third lithium salt) further 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 ionic 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.

[0113] Aminosulfonic acid and its salts are readily soluble in water and are highly acidic. When their content is high, they can corrode the positive electrode active material and damage the stability of the positive electrode interface film and / or the negative electrode interface film. In some embodiments, the mass content of the second additive in the non-aqueous electrolyte is C2, which is 0.005% to 0.1% based on the total mass of the non-aqueous electrolyte, and optionally 0.005% to 0.05%.

[0114] In some embodiments, the non-aqueous electrolyte may also include the first additive and the second additive described above.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] Secondary batteries The second aspect of this application provides a secondary battery, which includes an electrode assembly, a non-aqueous electrolyte, and an outer packaging. 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, and kinetic performance.

[0119] The secondary battery of this application may be a lithium secondary battery, and more particularly a lithium-ion secondary battery.

[0120] 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.

[0121] The secondary battery of this application uses the non-aqueous electrolyte of the first aspect of this application, which helps to form a dense, stable, low-resistance and highly ionicly conductive interface film on the surfaces of both the positive and negative electrode active materials. This balances the charge transfer resistance of the positive and negative electrodes, reduces their difference, and improves the performance of the secondary battery.

[0122] In the secondary battery of this application, the charge transfer resistance of the positive electrode is Rct1, and the charge transfer resistance of the negative electrode is Rct2, with Rct1 / Rct2 being 0.5 to 2, optionally 1.25 to 2, 1.3 to 2, 1.35 to 2, 1.4 to 2, 1.25 to 1.8, 1.3 to 1.8, 1.35 to 1.8, 1.4 to 1.8, 1.25 to 1.6, 1.3 to 1.6, 1.35 to 1.6, or 1.4 to 1.6. This results in a smaller difference in charge transfer resistance between the positive and negative electrodes, which can better improve the performance of the secondary battery.

[0123] The charge transfer resistance of the positive electrode is obtained through the following test method: The positive electrode is assembled into a symmetrical battery, and its electrochemical impedance spectroscopy is measured using the electrochemical AC impedance method on an electrochemical workstation. A Nyquist plot is plotted, and the obtained Nyquist plot is analyzed using the equivalent circuit curve fitting method. The semicircle diameter is taken as the charge transfer resistance of the positive electrode, Rct1. The test voltage can be 10mV, and the test frequency can be from 0.1Hz to 100K Hz. The positive electrode can be obtained by disassembling a secondary battery. For safety reasons, the secondary battery is generally left in a fully discharged state.

[0124] The charge transfer resistance of the negative electrode is obtained using the following test method: The negative electrode is assembled into a symmetrical battery, and its electrochemical impedance spectroscopy is measured using the electrochemical AC impedance method on an electrochemical workstation. A Nyquist plot is plotted, and the obtained Nyquist plot is analyzed using the equivalent circuit curve fitting method. The charge transfer resistance of the negative electrode is taken as Rct2, with the semicircle diameter as the reference value. The test voltage can be 10mV, and the test frequency can be from 0.1Hz to 100K Hz. The negative electrode can be obtained by disassembling a secondary battery. For safety reasons, the secondary battery is generally left in a fully discharged state.

[0125] The non-aqueous electrolyte includes a first electrolyte that wets the electrode assembly and a second electrolyte located between the electrode assembly and the outer packaging. The first electrolyte is obtained by discharging the secondary battery to its discharge cutoff voltage, disassembling the electrode assembly, centrifuging it, and then collecting the liquid obtained from the centrifugation process; this is the first electrolyte. The second electrolyte is a free electrolyte and can be obtained from the secondary battery's filling port.

[0126] The sum of the mass contents of the first lithium salt, the second lithium salt, the third lithium salt, the first additive, and the second additive in the first electrolyte is X1, based on the total mass of the first electrolyte. The sum of the mass contents of the first lithium salt, the second lithium salt, the third lithium salt, the first additive, and the second additive in the second electrolyte is X2, based on the total mass of the second electrolyte, and 0.5 ≤ X1 / X2 < 1.

[0127] [Positive electrode plate] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] In some embodiments, c = 0.

[0136] 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.

[0137] The inventors of this application unexpectedly discovered during their research that when the contents of the second lithium salt (A2) and the third lithium salt (A3) are reasonably adjusted to satisfy an A3 / A2 ratio of 0.04 to 30, a low-resistance interfacial film can be formed on the surface of the positive electrode active material. Furthermore, the B atoms in the structures of the second and third lithium salts readily combine with the O atoms in the positive electrode active material, reducing the charge transfer resistance of the positive electrode active material and thus lowering 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 the second and third lithium salts, 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.

[0138] 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.

[0139] 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.

[0140] In some embodiments, 0 < d < 0.50 and 0 < e < 0.50. Alternatively, 0 < d ≤ 0.30 and 0 < e ≤ 0.10.

[0141] In some embodiments, g = 2, h = 0.

[0142] In some embodiments, g = 0, h = 2.

[0143] In some embodiments, 0 < g < 2, 0 < h < 2, and g + h = 2.

[0144] As an example, the molecular formula is Li a Ni bCo c Mn d Al e M f O g A h Layered materials include, but are 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.

[0145] 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.

[0146] 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.

[0147] 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 content 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%.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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 can be N-methylpyrrolidone (NMP), but is not limited to this.

[0152] [Negative electrode plate] 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.

[0153] 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.

[0154] 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 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 negative electrode conductive agent is less than 5% based on the total mass of the negative electrode film layer.

[0155] 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.

[0156] 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.

[0157] 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 base material and a metal material layer formed on at least one surface of the polymer base material. 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 base material may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0158] 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.

[0159] [Isolation membrane] 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.

[0160] 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.

[0161] 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.

[0162] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and the non-aqueous electrolyte described above.

[0163] 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-type soft pack. The material of the soft pack can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0164] 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 1This is an example of a square-structured secondary battery 5.

[0165] 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.

[0166] 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 placed in an outer packaging, dried, and then injected with a non-aqueous electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained. In some embodiments, the method for preparing the secondary battery further includes a secondary electrolyte injection process after the formation process, wherein the content of the first lithium salt, the second lithium salt, the third lithium salt, the first additive, and the second additive in the second injected non-aqueous electrolyte is lower than that in the first injected non-aqueous electrolyte. Adding a secondary electrolyte injection process helps to reduce costs and improves the performance of the secondary battery. This is because some components in the auxiliary lithium salt and additives have poor inherent stability. Using only a single electrolyte injection process can easily reduce the stability of the non-aqueous electrolyte. However, the secondary battery of this application uses a two-stage electrolyte injection process, and the second-injected non-aqueous electrolyte contains fewer auxiliary lithium salts and additives, thereby increasing the stability of the non-aqueous electrolyte. In some embodiments, the electrolyte injection coefficient of the secondary battery is 2.0 g / Ah to 5.0 g / Ah, and the mass of the non-aqueous electrolyte is the sum of the masses of the first and second-injected non-aqueous electrolytes.

[0167] 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.

[0168] 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.

[0169] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0170] 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.

[0171] 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.

[0172] Electrical appliances 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.

[0173] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0174] 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.

[0175] 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.

[0176] Example 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.

[0177] The secondary batteries of Examples 1 to 51 and Comparative Examples 1 to 10 were all prepared according to the following method.

[0178] Preparation of positive electrode sheet 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 thoroughly 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.

[0179] Preparation of negative electrode sheet 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 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.

[0180] Separating membrane Porous polyethylene (PE) membrane is used as the separator.

[0181] Preparation of non-aqueous electrolyte Lithium 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 Tables 1 and 3, respectively. In Tables 1 and 3, the contents of the first, second, third, fourth, and fifth lithium salts, the first additive, and the second additive are based on the total mass of the non-aqueous electrolyte, and the contents of the first, second, and third solvents are based on the total mass of the non-aqueous solvent. " / " indicates that the corresponding component was not added.

[0182] Preparation of secondary batteries 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.

[0183] Test section (1) Cyclic performance test of secondary batteries at room temperature 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%.

[0184] (2) High-temperature cycle performance test of secondary batteries 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%.

[0185] (3) High-temperature storage performance test of secondary batteries 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 this period, the volume of the secondary battery 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%.

[0186] (4) Initial DC internal resistance test of secondary battery 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 a sampling time of 0.1 seconds is used. The voltage at the end of the discharge is recorded as U2. The initial DC internal resistance of the secondary battery is expressed as the DC internal resistance of the secondary battery at 50% SOC. The initial DC internal resistance of the secondary battery (mΩ) = (U1-U2) / I1.

[0187] (5) Test of charge transfer resistance of positive electrode After fully discharging the prepared secondary battery, the positive electrode was disassembled and assembled into a symmetrical battery. The non-aqueous electrolyte was then injected, and the electrochemical impedance spectroscopy (EIS) method was used on a Solartron 1470E CellTest multichannel electrochemical workstation to generate a Nyquist plot. The Nyquist plot was analyzed using Zview software with equivalent circuit curve fitting, and the charge transfer resistance of the positive electrode was defined as Rct1, with the semicircle diameter as the reference value. The test voltage was 10 mV, and the test frequency ranged from 0.1 Hz to 100 kHz.

[0188] (6) Test of charge transfer resistance of negative electrode plate After fully discharging the prepared secondary battery, the negative electrode was disassembled and assembled into a symmetrical battery. The non-aqueous electrolyte was injected, and the electrochemical impedance spectroscopy (EIS) method was used on a Solartron 1470E CellTest multichannel electrochemical workstation to generate a Nyquist plot. The Nyquist plot was analyzed using Zview software with equivalent circuit curve fitting, using the semicircular diameter as the charge transfer resistance (Rct²) of the negative electrode. The test voltage was 10 mV, and the test frequency ranged from 0.1 Hz to 100 kHz.

[0189] 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.

[0190] Table 1 shows the preparation parameters of the non-aqueous electrolytes for Examples 1 to 35 and Comparative Examples 1 to 10, and Table 2 shows the test results obtained by Examples 1 to 35 and Comparative Examples 1 to 10 according to the above performance test methods.

[0191] Table 3 shows the preparation parameters of the non-aqueous electrolyte in Examples 36 to 51, and Table 4 shows the test results obtained by Example 36 to 51 according to the above performance test method.

[0192] Table 1

[0193] Table 1 - Continued

[0194] Table 2

[0195] Table 2 - Continued

[0196] Table 3

[0197] Table 4

[0198] Based on the test results of Examples 1 to 35, it can be seen that by using the first lithium salt, the second lithium salt, and the third lithium salt of this application as auxiliary lithium salts in the non-aqueous electrolyte and controlling their total content to be below 1%, and at the same time satisfying that the content of the first lithium salt A1, the content of the second lithium salt A2, and the content of the third lithium salt A3 are A1 / A2 = 0.016 to 40 and A1 / (A2+A3) = 0.006 to 13.5, the secondary battery can simultaneously achieve a high capacity retention rate, a low volume expansion rate, and a low internal resistance.

[0199] In Comparative Examples 1 to 9, the non-aqueous electrolyte did not use the auxiliary lithium salt of this application, or only used a portion of the auxiliary lithium salt of this application. The resulting secondary batteries had low capacity retention and high volume expansion and internal resistance. Comparative Example 10 used LiBOB as the auxiliary lithium salt, which improved the volume expansion of the resulting secondary battery to some extent, but the capacity retention was still low and the internal resistance was still high.

[0200] Based on the test results of Examples 36 to 51, it can be seen that by using the first additive and / or the second additive in the non-aqueous electrolyte, it is helpful to improve at least one of the cycle performance, storage performance and kinetic performance of the secondary battery.

[0201] Based on the test results of Examples 37 to 43, it can be seen that when the non-aqueous electrolyte includes both the fourth lithium salt and the fifth lithium salt, and the mass ratio of the two, A4 / A5, is between 0.2 and 3, and optionally between 0.5 and 1.5, it helps to further improve the overall performance of the secondary battery.

[0202] 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 secondary battery, characterized in that, The secondary battery includes an electrode assembly, a non-aqueous electrolyte, and an outer packaging. The non-aqueous electrolyte comprises an electrolyte salt and a non-aqueous solvent. The electrolyte salt includes: The first lithium salt has the structure shown in Formula 1, where R1 represents a fluorine atom or a partially or fully fluorinated C1-C10 alkyl group, and its mass content in the non-aqueous electrolyte is A1, based on the total mass of the non-aqueous electrolyte. The second lithium salt has the structure shown in Formula 2, where R2 and R3 each independently represent a fluorine atom or at least one of the following groups that are partially or fully fluorinated: C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C8 aryl, C1-C10 alkoxy, C2-C10 alkenyloxy, C2-C10 alkynyloxy, and C6-C8 aryloxy, and its mass content in the non-aqueous electrolyte is A2, based on the total mass of the non-aqueous electrolyte; The third lithium salt, selected from lithium tetrafluoroborate, has a mass content of A3 in the non-aqueous electrolyte, based on the total mass of the non-aqueous electrolyte. Formula 1 Formula 2 A1 is 0.005% to 0.2%; A2 is 0.005% to 0.3%; A3 is 0.01% to 0.5%.

2. The secondary battery according to claim 1, characterized in that, A1 ranges from 0.01% to 0.1%.

3. The secondary battery according to claim 2, characterized in that, A1 is 0.02%~0.1%.

4. The secondary battery according to claim 1, characterized in that, A2 ranges from 0.01% to 0.3%.

5. The secondary battery according to claim 4, characterized in that, A2 is 0.02%~0.2%.

6. The secondary battery according to claim 1, characterized in that, A3 is 0.02% to 0.2%.

7. The secondary battery according to claim 6, characterized in that, A3 is 0.05%~0.2%.

8. The secondary battery according to claim 1, characterized in that, The non-aqueous electrolyte further includes: a first additive, comprising at least one of fluoroethylene carbonate, vinylene carbonate, ethylene sulfate, and 1,3-propanesulfonic acid lactone, wherein the mass content of the additive in the non-aqueous electrolyte is C1, and C1 is 0.05% to 2% based on the total mass of the non-aqueous electrolyte.

9. The secondary battery according to claim 8, characterized in that, C1 ranges from 0.1% to 1%.

10. The secondary battery according to claim 1, characterized in that, The non-aqueous electrolyte further includes a second additive, comprising at least one of aminosulfonic acid and its salt, wherein the mass content of the additive in the non-aqueous electrolyte is C2, and the mass content of C2 is 0.005% to 0.1% based on the total mass of the non-aqueous electrolyte.

11. The secondary battery according to claim 1, characterized in that, C2 is 0.005% to 0.05%.

12. The secondary battery according to claim 1, characterized in that, The electrolyte salt also includes at least one of a fourth lithium salt and a fifth lithium salt. The fourth lithium salt is lithium hexafluorophosphate, and its mass content in the non-aqueous electrolyte is A4, based on the total mass of the non-aqueous electrolyte. The fifth lithium salt is lithium bis(fluorosulfonyl)imide, and its mass content in the non-aqueous electrolyte is A5, based on the total mass of the non-aqueous electrolyte. The non-aqueous electrolyte meets the following requirements: A4+A5 is 10% to 20%.

13. The secondary battery according to claim 12, characterized in that, A4+A5 is 10% to 18%.

14. The secondary battery according to claim 1, characterized in that, The non-aqueous electrolyte satisfies the following conditions: A1+A2+A3 is less than 1%, A1 / A2 is 0.016 to 40, and A1 / (A2+A3) is 0.006 to 13.

5.

15. The secondary battery according to claim 1, characterized in that, A1 / A2 is between 0.03 and 10; and / or, A1 / (A2+A3) ranges from 0.02 to 3.

5.

16. The secondary battery according to claim 15, characterized in that, A1 / A2 ranges from 0.1 to 5.

17. The secondary battery according to claim 15, characterized in that, A1 / (A2+A3) ranges from 0.1 to 2.

18. The secondary battery according to claim 1, characterized in that, The non-aqueous electrolyte also satisfies that the A3 / A2 ratio is between 0.04 and 30.

19. The secondary battery according to claim 18, characterized in that, The non-aqueous electrolyte also satisfies that A3 / A2 is between 1 and 10.

20. The secondary battery according to claim 1, characterized in that, The first lithium salt includes at least one of the following compounds: ; and / or, The second lithium salt includes at least one of the following compounds: 。 21. The secondary battery according to claim 1, characterized in that, The A4 / A5 ratio is 0.09 to 3.

22. The secondary battery according to claim 21, characterized in that, The A4 / A5 ratio is 0.2 to 3.

23. The secondary battery according to claim 22, characterized in that, The A4 / A5 ratio is 0.5 to 1.

5.

24. The secondary battery according to claim 21, characterized in that, (A4+A5) / (A1+A2+A3) ranges from 10 to 200.

25. The secondary battery according to claim 24, characterized in that, (A4+A5) / (A1+A2+A3) ranges from 20 to 120.

26. The secondary battery according to claim 25, characterized in that, (A4+A5) / (A1+A2+A3) is between 40 and 100.

27. The secondary battery according to claim 1, characterized in that, 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 B1, 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 B2, 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 B3, based on the total mass of the non-aqueous solvent. The non-aqueous electrolyte meets the following requirements: B1 is 10% to 30%, B2 is 50% to 90%, and B3 is 0% to 20%.

28. The secondary battery according to claim 27, characterized in that, B1 is 10% to 30%, B2 is 70% to 90%, and B3 is 0% to 5%.

29. The secondary battery according to claim 27, characterized in that, B1 / (B2+B3) ranges from 0.1 to 0.

45.

30. The secondary battery according to claim 29, characterized in that, B1 / (B2+B3) is between 0.2 and 0.

3.

31. The secondary battery according to claim 8, characterized in that, The non-aqueous electrolyte also satisfies that (C1+A5) / B1 is 0.23 to 0.

8.

32. The secondary battery according to claim 31, characterized in that, The non-aqueous electrolyte also satisfies that (C1+A5) / B1 is 0.3 to 0.

8.

33. The secondary battery according to claim 32, characterized in that, The non-aqueous electrolyte also satisfies that (C1+A5) / B1 is 0.3 to 0.

6.

34. The secondary battery according to any one of claims 1-33, characterized in that, The electrode assembly includes a positive electrode and a negative electrode. The charge transfer resistance of the positive electrode is Rct1, and the charge transfer resistance of the negative electrode is Rct2, with Rct1 / Rct2 being between 0.5 and 2. The charge transfer resistance of the positive electrode was obtained by the following test method: the positive electrode was assembled into a symmetrical battery, and its electrochemical impedance spectroscopy was measured using the electrochemical AC impedance method of an electrochemical workstation. A Nyquist plot was plotted, and the obtained Nyquist plot was analyzed using the equivalent circuit curve fitting method. The semicircle diameter was taken as the charge transfer resistance of the positive electrode, Rct1. The charge transfer resistance of the negative electrode sheet is obtained by the following test method: The negative electrode sheet is assembled into a symmetrical battery, and its electrochemical impedance spectroscopy is tested by electrochemical AC impedance method of electrochemical workstation. Nyquist plot is plotted, and the obtained Nyquist plot is analyzed by equivalent circuit curve fitting method. The semi-circular diameter is taken as the charge transfer resistance of the negative electrode sheet as Rct2.

35. The secondary battery according to claim 34, characterized in that, Rct1 / Rct2 is between 1.25 and 2.

36. The secondary battery according to any one of claims 1-35, characterized in that, The non-aqueous electrolyte includes a first electrolyte that wets the electrode assembly and a second electrolyte located between the electrode assembly and the outer packaging. The sum of the mass contents of the first lithium salt, the second lithium salt, the third lithium salt, the first additive, and the second additive in the first electrolyte is X1, based on the total mass of the first electrolyte. The sum of the mass contents of the first lithium salt, the second lithium salt, the third lithium salt, the first additive, and the second additive in the second electrolyte is X2, based on the total mass of the second electrolyte. And 0.5 ≤ X1 / X2 < 1, The first electrolyte is obtained by the following test method: after discharging the secondary battery to the discharge cutoff voltage, the electrode assembly is disassembled and centrifuged. The liquid obtained after centrifugation is the first electrolyte.

37. The secondary battery according to any one of claims 1-36, characterized in that, 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.

38. The secondary battery according to claim 37, characterized in that, 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.

39. The secondary battery according to claim 38, characterized in that, A is selected from F.

40. The secondary battery according to claim 38, characterized in that, 0.50≤b＜0.98。 41. The secondary battery according to claim 38, characterized in that, 0＜c≤0.10。 42. The secondary battery according to claim 38, characterized in that, d = 0 and 0 < e ≤ 0.

10.

43. The secondary battery according to claim 38, characterized in that, e = 0 and 0 < d ≤ 0.

10.

44. The secondary battery according to claim 38, characterized in that, 0 < d ≤ 0.30 and 0 < e ≤ 0.

10.

45. A non-aqueous electrolyte, characterized in that, The non-aqueous electrolyte comprises an electrolyte salt and a non-aqueous solvent, wherein the electrolyte salt includes: The first lithium salt has the structure shown in Formula 1, where R1 represents a fluorine atom or a partially or fully fluorinated C1-C10 alkyl group, and its mass content in the non-aqueous electrolyte is A1, based on the total mass of the non-aqueous electrolyte. The second lithium salt has the structure shown in Formula 2, where R2 and R3 each independently represent a fluorine atom or at least one of the following groups that are partially or fully fluorinated: C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C8 aryl, C1-C10 alkoxy, C2-C10 alkenyloxy, C2-C10 alkynyloxy, and C6-C8 aryloxy, and its mass content in the non-aqueous electrolyte is A2, based on the total mass of the non-aqueous electrolyte; The third lithium salt, selected from lithium tetrafluoroborate, has a mass content of A3 in the non-aqueous electrolyte, based on the total mass of the non-aqueous electrolyte. Formula 1 Formula 2 A1 is 0.005% to 0.2%; A2 is 0.005% to 0.3%; A3 is 0.01% to 0.5%.

46. ​​The non-aqueous electrolyte according to claim 45, characterized in that, The non-aqueous electrolyte further includes: a first additive, comprising at least one of fluoroethylene carbonate, vinylene carbonate, ethylene sulfate, and 1,3-propanesulfonic acid lactone, wherein the mass content of the additive in the non-aqueous electrolyte is C1, and C1 is 0.05% to 2% based on the total mass of the non-aqueous electrolyte.

47. The non-aqueous electrolyte according to claim 45 or 46, characterized in that, The non-aqueous electrolyte further includes a second additive, comprising at least one of aminosulfonic acid and its salt, wherein the mass content of the additive in the non-aqueous electrolyte is C2, and the mass content of C2 is 0.005% to 0.1% based on the total mass of the non-aqueous electrolyte.

48. The non-aqueous electrolyte according to claim 45, characterized in that, The electrolyte salt also includes at least one of a fourth lithium salt and a fifth lithium salt. The fourth lithium salt is lithium hexafluorophosphate, and its mass content in the non-aqueous electrolyte is A4, based on the total mass of the non-aqueous electrolyte. The fifth lithium salt is lithium bis(fluorosulfonyl)imide, and its mass content in the non-aqueous electrolyte is A5, based on the total mass of the non-aqueous electrolyte. The non-aqueous electrolyte meets the following requirements: A4+A5 is 10% to 20%.

49. A battery module comprising a secondary battery according to any one of claims 1-44.

50. A battery pack comprising a secondary battery according to any one of claims 1-44 and a battery module according to claim 49.

51. An electrical device comprising at least one of the following: a secondary battery according to any one of claims 1-44, a battery module according to claim 49, and a battery pack according to claim 50.

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