Non-aqueous electrolyte and secondary battery, battery module, battery pack, and power using device comprising the same

Abstract

The application provides a non-aqueous electrolyte and a secondary battery, a battery module, a battery pack and a power utilization device comprising the same. The non-aqueous electrolyte comprises an electrolyte salt and a non-aqueous solvent, the electrolyte salt comprises a first lithium salt, a second lithium salt and a third lithium salt, the content A1 of the first lithium salt, the content A2 of the second lithium salt and the content A3 of the third lithium salt satisfy: A1+A2+A3 is below 1%, A1 / A2 is 0.016 to 40, and A1 / (A2+A3) is 0.006 to 13.5 based on the total mass of the non-aqueous electrolyte. The application can make the secondary battery simultaneously consider good cycle performance, storage performance and kinetic performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a non-aqueous electrolyte, a secondary battery, a battery module, a battery pack and a power utilization device comprising the same. BACKGROUND

[0002] In recent years, secondary batteries are widely applied in energy storage power supply systems such as hydraulic, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. With the application and promotion of secondary batteries, more and more attention is paid to the comprehensive performance of secondary batteries, for example, secondary batteries need to meet the requirements of high energy density, long cycle life, high safety performance, good rate performance, etc. Non-aqueous electrolyte plays a role in conducting ions between the positive electrode and the negative electrode, and is one of the key factors affecting the performance of secondary batteries. Therefore, it is urgent to provide a non-aqueous electrolyte with good comprehensive performance. SUMMARY

[0003] The purpose of the present application is to provide a non-aqueous electrolyte, a secondary battery, a battery module, a battery pack and a power utilization device comprising the same, which can simultaneously meet the requirements of good cycle performance, storage performance and kinetic performance of the secondary battery.

[0004] The first aspect of the present application provides a non-aqueous electrolyte comprising an electrolyte salt and a non-aqueous solvent, wherein the electrolyte salt comprises: a first lithium salt having a structure shown in Formula 1, R1 represents a fluorine atom or a partially fluorinated or fully fluorinated C1-C10 alkyl group, the mass content of the first lithium salt in the non-aqueous electrolyte is A1, based on the total mass of the non-aqueous electrolyte; a second lithium salt having a structure shown in Formula 2, R2 and R3 independently represent a fluorine atom or at least one selected from the group consisting of a partially fluorinated or fully fluorinated C1-C10 alkyl group, a C2-C10 alkenyl group, a C2-C10 alkynyl group, a C6-C8 aryl group, a C1-C10 alkoxy group, a C2-C10 alkenyloxy group, a C2-C10 alkynyloxy group, a C6-C8 aryloxy group, the mass content of the second lithium salt in the non-aqueous electrolyte is A2, based on the total mass of the non-aqueous electrolyte; a third lithium salt selected from lithium tetrafluoroborate, the mass content of the third lithium salt in the non-aqueous electrolyte is A3, based on the total mass of the non-aqueous electrolyte;

[0005]

[0006] The non-aqueous electrolyte satisfies: 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] The inventors have found through a large number of studies that by using the above-mentioned first lithium salt, second lithium salt and third lithium salt as auxiliary lithium salts in the non-aqueous electrolyte, controlling the total content of the auxiliary lithium salts to be less than 1%, and reasonably adjusting the content A1 of the first lithium salt, the content A2 of the second lithium salt and the content A3 of the third lithium salt to satisfy A1 / A2 = 0.016 to 40 and A1 / (A2+A3) = 0.006 to 13.5, the non-aqueous electrolyte obtained can simultaneously have high thermal stability, high ionic conductivity and a wide electrochemical window, and the non-aqueous electrolyte can also passivate the aluminum foil current collector and form a dense, stable, low-impedance and high-ionic-conductivity interface film on the surface of both the positive electrode active material and the negative electrode active material, so that the secondary battery using the non-aqueous electrolyte of the present application can simultaneously have good cycle performance, storage performance and kinetic performance.

[0008] In any embodiment of the present application, A1 / A2 is 0.03 to 10, and is optionally 0.1 to 5. This is advantageous for fully exerting the synergistic effect between the first lithium salt and the second lithium salt, so that a more dense, more stable and higher-ionic-conductivity interface film can be formed on the surface of the negative electrode active material.

[0009] In any embodiment of the present application, A1 / (A2+A3) is 0.02 to 3.5, and is optionally 0.1 to 2. This is advantageous for fully exerting the synergistic effect between the first lithium salt, the second lithium salt and the third lithium salt, so that a more dense, more stable and higher-ionic-conductivity interface film can be formed on the surface of the positive electrode active material.

[0010] In any embodiment of the present application, the non-aqueous electrolyte also satisfies A3 / A2 = 0.04 to 30, and is optionally 1 to 10. This is advantageous for fully exerting the synergistic effect between the second lithium salt and the third lithium salt, so that the cycle performance, storage performance and kinetic performance of the secondary battery can be further improved.

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

[0012] In any embodiment of the present application, A2 is 0.005% to 0.3%, and is optionally 0.01% to 0.3%.

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

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

[0015]

[0016] In any embodiment of the present application, the second lithium salt comprises at least one of the following compounds:

[0017]

[0018]

[0019] In any embodiment of the present application, the electrolyte salt further comprises at least one of a fourth lithium salt and a fifth lithium salt, the fourth lithium salt being lithium hexafluorophosphate, a mass content of the fourth lithium salt in the non-aqueous electrolyte being A4, based on a total mass of the non-aqueous electrolyte, the fifth lithium salt being lithium bisfluorosulfonylimide, a mass content of the fifth lithium salt in the non-aqueous electrolyte being A5, based on the total mass of the non-aqueous electrolyte, the non-aqueous electrolyte satisfying: A4+A5 being 10% to 20%, optionally 10% to 18%.

[0020] In any embodiment of the present application, A4 / A5 is 0.2 to 3, optionally 0.5 to 1.5. Thereby, the non-aqueous electrolyte is less prone to hydrolysis, and also capable of simultaneously taking into account higher thermal stability, at the same time, helping to form an interface film with lower impedance.

[0021] In any embodiment of the present application, (A4+A5) / (A1+A2+A3) is 10 to 200, optionally 20 to 120, more optionally 40 to 100. Thereby, helping the non-aqueous electrolyte to have higher thermal stability, higher ionic conductivity and wider electrochemical window at the same time, and the non-aqueous electrolyte is also capable of passivating aluminum foil current collector and forming a dense, stable, low-impedance and high-ionic-conductivity interface film on the surface of the positive active material and the negative active material.

[0022] In any embodiment of the present application, the non-aqueous solvent comprises: a first solvent comprising at least one of ethylene carbonate, propylene carbonate, and butylene carbonate, a mass content of the first solvent in the non-aqueous solvent being B1, based on a total mass of the non-aqueous solvent; a second solvent comprising at least one of methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate, a mass content of the second solvent in the non-aqueous solvent being B2, based on the total mass of the non-aqueous solvent; a third solvent comprising at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate, a mass content of the third solvent in the non-aqueous solvent being B3, based on the total mass of the non-aqueous solvent, the non-aqueous electrolyte satisfying: B1 being 10% to 30%, B2 being 50% to 90%, and B3 being 0% to 20%.

[0023] In any embodiment of the present application, B1 / (B2+B3) is 0.1 to 0.45, and is optionally 0.2 to 0.3. This helps to make the interface film formed on the surface of the negative active material more dense and smooth, thereby effectively inhibiting the growth of dendrites.

[0024] In any embodiment of the present application, the non-aqueous electrolyte further comprises: a first additive comprising at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, 1,3-propane sultone, and the mass content of the first additive in the non-aqueous electrolyte is C1, and C1 is 0.05% to 2%, and is optionally 0.1% to 1%, based on the total mass of the non-aqueous electrolyte. The first additive helps to further improve the interface performance of the positive electrode and / or the negative electrode, thereby further improving at least one of the cycle performance, the storage performance, and the kinetic performance of the secondary battery.

[0025] In any embodiment of the present application, the non-aqueous electrolyte further satisfies (C1+A5) / B1 is 0.3 to 0.8, and is optionally 0.3 to 0.6. This helps to fully exert the synergistic effect between the above components, effectively reduce the defects of the components when used alone, make the secondary battery have excellent cycle performance, and also avoid the deterioration of the kinetic performance and the power performance.

[0026] In any embodiment of the present application, the non-aqueous electrolyte further comprises: a second additive comprising at least one of sulfamic acid and salts thereof, and the mass content of the second additive in the non-aqueous electrolyte is C2, and C2 is 0.005% to 0.1%, and is optionally 0.005% to 0.05%, based on the total mass of the non-aqueous electrolyte. This helps to improve the cycle performance and the kinetic performance of the secondary battery.

[0027] The second aspect of the present application provides a secondary battery comprising an electrode assembly, a non-aqueous electrolyte, and an outer package, wherein the non-aqueous electrolyte is the non-aqueous electrolyte of the first aspect of the present application. Thus, the secondary battery of the present application can simultaneously have good cycle performance, storage performance, and kinetic performance.

[0028] In any embodiment of the present application, the electrode assembly comprises a positive electrode tab and a negative electrode tab, the charge transfer resistance of the positive electrode tab is Rct1, the charge transfer resistance of the negative electrode tab is Rct2, and Rct1 / Rct2 is 0.5 to 2, and is optionally 1.25 to 2. Thus, the difference between the charge transfer resistances of the positive electrode and the negative electrode is small, which can better improve the performance of the secondary battery.

[0029] The charge transfer resistance of the positive electrode tab is obtained by the following test method: the positive electrode tab is assembled into a symmetric battery, electrochemical impedance spectroscopy of the symmetric battery is tested by electrochemical impedance method of an electrochemical workstation, a Nyquist plot is drawn, and the obtained Nyquist plot is analyzed by equivalent circuit curve fitting method, and the diameter of the semicircle is taken as the charge transfer resistance of the positive electrode tab as Rct1. The charge transfer resistance of the negative electrode tab is obtained by the following test method: the negative electrode tab is assembled into a symmetric battery, electrochemical impedance spectroscopy of the symmetric battery is tested by electrochemical impedance method of an electrochemical workstation, a Nyquist plot is drawn, and the obtained Nyquist plot is analyzed by equivalent circuit curve fitting method, and the diameter of the semicircle is taken as the charge transfer resistance of the negative electrode tab as Rct2.

[0030] In any embodiment of the present application, the non-aqueous electrolyte comprises a first electrolyte infiltrating the electrode assembly and a second electrolyte between the electrode assembly and the outer package, 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 the secondary battery is discharged to the discharge cut-off voltage, the electrode assembly is disassembled and subjected to centrifugal treatment, and then the liquid obtained by the centrifugal treatment is taken as the first electrolyte.

[0031] In any embodiment of the present application, the positive electrode tab comprises a layered material with a molecular formula of Li a Ni b Co c Mn d Al e M f O g A h , M represents a transition metal site-doped cation, A represents an 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, and g+h=2.

[0032] In some embodiments of the present application, M is selected from at least one of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te and W.

[0033] In some embodiments of the present application, A is selected from at least one of F, N, P and S, and optionally, A is selected from F.

[0034] In some embodiments of the present application, 0

[0035] In some embodiments of the present application, c = 0.

[0036] In some embodiments of the present application, 0

[0037] In some embodiments of the present application, d = 0 and 0

[0038] In some embodiments of the present application, e = 0 and 0

[0039] In some embodiments of the present application, 0

[0040] The third aspect of the present application provides a battery module comprising the secondary battery of the second aspect of the present application.

[0041] The fourth aspect of the present application provides a battery pack comprising one of the secondary battery of the second aspect of the present application and the battery module of the third aspect of the present application.

[0042] The fifth aspect of the present application provides a power consuming device comprising at least one of the secondary battery of the second aspect of the present application, the battery module of the third aspect of the present application and the battery pack of the fourth aspect of the present application.

[0043] The secondary battery of the present application can simultaneously take into account good cycle performance, storage performance and kinetic performance, and the battery module, the battery pack and the power consuming device of the present application comprise the secondary battery provided by the present application, and thus at least have the same advantages as the secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the drawings.

[0045] FIG. 1 is a schematic diagram of an embodiment of the secondary battery of the present application.

[0046] FIG. 2 is a schematic diagram of an embodiment of the secondary battery of the present application. FIG. 1 is a schematic diagram of an embodiment of the secondary battery of the present application.

[0047] FIG. 3 is a schematic view of an embodiment of a battery module of the present application.

[0048] FIG. 4 is a schematic view of an embodiment of a battery pack of the present application.

[0049] FIG. 5 is a schematic view of an embodiment of a battery pack of the present application. FIG. 4 is an exploded schematic view of an embodiment of a battery pack shown in FIG. 1.

[0050] FIG. 6 is a schematic view of an embodiment of an electric device including a secondary battery of the present application as a power source.

[0051] In the drawings, the drawings are not necessarily drawn to actual scale. Reference signs are explained as follows: 1 battery pack, 2 upper case, 3 lower case, 4 battery module, 5 secondary battery, 51 case, 52 electrode assembly, 53 cover plate. DETAILED DESCRIPTION

[0052] Hereinafter, embodiments of a nonaqueous electrolyte solution of the present application and a secondary battery, a battery module, a battery pack, and an electric device including the same will be specifically disclosed with appropriate reference to the drawings. However, there can be cases where unnecessary detailed description is omitted. For example, there can be cases where detailed description of matters well known, repeated description of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0053] The ranges disclosed herein are intended to be "open" ranges, i.e., the upper and lower limits of the range are not included. The ranges can be "closed" ranges, i.e., the upper and lower limits of the range are included. The ranges can be any combination of open and closed ranges. For example, if a range of 60-120 and a range of 80-110 are listed, it is understood that a range of 60-110 and a range of 80-120 are also contemplated. Furthermore, if a minimum range value of 1 and 2 are listed, and if a maximum range value of 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise indicated, a numerical range "a-b" means a range of any combination of the numbers a and b, in which a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shorthand for listing all of those numbers. Also, when a parameter is stated to be an integer > 2, it is equivalent to state that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0054] Unless otherwise indicated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0055] Unless otherwise indicated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0056] Unless otherwise indicated, all steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0057] Unless otherwise indicated, the "includes" and "contains" mentioned in the present application mean open-ended and can also be closed-ended. For example, the "includes" and "contains" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0058] If not otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0059] In this application, the terms "plurality" and "plural" mean two or more.

[0060] In this document, the term "alkyl" refers to a saturated hydrocarbon group, both straight-chain and branched, including methyl, ethyl, propyl (e.g., n-propyl, isopropyl), butyl (e.g., n-butyl, isobutyl, sec-butyl, t-butyl), pentyl (e.g., n-pentyl, isopentyl, neopentyl). In various embodiments, an alkyl group can contain 1 to 10 carbon atoms, i.e., C1-C10 alkyl.

[0061] The term "alkenyl" refers to an unsaturated hydrocarbon group containing a carbon-carbon double bond, both straight-chain and branched, including one or more carbon-carbon double bonds. Examples of alkenyl groups include, but are not limited to, ethenyl, propenyl, allyl, butadienyl. In various embodiments, an alkenyl group can contain 2 to 10 carbon atoms, i.e., C2-C10 alkenyl.

[0062] The term "alkynyl" refers to an unsaturated hydrocarbon group containing a carbon-carbon triple bond, both straight-chain and branched, including one or more carbon-carbon triple bonds. Examples of alkynyl groups include, but are not limited to, ethynyl, propynyl, butynyl, butadiynyl. In various embodiments, an alkynyl group can contain 2 to 10 carbon atoms, i.e., C2-C10 alkynyl.

[0063] The term "aryl" refers to a carbocyclic ring system having aromatic properties, which can be monocyclic, polycyclic, or fused. Examples of aryl groups include, but are not limited to, phenyl. In various embodiments, an aryl group can contain 6 to 8 carbon atoms, i.e., C6-C8 aryl.

[0064] In this document, the term "alkoxy" refers to an alkyl group containing an oxygen atom (-O-), the term "alkenyloxy" refers to an alkenyl group containing an oxygen atom (-O-), the term "alkynyloxy" refers to an alkynyl group containing an oxygen atom (-O-), and the term "aryloxy" refers to an aryl group containing an oxygen atom (-O-).

[0065] Throughout this specification, substituents of compounds are disclosed in groups or in ranges. It is specifically intended that descriptions using such language encompass each and every individual subcombination. For example, the term "C1-C6alkyl" is specifically intended to individually disclose C1, C2, C3, C4, C5, C6, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C6, C2-C5, C2-C4, C2-C3, C3-C6, C3-C5, C3-C4, C4-C6, C4-C5, and C5-C6alkyl.

[0066] With the application and promotion of secondary batteries, more and more attention is paid to the comprehensive performance of the secondary batteries. Non-aqueous electrolyte is one of the key factors affecting the performance of the secondary batteries. At present, the most widely used non-aqueous electrolyte system in commercial applications is a mixed carbonate solution of lithium hexafluorophosphate. However, lithium hexafluorophosphate has poor thermal stability at high temperatures, and it will decompose to generate LiF and PF5 at a relatively high temperature. LiF will increase the interfacial impedance; PF5 has strong Lewis acidity, and will react with the lone pair electrons on the oxygen atoms in the solvent molecules to cause the decomposition of the solvent; in addition, PF5 has high sensitivity to trace amounts of water in the non-aqueous electrolyte, and will produce HF when encountering water, thereby increasing the acidity of the non-aqueous electrolyte, and then easily corroding the positive active material and the positive current collector, and causing the dissolution of transition metal ions in the positive active material. In addition, after the transition metal ions in the positive active material are dissolved and migrate to the negative electrode, they will be reduced into transition metals, which act as "catalysts" and catalyze the decomposition of the solid electrolyte interphase (SEI) film on the surface of the negative active material, generating by-products. Part of the by-products is gas, which causes the secondary battery to swell and affects the safety performance of the secondary battery; another part of the by-products is deposited on the surface of the negative active material, which hinders the lithium ion transmission channel and causes the impedance of the secondary battery to increase, thereby affecting the kinetic performance of the secondary battery; in addition, to make up for the loss of the interfacial 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.

[0067] Therefore, it is necessary to provide a non-aqueous electrolyte with good comprehensive performance.

[0068] The inventors of the present application surprisingly found, after a large amount of research, that when the non-aqueous electrolyte contains an appropriate amount of auxiliary lithium salt, the secondary battery can simultaneously have good cycle performance, storage performance, and kinetic performance.

[0069] Non-aqueous electrolyte

[0070] Specifically, the first aspect of the embodiments of the present application provides a non-aqueous electrolyte, comprising an electrolyte salt and a non-aqueous solvent.

[0071] The electrolyte salt includes: a first lithium salt having a structure shown in Formula 1, R1 represents a fluorine atom or a partially fluorinated or fully fluorinated C1-C10 alkyl group, a mass content of the first lithium salt in the non-aqueous electrolyte is A1 based on a total mass of the non-aqueous electrolyte; a second lithium salt having a structure shown in Formula 2, R2, R3 respectively independently represent a fluorine atom or at least one of a group consisting of a partially fluorinated or fully fluorinated C1-C10 alkyl group, C2-C10 alkenyl group, C2-C10 alkynyl group, C6-C8 aryl group, C1-C10 alkoxy group, C2-C10 alkenyloxy group, C2-C10 alkynyloxy group, C6-C8 aryloxy group, a mass content of the second lithium salt in the non-aqueous electrolyte is A2 based on a total mass of the non-aqueous electrolyte; and a third lithium salt selected from lithium tetrafluoroborate, a mass content of the third lithium salt in the non-aqueous electrolyte is A3 based on a total mass of the non-aqueous electrolyte.

[0072]

[0073]

[0074] In the present application, the non-aqueous electrolyte satisfies: A1+A2+A3 is less than 1%, A1 / A2 is 0.016 to 40, and A1 / (A2+A3) is 0.006 to 13.5.

[0075] The inventors found through a large number of studies that by using the above-mentioned first lithium salt, second lithium salt and third lithium salt as auxiliary lithium salts in the non-aqueous electrolyte to control the total content thereof to be less than 1% and reasonably adjusting the content A1 of the first lithium salt, the content A2 of the second lithium salt and the content A3 of the third lithium salt to satisfy A1 / A2 is 0.016 to 40 and A1 / (A2+A3) is 0.006 to 13.5, the obtained non-aqueous electrolyte can simultaneously have high thermal stability, high ionic conductivity and a wide electrochemical window, and the non-aqueous electrolyte can also passivate the aluminum foil current collector and form a dense, stable, low-impedance and high-ionic-conductivity interface film on the surface of the positive electrode active material and the negative electrode active material, so that the secondary battery using the non-aqueous electrolyte of the present application can simultaneously have good cycle performance, storage performance and kinetic performance.

[0076] Although the mechanism is not clear, the inventors speculate that the possible reasons include the following points.

[0077] First, by reasonably adjusting the content A1 of the first lithium salt and the content A2 of the second lithium salt to satisfy A1 / A2 is 0.016 to 40, it is helpful to form a dense, stable and high ion-conducting interface film on the surface of the negative electrode active material. The first lithium salt contains sulfonate anions, which can be reduced to form Li2SO4 and other high ion-conducting compounds, thereby facilitating the improvement of the ion transport properties of the negative electrode interface film; the molecular structure of the second lithium salt contains an oxalate group, and its reduction product can further react with the organic components such as (LiOCO2CH2)2 in the interface film to form complex and stable oligomers, which fully cover the surface of the negative electrode active material, prevent the non-aqueous electrolyte from directly contacting the negative electrode active material, and reduce the non-aqueous solvent embedded in 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 properties 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 the kinetic performance.

[0078] Second, by reasonably adjusting the content A1 of the first lithium salt, the content A2 of the second lithium salt, and the content A3 of the third lithium salt to satisfy A1 / (A2+A3) is 0.006 to 13.5, it is helpful to form a dense, stable and containing a small amount of LiF interface film on the surface of the positive electrode active material, increase the lithium ion transport channel of the positive electrode interface film, and reduce the lithium ion transport resistance; at the same time, it inhibits the irreversible phase change of the positive electrode active material and maintains the structural stability of the positive electrode active material, thereby the secondary battery has better capacity performance. In addition, the B atom in the molecular structure of the second lithium salt is easy to combine with the O atom in the positive electrode active material, thereby it can also reduce the charge transfer impedance of the positive electrode active material and the diffusion resistance of lithium ions in the bulk phase of the positive electrode active material. When A1 / (A2+A3) is greater than 13.5, the second lithium salt and the third lithium salt cannot effectively compensate for the deterioration of the battery internal resistance caused by too much first lithium salt, thereby the kinetic performance of the secondary battery is poor, and 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 content of LiF in the positive electrode interface film is too much, thereby increasing the positive electrode interface impedance and affecting the kinetic performance of the secondary battery.

[0079] Thirdly, the first lithium salt can form an interface film not only in the negative electrode but also in the positive electrode, thereby improving the capacity performance and kinetic performance of the secondary battery. However, the fluorosulfonate group in the first lithium salt is prone to corrode the aluminum foil current collector, affecting the performance of the secondary battery, for example, increasing the battery polarization and irreversible capacity loss, and even affecting the safety performance of the secondary battery. The main surface is as follows: part of the solid insoluble corrosion product will increase the internal resistance of the secondary battery; part of the soluble corrosion product will contaminate and accelerate the decomposition of the non-aqueous electrolyte, increasing the self-discharge of the secondary battery; Al 3+ may migrate to the negative electrode by diffusion and be reduced into aluminum dendrites. The B-O bond in the molecular structure of the second lithium salt can bond with Al 3+ and form a passivation film on the surface of the aluminum foil current collector, and the third lithium salt can be preferentially oxidized and decomposed on the surface of the aluminum foil current collector and form a passivation film, so that the non-aqueous electrolyte of the application can passivate the aluminum foil current collector, effectively improve the corrosion of the first lithium salt to the aluminum foil current collector, and reduce the irreversible capacity loss of the secondary battery.

[0080] Therefore, the reason why the secondary battery using the non-aqueous electrolyte of the application can simultaneously have good cycle performance, storage performance and kinetic performance may be that a synergistic effect is formed among the above components. By forming an interface film of the first lithium salt in the positive electrode and the negative electrode, the ionic conductivity of the non-aqueous electrolyte is improved by the synergistic effect among the second lithium salt, the third lithium salt and the first lithium salt, thereby making up for the defects of small dissociation degree and low ionic conductivity of the first lithium salt; a dense, stable, low-impedance and high-ionic-conductivity interface film is formed on the surface of the negative active material by the synergistic effect between the first lithium salt and the second lithium salt; a dense, stable and containing a small amount of LiF interface film is formed on the surface of the positive active material by the synergistic effect among the first lithium salt, the second lithium salt and the third lithium salt. As a result, the interface side reaction between the non-aqueous electrolyte and the electrode is reduced, the irreversible consumption of active lithium ions is reduced, the capacity performance of the secondary battery is increased, and the gas production is reduced; in addition, the interface films formed on the surfaces of the positive active material and the negative active material have low impedance and high ionic conductivity, and the internal resistance of the secondary battery is reduced.

[0081] 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, the synergistic effect between the first lithium salt and the second lithium salt can be fully exerted, thereby enabling the formation of a more compact, more stable, and more ionically conductive interface film on the surface of the negative active material.

[0082] 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, the synergistic effect between the first lithium salt, the second lithium salt, and the third lithium salt can be fully exerted, thereby enabling the formation of a more compact, more stable, and more ionically conductive interface film on the surface of the positive active material.

[0083] Since the second lithium salt contains an oxalate group in its molecular structure, it has lower thermal stability than the third lithium salt and is oxidized to form carbon dioxide gas upon heating. Therefore, when the content of the second lithium salt is high, the thermal stability of the non-aqueous electrolyte can be reduced, and the gas production of the secondary battery can be increased. Since BF4 -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.

[0084] 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.

[0085] 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%.

[0086] The second lithium salt contains an oxalate group in its molecular structure, which is oxidized to form carbon dioxide gas when heated, reducing the thermal stability of the nonaqueous electrolyte. In some embodiments, A2 is from 0.005% to 0.3%. Alternatively, A2 is from 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%, 0.02% to 0.18%, 0.02% to 0.16%, 0.02% to 0.14%, 0.02% to 0.12%, 0.02% to 0.1%, 0.05% to 0.3%, 0.05% to 0.26%, 0.05% to 0.22%, 0.05% to 0.2%, 0.05% to 0.18%, 0.05% to 0.16%, 0.05% to 0.14%, 0.05% to 0.12%, or 0.05% to 0.1%.

[0087] The third lithium salt has a content that is increased, which reduces the ionic conductivity of the nonaqueous electrolyte, which is not conducive to the formation of a stable interface film on the surface of the negative active material. In some embodiments, A3 is from 0.01% to 0.5%. Alternatively, A3 can be from 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%.

[0088] In some embodiments, R1 represents a fluorine atom or a partially or fully fluorinated C1-C6 alkyl group. Alternatively, R1 represents a fluorine atom or a partially or fully fluorinated methyl, ethyl, propyl group. More alternatively, R1 represents a fluorine atom, a trifluoromethyl group, a difluoromethyl group, or a monofluoromethyl group.

[0089] By way of example, the first lithium salt includes at least one of the following compounds:

[0090]

[0091] R2, R3 represent a fluorine atom or a fluorine-containing group, the presence of the fluorine atom or the fluorine-containing group helps to form thinner positive electrode interface film and / or negative electrode interface film, thereby helping the uniform transmission of lithium ions, and also effectively inhibiting the formation of lithium dendrites. In some embodiments, R2, R3 independently represent a fluorine atom or at least one of the group consisting of partially fluorinated or fully fluorinated C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, C6-C8 aryl, C1-C6 alkoxy, C2-C6 alkenyloxy, C2-C6 alkynyloxy, C6-C8 aryloxy. Alternatively, R2, R3 independently represent a fluorine atom or at least one of the group consisting of partially fluorinated or fully fluorinated methyl, ethyl, propyl, phenyl, methoxy, ethoxy, propoxy, phenoxy. More alternatively, R2, R3 both represent a fluorine atom.

[0092] As an example, the second lithium salt includes at least one of the following compounds:

[0093]

[0094] 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, and the mass content of the fourth lithium salt in the non-aqueous electrolyte is A4, based on the total mass of the non-aqueous electrolyte. The fifth lithium salt is lithium bisfluorosulfonylimide, and the mass content of the fifth lithium salt in the non-aqueous electrolyte is A5, based on the total mass of the non-aqueous electrolyte. The non-aqueous electrolyte satisfies: 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%.

[0095] The non-aqueous electrolyte of the present application uses lithium hexafluorophosphate and / or lithium bisfluorosulfonylimide as the main lithium salt. Lithium hexafluorophosphate has the characteristics of high ionic conductivity and not easy to corrode aluminum foil current collector, as the main lithium salt can improve the overall ionic conductivity and thermal stability of the non-aqueous electrolyte. The chemical formula of lithium bisfluorosulfonylimide is F2NO4S2﹒Li, the N atom is connected to two electron-withdrawing sulfonyl groups, thereby fully delocalizing the charge on the N atom, and further lithium bisfluorosulfonylimide has a lower lattice energy and is easy to dissociate, thereby improving the ionic conductivity of the non-aqueous electrolyte and reducing the viscosity of the non-aqueous electrolyte; in addition, lithium bisfluorosulfonylimide also has the characteristics of good high temperature resistance and not easy to hydrolyze, and can form a thinner, lower impedance and higher thermal stability interface film on the surface of the negative electrode active material, thereby reducing the side reaction between the negative electrode active material and the non-aqueous electrolyte.

[0096] In some embodiments, the non-aqueous electrolyte uses lithium hexafluorophosphate as the main lithium salt, i.e. A5 is 0%, and A4 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%.

[0097] In some embodiments, the non-aqueous electrolyte uses lithium bisfluorosulfonylimide as the main lithium salt, A4 is 0%, and 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%.

[0098] In some embodiments, the electrolyte salt can include both a fourth lithium salt and a fifth lithium salt. Optionally, A4 / A5 is 0.2 to 3, more optionally 0.3 to 2, 0.4 to 1.8, or 0.5 to 1.5. In this way, the non-aqueous electrolyte is less prone to hydrolysis, and also enables a higher thermal stability while at the same time, helping to form an interface film with a lower impedance.

[0099] In some embodiments, the non-aqueous electrolyte satisfies (A4+A5) / (A1+A2+A3) is 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 and the auxiliary lithium salt is within the appropriate range, the non-aqueous electrolyte has a higher thermal stability, a higher ionic conductivity, and a wider electrochemical window, and the non-aqueous electrolyte is also able to passivate the aluminum foil current collector and form a dense, stable, low-impedance, and high-ionic-conductivity interface film on the surface of both the positive electrode active material and the negative electrode active material.

[0100] In some embodiments, the non-aqueous electrolyte can also include other electrolyte salts, such as at least one of lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium difluorophosphate (LiPO2F2), lithium difluorophosphate dioxalate (LiDFOP), and lithium tetrafluorophosphate oxalate (LiTFOP). These other electrolyte salts can act as auxiliary lithium salts, to further improve the interface performance of the positive electrode and / or the negative electrode, or to improve 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 optionally less than 0.5%, based on the total mass of the non-aqueous electrolyte.

[0101] In some embodiments, the non-aqueous solvent can include at least one of a first solvent, a second solvent, and a third solvent.

[0102] The first solvent is a cyclic carbonate compound, which may include at least one of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), for example. Optionally, the first solvent includes ethylene carbonate (EC).

[0103] The second solvent is a chain carbonate compound, which may include at least one of methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC), for example. Optionally, the second solvent includes at least one of methyl ethyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC). More optionally, the second solvent includes methyl ethyl carbonate (EMC), diethyl carbonate (DEC), or a combination thereof.

[0104] In some embodiments, the non-aqueous solvent may 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 solution increases, and the ionic conductivity decreases, which is not conducive to the formation of a dense, stable, and low-resistance interface film. The first solvent can increase the ionic conductivity of the non-aqueous electrolyte solution due to its high dielectric constant, and the second solvent can reduce the viscosity of the non-aqueous electrolyte solution due to its small viscosity. Therefore, when the non-aqueous solvent includes both the first solvent and the second solvent, it is helpful for the non-aqueous electrolyte solution to have a suitable viscosity and ionic conductivity, which in turn facilitates the transmission of lithium ions.

[0105] In some embodiments, the non-aqueous solvent may further include a third solvent. The third solvent is a carboxylic acid ester compound, which may include at least one of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), and ethyl butyrate (EB), for example. The third solvent has the advantages of low viscosity and high dielectric constant, and its application in the non-aqueous electrolyte solution is helpful for the non-aqueous electrolyte solution to have a suitable viscosity and ionic conductivity, which in turn facilitates the transmission of lithium ions.

[0106] 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%.

[0107] The third solvent has poor oxidation resistance and is prone to oxidative decomposition when stored at a high state of charge, and thus 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%.

[0108] 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, in particular, contains a suitable amount of ethylene carbonate, the radicals formed by the decomposition of the second lithium salt can induce the ring-opening and polymerization of ethylene carbonate, making the interface film formed on the surface of the negative active material more dense and smooth, thereby effectively inhibiting the growth of dendrites.

[0109] The non-aqueous solvent of the present application can also include other solvents in addition to the above-mentioned first solvent, second solvent, and third solvent. As an example, the other solvents can include sulfone-based solvents such as sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE), etc.

[0110] In some embodiments, the non-aqueous electrolyte further includes: a first additive including at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl sulfate (DTD), and 1,3-propane sultone (PS), and the mass content of the first 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. 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 electrode and / or the negative electrode, thereby further improving at least one of the cycle performance, storage performance, and kinetic performance of the secondary battery.

[0111] In some embodiments, the non-aqueous electrolyte further comprises: a first additive comprising at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl sulfite (DTD), 1,3-propane sultone (PS), and a mass content of the first additive in the non-aqueous electrolyte is C1, based on a total mass of the non-aqueous electrolyte, and the content C1 of the first additive, the content A5 of lithium bisfluorosulfonylimide, and the content B1 of the first solvent satisfy (C1+A5) / B1 is 0.3 to 0.8, optionally 0.3 to 0.6. The first additive helps to form a film on the surface of the positive electrode and the negative electrode to reduce the continuous side reaction, thereby improving at least one of the cycle performance, the storage performance, and the kinetic performance of the secondary battery, but when the content of the first additive is too high, the positive electrode interfacial impedance and / or the negative electrode interfacial impedance increases, affecting the power performance of the secondary battery. Lithium bisfluorosulfonylimide can improve the ionic conductivity and the thermal stability of the non-aqueous electrolyte, and reduce the positive electrode interfacial impedance and / or the negative electrode interfacial impedance, but has a certain corrosion to the aluminum foil current collector, and when the content is too high, it will affect the cycle performance of the secondary battery. The first solvent has a high dielectric constant, which helps to dissociate the lithium salt, and thus can improve the ionic conductivity of the non-aqueous electrolyte to a certain extent, but when the content is too high, on the one hand, it will increase the viscosity of the non-aqueous electrolyte, and on the other hand, it will affect the thermal stability of the non-aqueous electrolyte, affecting the storage performance of the secondary battery. The inventors found in further research that by controlling (C1+A5) / B1 to be between 0.3 and 0.8, the synergistic effect between the above components can be fully utilized, and the defects of using each component alone can be effectively reduced, thereby the secondary battery can have excellent cycle performance, and the kinetic performance and the power performance can also be improved.

[0112] In some embodiments, the non-aqueous electrolyte further comprises: a second additive comprising at least one of sulfamic acid and a salt thereof. The molecular formula of sulfamic acid is H3NO3S, and the salt of sulfamic acid comprises at least one of an ammonium salt, an alkali metal salt, an alkaline earth metal salt, and an alkali-like metal salt. For example, the salt of sulfamic acid can comprise at least one of ammonium sulfamate, lithium sulfamate, sodium sulfamate, and zinc sulfamate. Optionally, the second additive comprises sulfamic acid, lithium sulfamate, or a combination thereof.

[0113] The sulfamic acid is strong in acidity and is usually used to prepare lithium bisfluorosulfonylimide. It has not been found to be applicable to non-aqueous electrolyte. The inventors of the present application surprisingly found that when the non-aqueous electrolyte containing the above-mentioned auxiliary lithium salt (the first lithium salt, the second lithium salt and the third lithium salt) further contains an appropriate amount of sulfamic acid and its salt, the cycle performance and kinetic performance of the secondary battery can be improved. Although the mechanism is not clear, the inventors speculate that the possible reason is that the sulfamic acid and its salt can help to improve the ionic conductivity of the non-aqueous electrolyte, reduce the viscosity of the non-aqueous electrolyte, and also to a certain extent, slow down the dissolution of lithium dendrites and other metals, thereby reducing the reduction deposition of lithium, aluminum and transition metal elements on the surface of the negative active material, so that the secondary battery can have improved cycle performance and kinetic performance.

[0114] The sulfamic acid and its salt are easily soluble in water and strong in acidity. When the content is high, it can corrode the positive active material and destroy 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%, or optionally 0.005% to 0.05%, based on the total mass of the non-aqueous electrolyte.

[0115] In some embodiments, the non-aqueous electrolyte can also simultaneously include the above-mentioned first additive and second additive.

[0116] The non-aqueous electrolyte of the present application can be prepared according to conventional methods in the art. For example, the additives, non-aqueous solvents, electrolyte salts, etc. can be mixed uniformly to obtain a non-aqueous electrolyte. The order of adding each material is not particularly limited, for example, the additives, electrolyte salts, etc. can be added to the non-aqueous solvent and mixed uniformly to obtain a non-aqueous electrolyte.

[0117] In the present application, the components in the non-aqueous electrolyte and their contents 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.

[0118] It should be noted that when testing the non-aqueous electrolyte of the present application, fresh non-aqueous electrolyte can be directly taken, or non-aqueous electrolyte can be obtained from a secondary battery. An exemplary method for obtaining non-aqueous electrolyte from a secondary battery includes the following steps: centrifuging the secondary battery after discharging to the discharge cut-off voltage (for safety reasons, the battery is generally in a full discharge state), and then taking an appropriate amount of the liquid obtained by centrifugation as the non-aqueous electrolyte. The non-aqueous electrolyte can also be directly obtained from the liquid inlet of the secondary battery.

[0119] Secondary battery

[0120] The second aspect of the embodiments of the present application provides a secondary battery, which comprises an electrode assembly, a non-aqueous electrolyte, and an outer package, wherein the non-aqueous electrolyte is the non-aqueous electrolyte of the first aspect of the present application, so that the secondary battery of the present application can simultaneously balance the cycle performance, storage performance, and kinetic performance.

[0121] The secondary battery of the present application can be a lithium secondary battery, in particular, a lithium ion secondary battery.

[0122] The electrode assembly generally comprises a positive electrode sheet, a negative electrode sheet, and a separator, which is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive electrode and the negative electrode from short-circuiting, while allowing lithium ions to pass through.

[0123] The secondary battery of the present application adopts the non-aqueous electrolyte of the first aspect of the present application, which helps to form a dense, stable, low-resistance, and high-ionic-conductivity interface film on the surface of both the positive active material and the negative active material, so as to balance the charge transfer resistance of the positive electrode and the negative electrode, reduce the difference, and improve the performance of the secondary battery.

[0124] In the secondary battery of the present application, the charge transfer resistance of the positive electrode sheet is Rct1, the charge transfer resistance of the negative electrode sheet is Rct2, and Rct1 / Rct2 is 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. Thus, the difference in the charge transfer resistance of the positive electrode and the negative electrode is small, which can better improve the performance of the secondary battery.

[0125] The charge transfer resistance of the positive electrode sheet is obtained by the following test method: the positive electrode sheet is assembled into a symmetric battery, and the electrochemical impedance spectrum thereof is tested by the electrochemical impedance method of an electrochemical workstation, a Nyquist plot is drawn, and the obtained Nyquist plot is analyzed by an equivalent circuit curve fitting method, with the half-circle diameter as the charge transfer resistance of the positive electrode sheet being Rct1. The test voltage can be 10 mV, and the test frequency can be 0.1 Hz to 100 K Hz. The positive electrode sheet can be obtained by disassembling the secondary battery, and for safety reasons, the secondary battery is generally in a full discharge state.

[0126] The charge transfer resistance of the negative electrode tab is obtained by the following test method: the negative electrode tab is assembled into a symmetric battery, and the electrochemical impedance spectrum thereof is tested by electrochemical impedance method of an electrochemical workstation, a Nyquist plot is drawn, and the obtained Nyquist plot is analyzed by equivalent circuit curve fitting method, so that the half-circle diameter is taken as the charge transfer resistance of the negative electrode tab as Rct2. The test voltage can be 10 mV, and the test frequency can be 0.1 Hz to 100 K Hz. The negative electrode tab can be obtained by disassembling the secondary battery. For safety, the secondary battery is generally in a full discharge state.

[0127] The non-aqueous electrolyte includes a first electrolyte infiltrating the electrode assembly and a second electrolyte between the electrode assembly and the outer package. The first electrolyte is obtained by the following test method: the electrode assembly is disassembled after the secondary battery is discharged to the discharge cut-off voltage and is subjected to centrifugal treatment, and then the liquid obtained by the centrifugal treatment is taken as the first electrolyte. The second electrolyte is free electrolyte, which can be obtained by leading out from the liquid inlet of the secondary battery.

[0128] 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, 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.

[0129] [Positive electrode tab]

[0130] In some embodiments, the positive electrode tab includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite in the thickness direction of itself, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0131] The positive electrode film layer includes a positive electrode active material, which can be any positive electrode active material known in the art for use in secondary batteries. For example, the positive electrode active material can include at least one of lithium transition metal oxides, lithium-containing phosphates of olivine structure, and modified compounds of each thereof. Examples of the lithium transition metal oxides can 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 modified compounds of each thereof. Examples of the lithium-containing phosphates of olivine structure can include at least one of lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese phosphate, a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon, and modified compounds of each thereof. The present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries can also be used. These positive electrode active materials can be used alone or in combination of two or more.

[0132] In some embodiments, the positive electrode active material includes a layered material of formula Li a Ni b Co c Mn d Al e M f O g A h , M represents a transition metal site-doped cation, A represents an 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, and g+h=2.

[0133] In some embodiments, the positive electrode active material includes a layered material of formula Li a Ni b Co c Mn d Al e M f O g A h , which is optionally doped with M cations, A anions, or both M cations and A anions. The doped layered material has a more stable crystal structure, and can further improve the electrochemical performance of the secondary battery, such as cycle performance and kinetic performance.

[0134] 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.

[0135] In some embodiments, A is selected from at least one of F, N, P and S. Optionally, A is selected from F. After modification by F doping, Li a Ni b Co c Mn d Al e M f O g A h crystal structure is more stable, thereby enabling the secondary battery to have better cycle performance and kinetic performance.

[0136] a, b, c, d, e, f, g, h satisfy the following conditions: enabling Li a Ni b Co c Mn d Al e M f O g A h to remain electrically neutral.

[0137] 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.

[0138] In some embodiments, c = 0.

[0139] 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 less abundant in the earth's crust, difficult to mine, and expensive, so low-cobalt or cobalt-free is an inevitable development trend for positive active materials. However, cobalt contributes greatly to the lithium ion diffusion rate of positive active materials, and low-cobalt or cobalt-free reduces the lithium ion diffusion rate of positive active materials, affecting the cycle performance of secondary batteries. Researchers have been committed to improving the lithium ion diffusion rate of low-cobalt or cobalt-free positive active materials, but there is currently no good solution.

[0140] The inventors of the present application accidentally found that when the content A2 of the second lithium salt and the content A3 of the third lithium salt are reasonably adjusted and satisfy A3 / A2 = 0.04 to 30, a low-resistance interface film can also be formed on the surface of the positive electrode active material, and the B atoms in the structures of the second lithium salt and the third lithium salt are also easy to combine with the O atoms in the positive electrode active material, thereby reducing the charge transfer resistance of the positive electrode active material, and thus reducing the diffusion resistance of lithium ions in the bulk phase of the positive electrode active material. Therefore, when the non-aqueous electrolyte contains appropriate contents of the second lithium salt and the third lithium salt, the low-cobalt or cobalt-free positive electrode active material can have a significantly improved lithium ion diffusion rate, and the lithium ions in the bulk phase of the low-cobalt or cobalt-free positive electrode active material can be timely supplemented to the surface, thereby avoiding over-delithiation of the surface of the low-cobalt or cobalt-free positive electrode active material, and thus stabilizing the crystal structure of the low-cobalt or cobalt-free positive electrode active material. Since the crystal structure of the low-cobalt or cobalt-free positive electrode active material is more stable, the probability of problems such as irreversible distortion and increased lattice defects of the positive electrode active material due to over-delithiation of the surface of the low-cobalt or cobalt-free positive electrode active material can be greatly reduced.

[0141] In some embodiments, d = 0 and 0 < e < 0.50. Optionally, 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.

[0142] 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.

[0143] In some embodiments, 0 < d < 0.50 and 0 < e < 0.50. Optionally, 0 < d < 0.30 and 0 < e < 0.10.

[0144] In some embodiments, g = 2 and h = 0.

[0145] In some embodiments, g = 0 and h = 2.

[0146] In some embodiments, 0 < g < 2, 0 < h < 2, and g + h = 2.

[0147] 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 O2.

[0148] Li a Ni b Co c Mn d Al e M f O g A h may 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, a M element precursor, and an A element precursor are mixed and then sintered to obtain. The sintering atmosphere can be an oxygen-containing atmosphere, for example, an air atmosphere or an oxygen atmosphere. The O2concentration of the sintering atmosphere is, for example, 70% to 100%. The sintering temperature and the sintering time can be adjusted according to actual conditions.

[0149] As an example, the lithium source includes, but is not limited to, at least one of lithium oxide (Li20), lithium phosphate (Li3P04), lithium dihydrogen phosphate (LiH2P04), lithium acetate (CH3COOLi), lithium hydroxide (LiOH), lithium carbonate (Li2C03), and lithium nitrate (LiN03). As an example, the nickel source includes, but is not limited to, at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. As an example, the cobalt source includes, but is not limited to, at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. As an example, the manganese source includes, but is not limited to, at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. As an example, the aluminum source includes, but is not limited to, at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate. As an example, the M element precursor includes, but is not limited to, at least one of an oxide, a nitrate compound, a carbonate compound, a hydroxide compound, and an acetate compound of the M element. As an example, the A element precursor includes, but is 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 hydrosulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur.

[0150] In some embodiments, the mass percentage of the layered material of formula Li a Ni b Co c Mn d Al e M f O g A h may be 80% to 99%. For example, the mass percentage of the layered material of formula Li a Ni b Co c Mn d Al e M f O g A h may be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any range derivable therein. Alternatively, the mass percentage of the layered material of formula Li a Ni b Co c Mn d Al e M f O g A hThe mass percentage content 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%.

[0151] In some embodiments, the positive electrode film layer further optionally includes a positive electrode conductive agent. The present application does not have a particular limitation on the type of the positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of super-p, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage content of the positive electrode conductive agent is 5% or less based on the total mass of the positive electrode film layer.

[0152] In some embodiments, the positive electrode film layer further optionally includes a positive electrode binder. The present application does not have a particular limitation on the type of the positive electrode binder. As an example, the positive electrode binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin. In some embodiments, the mass percentage content of the positive electrode binder is 5% or less based on the total mass of the positive electrode film layer.

[0153] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. As an example of the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material can be selected from at least one of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer can be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0154] The positive electrode film layer is generally formed by coating a positive electrode slurry on a positive electrode current collector, drying, and cold-pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring uniformly. The solvent can be N-methyl pyrrolidone (NMP), but is not limited thereto.

[0155] [Negative electrode tab]

[0156] In some embodiments, the negative electrode tab includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces opposite in the thickness direction of the negative electrode current collector, and the negative electrode film layer is disposed on either one or both of the two opposite surfaces of the negative electrode current collector.

[0157] The negative electrode active material can be any of the negative electrode active materials conventionally 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, a silicon-based material, a tin-based material, and lithium titanate. The silicon-based material can include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material can include at least one of elemental tin, tin oxide, and tin alloy material. The present application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0158] In some embodiments, the negative electrode film layer can also optionally include a negative electrode conductive agent. The present application does not have a particular limitation on the type of the negative electrode conductive agent, and as an example, the negative electrode conductive agent can include at least one of super P, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage content of the negative electrode conductive agent is 5% or less based on the total mass of the negative electrode film layer.

[0159] In some embodiments, the negative electrode film layer can also optionally include a negative electrode binder. The present application does not have a particular limitation on the type of the negative electrode binder, and as an example, the negative electrode binder can include at least one of styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage content of the negative electrode binder is 5% or less based on the total mass of the negative electrode film layer.

[0160] In some embodiments, the negative electrode film layer can also optionally include other auxiliary agents. As an example, the other auxiliary agents can include a thickening agent, such as carboxymethyl cellulose sodium (CMC-Na), PTC thermistor material, and the like. In some embodiments, the mass percentage content of the other auxiliary agents is 2% or less based on the total mass of the negative electrode film layer.

[0161] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. As an example of a metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material can be selected from at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer can be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0162] The negative electrode film layer is generally formed by coating a negative electrode slurry on a negative electrode current collector, drying, and cold-pressing. The negative electrode slurry is generally formed by dispersing a negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring uniformly. The solvent can be N-methyl pyrrolidone (NMP) or deionized water, but is not limited thereto.

[0163] [Separator]

[0164] The separator is disposed between the positive electrode tab and the negative electrode tab, and mainly functions to prevent short circuiting of the positive electrode and the negative electrode while allowing lithium ions to pass therethrough. The type of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0165] In some embodiments, the material of the separator can include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different.

[0166] In some embodiments, the positive electrode tab, the separator, and the negative electrode tab can be used to manufacture an electrode assembly through a winding process or a stacking process.

[0167] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the non-aqueous electrolyte solution.

[0168] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), and the like.

[0169] The shape of the secondary battery is not particularly limited in the present application, and the secondary battery can be cylindrical, square, or any other shape. For example, FIG. 1is a square structure secondary battery 5 as an example.

[0170] In some embodiments, as shown in FIG. 2 The outer package can include a housing 51 and a cover plate 53. The housing 51 can include a bottom plate and side plates connected to the bottom plate, which enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The non-aqueous electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to the needs.

[0171] The preparation method of the secondary battery of the present application is known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet and the non-aqueous electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, the separator, the negative electrode sheet can be formed into an electrode assembly through a winding process or a stacking process, the electrode assembly is placed in an outer package, and after drying, the non-aqueous electrolyte is injected, and then the vacuum packaging, standing, formation, shaping and other processes are carried out to obtain the secondary battery. In some embodiments, the preparation method of the secondary battery further includes a secondary injection process carried out after the formation process, and the contents 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 are lower than those in the first injected non-aqueous electrolyte. By increasing the secondary injection process, it helps to reduce the cost, while being able to improve the performance of the secondary battery. This is because part of the components in the auxiliary lithium salt and the additive have poor stability by themselves, and when only one injection process is used, the stability of the non-aqueous electrolyte is easily reduced, while the secondary battery of the present application uses a secondary injection process, and the second injected non-aqueous electrolyte contains less auxiliary lithium salt and additive, thereby increasing the stability of the non-aqueous electrolyte. In some embodiments, the 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 mass of the first injected non-aqueous electrolyte and the second injected non-aqueous electrolyte.

[0172] In some embodiments of the present application, the secondary battery according to the present application can be assembled into a battery module, and 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.

[0173] FIG. 3 is a schematic view of a battery module 4 as an example. As shown in FIG. 3 In the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be used. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0174] Optionally, the battery module 4 can further include a housing having an accommodation space, and the plurality of secondary batteries 5 can be accommodated in the accommodation space.

[0175] In some embodiments, the above-described battery module can 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.

[0176] FIG. 4 and FIG. 5 is a schematic view of a battery pack 1 as an example. As shown in FIG. 4 and FIG. 5 indicated, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, the upper box body 2 is used to cover the lower box body 3, and forms a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0177] Power consuming device

[0178] The embodiments of the present application further provide an electric device, which includes at least one of the secondary battery, the battery module or the battery pack of the present application. The secondary battery, the battery module or the battery pack can be used as a power source of the electric device, or can be used as an energy storage unit of the electric device. The electric device can be, but is not limited to, a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0179] The electric device can select a secondary battery, a battery module or a battery pack according to its use requirements.

[0180] FIG. 6 is a schematic view of an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of high power and high energy density of the electric device, a battery pack or a battery module can be used.

[0181] As another example of an electric device, it can be a mobile phone, a tablet computer, a notebook computer, etc. The electric device usually requires thin and light, and a secondary battery can be used as a power source.

[0182] Example

[0183] The present application is described in more detail by the following examples, which are merely illustrative and not limiting the scope of the present application, since various modifications and changes in the examples disclosed herein will occur to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported herein are based upon the weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used without further purification, and the instruments used in the examples are commercially available.

[0184] The secondary batteries of Examples 1 to 51 and Comparative Examples 1 to 10 were prepared according to the following method.

[0185] Preparation of positive electrode sheet

[0186] The positive active material LiNi 0.6 Co 0.2 Mn 0.2 O2, a conductive agent carbon black, and a binder polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:1.4:1.1 in an appropriate amount of a solvent NMP to form a uniform positive electrode slurry; the positive electrode slurry was uniformly coated on the surface of a positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained.

[0187] Preparation of negative electrode sheet

[0188] The negative active material graphite, a binder styrene butadiene rubber (SBR), a thickening agent sodium carboxymethyl cellulose (CMC-Na), and a conductive agent carbon black (Super P) were mixed in a weight ratio of 96.2:1.8:1.2:0.8 in an appropriate amount of a solvent deionized water to form a uniform negative electrode slurry; the negative electrode slurry was uniformly coated on the surface of a negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode sheet was obtained.

[0189] Separator film

[0190] A porous polyethylene (PE) film was used as a separator film.

[0191] Preparation of non-aqueous electrolyte

[0192] The lithium salt and the additive were mixed in a non-aqueous solvent to obtain a non-aqueous electrolyte. The compositions and contents of the components are shown in Tables 1 and 3, respectively. In Tables 1 and 3, the contents of the first lithium salt, the second lithium salt, the third lithium salt, the fourth lithium salt, the fifth lithium salt, the first additive, and the second additive are based on the total mass of the non-aqueous electrolyte, the contents of the first solvent, the second solvent, and the third solvent are based on the total mass of the non-aqueous solvent, and “ / ” indicates that the corresponding component was not added.

[0193] Preparation of secondary battery

[0194] Stacking and winding the positive electrode sheet, the separator, and the negative electrode sheet in order to obtain an electrode assembly; placing the electrode assembly into an outer package, adding the above non-aqueous electrolyte, and obtaining a secondary battery after processes such as packaging, standing, formation, and aging.

[0195] Test section

[0196] (1) Secondary battery normal temperature cycle performance test

[0197] At 25℃, the secondary battery is charged at 1C constant current to 4.3V, and continues to be charged at constant voltage until the current is 0.05C, at which time the secondary battery is fully charged, and the charge capacity at this time is recorded, which is the first cycle charge capacity; after the secondary battery is placed for 5min, it is discharged at 1C constant current to 2.8V, which is one cycle of charge and discharge process, and the discharge capacity at this time is recorded, which is the first cycle discharge capacity. The secondary battery is tested by the above method for cycle charge and discharge, and the discharge capacity after each cycle is recorded. The capacity retention rate of the secondary battery at 25℃ after 600 cycles (%) = the discharge capacity after 600 cycles / the first cycle discharge capacity x 100%.

[0198] (2) Secondary battery high temperature cycle performance test

[0199] At 45℃, the secondary battery is charged at 1C constant current to 4.3V, and continues to be charged at constant voltage until the current is 0.05C, at which time the secondary battery is fully charged, and the charge capacity at this time is recorded, which is the first cycle charge capacity; after the secondary battery is placed for 5min, it is discharged at 1C constant current to 2.8V, which is one cycle of charge and discharge process, and the discharge capacity at this time is recorded, which is the first cycle discharge capacity. The secondary battery is tested by the above method for cycle charge and discharge, and the discharge capacity after each cycle is recorded. The capacity retention rate of the secondary battery at 45℃ after 600 cycles (%) = the discharge capacity after 600 cycles / the first cycle discharge capacity x 100%.

[0200] (3) Secondary battery high temperature storage performance test

[0201] At 60℃, the secondary battery is charged at 1C constant current to 4.3V, and continues to be charged at constant voltage until the current is 0.05C, at which time the volume of the secondary battery is tested by the drainage method and recorded as V0; the secondary battery is placed in a constant temperature oven at 60℃, and after 30 days, it is taken out, at which time the volume of the secondary battery is tested by the drainage method and recorded as V1. The volume expansion rate of the secondary battery after 30 days of storage at 60℃ (%) = [(V1-V0) / V0] x 100%.

[0202] (4) Secondary battery initial direct current resistance test

[0203] The secondary battery is charged at 1 C constant current to 4.3 V at 25 °C, and continues to be charged at constant voltage until the current is 0.05 C, at which time the secondary battery is fully charged; the secondary battery is discharged at 0.5 C constant current and adjusted to 50% SOC, at which time the voltage of the secondary battery is recorded as U1; the secondary battery is discharged at a current of 4 C, I1, for 30 seconds, with a 0.1 second sampling point, and the voltage at the end of the discharge is recorded as U2. The discharge DC internal resistance of the secondary battery at 50% SOC represents the initial DC internal resistance of the secondary battery, and the initial DC internal resistance of the secondary battery (mΩ) = (U1-U2) / I1.

[0204] (5) Charge transfer resistance test of positive electrode tab

[0205] The positive electrode tab is disassembled after the above-prepared secondary battery is fully discharged, the positive electrode tab is assembled into a symmetric battery, the above non-aqueous electrolyte is injected, and then an electrochemical impedance method of a Solartron 1470E CellTest multi-channel electrochemical workstation is used for testing, and a Nyquist plot is drawn; the Nyquist plot obtained is analyzed by an equivalent circuit curve fitting method using Zview software, and the diameter of the semicircle is taken as the charge transfer resistance of the positive electrode tab, Rct1. The test voltage is 10 mV, and the test frequency is 0.1 Hz to 100 K Hz.

[0206] (6) Charge transfer resistance test of negative electrode tab

[0207] The negative electrode tab is disassembled after the above-prepared secondary battery is fully discharged, the negative electrode tab is assembled into a symmetric battery, the above non-aqueous electrolyte is injected, and then an electrochemical impedance method of a Solartron 1470E CellTest multi-channel electrochemical workstation is used for testing, and a Nyquist plot is drawn; the Nyquist plot obtained is analyzed by an equivalent circuit curve fitting method using Zview software, and the diameter of the semicircle is taken as the charge transfer resistance of the negative electrode tab, Rct2. The test voltage is 10 mV, and the test frequency is 0.1 Hz to 100 K Hz.

[0208] To ensure the reliability of the test results, at least 3 parallel samples can be used for testing and the average value is taken as the test result.

[0209] Table 1 gives the non-aqueous electrolyte preparation parameters of Examples 1 to 35 and Comparative Examples 1 to 10, and Table 2 gives the test results of Examples 1 to 35 and Comparative Examples 1 to 10 according to the above performance test method.

[0210] Table 3 gives the non-aqueous electrolyte preparation parameters of Examples 36 to 51, and Table 4 gives the test results of Examples 36 to 51 according to the above performance test method.

[0211] Table 3 gives the non-aqueous electrolyte preparation parameters of Examples 36 to 51, and Table 4 gives the test results of Examples 36 to 51 according to the above performance test method.

[0212]

[0213]

[0214]

[0215]

[0216]

[0217] The test results of Examples 1 to 35 show that, by using the first lithium salt, the second lithium salt and the third lithium salt of the present application as auxiliary lithium salts in the non-aqueous electrolyte and controlling the total content of the auxiliary lithium salts to be less than 1%, and by controlling the content A1 of the first lithium salt, the content A2 of the second lithium salt and the content A3 of the third lithium salt to satisfy A1 / A2 = 0.016 to 40 and A1 / (A2+A3) = 0.006 to 13.5, the secondary battery can simultaneously have a high capacity retention rate, a low volume expansion rate and a low internal resistance.

[0218] In Comparative Examples 1 to 9, the non-aqueous electrolyte does not use the auxiliary lithium salts of the present application, or only uses part of the auxiliary lithium salts of the present application, and the capacity retention rate of the prepared secondary battery is low, and the volume expansion rate and the internal resistance are high. Comparative Example 10 uses LiBOB as an auxiliary lithium salt, and the volume expansion rate of the obtained secondary battery is improved to a certain extent, but the capacity retention rate is still low, and the internal resistance is still high.

[0219] The test results of Examples 36 to 51 show that, by using the first additive and / or the second additive in the non-aqueous electrolyte, at least one of the cycle performance, the storage performance and the kinetic performance of the secondary battery can be improved.

[0220] The test results of Examples 37 to 43 show that, when the non-aqueous electrolyte simultaneously includes the fourth lithium salt and the fifth lithium salt, and the mass ratio A4 / A5 of the two is between 0.2 and 3, and optionally between 0.5 and 1.5, the comprehensive performance of the secondary battery can be further improved.

[0221] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having substantially the same configuration and playing the same role and effect as the technical idea within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, and other ways constructed by combining part of the components in the embodiments are also included in the scope of the present application.

Claims

1. A non-aqueous electrolyte comprising an electrolyte salt and a non-aqueous solvent, characterized in that, 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 The non-aqueous electrolyte meets the following requirements: A1+A2+A3 is less than 1%, A1 / A2 is 0.016 to 40, and A1 / (A2+A3) is 0.006 to 13.5; 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; 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.

2. The non-aqueous electrolyte 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.

3. The non-aqueous electrolyte according to claim 2, characterized in that, A1 / A2 ranges from 0.1 to 5.

4. The non-aqueous electrolyte according to claim 2, characterized in that, A1 / (A2+A3) ranges from 0.1 to 2.

5. The non-aqueous electrolyte according to claim 1 or 2, characterized in that, The non-aqueous electrolyte also satisfies that the A3 / A2 ratio is between 0.04 and 30.

6. The non-aqueous electrolyte according to claim 5, characterized in that, The non-aqueous electrolyte also satisfies that A3 / A2 is between 1 and 10.

7. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous electrolyte satisfies at least one of the following conditions (1) to (3): (1) A1 is 0.005% to 0.2%; (2) A2 is 0.005% to 0.3%; (3) A3 is 0.01% to 0.5%.

8. The non-aqueous electrolyte according to claim 7, characterized in that, A1 ranges from 0.01% to 0.1%.

9. The non-aqueous electrolyte according to claim 7, characterized in that, A2 ranges from 0.01% to 0.3%.

10. The non-aqueous electrolyte according to claim 7, characterized in that, A3 is 0.02% to 0.2%.

11. The non-aqueous electrolyte 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: 。 12. The non-aqueous electrolyte according to claim 11, 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 non-aqueous electrolyte according to claim 12, characterized in that, A4+A5 is 10% to 18%.

14. The non-aqueous electrolyte according to claim 12, characterized in that, The A4 / A5 ratio is 0.2 to 3.

15. The non-aqueous electrolyte according to claim 12, characterized in that, The A4 / A5 value is 0.5 to 1.

5.

16. The non-aqueous electrolyte according to claim 12, characterized in that, (A4+A5) / (A1+A2+A3) ranges from 10 to 200.

17. The non-aqueous electrolyte according to claim 16, characterized in that, (A4+A5) / (A1+A2+A3) ranges from 20 to 120.

18. The non-aqueous electrolyte according to claim 17, characterized in that, (A4+A5) / (A1+A2+A3) is between 40 and 100.

19. The non-aqueous electrolyte according to claim 12, 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%.

20. The non-aqueous electrolyte according to claim 19, characterized in that, B1 / (B2+B3) ranges from 0.1 to 0.

45.

21. The non-aqueous electrolyte according to claim 20, characterized in that, B1 / (B2+B3) is between 0.2 and 0.

3.

22. The non-aqueous electrolyte according to claim 1, characterized in that, Based on the total mass of the non-aqueous electrolyte, C1 is 0.1% to 1%.

23. The non-aqueous electrolyte according to claim 19, characterized in that, The non-aqueous electrolyte also satisfies that (C1+A5) / B1 is 0.3 to 0.

8.

24. The non-aqueous electrolyte according to claim 23, characterized in that, The non-aqueous electrolyte also satisfies that (C1+A5) / B1 is 0.3 to 0.

6.

25. The non-aqueous electrolyte according to claim 1, characterized in that, C2 is 0.005% to 0.05%.

26. A secondary battery, comprising an electrode assembly, a non-aqueous electrolyte, and an outer packaging, characterized in that, The non-aqueous electrolyte is the non-aqueous electrolyte according to any one of claims 1-25.

27. The secondary battery according to claim 26, 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.

28. The secondary battery according to claim 27, characterized in that, Rct1 / Rct2 is between 1.25 and 2.

29. The secondary battery according to claim 26, 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.

30. The secondary battery according to claim 27, 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.

31. The secondary battery according to claim 30, 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.

32. The secondary battery according to claim 31, characterized in that, A is selected from F.

33. The secondary battery according to claim 31, characterized in that, 0.50≤b＜0.98。 34. The secondary battery according to claim 31, characterized in that, 0＜c≤0.10。 35. The secondary battery according to claim 31, characterized in that, d = 0 and 0 < e ≤ 0.

10.

36. The secondary battery according to claim 31, characterized in that, e = 0 and 0 < d ≤ 0.

10.

37. The secondary battery according to claim 31, characterized in that, 0 < d ≤ 0.30 and 0 < e ≤ 0.

10.

38. A battery module comprising a secondary battery according to any one of claims 26-37.

39. A battery pack comprising a secondary battery according to any one of claims 26-37 and a battery module according to claim 38.

40. An electrical device comprising at least one of the following: a secondary battery according to any one of claims 26-37, a battery module according to claim 38, and a battery pack according to claim 39.

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