Nonaqueous electrolyte, secondary battery containing the same, battery module, battery pack, and electric device

Abstract

To provide a nonaqueous electrolyte that simultaneously achieves a good cycle performance, a storage performance, and a dynamic performance of a secondary battery, the secondary battery containing the same, a battery module, a battery pack, and an electric device.SOLUTION: A nonaqueous electrolyte includes an electrolyte salt, and a nonaqueous solvent. The electrolyte salt includes a first lithium salt, a second lithium salt, and a third lithium salt. When calculated based on the total mass of the nonaqueous electrolyte, a content A1 of the first lithium salt, a content A2 of the second lithium salt, and a content A3 of the third lithium salt satisfy the following conditions: A1+A2+A3 is 1% or less, A1 / A2 is 0.016 to 40, and A1 / (A2+A3) is 0.006 to 13.5. The present application can simultaneously achieve a good cycle performance, a storage performance, and a dynamic performance of a secondary battery.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application relates to the field of battery technology, and more particularly to a non-aqueous electrolyte solution and a secondary battery, battery module, battery pack, and electric device containing the same. [Background technology]

[0002] In recent years, secondary batteries have been widely applied in energy storage power systems such as hydroelectric, thermal, wind, and solar power plants, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. With the increasing application and popularity of secondary batteries, their overall performance has received increasing attention. For example, secondary batteries must simultaneously satisfy the following requirements: high energy density, long cycle life, high safety performance, and high power consumption. Non-aqueous electrolytes function as ionic conduction between the positive and negative electrodes, which is one of the important factors affecting secondary battery performance. Therefore, it is necessary to provide non-aqueous electrolytes with good overall performance. Summary of the Invention

[0003] The present application aims to provide a non-aqueous electrolyte that simultaneously achieves good cycle performance, storage performance, and dynamic performance of a secondary battery, and a secondary battery, battery module, battery pack, and electrical device that include the same.

[0004] A first aspect of the present application provides a non-aqueous electrolyte solution comprising an electrolyte salt and a non-aqueous solvent, wherein the electrolyte salt comprises a first lithium salt, a second lithium salt, and a third lithium salt, wherein the first lithium salt has a structure represented by Formula 1, R1 represents a fluorine atom or a partially or fully fluorinated C1-C10 alkyl, and its mass content in the non-aqueous electrolyte solution is A1, calculated based on the total mass of the non-aqueous electrolyte solution; the second lithium salt has a structure represented by Formula 2, R2 and R3 represent a fluorine atom or a partially or fully fluorinated C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C8 each independently represents at least one selected from the group consisting of aryl, C1-C10 alkoxy, C2-C10 alkenyloxy, C2-C10 alkynyloxy, and C6-C8 aryloxy, and its mass content in the non-aqueous electrolyte solution is A2 when calculated based on the total mass of the non-aqueous electrolyte solution; the third lithium salt is selected from lithium tetrafluoroborate, and its mass content in the non-aqueous electrolyte solution is A3 when calculated based on the total mass of the non-aqueous electrolyte solution; and the non-aqueous electrolyte solution satisfies the following: A1+A2+A3 is 1% or less; A1 / A2 is 0.016 to 40; and A1 / (A2+A3) is 0.006 to 13.5. [ka] [ka]

[0005] The inventors have conducted extensive research and found that, when the first, second, and third lithium salts are used as auxiliary lithium salts in a non-aqueous electrolyte, and their total content is controlled to 1% or less, and 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 are rationally adjusted so that A1 / A2 is 0.016 to 40 and A1 / (A2+A3) is 0.006 to 13.5, the resulting non-aqueous electrolyte can simultaneously exhibit high thermal stability, high ionic conductivity, and a wide electrochemical window. The non-aqueous electrolyte can also inactivate the aluminum foil current collector and form dense, stable, low-resistance, and highly conductive interfacial films on the surfaces of both the positive and negative electrode active materials, thereby enabling secondary batteries using the non-aqueous electrolyte of the present invention to simultaneously achieve good cycle performance, storage performance, and kinetic performance.

[0006] In any embodiment of the present application, A1 / A2 is 0.03 to 10, and preferably 0.1 to 5. This helps to fully exert the synergistic effect between the first lithium salt and the second lithium salt, thereby forming a denser, more stable, and more ion-conductive interfacial film on the surface of the negative electrode active material.

[0007] In any embodiment of the present application, A1 / (A2+A3) is 0.02 to 3.5, and preferably 0.1 to 2. This helps to fully exert the synergistic effect among the first lithium salt, the second lithium salt, and the third lithium salt, thereby forming a denser, more stable, and more ion-conductive interfacial film on the surface of the positive electrode active material.

[0008] In any embodiment of the present application, the nonaqueous electrolyte solution further satisfies A3 / A2 of 0.04 to 30, and preferably A3 / A2 of 1 to 10. This helps to fully exert the synergistic effect between the second lithium salt and the third lithium salt, thereby further improving the cycle performance, storage performance, and kinetic performance of the secondary battery.

[0009] In any embodiment of the present application, A1 is 0.005% to 0.2%, and preferably 0.01% to 0.1%.

[0010] In any embodiment of the present application, A2 is 0.005% to 0.3%, and preferably 0.01% to 0.3%.

[0011] In any embodiment of the present application, A3 is 0.01% to 0.5%, and preferably 0.02% to 0.2%.

[0012] In any embodiment of the present application, the first lithium salt comprises at least one of the following compounds: [ka]

[0013] The second lithium salt includes at least one of the following compounds: [ka]

[0014] In any embodiment of the present application, the electrolyte salt further includes at least one of a fourth lithium salt and a fifth lithium salt, the fourth lithium salt being lithium hexafluorophosphate, and its mass content in the non-aqueous electrolyte solution is A4, calculated based on the total mass of the non-aqueous electrolyte solution; the fifth lithium salt being lithium bisfluorosulfonylimide, and its mass content in the non-aqueous electrolyte solution is A5, calculated based on the total mass of the non-aqueous electrolyte solution; and the non-aqueous electrolyte solution satisfies that A4+A5 is 10% to 20%, preferably A4+A5 is 10% to 18%.

[0015] In any embodiment of the present application, A4 / A5 is 0.2 to 3, and preferably 0.5 to 1.5, which makes the nonaqueous electrolyte solution less susceptible to hydrolysis and simultaneously achieves higher thermal stability, and also helps form an interfacial film with lower impedance.

[0016] In any embodiment of the present application, (A4+A5) / (A1+A2+A3) is 10 to 200, preferably 20 to 120, and more preferably 40 to 100. This helps the nonaqueous electrolyte to simultaneously have high thermal stability, high ionic conductivity, and a wide electrochemical window, and the nonaqueous electrolyte can further inactivate the aluminum foil current collector and form dense, stable, low-resistance, and highly conductive interfacial films on the surfaces of both the positive and negative electrode active materials.

[0017] In any embodiment of the present application, the non-aqueous solvent includes a first solvent, a second solvent, and a third solvent, the first solvent includes at least one of ethylene carbonate, propylene carbonate, and butylene carbonate, and the mass content of the first solvent in the non-aqueous solvent is B1, calculated based on the total mass of the non-aqueous solvent, and the second solvent includes at least one of ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate. The mass content of the third solvent in the non-aqueous solvent is B2, calculated based on the total mass of the non-aqueous solvent; the third solvent includes at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate, and the mass content of the third solvent in the non-aqueous solvent is B3, calculated based on the total mass of the non-aqueous solvent; and preferably, the non-aqueous electrolyte solution satisfies the following: B1 is 10% to 30%, B2 is 50% to 90%, and B3 is 0% to 20%.

[0018] In any embodiment of the present application, B1 / (B2+B3) is 0.1 to 0.45, preferably 0.2 to 0.3, which helps make the interfacial film formed on the surface of the negative electrode active material denser and smoother, thereby effectively suppressing the growth of dendrites.

[0019] In any embodiment of the present application, the non-aqueous electrolyte further comprises a first additive, the first additive comprising at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, and 1,3-propane sultone, and the mass content of the first additive in the non-aqueous electrolyte is C1, which is 0.05% to 2%, preferably 0.1% to 1%, calculated based on the total mass of the non-aqueous electrolyte. The first additive serves to further improve the interfacial properties of the positive electrode and / or negative electrode, thereby further improving at least one of the cycle performance, storage performance, and kinetic performance of the secondary battery.

[0020] In any embodiment of the present application, the nonaqueous electrolyte solution further satisfies (C1+A5) / B1 is 0.3 to 0.8, and preferably (C1+A5) / B1 is 0.3 to 0.6, thereby fully exerting the synergistic effects among the components, effectively reducing defects when each component is used alone, allowing the secondary battery to have excellent cycle performance, and further preventing deterioration of dynamic performance and power performance.

[0021] In any embodiment of the present application, the non-aqueous electrolyte further includes a second additive, the second additive including at least one of sulfamic acid and its salt, and the mass content of the second additive in the non-aqueous electrolyte is C2, calculated based on the total mass of the non-aqueous electrolyte, and C2 is 0.005% to 0.1%, preferably 0.005% to 0.05%, which helps improve the cycle performance and kinetic performance of the secondary battery.

[0022] A second aspect of the present application provides a secondary battery including an electrode assembly, a non-aqueous electrolyte, and an exterior body, 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 achieve good cycle performance, storage performance, and kinetic performance.

[0023] In any embodiment of the present application, the electrode assembly includes a positive electrode sheet and a negative electrode sheet, 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, preferably 1.25 to 2. This reduces the difference in charge transfer resistance between the positive electrode and the negative electrode, thereby further improving the performance of the secondary battery.

[0024] The charge transfer resistance of the positive electrode sheet is obtained by the following test method. The positive electrode sheet is assembled into a symmetrical battery, and its electrochemical impedance spectrum is measured using the electrochemical AC impedance method on an electrochemical workstation. A Nyquist diagram is then created, and the obtained Nyquist diagram is analyzed using the equivalent circuit curve fitting method. The semicircular diameter is taken as the charge transfer resistance Rct1 of the positive electrode sheet. 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 spectrum is measured using the electrochemical AC impedance method on an electrochemical workstation. A Nyquist diagram is then created, and the obtained Nyquist diagram is analyzed using the equivalent circuit curve fitting method. The semicircular diameter is taken as the charge transfer resistance Rct2 of the negative electrode sheet.

[0025] In any embodiment of the present application, the non-aqueous electrolyte includes a first electrolyte that infiltrates the electrode assembly and a second electrolyte that is located between the electrode assembly and the exterior body. When calculated 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 first electrolyte is X1. When calculated based on the total mass of the second 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, and 0.5 ≦ X1 / X2 < 1. The first electrolyte is obtained by the following test method. After discharging the secondary battery to the discharge cut-off voltage, the electrode assembly is disassembled and centrifuged, and the liquid obtained by centrifugation is the first electrolyte.

[0026] In any embodiment of the present application, the positive electrode sheet includes a layered material having the molecular formula Li a Ni b Co c Mn d Al e M f O g A h where M represents a doping cation at the transition metal site, A represents a doping anion at the oxygen site, 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.

[0027] 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.

[0028] In some embodiments of the present application, A is selected from at least one of F, N, P, and S, and preferably, A is selected from F.

[0029] In some embodiments of the present application, 0 < b < 0.98, and preferably, 0.50 ≦ b < 0.98.

[0030] In some embodiments of the present application, c = 0.

[0031] In some embodiments of the present application, 0 < c ≤ 0.20, and preferably, 0 < c ≤ 0.10.

[0032] In some embodiments of the present application, d = 0 and 0 < e < 0.50, and preferably, d = 0 and 0 < e ≤ 0.10.

[0033] In some embodiments of the present application, e = 0 and 0 < d < 0.50, and preferably, e = 0 and 0 < d ≤ 0.10.

[0034] In some embodiments of the present application, 0 < d < 0.50 and 0 < e < 0.50, and preferably, 0 < d ≤ 0.30 and 0 < e ≤ 0.10.

[0035] The third aspect of the present application provides a battery module including the secondary battery of the second aspect of the present application.

[0036] The fourth aspect of the present application provides a battery pack including one of the secondary battery of the second aspect of the present application and the battery module of the third aspect.

[0037] The fifth aspect of the present application provides an electrical device including at least one of the secondary battery of the second aspect of the present application, the battery module of the third aspect, and the battery pack of the fourth aspect.

[0038] The secondary battery of the present application can simultaneously achieve good cycle performance, storage performance, and kinetic performance. Since the battery module, battery pack, and electrical device of the present application include the secondary battery provided by the present application, they have at least the same advantages as the secondary battery.

Brief Description of the Drawings

[0039] In order to more clearly explain the technical solutions of the embodiments of the present application, the drawings necessary for the embodiments of the present application will be briefly described below. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can further obtain other drawings based on the drawings without any creative efforts. [Figure 1] 1 is a schematic diagram of an embodiment of a secondary battery of the present application. [Figure 2] FIG. 2 is an exploded schematic view of the embodiment of the secondary battery of FIG. [Figure 3] 1 is a schematic diagram of an embodiment of a battery module of the present application. [Figure 4] 1 is a schematic diagram of an embodiment of a battery pack of the present application. [Figure 5] 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4. [Figure 6] 1 is a schematic diagram of an embodiment of an electrical device including a secondary battery of the present application as a power source.

[0040] In the drawings, the drawings are not drawn to scale. The reference numerals in the drawings are as follows: 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 secondary battery, 51 case, 52 electrode assembly, 53 cover plate. DETAILED DESCRIPTION OF THE INVENTION

[0041] Hereinafter, embodiments of the nonaqueous electrolyte solution of the present application, as well as secondary batteries, battery modules, battery packs, and electrical devices each including the same, will be described in detail with appropriate reference to the drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of actual identical structures may be omitted. This is to prevent the following description from becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0042] "Ranges" disclosed herein are defined in the form of lower and upper limits. A given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner may or may not include the end values. They may be arbitrarily combined. That is, any lower limit may be combined with any upper limit to form a single range. For example, if ranges of 60 to 120 and 80 to 110 are recited for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 and maximum range values ​​of 3, 4, and 5 are recited, all of the ranges of 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are also contemplated. Unless otherwise specified, a numerical range "a to b" herein refers to all real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" in this specification indicates all real numbers between "0 and 5," and "0 to 5" is a thumbnail of combinations of these numerical values. Furthermore, when a parameter is expressed as an integer ≧2, this is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present application.

[0044] Unless otherwise stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present application.

[0045] Unless otherwise specified, all steps herein can be performed in sequence, randomly, and preferably in sequence. For example, if the method includes steps (a) and (b), the method can include steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, if the method further includes step (c), step (c) can be added to the method in any order; for example, the method can include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), etc.

[0046] Unless otherwise specified, the terms "comprise" and "contain" used herein refer to an open system, but may also refer to a closed system. For example, the terms "comprise" and "contain" may further include or contain other components not listed, or may only include or contain the listed components.

[0047] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the short phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfies "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) but B is true (or exists); or A and B are both true (or exist).

[0048] As used herein, the terms "plurality" and "plurality" refer to two or more than two.

[0049] As used herein, the term "alkyl" refers to a saturated hydrocarbon group, including both straight-chain and branched structures. Examples of alkyl include, but are not limited to, methyl, ethyl, propyl (e.g., n-propyl, isopropyl), butyl (e.g., n-butyl, isobutyl, sec-butyl, tert-butyl), and pentyl (e.g., n-pentyl, isopentyl, neopentyl). In various embodiments, C1-C10 alkyl means that the alkyl can contain 1 to 10 carbon atoms.

[0050] The term "alkenyl" refers to an unsaturated hydrocarbon group containing a carbon-carbon double bond, including both linear and branched structures, and may contain one or more carbon-carbon double bonds. Examples of alkenyl include, but are not limited to, vinyl, propenyl, allyl, and butadiene. In various embodiments, C2-C10 alkenyl means that the alkenyl can contain from 2 to 10 carbon atoms.

[0051] The term "alkynyl" refers to an unsaturated hydrocarbon group containing a carbon-carbon triple bond, including both straight-chain and branched structures, and may contain one or more carbon-carbon triple bonds. Examples of alkynyl include, but are not limited to, ethynyl, propynyl, butynyl, and butynyl. In various embodiments, a C2-C10 alkynyl means that the alkynyl can contain from 2 to 10 carbon atoms.

[0052] The term "aryl" refers to a carbocyclic ring system having aromatic character, which may be monocyclic, polycyclic, or fused ring. Examples of aryl include, but are not limited to, phenyl. In various embodiments, C6-C8 aryl means that the aryl may contain from 6 to 8 carbon atoms.

[0053] As used herein, the term "alkoxy" refers to an alkyl containing an oxygen atom (-O-), the term "alkenyloxy" refers to an alkenyl containing an oxygen atom (-O-), the term "alkynyloxy" refers to an alkyl containing an oxygen atom (-O-), and the term "aryloxy" refers to an alkyl containing an oxygen atom (-O-).

[0054] At various points in this specification, substituents of compounds are disclosed in groups or in ranges. It is expressly contemplated that such descriptions include each subcombination of the members of these groups and ranges. For example, the term "C1-C6 alkyl" is expressly contemplated to separately disclose C1, C2, C3, C4, C5, C6, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C6, C2-C5, C2-C4, C2-C3, C3-C6, C3-C5, C3-C4, C4-C6, C4-C5, and C5-C6 alkyl.

[0055] As secondary batteries become more widely used and adopted, their overall performance is receiving increasing attention. Non-aqueous electrolytes are one of the key factors affecting secondary battery performance. The most widely used non-aqueous electrolyte system currently in commercial use is a mixed carbonate ester solution of lithium hexafluorophosphate. However, lithium hexafluorophosphate has poor thermal stability at high temperatures and decomposes to form LiF and PF5. LiF increases interfacial resistance. PF5 has strong Lewis acidity and interacts with the lone electrons on oxygen atoms in the solvent molecules, causing the solvent to decompose. Furthermore, PF5 is highly sensitive to trace amounts of moisture in non-aqueous electrolytes. When exposed to water, it generates HF, which increases the acidity of the non-aqueous electrolyte, further corroding the positive electrode active material and positive electrode current collector and leading to the leaching of transition metal ions in the positive electrode active material. Furthermore, transition metal ions in the positive electrode active material dissolve and migrate to the negative electrode, where they then transform into transition metals. The resulting transition metals act as catalysts, catalyzing the decomposition of the solid electrolyte interphase (SEI) on the surface of the negative electrode active material and generating by-products. Some of these by-products are gases, causing secondary battery expansion and affecting the safety performance of the secondary battery. Another portion of these by-products accumulates on the surface of the negative electrode active material, blocking the lithium ion transmission channels and increasing the resistance of the secondary battery, thereby affecting the dynamic performance of the secondary battery. Furthermore, as an interfacial film that compensates for losses, the nonaqueous electrolyte and active lithium ions inside the battery are continuously consumed, irreversibly affecting the capacity retention rate of the secondary battery.

[0056] Therefore, there is a need to provide a non-aqueous electrolyte with good overall performance.

[0057] After extensive research, the inventors of the present application have surprisingly discovered that when a non-aqueous electrolyte contains an appropriate amount of auxiliary lithium salt, the secondary battery can simultaneously achieve good cycle performance, storage performance, and dynamic performance. non-aqueous electrolyte

[0058] Specifically, a first aspect of the present invention provides a non-aqueous electrolyte solution containing an electrolyte salt and a non-aqueous solvent.

[0059] The electrolyte salt includes a first lithium salt, a second lithium salt, and a third lithium salt, wherein the first lithium salt has a structure represented by Formula 1, R1 represents a fluorine atom or a partially or fully fluorinated C1-C10 alkyl, and its mass content in the non-aqueous electrolyte is A1, calculated based on the total mass of the non-aqueous electrolyte; the second lithium salt has a structure represented by Formula 2, and R2 and R3 each independently represent at least one selected from the group consisting of a fluorine atom, a partially or fully fluorinated C1-C10 alkyl, a C2-C10 alkenyl, a C2-C10 alkynyl, a C6-C8 aryl, a C1-C10 alkoxy, a C2-C10 alkenyloxy, a C2-C10 alkynyloxy, and a C6-C8 aryloxy. The mass content of the third lithium salt in the non-aqueous electrolyte solution is A2, calculated based on the total mass of the non-aqueous electrolyte solution, and the third lithium salt is selected from lithium tetrafluoroborate, and the mass content of the third lithium salt in the non-aqueous electrolyte solution is A3, calculated based on the total mass of the non-aqueous electrolyte solution. [ka] [ka]

[0060] In the present application, the nonaqueous electrolyte solution satisfies the conditions that A1+A2+A3 is 1% or less, A1 / A2 is 0.016 to 40, and A1 / (A2+A3) is 0.006 to 13.5.

[0061] The inventors have conducted extensive research and found that, when the first, second, and third lithium salts are used as auxiliary lithium salts in a non-aqueous electrolyte, and their total content is controlled to 1% or less, and 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 are rationally adjusted so that A1 / A2 is 0.016 to 40 and A1 / (A2+A3) is 0.006 to 13.5, the resulting non-aqueous electrolyte can simultaneously exhibit high thermal stability, high ionic conductivity, and a wide electrochemical window. The non-aqueous electrolyte can also inactivate the aluminum foil current collector and form dense, stable, low-resistance, and highly conductive interfacial films on the surfaces of both the positive and negative electrode active materials, thereby enabling secondary batteries using the non-aqueous electrolyte of the present invention to simultaneously achieve good cycle performance, storage performance, and kinetic performance.

[0062] Although the mechanism is unclear, possible causes speculated by the inventors include the following:

[0063] First, rationally adjusting the content A1 of the first lithium salt and the content A2 of the second lithium salt so that the A1 / A2 ratio is between 0.016 and 40 helps form a dense, stable, and highly conductive interfacial film on the surface of the negative electrode active material. The first lithium salt contains a sulfonate anion and can be reduced to form a highly conductive compound such as Li2SO4, which is advantageous for improving the ion permeability of the negative electrode interfacial film. The molecular structure of the second lithium salt contains an oxalic acid group, and its reduction product further reacts with organic components such as (LiOCO2CH2)2 in the interfacial film to form a complex and stable oligomer, which is thoroughly coated on the surface of the negative electrode active material, preventing direct contact between the nonaqueous electrolyte and the negative electrode active material and reducing the embedding of the nonaqueous solvent in the negative electrode active material. If the A1 / A2 ratio is greater than 40, the negative electrode interfacial film cannot be sufficiently coated on the surface of the negative electrode active material, which increases the irreversible consumption of lithium ions and reduces the capacity retention rate of the secondary battery. If A1 / A2 is less than 0.016, the ion transmission characteristics of the negative electrode interfacial film are poor, the internal resistance of the secondary battery increases, and the dynamic performance deteriorates.

[0064] Second, rationally adjusting the content of the first lithium salt A1, the content of the second lithium salt A2, and the content of the third lithium salt A3 so that A1 / (A2+A3) is between 0.006 and 13.5 helps form a dense, stable interfacial film containing a small amount of LiF on the surface of the positive electrode active material, increasing the lithium ion transmission channels in the positive electrode interfacial film and reducing the lithium ion transport resistance. At the same time, irreversible changes in the positive electrode active material are suppressed, maintaining the structural stability of the positive electrode active material, and thereby improving the capacity of secondary batteries. Furthermore, the B atoms in the structure easily bond with the O atoms in the positive electrode active material, thereby reducing the charge transfer resistance of the positive electrode active material and the lithium ion diffusion resistance within the positive electrode active material bulk phase. When A1 / (A2+A3) is greater than 13.5, the second and third lithium salts cannot effectively compensate for the deterioration of the battery internal resistance caused by excess first lithium salt. This results in poor dynamic performance of the secondary battery, and at the same time, the positive electrode interfacial film cannot sufficiently cover the surface of the positive electrode active material, increasing the irreversible consumption of lithium ions and reducing the capacity retention rate of the secondary battery.If A1 / (A2+A3) is less than 0.006, the LiF content in the positive electrode interfacial film is too high, which increases the positive electrode interfacial resistance and affects the dynamic performance of the secondary battery.

[0065] Third, the first lithium salt can form an interfacial film not only on the negative electrode but also on the positive electrode, thereby improving the capacity and dynamic performance of the secondary battery. However, the fluorosulfonic acid group in the first lithium salt is prone to corroding the aluminum foil current collector, affecting the performance of the secondary battery, such as increasing battery polarization and irreversible capacity loss, and further affecting the safety performance of the secondary battery. This is mainly manifested in the following aspects: some solid insoluble corrosion products increase the internal resistance of the secondary battery; some soluble corrosion products contaminate and promote the decomposition of the non-aqueous electrolyte, increasing the self-discharge of the secondary battery; and the Al generated during the corrosion process 3+ The BO bond in the molecular structure of the second lithium salt is reduced to aluminum dendrites by diffusion. 3+The third lithium salt can be preferentially oxidized and decomposed to form a passivation film on the surface of the aluminum foil current collector, thereby effectively preventing corrosion of the aluminum foil current collector by the first lithium salt and reducing irreversible capacity loss in the secondary battery.

[0066] Therefore, the reason why secondary batteries using the nonaqueous electrolyte of the present invention simultaneously achieve excellent cycle performance, storage performance, and dynamic performance is due to the synergistic effect between the above components. The first lithium salt forms an interfacial film on both the positive and negative electrodes, and the synergistic effect between the second lithium salt, the third lithium salt, and the first lithium salt improves the ionic conductivity of the nonaqueous electrolyte, thereby compensating for the deficiency of the first lithium salt, which has a low dissociation degree and low ionic conductivity. The synergistic effect between the first lithium salt and the second lithium salt forms a dense, stable, low-resistance, and highly conductive interfacial film on the surface of the negative electrode active material. The synergistic effect between the first lithium salt, the second lithium salt, and the third lithium salt forms a dense, stable interfacial film on the surface of the positive electrode active material, which contains a small amount of LiF. This reduces interfacial side reactions between the nonaqueous electrolyte and the electrode, reducing irreversible consumption of active lithium ions, increasing the capacity of the secondary battery, and reducing gas generation. Furthermore, the interfacial films formed on the surfaces of the positive electrode active material and the negative electrode active material have low resistance and high conductivity, and the internal resistance of the secondary battery is reduced.

[0067] In some embodiments, A1 / A2 may 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 an appropriate range, it helps to fully utilize the synergistic effect between the first lithium salt and the second lithium salt, thereby forming a denser, more stable, and more ion-conductive interfacial film on the surface of the negative electrode active material.

[0068] In some embodiments, A1 / (A2+A3) is 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, 0.0 It may be 2 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 an appropriate range, it helps to fully exert the synergistic effect among the first lithium salt, the second lithium salt, and the third lithium salt, thereby making it possible to form a denser, more stable, and more ion-conductive interfacial film on the surface of the positive electrode active material.

[0069] The second lithium salt has a molecular structure containing one oxalic acid group, which means that its thermal stability is lower than that of the third lithium salt and it is oxidized to form carbon dioxide gas when heated. Therefore, if its content is high, it may reduce the thermal stability of the non-aqueous electrolyte and increase the amount of gas generated in the secondary battery. -Because the ionic radius of the second lithium salt is small, it is prone to association. Therefore, a high content of the third lithium salt may reduce the ionic conductivity of the non-aqueous electrolyte. Through extensive research, the inventors have found that by rationally adjusting the content A2 of the second lithium salt and the content A3 of the third lithium salt so that the ratio A3 / A2 is between 0.04 and 30, the non-aqueous electrolyte can simultaneously exhibit high thermal stability and high ionic conductivity. This not only forms low-resistance, highly conductive interfacial films on both the positive and negative electrodes, but also provides better protection for the aluminum foil current collector, thereby further improving the cycle performance, storage performance, and dynamic performance of the secondary battery. If the ratio A3 / A2 is greater than 30, the second lithium salt's effect of reducing the negative electrode interfacial resistance may be weak, and the third lithium salt may not be able to compensate for the deterioration of the dynamic performance of the secondary battery. If the ratio A3 / A2 is less than 0.04, the presence of too many second lithium salts may reduce the thermal stability of the non-aqueous electrolyte, resulting in reduced storage performance of the secondary battery.

[0070] In some embodiments, preferably, 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 A3 / A2 ratio may be 0.5 to 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 the appropriate range, it helps to fully exert the synergistic effect between the second lithium salt and the third lithium salt, thereby further improving the cycle performance, storage performance, and kinetic performance of the secondary battery.

[0071] The first lithium salt is likely to form an associated ion pair in the non-aqueous solvent, thereby reducing the ionic conductivity of the non-aqueous electrolyte. In some embodiments, A1 is 0.005% to 0.2%. Preferably, A1 is 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%.

[0072] The second lithium salt molecular structure contains one oxalic acid group, which oxidizes when heated to form carbon dioxide gas, reducing the thermal stability of the nonaqueous electrolyte. In some embodiments, A2 is 0.005% to 0.3%. Preferably, A2 is 0.01% to 0.3%, 0.01% to 0.26%, 0.01% to 0.22%, 0.01% to 0.2%, 0.01% to 0.18%, 0.01% to 0.16%, 0.01% to 0.14%, 0.01% to 0.12%, 0.01% to 0.1%, 0.02% to 0.3%, 0.02% to 0.26%, 0.02% to 0.22%, 0.02% to 0.2%, or 0.0 2% to 0.18%, 0.02% to 0.16%, 0.02% to 0.14%, 0.02% to 0.12%, 0.02% to 0.1%, 0.05% to 0.3%, 0.05% to 0.26%, 0.05% to 0.22%, 0.05% to 0.2%, 0.05% to 0.18%, 0.05% to 0.16%, 0.05% to 0.14%, 0.05% to 0.12%, or 0.05% to 0.1%.

[0073] In some embodiments, A3 is 0.01% to 0.5%. Preferably, A3 may be 0.01% to 0.45%, 0.01% to 0.4%, 0.01% to 0.35%, 0.01% to 0.3%, 0.01% to 0.25%, 0.01% to 0.2%, 0.01% to 0.15%, 0.01% to 0.1%, 0.02% to 0.45%, 0.02% to 0.4%, 0.02% to 0.35%, 0.02% to 0.3%, 0.02% to 0.25%, 0.02% to 0.2%, 0.02% to 0.15%, or 0.02% to 0.1%.

[0074] In some embodiments, R1 represents a fluorine atom, or a partially or fully fluorinated C1-C6 alkyl. Preferably, R1 represents a fluorine atom, or a partially or fully fluorinated methyl, ethyl, or propyl. Preferably, R1 represents a fluorine atom, trifluoromethyl, difluoromethyl, or monofluoromethyl.

[0075] For example, the first lithium salt includes at least one of the following compounds: [ka]

[0076] R2 and R3 each represent a fluorine atom or a fluorine-containing group. The presence of the fluorine atom or fluorine-containing group contributes to the formation of a thinner positive electrode interfacial film and / or a negative electrode interfacial film, thereby contributing to uniform lithium ion transport and effectively suppressing the formation of lithium dendrites. In some embodiments, R2 and R3 each represent a fluorine atom or at least one independently selected from the group consisting of partially or fully fluorinated C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, C6-C8 aryl, C1-C6 alkoxy, C2-C6 alkenyloxy, C2-C6 alkynyloxy, and C6-C8 aryloxy. Preferably, R2 and R3 each represent a fluorine atom or at least one independently selected from the group consisting of partially or fully fluorinated methyl, ethyl, propyl, phenyl, methoxy, ethoxy, propoxy, and phenoxy. Preferably, R2 and R3 each represent a fluorine atom.

[0077] For example, the second lithium salt includes at least one of the following compounds: [ka]

[0078] In some embodiments, the electrolyte salt further includes at least one of a fourth lithium salt and a fifth lithium salt, wherein the fourth lithium salt is lithium hexafluorophosphate, and its mass content in the non-aqueous electrolyte solution is A4, calculated based on the total mass of the non-aqueous electrolyte solution, and the fifth lithium salt is lithium bisfluorosulfonylimide, and its mass content in the non-aqueous electrolyte solution is A5, calculated based on the total mass of the non-aqueous electrolyte solution, and the non-aqueous electrolyte solution satisfies A4+A5 = 10% to 20%, preferably 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%.

[0079] The nonaqueous electrolyte of the present application uses lithium hexafluorophosphate and / or lithium bisfluorosulfonylimide as the primary lithium salt. Lithium hexafluorophosphate has high ionic conductivity and is resistant to corrosion of the aluminum foil current collector. As the primary lithium salt, it can improve the ionic conductivity and thermal stability of the entire nonaqueous electrolyte. The chemical formula of lithium bisfluorosulfonylimide is F2NO4S2Li. The N atom is bonded to two electron-withdrawing sulfonyl groups, which allows the charge on the N atom to be fully removed. Furthermore, lithium bisfluorosulfonylimide has a lower crystal lattice energy and is easily dissociated, thereby improving the ionic conductivity and reducing the viscosity of the nonaqueous electrolyte. Furthermore, lithium bisfluorosulfonylimide has high high-temperature resistance and is resistant to hydrolysis. It can form a thinner interfacial film on the surface of the negative electrode active material, which has lower impedance and higher thermal stability, thereby reducing side reactions between the negative electrode active material and the nonaqueous electrolyte.

[0080] In some embodiments, the non-aqueous electrolyte contains lithium hexafluorophosphate as the main lithium salt, i.e., A5 is 0% and A4 is 10% to 20%, preferably 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%.

[0081] In some embodiments, the non-aqueous electrolyte contains lithium bisfluorosulfonylimide as the main lithium salt, i.e., A4 is 0% and A5 is 10% to 20%, preferably 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%.

[0082] In some embodiments, the electrolyte salt may simultaneously contain a fourth lithium salt and a fifth lithium salt. Preferably, A4 / A5 is 0.2 to 3, more preferably 0.3 to 2, 0.4 to 1.8, or 0.5 to 1.5. This makes the nonaqueous electrolyte solution less susceptible to hydrolysis and simultaneously achieves higher thermal stability, and also helps form an interfacial film with lower impedance.

[0083] In some embodiments, the non-aqueous electrolyte satisfies the ratio (A4+A5) / (A1+A2+A3) of 10 to 200. Preferably, (A4+A5) / (A1+A2+A3) is 15 to 250, 20 to 120, 40 to 100, or 40 to 80. When the mass ratio of the main lithium salt to the auxiliary lithium salt is within an appropriate range, the non-aqueous electrolyte simultaneously exhibits high thermal stability, high ionic conductivity, and a wider electrochemical window, and the non-aqueous electrolyte can also inert the aluminum foil current collector and form a dense, stable, low-resistance, and highly conductive interfacial film on the surfaces of both the positive and negative electrode active materials.

[0084] In some embodiments, the non-aqueous electrolyte solution may further contain other electrolyte salts, such as at least one of lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium difluorophosphate (LiPOF), lithium difluorodisalophosphate (LiDFOP), and lithium tetrafluorooxalophosphate (LiTFOP). These other electrolyte salts may serve as auxiliary lithium salts and may further improve the interfacial properties of the positive electrode and / or negative electrode, or improve the ionic conductivity or thermal stability of the non-aqueous electrolyte solution. Preferably, the total mass content of these other electrolyte salts in the non-aqueous electrolyte solution is 1% or less, preferably 0.5% or less, calculated based on the total mass of the non-aqueous electrolyte solution.

[0085] In some embodiments, the non-aqueous solvent can include at least one of a first solvent, a second solvent, and a third solvent.

[0086] The first solvent is a cyclic carbonate compound, and may include, for example, at least one of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Preferably, the first solvent includes ethylene carbonate (EC).

[0087] The second solvent is a chain carbonate compound, and may include, for example, at least one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). Preferably, the second solvent may include at least one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC). Preferably, the second solvent includes ethyl methyl carbonate (EMC), diethyl carbonate (DEC), or a combination thereof.

[0088] In some embodiments, the non-aqueous solvent preferably includes at least a first solvent and a second solvent. If the content of the electrolyte salt is high, the viscosity of the non-aqueous electrolyte increases, the ionic conductivity decreases, and it is disadvantageous to form a dense, stable, and low-impedance interfacial film. The first solvent has a high dielectric constant, which can increase the conductivity of the non-aqueous electrolyte, and the second solvent has a low viscosity, which can decrease the viscosity of the non-aqueous electrolyte. Therefore, when the non-aqueous solvent includes both the first solvent and the second solvent, it helps the non-aqueous electrolyte to have appropriate viscosity and ionic conductivity, which is also advantageous for the transport of lithium ions.

[0089] In some embodiments, the non-aqueous solvent may further include a third solvent. The third solvent may be a carboxylic acid ester compound, such as at least one of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), and ethyl butyrate (EB). The third solvent has the advantages of low viscosity and high dielectric constant, and when applied to a non-aqueous electrolyte, it helps the non-aqueous electrolyte have appropriate viscosity and ionic conductivity, and further helps transport lithium ions.

[0090] In some embodiments, when all calculations are based on the total mass of the non-aqueous solvent, 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, and the non-aqueous solvent satisfies the following: B1 is 10% to 30%, B2 is 50% to 90%, and B3 is 0% to 20%.

[0091] The third solvent has low oxidation resistance and is prone to oxidative decomposition when stored in a highly charged state, so its content is not very high. In some embodiments, B3 is 0%. In some embodiments, B3 is 2% to 20%, preferably 5% to 10%.

[0092] In some embodiments, B1 / (B2+B3) is 0.1 to 0.45, preferably 0.2 to 0.3. When the non-aqueous solvent contains an appropriate amount of the first solvent, particularly an appropriate amount of ethylene carbonate, the radicals formed by decomposition of the second lithium salt can induce ring-opening and polymerization of ethylene carbonate, making the interfacial film formed on the surface of the negative electrode active material denser and smoother, thereby effectively suppressing dendrite growth.

[0093] The non-aqueous solvent of the present application may further include a solvent other than the first, second, and third solvents. For example, the other solvent may include a sulfone-based solvent such as tetramethylene sulfone (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0094] In some embodiments, the non-aqueous electrolyte further includes a first additive, which includes at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ester sulfate (DTD), and 1,3-propane sultone (PS). The mass content of the first additive in the non-aqueous electrolyte is C1, which is 0.05% to 2% based on the total mass of the non-aqueous electrolyte. Preferably, 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 further improves the interfacial properties of the positive electrode and / or negative electrode, thereby further improving at least one of the cycle performance, storage performance, and kinetic performance of the secondary battery.

[0095] In some embodiments, the non-aqueous electrolyte further comprises a first additive, the first additive comprising at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ester sulfate (DTD), and 1,3-propane sultone (PS), and the mass content of the first additive in the non-aqueous electrolyte is C1, calculated based on the total mass of the non-aqueous electrolyte. The first additive content C1, the lithium bisfluorosulfonylimide content A5, and the first solvent content B1 satisfy the following relationship: (C1+A5) / B1 is 0.3 to 0.8, preferably 0.3 to 0.6. The first additive forms a film on the surfaces of the positive and negative electrodes, which helps reduce persistent side reactions and thereby improves at least one of the cycle performance, storage performance, and kinetic performance of the secondary battery. However, a high content of the first additive increases the positive electrode interfacial resistance and / or the negative electrode interfacial resistance, affecting the power performance of the secondary battery. Lithium bisfluorosulfonylimide can improve the ionic conductivity and thermal stability of non-aqueous electrolytes and reduce the positive and / or negative electrode interfacial resistance. However, it also causes some corrosion of aluminum foil current collectors, and high concentrations of the first solvent can affect the cycle performance of secondary batteries. The first solvent has a high dielectric constant and contributes to the dissociation of lithium salts, thereby improving the ionic conductivity of non-aqueous electrolytes to a certain extent. However, high concentrations of the first solvent increase the viscosity of the non-aqueous electrolyte and affect its thermal stability, thereby affecting the storage performance of secondary batteries. After further research, the inventors of the present application found that controlling the (C1+A5) / B1 ratio between 0.3 and 0.8 effectively maximizes the synergistic effects of the components, effectively reducing the defects of each component when used alone, resulting in excellent cycle performance of secondary batteries and preventing deterioration in kinetic and power performance.

[0096] In some embodiments, the non-aqueous electrolyte further includes a second additive, the second additive including at least one of sulfamic acid and its salts. The molecular formula of sulfamic acid is HNOS, and the sulfamate salt includes at least one of ammonium salt, alkali metal salt, alkaline earth metal salt, and analogous alkaline earth metal salt. For example, the sulfamate salt may include at least one of ammonium sulfamate, lithium sulfamate, sodium sulfamate, and zinc sulfamate. Preferably, the second additive includes sulfamic acid, lithium sulfamate, or a combination thereof.

[0097] Sulfamic acid is highly acidic and is commonly used to prepare lithium bis(fluorosulfonylimide). However, its application in non-aqueous electrolytes has not been previously reported. Through further research, the present inventors surprisingly found that adding an appropriate amount of sulfamic acid and its salts to a non-aqueous electrolyte containing the auxiliary lithium salts (first, second, and third lithium salts) can improve the cycle and dynamic performance of secondary batteries. While the mechanism is unclear, the inventors speculate that the possible causes are as follows: Sulfamic acid and its salts improve the ionic conductivity and reduce the viscosity of the non-aqueous electrolyte, and at the same time, they can slowly dissolve metals, such as lithium dendrites, to a certain extent. This can reduce the amount of elemental lithium, aluminum, and transition metals, which have been reduced and deposited on the surface of the negative electrode active material, thereby improving the cycle and dynamic performance of secondary batteries.

[0098] Sulfamic acid and its salts are easily soluble in water and highly acidic, and when present in high amounts, they corrode the positive electrode active material and destroy the stability of the positive electrode interfacial film and / or the negative electrode interfacial 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%, preferably 0.005% to 0.05%, calculated based on the total mass of the non-aqueous electrolyte.

[0099] In some embodiments, the non-aqueous electrolyte may further include the first additive and the second additive simultaneously.

[0100] The nonaqueous electrolyte of the present application can be produced according to a general method in this field. For example, the additive, the nonaqueous solvent, the electrolyte salt, etc. can be uniformly mixed to obtain the nonaqueous electrolyte. The order of addition of each material is not particularly limited. For example, the additive, the electrolyte salt, etc. can be added to the nonaqueous solvent and mixed uniformly to obtain the nonaqueous electrolyte.

[0101] In the present application, the components and their contents in the non-aqueous electrolyte solution can be measured by methods known in the art, such as gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), and nuclear magnetic resonance spectroscopy (NMR).

[0102] It should be noted that in the case of the nonaqueous electrolyte test of the present application, a freshly produced nonaqueous electrolyte can be directly obtained, or the nonaqueous electrolyte can be obtained from a secondary battery. One exemplary method for obtaining a nonaqueous electrolyte from a secondary battery includes the following steps: the secondary battery is discharged to a discharge cut-off voltage (for safety reasons, the battery is generally fully charged), and then centrifuged. The liquid obtained after an appropriate amount of centrifugation is the nonaqueous electrolyte. The nonaqueous electrolyte can also be obtained directly from the filling port of the secondary battery. secondary battery

[0103] A second aspect of the present application provides a secondary battery, the secondary battery including an electrode assembly, a non-aqueous electrolyte, and an outer casing, wherein the non-aqueous electrolyte is the non-aqueous electrolyte of the first aspect of the present application, thereby enabling the secondary battery of the present application to simultaneously achieve good cycle performance, storage performance, and kinetic performance.

[0104] The secondary battery of the present application may be a lithium secondary battery, and in particular, may be a lithium ion secondary battery.

[0105] An electrode assembly generally includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is disposed between the positive electrode sheet and the negative electrode sheet and serves mainly to prevent short circuits between the positive electrode and the negative electrode, while also allowing lithium ions to pass through.

[0106] The secondary battery of the present application uses the nonaqueous electrolyte of the first aspect of the present application, which helps to form dense, stable, low-resistance, and highly conductive interfacial films on the surfaces of both the positive electrode active material and the negative electrode active material, thereby balancing the charge transfer resistance of the positive electrode and the negative electrode, reducing the difference between them, and improving the performance of the secondary battery.

[0107] 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, and preferably 1.25 to 2, 1.3 to 2, 1.35 to 2, 1.4 to 2, 1.25 to 1.8, 1.3 to 1.8, 1.35 to 1.8, 1.4 to 1.8, 1.25 to 1.6, 1.3 to 1.6, 1.35 to 1.6, or 1.4 to 1.6. This reduces the difference in charge transfer resistance between the positive electrode and the negative electrode, further improving the performance of the secondary battery.

[0108] The charge transfer resistance of the positive electrode sheet is measured by the following test method. The positive electrode sheet is assembled into a symmetrical battery, and its electrochemical impedance spectrum is measured using the electrochemical AC impedance method of an electrochemical workstation to create a Nyquist diagram. The obtained Nyquist diagram is analyzed using an equivalent circuit curve approximation method, and the semicircular diameter is taken as the charge transfer resistance Rct1 of the positive electrode sheet. The test voltage may be 10 mV, and the test frequency may be 0.1 Hz to 100 kHz. The positive electrode sheet can be obtained by disassembling a secondary battery, and for safety reasons, the secondary battery is generally fully charged.

[0109] The charge transfer resistance of the negative electrode sheet is measured by the following test method. The negative electrode sheet is assembled into a symmetrical battery, and its electrochemical impedance spectrum is measured using the electrochemical AC impedance method of an electrochemical workstation to create a Nyquist diagram. The obtained Nyquist diagram is analyzed using an equivalent circuit curve approximation method, and the semicircular diameter is taken as the charge transfer resistance Rct2 of the negative electrode sheet. The test voltage may be 10 mV, and the test frequency may be 0.1 Hz to 100 kHz. The negative electrode sheet can be obtained by disassembling a secondary battery, and for safety reasons, the secondary battery is generally fully charged.

[0110] The nonaqueous electrolyte includes a first electrolyte that permeates the electrode assembly and a second electrolyte that is located between the electrode assembly and the exterior body. The first electrolyte is obtained by the following test method: After discharging the secondary battery to an end-of-discharge voltage, the electrode assembly is disassembled and centrifuged, and the liquid obtained by the subsequent centrifugation is the first electrolyte. The second electrolyte is a free electrolyte that can be obtained by withdrawing it from a filling port of the secondary battery.

[0111] When calculated based on the total mass of the first electrolyte solution, 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 solution is X1, and when calculated based on the total mass of the second electrolyte solution, 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 solution is X2, where 0.5≦X1 / X2<1. [Positive electrode sheet]

[0112] In some embodiments, the positive electrode sheet 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 opposing surfaces in its thickness direction, and the positive electrode film layer is provided on either one or both of the two opposing surfaces of the positive electrode current collector.

[0113] The positive electrode film layer includes a positive electrode active material, which may be a positive electrode active material known in the art for use in secondary batteries. For example, the positive electrode active material may include at least one of a lithium transition metal oxide, a lithium-containing phosphate having an olivine structure, and a modified compound thereof. Examples of lithium transition metal oxides include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and a modified compound thereof. Examples of lithium-containing phosphates having an olivine structure include at least one of lithium iron phosphate, a lithium iron phosphate-carbon composite, lithium manganese phosphate, a lithium manganese phosphate-carbon composite, lithium manganese iron phosphate, a lithium manganese iron phosphate-carbon composite, and a modified compound thereof. The present application is not limited to these materials, and other conventional materials used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used singly or in combination of two or more.

[0114] In some embodiments, the positive electrode active material has the molecular formula Li a Ni b Co c Mn d Al e M f O g A h wherein M represents a doping cation at the transition metal site, A represents a doping anion at the oxygen site, and 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, and b+c+d+e+f=1, g+h=2.

[0115] The molecular formula is Li a Ni b Co c Mn d Al e M f Og A h The layered material of can be modified by M cation doping, A anion doping or simultaneous doping of M cation and A anion. The layered material obtained after doping has a more stable crystal structure and can further improve the electrochemical performance of the secondary battery, such as cycle performance, kinetic performance, etc.

[0116] 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.

[0117] In some embodiments, A is selected from at least one of F, N, P, and S. Preferably, A is selected from F. After the F doping modification, Li a Ni b Co c Mn d Al e M f O g A h The crystal structure of has a more stable crystal structure, so that the secondary battery can have better cycle performance and kinetic performance.

[0118] The values of a, b, c, d, e, f, g, h satisfy the following conditions to maintain the electrical neutrality of Li a Ni b Co c Mn d Al[[ID=4]] e M f O g A h of.

[0119] In some embodiments, 0 < b < 0.98. Preferably, 0.50 ≤ b < 0.98, 0.55 ≤ b < 0.98, 0.60 ≤ b < 0.98, 0.65 ≤ b < 0.98, 0.70 ≤ b < 0.98, 0.75 ≤ b < 0.98 or 0.80 ≤ b < 0.98.

[0120] In some embodiments, c = 0.

[0121] In some embodiments, 0 < c ≤ 0.20. Preferably, 0 < c ≤ 0.15, 0 < c ≤ 0.10, 0 < c ≤ 0.09, 0 < c ≤ 0.08, 0 < c ≤ 0.07, 0 < c ≤ 0.06, 0 < c ≤ 0.05, 0 < c ≤ 0.04, 0 < c ≤ 0.03, 0 < c ≤ 0.02 or 0 < c ≤ 0.01. Cobalt has a low content in the earth's crust, is difficult to extract and is expensive. Therefore, low cobalt or cobalt-free is an inevitable development trend of the cathode active material. However, cobalt greatly contributes to the lithium ion diffusion rate of the cathode active material, and low cobalt or cobalt-free reduces the lithium ion diffusion rate of the cathode active material, affecting the cycle performance of the secondary battery. Researchers are working hard to improve the lithium ion diffusion rate of low cobalt or cobalt-free cathode active materials, but there is still no good solution at present.

[0122] During the research process, the inventors of the present application unexpectedly found that when the content A2 of the second lithium salt and the content A3 of the third lithium salt are reasonably adjusted to satisfy 0.04 ≤ A3 / A2 ≤ 30, a low-resistance interfacial film can be formed on the surface of the positive electrode active material. The B atoms in the structures of the second lithium salt and the third lithium salt are more likely to bond with the O atoms in the positive electrode active material, reducing the charge transfer resistance of the positive electrode active material, thereby reducing the diffusion resistance of lithium ions in the bulk phase of the positive electrode active material. Therefore, when the non-aqueous electrolyte contains appropriate amounts of the second lithium salt and the third lithium salt, the positive electrode active material with low cobalt or no cobalt can have a significantly improved lithium ion diffusion rate. Lithium ions in the bulk phase of the positive electrode active material with low cobalt or no cobalt can be timely replenished to the surface, preventing excessive lithium release from the surface of the positive electrode active material with low cobalt or no cobalt, thereby stabilizing the crystal structure of the positive electrode active material with low cobalt or no cobalt. Since the crystal structure of the low-cobalt or cobalt-free positive electrode active material is more stable, the probability of problems such as instability of the structural, chemical, or electrochemical properties of the positive electrode active material due to delithiation occurring on the surface of the low-cobalt or cobalt-free positive electrode active material can be significantly reduced. For example, the problem of increased irreversible strain and lattice defects in the positive electrode active material can be solved.

[0123] In some embodiments, d = 0 and 0 < e < 0.50. Preferably, d = 0 and 0 < e ≤ 0.45, d = 0 and 0 < e ≤ 0.40, d = 0 and 0 < e ≤ 0.35, d = 0 and 0 < e ≤ 0.30, d = 0 and 0 < e ≤ 0.25, d = 0 and 0 < e ≤ 0.20, d = 0 and 0 < e ≤ 0.15, or d = 0 and 0 < e ≤ 0.10.

[0124] In some embodiments, e = 0 and 0 < d < 0.50. Preferably, e = 0 and 0 < d ≤ 0.45, e = 0 and 0 < d ≤ 0.40, e = 0 and 0 < d ≤ 0.35, e = 0 and 0 < d ≤ 0.30, e = 0 and 0 < d ≤ 0.25, e = 0 and 0 < d ≤ 0.20, e = 0 and 0 < d ≤ 0.15 or e = 0 and 0 < d ≤ 0.10.

[0125] In some embodiments, 0 < d < 0.50 and 0 < e < 0.50. Preferably, 0 < d ≤ 0.30 and 0 < e ≤ 0.10.

[0126] In some embodiments, g = 2 and h = 0.

[0127] In some embodiments, g = 0 and h = 2.

[0128] In some embodiments, 0 < g < 2, 0 < h < 2, and g + h = 2.

[0129] As an example, the layered material of the formula Li a Ni b Co c Mn d Al e M f O g A h is LiNi 0.8 Co 0.1 Mn 0.1 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 Mn0.3 O2, LiNi 0.63 Co 0.07 Mn 0.3 O2, LiNi 0.61 Co 0.09 Mn 0.3 The present invention is not limited to the above.

[0130] Li a Ni b Co c Mn d Al e M f O g A h can be produced according to common methods in the art. An exemplary production method is as follows: It is obtained by mixing a lithium source, a nickel source, a cobalt source, a manganese source, an aluminum source, an M element precursor, and an A element precursor, followed by sintering. The sintering atmosphere may be an oxygen-containing atmosphere, such as an air atmosphere or an oxygen atmosphere. The O2 concentration of the sintering atmosphere is, for example, 70% to 100%. The sintering temperature and sintering time can be adjusted according to the actual situation.

[0131] For example, the lithium source may include, but is not limited to, at least one of lithium oxide (LiO), lithium phosphate (LiPO), lithium dihydrogen phosphate (LiHPO), lithium acetate (CHCOOLi), lithium hydroxide (LiOH), lithium carbonate (LiCO), and lithium nitrate (LiNO). For example, the nickel source may include, but is not limited to, at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. For example, the cobalt source may include, but is not limited to, at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. For example, the manganese source may include, but is not limited to, at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. For example, the aluminum source may include, but is not limited to, at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate. By way of example, the M element precursor may include, but is not limited to, at least one of an M element oxide, a nitrate compound, a carbonate compound, a hydroxide compound, and an acetate compound. By way of example, the A element precursor may include, 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 hydrogen sulfate, ammonium hydrogen sulfite, ammonium sulfite, ammonium hydrogen sulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur.

[0132] In some embodiments, the molecular formula is Li when calculated based on the total mass of the positive electrode layer. a Ni b Co c Mn d Al e M f O g A h The mass percentage of the layered material is 80% to 99%. For example, the molecular formula is Li aNi b Co c Mn d Al e M f O g A h The mass percentage of the layered material may be any of the following: 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more. Preferably, the molecular formula of the layered material is Li. a Ni b Co c Mn d Al e M f O g A h The mass percentage of the layered material is 85% to 99%, 90% to 99%, 95% to 99%, 80% to 98%, 85% to 98%, 90% to 98%, 95% to 98%, 80% to 97%, 85% to 97%, 90% to 97%, or 95% to 97%.

[0133] In some embodiments, the positive electrode film layer may preferably include a positive electrode conductive agent. The present application does not particularly limit the type of the positive electrode conductive agent, and as an example, the positive electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent is 5% or less, calculated based on the total mass of the positive electrode film layer.

[0134] In some embodiments, the positive electrode film layer may preferably include a positive electrode binder. The present application does not particularly limit the type of the positive electrode binder, and as an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin. In some embodiments, the mass percentage of the positive electrode binder is 5% or less, calculated based on the total mass of the positive electrode film layer.

[0135] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. An example of the metal foil is aluminum foil. The composite current collector may include a polymeric layer and a metal layer formed on at least one surface of the polymeric layer. For example, the metal layer may be selected from at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. For example, the polymeric layer may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0136] The positive electrode film layer is typically formed by applying a positive electrode slurry to a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP). [Negative electrode sheet]

[0137] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces facing each other in a thickness direction thereof, and the negative electrode film layer is provided on one or both of the two facing surfaces of the negative electrode current collector.

[0138] The negative electrode active material may be a negative electrode active material known in the art for use in secondary batteries. For example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy material. The present application is not limited to these materials, and other known materials used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination.

[0139] In some embodiments, the negative electrode film layer may preferably include a negative electrode conductive agent. The present application does not particularly limit the type of the negative electrode conductive agent, and for example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent is 5% or less, calculated based on the total mass of the negative electrode film layer.

[0140] In some embodiments, the negative electrode film layer may preferably include a negative electrode binder. The present application does not particularly limit the type of the negative electrode binder, and as an example, the negative electrode binder may include at least one of styrene butadiene rubber (SBR), water-soluble unsaturated resin (SR-1B), water-soluble 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 of the negative electrode binder is 5% or less, calculated based on the total mass of the negative electrode film layer.

[0141] In some embodiments, the negative electrode membrane layer may preferably contain other additives. For example, the other additives may include a thickener, such as carboxymethylcellulose sodium (CMC-Na), a PTC thermistor material, etc. In some embodiments, the mass percentage of the other additives is 2% or less, calculated based on the total mass of the negative electrode membrane layer.

[0142] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. An example of the metal foil is copper foil. The composite current collector may include a polymeric material layer and a metal material layer formed on at least one surface of the polymeric material layer. For example, the metal material may be selected from at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. For example, the polymeric material layer may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0143] The negative electrode film layer is generally formed by applying a negative electrode slurry to a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water. [Separator]

[0144] The separator is disposed between the positive electrode sheet and the negative electrode sheet and serves to prevent short circuits between the positive electrode and the negative electrode while allowing lithium ions to pass through. The present application does not particularly limit the type of separator, and any known porous separator having good chemical and mechanical stability may be selected.

[0145] In some embodiments, the separator may be made of at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0146] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be wound or stacked to form an electrode assembly.

[0147] In some embodiments, the secondary battery may include an exterior body that can be used to seal the electrode assembly and the non-aqueous electrolyte.

[0148] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0149] The present application does not particularly limit the shape of the secondary battery, which may be cylindrical, rectangular, or any other shape. Figure 1 shows a secondary battery 5 having a rectangular structure as an example.

[0150] In some embodiments, as shown in FIG. 2 , the exterior body may include a case 51 and a cover plate 53. The case 51 includes a bottom plate and side plates connected to the bottom plate, which together form a housing cavity. The case 51 has an opening communicating with the housing cavity, and the cover plate 53 is used to cover the opening, thereby sealing the housing cavity. The positive electrode sheet, the negative electrode sheet, and the separator are wound or stacked to form an electrode assembly 52. ​​The electrode assembly 52 is sealed in the housing cavity. A non-aqueous electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more and can be adjusted according to needs.

[0151] Methods for manufacturing the secondary battery of the present application are well known. In some embodiments, a secondary battery can be formed by assembling a positive electrode sheet, a separator, a negative electrode sheet, and a non-aqueous electrolyte. For example, a positive electrode sheet, a separator, and a negative electrode sheet are wound or stacked to form an electrode assembly. The electrode assembly is placed in a housing and dried. After that, a non-aqueous electrolyte is injected. The secondary battery is then obtained through processes such as vacuum sealing, standing, chemical formation, and shaping. In some embodiments, the method for manufacturing the secondary battery further includes a second liquid injection process performed after the chemical formation process, in which the contents of the first lithium salt, the second lithium salt, the third lithium salt, the first additive, and the second additive in the non-aqueous electrolyte injected the second time are lower than those in the non-aqueous electrolyte injected the first time. Increasing the number of liquid injection processes can help reduce costs and simultaneously improve the performance of the secondary battery. This is because the stability of some components in the auxiliary lithium salt and additives themselves is low, and when only a single liquid injection process is used, the stability of the nonaqueous electrolyte is easily reduced. However, the secondary battery of the present application uses a double liquid injection process, and the nonaqueous electrolyte injected the second time contains less auxiliary lithium salt and additives, thereby improving the stability of the nonaqueous 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 nonaqueous electrolyte is the sum of the masses of the nonaqueous electrolyte injected the first time and the nonaqueous electrolyte injected the second time.

[0152] In some embodiments of the present application, the secondary battery of the present application can be assembled into a battery module, and the number of secondary batteries included in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0153] Fig. 3 is a schematic diagram of an example battery module 4. As shown in Fig. 3, in the battery module 4, a plurality of secondary batteries 5 may be arranged in order along the length of the battery module 4. Of course, they may be arranged in any other manner. The plurality of secondary batteries 5 may further be fixed by fasteners.

[0154] Preferably, the battery module 4 further includes a housing having an accommodating space, and the plurality of secondary batteries 5 are accommodated in the accommodating space.

[0155] In some embodiments, the battery modules can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0156] 4 and 5 are schematic diagrams of an example battery pack 1. As shown in FIGS. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper housing 2 and a lower housing 3, covers the upper housing 2 and the lower housing 3, and is used to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 may be disposed in any desired position within the battery box. Electrical equipment

[0157]

[0010] Embodiments of the present application further provide an electric device, the electric device including at least one of the secondary battery, battery module, or battery pack of the present application. The secondary battery, battery module, or battery pack may be used as a power source for the electric device or as an energy storage unit for the electric device. The electric device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0158] The electric device can select a secondary battery, a battery module or a battery pack according to its usage needs.

[0159] 6 is a schematic diagram of an example electric device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, in which a battery pack or battery module can be used to meet the high power and high energy density demands of the electric device.

[0160] Other examples of electrical devices include mobile phones, tablet computers, notebook computers, etc. These electrical devices are generally required to be thin and can use secondary batteries as their power source. Example

[0161] The following examples will more specifically illustrate the contents of the present disclosure, and these examples are merely used for illustrative purposes, and it will be apparent to those skilled in the art that various modifications and variations can be made within the scope of the contents of the present disclosure. Unless otherwise specified, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples can be purchased or synthesized according to conventional methods and can be used directly without further treatment, and all equipment used in the examples can be purchased.

[0162] The secondary batteries of Examples 1 to 51 and Comparative Examples 1 to 10 were all manufactured by the following method.

[0163] Positive electrode sheet manufacturing

[0164] Positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O2, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.4:1.1 with an appropriate amount of NMP solvent and stirred thoroughly to form a uniform positive electrode slurry. The positive electrode slurry is then evenly applied to the surface of the positive electrode current collector aluminum foil, dried, and cold pressed to obtain a positive electrode sheet.

[0165] Manufacture of negative electrode sheets

[0166] The negative electrode active material is graphite, the binder is styrene butadiene rubber (SBR), the thickener is sodium carboxymethyl cellulose (CMC-Na), and the conductive agent is carbon black (Super P). Mix the mixture in a weight ratio of 96.2:1.8:1.2:0.8 with an appropriate amount of deionized water as the solvent and stir thoroughly to form a uniform negative electrode slurry. The negative electrode slurry is then evenly applied to the surface of the negative electrode current collector copper foil, dried, and cold-pressed to obtain a negative electrode sheet.

[0167] Separator

[0168] A porous polyethylene (PE) film is used as the separator.

[0169] Non-aqueous electrolyte production

[0170] The lithium salt and additives are added to the non-aqueous solvent and mixed uniformly to obtain a non-aqueous electrolyte. The composition and content of each component are shown in Tables 1 and 3, respectively. In Tables 1 and 3, the contents of the first lithium salt, second lithium salt, third lithium salt, fourth lithium salt, fifth lithium salt, first additive, and second additive are all calculated based on the total weight of the non-aqueous electrolyte, and the contents of the first solvent, second solvent, and third solvent are all calculated based on the total weight of the non-aqueous solvent. " / " indicates that the corresponding component is not added.

[0171] Secondary battery manufacturing

[0172] The positive electrode sheet, separator, and negative electrode sheet are stacked in this order and wound to obtain an electrode assembly, which is then placed in an outer casing, to which the non-aqueous electrolyte solution is added, and after undergoing steps such as sealing, standing, chemical conversion, and aging, a secondary battery is obtained.

[0173] Testing section

[0174] (1) Room temperature cycle performance test of secondary batteries

[0175] At 25°C, the secondary battery was charged to 4.3V at a constant current of 1C, and then continued to charge at a constant voltage until the current reached 0.05C. At this point, the secondary battery was fully charged. The charge capacity at this point was recorded and this was the charge capacity of the first loop. After leaving the secondary battery stationary for 5 minutes, it was discharged to 2.8V at a constant current of 1C. This constitutes one cycle of charge / discharge. The discharge capacity at this point was recorded and this was the discharge capacity of the first loop. The secondary battery was subjected to a cycle charge / discharge test according to the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) after 600 cycles of the secondary battery at 25°C = discharge capacity after 600 cycles / discharge capacity of the first loop × 100%.

[0176] (2) High-temperature cycle performance test of secondary batteries

[0177] At 45°C, the secondary battery was charged to 4.3V at a constant current of 1C, and then continued to charge at a constant voltage until the current reached 0.05C. At this point, the secondary battery was fully charged. The charge capacity at this point was recorded and this was the charge capacity of the first loop. After leaving the secondary battery stationary for 5 minutes, it was discharged to 2.8V at a constant current of 1C. This constitutes one cycle of charge / discharge. The discharge capacity at this point was recorded and this was the discharge capacity of the first loop. The secondary battery was subjected to a cycle charge / discharge test according to the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) after 600 cycles of the secondary battery at 45°C = discharge capacity after 600 cycles / discharge capacity of the first loop × 100%.

[0178] (3) High-temperature storage performance test of secondary batteries

[0179] At 60°C, charge the secondary battery at a constant current of 1C up to 4.3V, then continue charging at a constant voltage until the current reaches 0.05C. At this point, measure the volume of the secondary battery using the drainage method and mark it as V0. Place the secondary battery in an incubator at 60°C and store it for 30 days, then remove it and measure the volume of the secondary battery using the drainage method and mark it as V1. The volume expansion rate (%) of the secondary battery after storing it at 60°C for 30 days = [(V1 - V0) / V0] x 100%.

[0180] (4) Initial DC internal resistance test for secondary batteries

[0181] At 25°C, charge the secondary battery at a constant current of 1C to 4.3V, then continue charging at a constant voltage until the current reaches 0.05C, at which point the secondary battery is fully charged. Discharge the secondary battery at a constant current of 0.5C and adjust the secondary battery to 50% SOC. The secondary battery's voltage at this point is recorded as U1. Discharge the secondary battery at a constant current of 4C I1 for 30 seconds, using a 0.1-second measurement. The voltage at the end of discharge is recorded as U2. The discharge DC internal resistance of the secondary battery at 50% SOC refers to the initial DC internal resistance of the secondary battery, and the initial DC internal resistance of the secondary battery (mΩ) is calculated as (U1 - U2) / I1.

[0182] (5) Charge transfer resistance test of positive electrode sheet

[0183] After fully charging the secondary battery, the positive electrode sheet was disassembled and reassembled into a symmetrical battery. The nonaqueous electrolyte was then injected and tested using the electrochemical AC impedance method on a Solartron 1470E CellTest multi-channel electrochemical workstation to generate a Nyquist diagram. The Nyquist diagram obtained was analyzed using the equivalent circuit curve fitting method with Zview software, and the semicircular diameter was taken as the charge transfer resistance (Rct1) of the positive electrode sheet. The test voltage was 10 mV and the test frequency was 0.1 Hz to 100 kHz.

[0184] (6) Charge transfer resistance test of negative electrode sheet

[0185] After fully charging the secondary battery, the negative electrode sheet was disassembled and reassembled into a symmetrical battery. The nonaqueous electrolyte was then added and tested using the electrochemical AC impedance method on a Solartron 1470E CellTest multi-channel electrochemical workstation to generate a Nyquist diagram. The Nyquist diagram was analyzed using the equivalent circuit curve fitting method with Zview software, and the semicircular diameter was taken as the charge transfer resistance (Rct2) of the negative electrode sheet. The test voltage was 10 mV and the test frequency was 0.1 Hz to 100 kHz.

[0186] To ensure the reliability of the test results, each test above should be carried out using at least three parallel samples, and the average value should be used as the test result.

[0187] Table 1 shows the manufacturing parameters of the nonaqueous electrolytes of Examples 1 to 35 and Comparative Examples 1 to 10, and Table 2 shows the test results of Examples 1 to 35 and Comparative Examples 1 to 10 according to the above performance test method.

[0188] Table 3 shows the manufacturing parameters for the non-aqueous electrolytes of Examples 36 to 51, and Table 4 shows the test results for Examples 36 to 51 according to the above performance test method. [Table 1] JPEG2025128181000011.jpg248141 [Table 2] JPEG2025128181000013.jpg248133 [Table 3] [Table 4]

[0189] As can be seen from the test results of Examples 1 to 35, when the first lithium salt, second lithium salt, and third lithium salt of the present invention are used as auxiliary lithium salts in a nonaqueous electrolyte solution to control their total content to 1% or less, and 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 the following conditions: A1 / A2 is 0.016 to 40, and A1 / (A2+A3) is 0.006 to 13.5, the secondary battery can simultaneously achieve a high capacity retention rate, a low volume expansion rate, and a low internal resistance.

[0190] In Comparative Examples 1 to 9, the nonaqueous electrolyte did not use the auxiliary lithium salt of the present invention or only used a portion of the auxiliary lithium salt of the present invention, and the resulting secondary batteries had low capacity retention, high volume expansion coefficients, and high internal resistance. In Comparative Example 10, LiBOB was used as the auxiliary lithium salt, and the resulting secondary battery had a certain improvement in volume expansion coefficient, but still had low capacity retention and high internal resistance.

[0191] As can be seen from the test results of Examples 36 to 51, the use of the first additive and / or the second additive in the non-aqueous electrolyte helps to improve at least one of the cycle performance, storage performance, and dynamic performance of the secondary battery.

[0192] As can be seen from the test results of Examples 37 to 43, when the nonaqueous electrolyte solution simultaneously contains the fourth lithium salt and the fifth lithium salt and the mass ratio A4 / A5 of the two is between 0.2 and 3, preferably between 0.5 and 1.5, it helps to further improve the overall performance of the secondary battery.

[0193] Anything that has substantially the same configuration as the technical idea and provides similar effects within the scope of the technical solution of the present application is included in the technical scope of the present application. In addition, various modifications that a person skilled in the art can make to the embodiments and other forms constructed by combining some of the components of the embodiments are also included in the scope of the present application, as long as they do not deviate from the spirit of the present application.

Claims

1. A secondary battery including an electrode assembly, a non-aqueous electrolyte, and an outer casing, the non-aqueous electrolyte solution contains an electrolyte salt and a non-aqueous solvent, the electrolyte salt includes a first lithium salt, a second lithium salt, and a third lithium salt; The first lithium salt has a structure represented by Formula 1, wherein R １ represents a fluorine atom or a partially or fully fluorinated C1-C10 alkyl, and its mass content in the non-aqueous electrolyte solution is A1 when calculated based on the total mass of the non-aqueous electrolyte solution; The second lithium salt has a structure represented by Formula 2, wherein R ２ and R ３ each independently represents at least one selected from the group consisting of a fluorine atom, or a 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 the mass content thereof in the non-aqueous electrolyte solution is A2 when calculated based on the total mass of the non-aqueous electrolyte solution; the third lithium salt is selected from lithium tetrafluoroborate, and its mass content in the non-aqueous electrolyte solution is A3, calculated based on the total mass of the non-aqueous electrolyte solution; The nonaqueous electrolyte solution is (1) A1 is 0.005% to 0.2%; (2) A2 is 0.005% to 0.3%; (3) A3 is a secondary battery that satisfies the condition of 0.01% to 0.5%. 【Chemical 1】 【Chemistry 2】

2. A1 / A2 is 0.03 to 10, and / or A1 / (A2+A3) is 0.02 to 3.5; The secondary battery according to claim 1 .

3. The nonaqueous electrolyte solution further satisfies A3 / A2 of 0.04 to 30. The secondary battery according to claim 1 .

4. The nonaqueous electrolyte solution satisfies the following conditions: A1 + A2 + A3 is 1% or less; A1 / A2 is 0.016 to 40; and A1 / (A2+A3) is 0.006 to 13.

5. The secondary battery according to any one of claims 1 to 3.

5. The first lithium salt includes at least one of the following compounds: 【Chemistry 3】 and / or The secondary battery according to claim 1 , wherein the second lithium salt comprises at least one of the following compounds: 【Chemistry 4】

6. the electrolyte salt further includes at least one of a fourth lithium salt and a fifth lithium salt; the fourth lithium salt is lithium hexafluorophosphate, and its mass content in the non-aqueous electrolyte solution is A4, calculated based on the total mass of the non-aqueous electrolyte solution; the fifth lithium salt is lithium bisfluorosulfonylimide, and its mass content in the non-aqueous electrolyte solution is A5, calculated based on the total mass of the non-aqueous electrolyte solution; The nonaqueous electrolyte satisfies that A4+A5 is 10% to 20%. The secondary battery according to claim 1 .

7. (A4+A5) / (A1+A2+A3) is 10 to 200. The secondary battery according to claim 6.

8. the non-aqueous solvent includes a first solvent, a second solvent, and a third solvent; the first solvent includes at least one of ethylene carbonate, propylene carbonate, and butylene carbonate, and the mass content of the first solvent in the non-aqueous solvent is B1, calculated based on the total mass of the non-aqueous solvent; the second solvent includes at least one of ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate, and the mass content of the second solvent in the non-aqueous solvent is B2, calculated based on the total mass of the non-aqueous solvent; the third solvent includes at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate, and the mass content of the third solvent in the non-aqueous solvent is B3, calculated based on the total mass of the non-aqueous solvent; The nonaqueous electrolyte solution satisfies the following: B1 is 10% to 30%, B2 is 50% to 90%, and B3 is 0% to 20%. The secondary battery according to claim 1 .

9. The non-aqueous electrolyte further includes a first additive, the first additive including at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, and 1,3-propane sultone, and the mass content of the first additive in the non-aqueous electrolyte is C1, which is 0.05% to 2%, calculated based on the total mass of the non-aqueous electrolyte. The secondary battery according to claim 1 .

10. The nonaqueous electrolyte solution further satisfies (C1+A5) / B1 is 0.3 to 0.

8. The secondary battery according to claim 9.

11. The non-aqueous electrolyte further includes a second additive, the second additive including at least one of sulfamic acid and a salt thereof, and the mass content of the second additive in the non-aqueous electrolyte is C2, calculated based on the total mass of the non-aqueous electrolyte, and C2 is 0.005% to 0.1%. The secondary battery according to claim 1 .

12. the electrode assembly includes a positive electrode sheet and a negative electrode sheet, the positive electrode sheet has a charge transfer resistance Rct1, the negative electrode sheet has a charge transfer resistance Rct2, and Rct1 / Rct2 is 0.5 to 2; The charge transfer resistance of the positive electrode sheet is obtained by a test method in which the positive electrode sheet is assembled into a symmetrical battery, an electrochemical impedance spectrum thereof is measured using an electrochemical AC impedance method on an electrochemical workstation, a Nyquist diagram is created, the Nyquist diagram obtained is analyzed using an equivalent circuit curve approximation method, and the semicircular diameter is defined as the charge transfer resistance Rct1 of the positive electrode sheet, The charge transfer resistance of the negative electrode sheet is obtained by a test method in which the negative electrode sheet is assembled into a symmetrical battery, the electrochemical impedance spectrum is measured using an electrochemical AC impedance method on an electrochemical workstation, a Nyquist diagram is created, the Nyquist diagram obtained is analyzed using an equivalent circuit curve approximation method, and the semicircular diameter is defined as the charge transfer resistance Rct2 of the negative electrode sheet. The secondary battery according to claim 1 .

13. the nonaqueous electrolyte includes a first electrolyte that permeates the electrode assembly and a second electrolyte that is located between the electrode assembly and the exterior body; When calculated based on the total mass of the first electrolyte solution, 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 solution is X1; When calculated based on the total mass of the second electrolyte solution, 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 solution is X2; 0.5≦X1 / X2<1, the first electrolytic solution is obtained by a test method in which the secondary battery is discharged to a discharge end voltage, the electrode assembly is disassembled, and the assembly is centrifuged, and the liquid obtained by the centrifugal treatment is the first electrolytic solution; The secondary battery according to claim 1 .

14. The positive electrode sheet has a molecular formula of Li ａ Ni ｂ Co ｃ Mn ｄ Al ｅ M ｆ O ｇ A ｈ M represents a doping cation at the transition metal site, A represents a doping anion at the oxygen site, and 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, and b+c+d+e+f=1, g+h=2. The secondary battery according to claim 1 .

15. Li ａ Ni ｂ Co ｃ Mn ｄ Al ｅ M ｆ O ｇ A ｈ は、 (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; The secondary battery according to claim 14, which satisfies at least one of the above conditions (1) to (8).

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

17. A battery pack comprising the secondary battery according to claim 1 and one of the battery modules according to claim 16.

18. An electric device comprising at least one of the secondary battery according to claim 1, the battery module according to claim 16, and the battery pack according to claim 17.

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