Nonaqueous electrolyte, secondary battery including same, battery module, battery pack, and electric device

Abstract

The present application provides a non-aqueous electrolyte, and a secondary battery, a battery module, a battery pack, and an electric device each including the non-aqueous electrolyte. The non-aqueous electrolyte includes an electrolyte salt and a non-aqueous solvent, and 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 non-aqueous electrolyte, 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 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. The present application can simultaneously achieve good cycle performance, storage performance, and kinetic performance of the secondary battery.

Description

[Technical field]

[0001] The present application relates to the field of battery technology, and more particularly to a non-aqueous electrolyte and a secondary battery, a battery module, a battery pack, and an electric device each 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 stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. With the application and popularity of secondary batteries, their overall performance has attracted more and more attention, for example, secondary batteries need to simultaneously meet high energy density, long cycle life, high safety performance, high multiplication performance, etc. Non-aqueous electrolyte plays an ion conduction role between the positive electrode and the negative electrode, which is one of the important factors that affect the performance of secondary batteries. Therefore, it is necessary to provide a non-aqueous electrolyte with good overall performance. Summary of the Invention

[0003] An object of the present application is to provide a nonaqueous 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 electric device each containing 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, the first lithium salt having 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 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 R 2 and R 3each independently represents at least one selected from the group consisting of a fluorine atom, or 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 content by mass of which 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, the content by mass of which 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 found through extensive research that, when the above-mentioned first lithium salt, second lithium salt and third lithium salt are used as auxiliary lithium salts in a non-aqueous electrolyte, and the total content is controlled to be 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 reasonably adjusted to satisfy that A1 / A2 is 0.016-40 and A1 / (A2+A3) is 0.006-13.5, the obtained non-aqueous electrolyte can simultaneously have high thermal stability, high ionic conductivity and a wide electrochemical window, and the non-aqueous electrolyte can further inactivate the aluminum foil current collector and form a dense, stable, low-resistance and highly conductive interfacial film on the surface of the positive electrode active material and the negative electrode active material, so that the secondary battery using the non-aqueous electrolyte of the present application can simultaneously 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, and thus can form 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 further satisfies A3 / A2 being 0.04 to 30, and preferably satisfies A3 / A2 being 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 dynamic 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%, 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 is lithium hexafluorophosphate and its mass content in the non-aqueous electrolyte solution is A4 when 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 when calculated based on the total mass of the non-aqueous electrolyte solution, and the non-aqueous electrolyte solution satisfies A4+A5 being 10% to 20%, preferably A4+A5 being 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 allows the nonaqueous electrolyte to simultaneously achieve resistance to hydrolysis and higher thermal stability, and at the same time helps to form an interface 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 preferably 40 to 100. This helps the nonaqueous electrolyte to have high thermal stability, high ionic conductivity, and a wide electrochemical window at the same time, and the nonaqueous electrolyte can further inactivate the aluminum foil current collector and form a dense, stable, low-resistance, and highly conductive interfacial film on the surface of both the positive electrode active material and the negative electrode active material.

[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 thereof in the non-aqueous solvent is B2 when calculated based on the total mass of the non-aqueous solvent, and 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 thereof in the non-aqueous solvent is B3 when calculated based on the total mass of the non-aqueous solvent, and preferably, the non-aqueous electrolyte satisfies that 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 interface 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 comprises at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, and 1,3-propane sultone, and the mass content thereof in the non-aqueous electrolyte is C1, calculated based on the total mass of the non-aqueous electrolyte, and C1 is 0.05% to 2%, preferably 0.1% to 1%. The first additive serves to further improve the interface 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 further satisfies (C1+A5) / B1 is 0.3 to 0.8, and preferably satisfies (C1+A5) / B1 is 0.3 to 0.6, thereby fully exerting the synergistic effect between the above 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 includes at least one of sulfamic acid and its salt, and 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, which is helpful in improving 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 makes it possible to reduce the difference in charge transfer resistance between the positive electrode and the negative electrode, and to further improve 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 of an electrochemical workstation, a Nyquist diagram is created, and the obtained Nyquist diagram is analyzed using an equivalent circuit curve approximation method, and the semicircle diameter is 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 of an electrochemical workstation, a Nyquist diagram is created, and the obtained Nyquist diagram is analyzed using an equivalent circuit curve approximation method, and the semicircle diameter is the charge transfer resistance Rct2 of the negative electrode sheet.

[0025] In any embodiment of the present application, the nonaqueous electrolyte includes a first electrolyte infiltrating the electrode assembly and a second electrolyte located between the electrode assembly and the exterior body, and 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 first electrolyte, and 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 when calculated based on the total mass of the second electrolyte, and 0.5≦X1 / X2<1. The first electrolyte is obtained by the following test method. After discharging the secondary battery to a discharge end voltage, the electrode assembly is disassembled and centrifuged, and the liquid obtained by the centrifugal treatment is the first electrolyte.

[0026] In any embodiment of the present application, the positive electrode sheet has a molecular formula of Li a Ni b Co c Mn d Al e M f O g A hIt contains a layered material, where M represents a doping cation of a transition metal site, A represents a doping anion of an 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] A fourth aspect of the present application provides a battery pack including the secondary battery of the second aspect of the present application and one of the battery modules of the third aspect.

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

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

[0039] In order to more clearly describe 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 making creative efforts. [Figure 1] 1 is a schematic diagram of an embodiment of a secondary battery of the present application. [Diagram 2] FIG. 2 is an exploded schematic view of the embodiment of the secondary battery of FIG. 1. [Diagram 3] FIG. 1 is a schematic diagram of an embodiment of a battery module of the present application. [Figure 4] FIG. 1 is a schematic diagram of an embodiment of a battery pack of the present application. [Diagram 5] 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4. [Figure 6] FIG. 1 is a schematic diagram of an embodiment of an electrical device that includes 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 PREFERRED EMBODIMENTS

[0041] Hereinafter, the nonaqueous electrolyte and the secondary battery, battery module, battery pack, and electric device including the same according to the present application will be described in detail with appropriate reference to the drawings. However, more detailed description than necessary may be omitted. For example, detailed description of already well-known matters and duplicated description of the same actual structure may be omitted. This is to prevent the following description from becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. In addition, 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] The "ranges" disclosed herein are defined in the form of lower and upper limits, where a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits 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 range. For example, when reciting ranges of 60-120 and 80-110 for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Also, when reciting minimum range values ​​1 and 2 and maximum range values ​​3, 4 and 5, all of the ranges 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 are contemplated. In this application, unless otherwise stated, a numerical range "a-b" refers to all real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" in this specification represents all real numbers between "0-5", with "0-5" being 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 stated, all steps in the present application can be performed in sequence, can be performed randomly, and are preferably performed in sequence. For example, if the method includes steps (a) and (b), the method can include steps (a) and (b) performed in sequence, or can include 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), can include steps (a), (c) and (b), can include steps (c), (a) and (b), etc.

[0046] Unless otherwise specified, the terms "comprise" and "contain" referred to in this application indicate an open system, but may also be 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 both A and B are true (or exist).

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

[0049] As used herein, the term "alkyl" refers to a saturated hydrocarbon group, including linear structures as well as 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), 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 linear as well as branched structures, and the number of carbon-carbon double bonds may be one or more. Examples of alkenyl include, but are not limited to, vinyl, propenyl, allyl, and butadiene. In various embodiments, C2-C10 alkenyl means that the alkenyl may contain from 2 to 10 carbon atoms.

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

[0052] The term "aryl" refers to a carbocyclic ring system having aromatic character, the structure 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 places in this specification, substituents of compounds are disclosed in groups or ranges. It is specifically anticipated that such descriptions include each subcombination of the members of these groups and ranges. For example, the term "C1-C6 alkyl" is specifically anticipated to 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 individually.

[0055] As secondary batteries are applied and popularized, their overall performance is receiving more and more attention. Non-aqueous electrolyte is one of the important factors that affect the performance of secondary batteries. The non-aqueous electrolyte system that is currently most widely used commercially is a mixed carbonate ester solution of lithium hexafluorophosphate. However, lithium hexafluorophosphate has low thermal stability in high temperature environments and decomposes at high temperatures to form LiF and PF. 5 LiF increases the interface resistance. PF 5 has a strong Lewis acidity and acts on the lone electron on the oxygen atom in the solvent molecule to decompose the solvent. 5is highly sensitive to traces of moisture in the non-aqueous electrolyte, and generates HF when exposed to water, which increases the acidity of the non-aqueous electrolyte and is prone to corroding the positive electrode active material and the positive electrode current collector, resulting in the dissolution of transition metal ions in the positive electrode active material. In addition, the transition metal ions in the positive electrode active material dissolve and transition to the negative electrode, and then transition to a transition metal. The transition metal thus generated corresponds to a "catalyst" and catalyzes the decomposition of the solid electrolyte interphase (SEI) on the surface of the negative electrode active material, generating by-products. Since a part of the by-products is gas, the secondary battery expands, affecting the safety performance of the secondary battery. Another part of the by-products is deposited on the surface of the negative electrode active material, blocking the lithium ion transmission channel, increasing the resistance of the secondary battery, and thereby affecting the dynamic performance of the secondary battery. In addition, it is an interface film that supplements losses, and the non-aqueous 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 the 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 embodiment provides a non-aqueous electrolyte solution including 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, the first lithium salt having a structure represented by Formula 1, R 1 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 R 3 each independently represents at least one selected from the group consisting of a fluorine atom, a partially fluorinated 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 nonaqueous electrolyte is A2 when calculated based on the total mass of the nonaqueous electrolyte, and the third lithium salt is selected from lithium tetrafluoroborate, and the mass content of the nonaqueous electrolyte is A3 when calculated based on the total mass of the nonaqueous electrolyte. [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 found through extensive research that, when the above-mentioned first lithium salt, second lithium salt and third lithium salt are used as auxiliary lithium salts in a non-aqueous electrolyte, and the total content is controlled to be 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 reasonably adjusted to satisfy that A1 / A2 is 0.016-40 and A1 / (A2+A3) is 0.006-13.5, the obtained non-aqueous electrolyte can simultaneously have high thermal stability, high ionic conductivity and a wide electrochemical window, and the non-aqueous electrolyte can further inactivate the aluminum foil current collector and form a dense, stable, low-resistance and highly conductive interfacial film on the surface of the positive electrode active material and the negative electrode active material, so that the secondary battery using the non-aqueous electrolyte of the present application can simultaneously achieve good cycle performance, storage performance and kinetic performance.

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

[0063] First, when the content A1 of the first lithium salt and the content A2 of the second lithium salt are reasonably adjusted so that A1 / A2 is 0.016-40, it is helpful to form a dense, stable and highly conductive interfacial film on the surface of the negative electrode active material. The first lithium salt contains sulfonate anions and can be reduced to Li 2 SO 4 The second lithium salt can form a highly conductive compound such as , which is advantageous in improving the ion permeability of the negative electrode interfacial film. The molecular structure of the second lithium salt contains one oxalic acid group, and the reduction product thereof is (LiOCO 2 CH 2 ) 2It further reacts with organic components such as ZnO, Fe, and ZnO to form complex and stable oligomers, which are fully coated on the surface of the negative electrode active material, preventing the non-aqueous electrolyte from directly contacting the negative electrode active material and reducing the embedding of the non-aqueous solvent in the negative electrode active material. If A1 / A2 is greater than 40, the negative electrode interfacial film cannot be fully 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 properties of the negative electrode interfacial film are poor, which increases the internal resistance of the secondary battery and deteriorates its dynamic performance.

[0064] Second, 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 can be reasonably adjusted to satisfy A1 / (A2+A3) being 0.006-13.5, which is conducive to forming a dense, stable and small amount of LiF-containing interfacial film on the surface of the positive electrode active material, increasing the lithium ion transmission channel of the positive electrode interfacial film, and reducing the transport resistance of lithium ions. At the same time, the irreversible change of the positive electrode active material can be suppressed, and the structural stability of the positive electrode active material can be maintained, so that the secondary battery has a better capacity. In addition, the B atom in the structure is easily bonded with the O atom in the positive electrode active material, which can reduce the charge transfer resistance of the positive electrode active material and reduce the diffusion resistance of lithium ions in the positive electrode active material phase. When A1 / (A2+A3) is greater than 13.5, the second lithium salt and the third lithium salt cannot effectively compensate for the deterioration of the battery internal resistance caused by the excess of the first lithium salt. This leads to poor dynamic performance of the secondary battery, and at the same time, the positive electrode interfacial film cannot fully cover the surface of the positive electrode active material, which increases the irreversible consumption of lithium ions and reduces the capacity retention rate of the secondary battery.When A1 / (A2+A3) is less than 0.006, the content of LiF in the positive electrode 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 not only form an interface film 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 corrode the aluminum foil current collector, which affects the performance of the secondary battery, such as increasing the 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; 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 to the negative electrode. 3+ The first lithium salt can be combined with the second lithium salt to form a layer of passivation film on the surface of the aluminum foil current collector, and the third lithium salt can be preferentially oxidized and decomposed on the surface of the aluminum foil current collector to form a layer of passivation film. Therefore, the non-aqueous electrolyte of the present application can passivate the aluminum foil current collector, effectively improving the corrosion of the first lithium salt to the aluminum foil current collector, and reducing the irreversible capacity loss of the secondary battery.

[0066] Therefore, the reason why the secondary battery using the nonaqueous electrolyte of the present application can simultaneously achieve good cycle performance, storage performance, and dynamic performance is that a synergistic effect is formed between the above components. The first lithium salt forms an interface film on both the positive electrode and the negative electrode, 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 defect of the first lithium salt having a small 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 interface 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 interface film containing a small amount of LiF on the surface of the positive electrode active material. This reduces the interfacial side reaction between the nonaqueous electrolyte and the electrode, reduces the irreversible consumption of active lithium ions, increases the capacity of the secondary battery, and reduces the amount of gas generated. In addition, the interface 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 0.03-40, 0.03-30, 0.03-20, 0.03-15, 0.03-10, 0.03-8, 0.03-6, 0.05-40, 0.05-30, 0.05-20, 0.05-15, 0.05-10, 0.05-8, 0.05-6, 0.05-5, 0.1-40, 0.1-30, 0.1-20, 0.1-15, 0.1-10, 0.1-8, 0.1-6, 0.1-5, 0.2-40, 0.2-30, 0.2-20, 0.2-15, 0.2-10, 0.2-8, 0.2-6, 0.2-5, or 0.2-2.5. When A1 / A2 is within a suitable range, it is conducive to fully exerting the synergistic effect between the first lithium salt and the second lithium salt, so that a denser, more stable and more ion-conductive interfacial film can be formed 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 between 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.

[0069] The molecular structure of the second lithium salt contains an oxalic acid group, so 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 by the secondary battery. BF 4 -The ionic radius of the second lithium salt is small, so it is easy to associate, and therefore a high content of the third lithium salt may reduce the ionic conductivity of the non-aqueous electrolyte. The inventors have conducted a large amount of research and found that if the content A2 of the second lithium salt and the content A3 of the third lithium salt are reasonably adjusted to satisfy A3 / A2 being 0.04 to 30, the non-aqueous electrolyte can have high thermal stability and high ionic conductivity at the same time, and can form low-resistance and high-conductivity interface films on both the positive and negative electrodes, as well as better protect the aluminum foil current collector, thereby further improving the cycle performance, storage performance and dynamic performance of the secondary battery. If A3 / A2 is greater than 30, the second lithium salt may not be able to reduce the negative electrode interface resistance, and may not be able to compensate for the deterioration of the dynamic performance of the secondary battery caused by the third lithium salt. If A3 / A2 is less than 0.04, many second lithium salts may reduce the thermal stability of the non-aqueous electrolyte, and the storage performance of the secondary battery may be reduced.

[0070] In some embodiments, A3 / A2 is preferably 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 It 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 an 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, and reduces 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 non-aqueous 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%, 0.0 2%~0.18%, 0.02%~0.16%, 0.02%~0.14%, 0.02%~0.12%, 0.02%~0.1%, 0.05%~0.3%, 0.05%~0.26%, 0.05%~0.22%, 0.05%~0.2%, 0.05%~0.18%, 0.05%~0.16%, 0.05%~0.14%, 0.05%~0.12% or 0.05%~0.1%.

[0073] When the content of the third lithium salt increases, the ionic conductivity of the non-aqueous electrolyte decreases, which is disadvantageous to the formation of a stable interfacial film on the surface of the negative electrode active material. In some embodiments, A3 is 0.01% to 0.5%. 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, R 1 represents a fluorine atom or a partially or fully fluorinated C1-C6 alkyl. 1 represents a fluorine atom, or a partially or fully fluorinated methyl, ethyl, or propyl. 1 represents a fluorine atom, trifluoromethyl, difluoromethyl or monofluoromethyl.

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

[0076] R 2 and R 3 represents a fluorine atom or a fluorine-containing group, and the presence of the fluorine atom or the fluorine-containing group can help to form a thinner positive electrode interfacial film and / or a negative electrode interfacial film, thereby helping to uniformly transport lithium ions and effectively suppressing the formation of lithium dendrites. 2 and R 3represents at least one member independently selected from the group consisting of a fluorine atom, partially fluorinated or fully fluorinated C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, C6-C8 aryl, C1-C6 alkoxy, C2-C6 alkenyloxy, C2-C6 alkynyloxy, and C6-C8 aryloxy. 2 and R 3 represents at least one independently selected from the group consisting of a fluorine atom, or partially or completely fluorinated methyl, ethyl, propyl, phenyl, methoxy, ethoxy, propoxy, and phenoxy. 2 and R 3 Each of these represents a fluorine atom.

[0077] By way of 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, the fourth lithium salt is lithium hexafluorophosphate, and its mass content in the non-aqueous electrolyte is A4 when calculated based on the total mass of the non-aqueous electrolyte, the fifth lithium salt is lithium bisfluorosulfonylimide, and its mass content in the non-aqueous electrolyte is A5 when calculated based on the total mass of the non-aqueous electrolyte, and the non-aqueous electrolyte satisfies A4+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%.

[0079] The non-aqueous electrolyte of the present invention contains lithium hexafluorophosphate and / or lithium bisfluorosulfonylimide as the main lithium salt. Lithium hexafluorophosphate has the properties of high ionic conductivity and being less corrosive to the aluminum foil current collector, and as the main lithium salt, it can improve the ionic conductivity and thermal stability of the entire non-aqueous electrolyte. The chemical formula of lithium bisfluorosulfonylimide is F 2 NO 4 S 2 Li, and the N atom is bonded to two electron-withdrawing sulfonyl groups, so that the charge on the N atom is fully removed, and the lithium bisfluorosulfonylimide has a lower crystal lattice energy and is easy to dissociate, which can improve the ionic conductivity of the non-aqueous electrolyte and reduce the viscosity of the non-aqueous electrolyte. In addition, the lithium bisfluorosulfonylimide has the characteristics of high resistance to high temperatures and resistance to hydrolysis, and 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 the side reaction between the negative electrode active material and the non-aqueous electrolyte.

[0080] In some embodiments, the non-aqueous electrolyte has lithium hexafluorophosphate as the main lithium salt, i.e., A5 is 0% and A4 is 10%-20%, preferably 10%-18%, 10%-17%, 10%-16%, 10%-15%, 12%-18%, 12%-17%, 12%-16%, or 12%-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%-20%, preferably 10%-18%, 10%-17%, 10%-16%, 10%-15%, 12%-18%, 12%-17%, 12%-16%, or 12%-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 interface film with lower impedance.

[0083] In some embodiments, the non-aqueous electrolyte satisfies (A4+A5) / (A1+A2+A3) is 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 and the auxiliary lithium salt is within a suitable range, the non-aqueous electrolyte can simultaneously have high thermal stability, high ionic conductivity, and a wider electrochemical window, and the non-aqueous electrolyte can further inactivate the aluminum foil current collector and form a dense, stable, low-resistance, and highly conductive interfacial film on the surface of both the positive electrode active material and the negative electrode active material.

[0084] In some embodiments, the non-aqueous electrolyte may further include other electrolyte salts, such as lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorodisalophosphate (LiDFOP), and lithium tetrafluorooxalophosphate (LiTFOP). These other electrolyte salts may be auxiliary lithium salts, and serve to further improve the interface properties of the positive electrode and / or the negative electrode, or to improve the ionic conductivity or thermal stability of the non-aqueous electrolyte. Preferably, calculated based on the total mass of the non-aqueous electrolyte, the total mass content of these other electrolyte salts in the non-aqueous electrolyte is 1% or less, and preferably 0.5% or less.

[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 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. When the content of the electrolyte salt is high, the viscosity of the non-aqueous electrolyte increases, the ion conductivity decreases, and it is disadvantageous to form a dense, stable and low impedance interfacial film. The first solvent has a high dielectric constant, so that the conductivity of the non-aqueous electrolyte can be increased, and the second solvent has a small viscosity, so that the viscosity of the non-aqueous electrolyte can be reduced. Therefore, when the non-aqueous solvent includes the first solvent and the second solvent at the same time, it is helpful for the non-aqueous electrolyte to have an appropriate viscosity and ion conductivity, and is further advantageous for the transport of lithium ions.

[0089] In some embodiments, the non-aqueous solvent may further include a third solvent. The third solvent is a carboxylate compound, and may include at least one of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), and ethyl butyrate (EB). 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 to 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 content of the first solvent, particularly when the non-aqueous solvent contains an appropriate content of ethylene carbonate, the radicals formed by the decomposition of the second lithium salt can induce ring-opening and polymerization of ethylene carbonate, making the interface film formed on the surface of the negative electrode active material denser and smoother, thereby effectively inhibiting the growth of dendrites.

[0093] The non-aqueous solvent of the present application may further include other solvents in addition to the first, second, and third solvents. As an example, the other solvents may include sulfone-based solvents 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 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, which is 0.05% to 2%, calculated 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 serves to further improve the interface properties of the positive electrode and / or the negative electrode, thereby further improving at least one of the cycle performance, storage performance, and kinetic performance of the secondary battery.

[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, and the content C1 of the first additive, the content A5 of the lithium bisfluorosulfonylimide, and the content B1 of the first solvent satisfy (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 to help reduce persistent side reactions, thereby improving at least one of the cycle performance, storage performance, and kinetic performance of the secondary battery, but when the content of the first additive is high, the positive electrode interface resistance and / or the negative electrode interface resistance increases, affecting the power performance of the secondary battery. Lithium bisfluorosulfonylimide can improve the ionic conductivity and thermal stability of the non-aqueous electrolyte and reduce the positive electrode interface resistance and / or the negative electrode interface resistance, but there is a certain corrosion to the aluminum foil current collector, and when its content is high, it affects the cycle performance of the secondary battery. The first solvent has a high dielectric constant and contributes to the dissociation of the lithium salt, so that it can improve the ionic conductivity of the non-aqueous electrolyte to a certain extent, but when its content is high, it increases the viscosity of the non-aqueous electrolyte on the one hand and affects the thermal stability of the non-aqueous electrolyte on the other hand, affecting the storage performance of the secondary battery. After further research, the inventors of the present application found that by controlling (C1+A5) / B1 to be between 0.3 and 0.8, it is useful to fully exert the synergistic effect between the above-mentioned components, effectively reducing the defects when each component is used alone, and thus the secondary battery has excellent cycle performance and can prevent deterioration of dynamic performance and power performance.

[0096] In some embodiments, the non-aqueous electrolyte further comprises a second additive, the second additive comprising at least one of sulfamic acid and a salt thereof. The molecular formula of sulfamic acid is H 3 NO 3S, and the sulfamate comprises at least one of an ammonium salt, an alkali metal salt, an alkaline earth metal salt, and an analogous alkaline earth metal salt, and, as an example, the sulfamate may comprise at least one of an ammonium sulfamate, a lithium sulfamate, a sodium sulfamate, and a zinc sulfamate. Preferably, the second additive comprises sulfamic acid, a lithium sulfamate, or a combination thereof.

[0097] Sulfamic acid is highly acidic and is generally used to prepare lithium bisfluorosulfonylimide, and it has not been found that it can be applied to non-aqueous electrolytes at present. The inventors of the present application have been surprised to find in further research that if the non-aqueous electrolyte containing the auxiliary lithium salts (first lithium salt, second lithium salt, and third lithium salt) further contains an appropriate amount of sulfamic acid and its salt, it helps to improve the cycle performance and dynamic performance of the secondary battery. Although the mechanism is not clear, the possible causes speculated by the inventors are as follows. Sulfamic acid and its salt improve the ionic conductivity of the non-aqueous electrolyte and help to reduce the viscosity of the non-aqueous electrolyte, and at the same time, can slowly dissolve metals such as lithium dendrites to a certain extent. This can reduce the amount of lithium element, aluminum element, transition metal element, etc. that are reduced and deposited on the surface of the negative electrode active material, and the secondary battery can have improved cycle performance and dynamic performance.

[0098] Sulfamic acid and its salts are easily soluble in water and highly acidic, and when the content is high, it corrodes the positive electrode active material and destroys the stability of the positive electrode interfacial film and / or the negative electrode interfacial film. In some embodiments, calculated based on the total mass of the nonaqueous electrolyte, the mass content of the second additive in the nonaqueous electrolyte is C2, and C2 is 0.005% to 0.1%, preferably 0.005% to 0.05%.

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

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

[0101] In the present application, each component and its content in the non-aqueous electrolyte can be measured according to a method known in the art, for example, gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), etc.

[0102] It should be noted that in the case of the non-aqueous electrolyte test of the present application, a freshly manufactured non-aqueous electrolyte can be taken directly, and the non-aqueous electrolyte can also be taken from a secondary battery. One exemplary method for taking a non-aqueous electrolyte from a secondary battery includes the following steps: A secondary battery is discharged to a discharge end voltage (for safety reasons, the battery is generally fully charged), and then centrifuged, and the liquid obtained by taking an appropriate amount of centrifugation is the non-aqueous electrolyte. The non-aqueous electrolyte may also be taken directly from the electrolyte inlet of the secondary battery. secondary battery

[0103] A second aspect of an embodiment of the present application provides a secondary battery, the 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, thereby allowing 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] The 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 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 serves to form a dense, stable, low-resistance and highly conductive interfacial film on the surface 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 therebetween, and serving to improve 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, 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, and can further improve the performance of the secondary battery.

[0108] 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 of an electrochemical workstation, a Nyquist diagram is created, and the obtained Nyquist diagram is analyzed using an equivalent circuit curve approximation method, and the semicircle 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, the secondary battery is generally fully charged.

[0109] 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 of an electrochemical workstation, a Nyquist diagram is created, and the obtained Nyquist diagram is analyzed using an equivalent circuit curve approximation method, and the semicircle 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, 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 a discharge end 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, and 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, 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, and 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, 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 a thickness direction thereof, 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, and the positive electrode active material may be a positive electrode active material used in a secondary battery known in the art. For example, the positive electrode active material may include at least one of lithium transition metal oxide, lithium-containing phosphate with an olivine structure, and modified compounds thereof. Examples of lithium transition metal oxides may include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. Examples of lithium-containing phosphate with an olivine structure may include at least one of lithium iron phosphate, lithium iron phosphate and carbon composite material, lithium manganese phosphate, lithium manganese phosphate and carbon composite material, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composite material, and modified compounds thereof. The present application is not limited to these materials, and other conventionally known materials used as secondary battery positive electrode active materials may be used. These positive electrode active materials may be used alone 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 and 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, b+c+d+e+f=1, and 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 and modification with M cations and A anions. 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 F doping modification, Li a Ni b Co c Mn d Al e M f O g A h The crystal structure of is more stable, 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 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 and expensive to extract, and thus, 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 inventor of the present application surprisingly 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 further formed on the surface of the cathode 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 cathode active material, reducing the charge transfer resistance of the cathode active material, thereby reducing the diffusion resistance of lithium ions in the bulk of the cathode active material. Therefore, when the non-aqueous electrolyte contains appropriate contents of the second lithium salt and the third lithium salt, the low-cobalt or cobalt-free cathode active material can have a significantly improved lithium ion diffusion rate, enabling the lithium ions in the bulk of the low-cobalt or cobalt-free cathode active material to be timely replenished to the surface, preventing excessive lithium release from the surface of the low-cobalt or cobalt-free cathode active material, and thereby stabilizing the crystal structure of the low-cobalt or cobalt-free cathode active material. Since the crystal structure of the low-cobalt or cobalt-free cathode active material is more stable, the probability of problems such as instability of the structural, chemical, or electrochemical properties of the cathode active material due to delithiation occurring on the surface of the low-cobalt or cobalt-free cathode active material can be significantly reduced. For example, the problem of increased irreversible strain and lattice defects in the cathode 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, a 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 O 2 、LiNi 0.6 Co 0.2 Mn 0.2 O 2 、LiNi 0.5 Co 0.2 Mn 0.3 O 2 、LiNi 0.8 Co 0.05 Mn 0.15 O 2 、LiNi 0.7 Mn 0.3 O 2 、LiNi 0.69 Co 0.01 Mn 0.3 O 2 、LiNi 0.68Co 0.02 Mn 0.3 O 2 , LiNi 0.65 Co 0.05 Mn 0.3 O 2 , LiNi 0.63 Co 0.07 Mn 0.3 O 2 , LiNi 0.61 Co 0.09 Mn 0.3 O 2 At least one of the following may be included, but is not limited to these.

[0130] Li a Ni b Co c Mn d Al e M f O g A h can be produced according to a general method in the art. An exemplary production method is as follows. The lithium source, nickel source, cobalt source, manganese source, aluminum source, M element precursor, and A element precursor are mixed and then sintered to obtain the product. The sintering atmosphere may be an oxygen-containing atmosphere, for example, an air atmosphere or an oxygen atmosphere. The O atmosphere of the sintering atmosphere may be an oxygen-containing atmosphere, for example, an air atmosphere or an oxygen atmosphere. 2 The concentration is, for example, 70% to 100%. The sintering temperature and sintering time can be adjusted according to the actual situation.

[0131] As an example, the lithium source may be lithium oxide (Li 2 O), lithium phosphate (Li 3 PO 4 ), lithium dihydrogen phosphate (LiH 2 PO 4 ), lithium acetate (CH 3 COOLi), lithium hydroxide (LiOH), lithium carbonate (Li 2 CO 3 ) and lithium nitrate (LiNO 3) is included, but is not limited to. For example, the nickel source includes at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. For example, the cobalt source includes at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. For example, the manganese source includes at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. For example, the aluminum source includes at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate. For example, the M element precursor includes at least one of M element oxide, nitrate compound, carbonate compound, hydroxide compound, and acetate compound. By way of example, elemental precursors include 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, but are not limited to these.

[0132] In some embodiments, the molecular formula is Li a Ni b Co c Mn d Al e M f O g A h The mass percentage of the layered material is 80% to 99%. For example, the molecular formula is Li a Ni b Co c Mn d Al e M f O g A hThe mass percentage of the layered material 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. 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 includes 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 ternary copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene ternary copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and 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 may be an aluminum 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 aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. For example, the polymeric material layer may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0136] The positive electrode film layer is generally formed by applying a positive electrode slurry to a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring 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 opposing surfaces in a thickness direction thereof, and the negative electrode film layer is provided on either one or both of the two opposing surfaces of the negative electrode current collector.

[0138] The negative electrode active material may be a negative electrode active material used in a secondary battery known in the art. As an example, the negative electrode active material may include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, but is not limited thereto. 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 conventionally known materials used as negative electrode active materials for secondary batteries may be used. These negative electrode active materials may be used alone or in combination of two or more.

[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 as an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent is 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-based acrylic resin (e.g., polyacrylic acid (PAA), polymethacrylic acid (PMAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage 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 include other auxiliary agents. For example, the other auxiliary agents may include a thickener, such as sodium carboxymethylcellulose (CMC-Na), a PTC thermistor material, etc. In some embodiments, the mass percentage of the other auxiliary agents 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 can be a metal foil or a composite current collector. An example of the metal foil can be copper foil. The composite current collector can 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 can 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 can be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[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 generally formed by dispersing a negative electrode active material, a conductive agent if necessary, a binder if necessary, and any other auxiliary agent 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 mainly serves to prevent short circuit between the positive electrode and the negative electrode, and at the same time allows lithium ions to pass through. The present application does not particularly limit the type of the separator, and any known porous separator having good chemical stability 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 monolayer film or a multilayer composite film. When the separator is a multilayer composite thin 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 produce 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 body of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior body 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 a side plate connected to the bottom plate, and the bottom plate and the side plate surround and form a receiving cavity. The case 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening, thereby sealing the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator form an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is sealed in the receiving cavity. The non-aqueous electrolyte is infiltrated 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 demand.

[0151] The method for manufacturing the secondary battery of the present application is known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and a non-aqueous electrolyte may be assembled to form a secondary battery. As an example, a positive electrode sheet, a separator, and a negative electrode sheet are wound or laminated to form an electrode assembly, the electrode assembly is placed in an exterior body, and a non-aqueous electrolyte is injected after drying, and a secondary battery is 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, and the contents of the first lithium salt, the second lithium salt, the third lithium salt, the first additive, and the second additive in the 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 helps to reduce costs and improve the performance of the secondary battery at the same time. This is because the stability of some components in the auxiliary lithium salt and additives themselves is low, and when only a one-time liquid injection process is used, the stability of the non-aqueous electrolyte is easily reduced, whereas the secondary battery of the present application uses a two-time liquid injection process, and the non-aqueous electrolyte injected the second time contains less auxiliary lithium salt and additives, thereby improving the stability of the non-aqueous electrolyte. In some embodiments, the injection coefficient of the secondary battery is 2.0g / Ah to 5.0g / Ah, and the mass of the non-aqueous electrolyte is the sum of the masses of the non-aqueous electrolyte injected the first time and the non-aqueous 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, the multiple secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may be arranged in any other manner. The multiple secondary batteries 5 may further be fixed by a fastener.

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

[0155] In some embodiments, the above 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 Fig. 4 and Fig. 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper housing 2 and a lower housing 3, and is used to cover the upper housing 2 and the lower housing 3 and form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arbitrarily arranged in the battery box. Electrical equipment

[0157] An embodiment of the present application further provides 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 of the electric device, or may be used as an energy storage unit of the electric device. The electric device may be, but is not limited to, a mobile device (such as a mobile phone, a laptop, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[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 the electric device may be a mobile phone, a tablet computer, a notebook computer, etc. Such electric devices are generally required to be thin and can use a secondary battery as a power source. Working Example

[0161] The following examples will more specifically describe the contents disclosed in the present application, and these examples are merely used to illustrate the invention, and it will be apparent to those skilled in the art that various modifications and changes can be made within the scope of the contents disclosed in the present application.Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass metering, all reagents used in the examples can be purchased or synthesized according to conventional methods, and can be used directly without further processing, and all devices 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] Manufacture of positive electrode sheets

[0164] Positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O 2 The conductive agent carbon black and the binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.4:1.1 in an appropriate amount of NMP solvent with sufficient stirring to form a uniform positive electrode slurry. The positive electrode slurry is evenly applied to the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained.

[0165] Manufacture of negative electrode sheets

[0166] The negative electrode active material graphite, binder styrene butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC-Na), conductive agent carbon black (Super P) are mixed in a weight ratio of 96.2:1.8:1.2:0.8 with an appropriate amount of solvent deionized water and stirred thoroughly to form a uniform negative electrode slurry. The negative electrode slurry is 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] Production of non-aqueous electrolyte

[0170] The lithium salt and additive 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, the second lithium salt, the third lithium salt, the fourth lithium salt, the fifth lithium salt, the first additive, and the second additive are all calculated based on the total mass of the non-aqueous electrolyte, and the contents of the first solvent, the second solvent, and the third solvent are all calculated based on the total mass of the non-aqueous solvent, and " / " indicates that the corresponding component is not added.

[0171] Secondary battery manufacturing

[0172] The positive electrode sheet, the separator, and the negative electrode sheet are laminated in this order and wound to obtain an electrode assembly. The electrode assembly is placed in an outer casing, the nonaqueous electrolyte is added, and the secondary battery is obtained after going through steps such as sealing, standing, chemical conversion, and aging.

[0173] Testing Part

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

[0175] At 25°C, the secondary battery is charged to 4.3V at a constant current of 1C, and then continues to be charged at a constant voltage until the current becomes 0.05C. At this time, the secondary battery is fully charged, and the charge capacity at this time is recorded, which is the charge capacity of the first loop. After leaving the secondary battery to stand for 5 minutes, it is discharged to 2.8V at a constant current of 1C, which is one cycle charge / discharge process. The discharge capacity at this time is recorded, which is the discharge capacity of the first loop. The secondary battery is subjected to a cycle charge / discharge test according to the above method, and the discharge capacity after each loop cycle is recorded. The capacity retention rate (%) after 600 loop cycles of the secondary battery at 25°C = discharge capacity after 600 loop 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 is charged to 4.3V at a constant current of 1C, and then continues to be charged at a constant voltage until the current becomes 0.05C. At this time, the secondary battery is fully charged, and the charge capacity at this time is recorded, which is the charge capacity of the first loop. After leaving the secondary battery to stand for 5 minutes, it is discharged to 2.8V at a constant current of 1C, which is one cycle charge / discharge process. The discharge capacity at this time is recorded, which is the discharge capacity of the first loop. The secondary battery is subjected to a cycle charge / discharge test according to the above method, and the discharge capacity after each cycle is recorded. The capacity retention rate (%) after 600 loop cycles of the secondary battery at 45°C = discharge capacity after 600 loop 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 drops to 0.05C. At this time, measure the volume of the secondary battery using the drainage method, and V 0 The secondary battery is placed in an incubator at 60°C and stored for 30 days, after which it is taken out and the volume of the secondary battery is measured by the drainage method. 1 The volume expansion rate (%) of the secondary battery after storing it at 60°C for 30 days = [(V 1 -V 0) / V 0 ]×100%.

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

[0181] At 25°C, charge the secondary battery to 4.3V at a constant current of 1C, and continue charging at a constant voltage until the current becomes 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. At this point, the voltage of the secondary battery is U 1 The secondary battery is charged at a current of 4C I 1 Discharge at a constant current for 30 seconds, and measure the voltage at the end of discharge using a 0.1 second measurement. 2 The discharge DC internal resistance of the secondary battery at 50% SOC indicates the initial DC internal resistance of the secondary battery, and the initial DC internal resistance of the secondary battery (mΩ) = (U 1 -U 2 ) / I 1 It is.

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

[0183] After the secondary battery is fully charged, the positive electrode sheet is disassembled, the positive electrode sheet is assembled into a symmetrical battery, the non-aqueous electrolyte is injected, and then the battery is tested using the electrochemical AC impedance method of a Solartron 1470E CellTest multi-channel electrochemical workstation to create a Nyquist diagram. The Nyquist diagram obtained is analyzed using the equivalent circuit curve fitting method using Zview software, and the semicircle diameter is the charge transfer resistance Rct1 of the positive electrode sheet. The test voltage is 10 mV, and the test frequency is 0.1 Hz to 100 KHz.

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

[0185] After the secondary battery is fully charged, the negative electrode sheet is disassembled, the negative electrode sheet is assembled into a symmetrical battery, the non-aqueous electrolyte is injected, and then the battery is tested using the electrochemical AC impedance method of a Solartron 1470E CellTest multi-channel electrochemical workstation to create a Nyquist diagram. The Nyquist diagram obtained using the equivalent circuit curve fitting method using Zview software is analyzed, and the semicircle diameter is the charge transfer resistance Rct2 of the negative electrode sheet. The test voltage is 10 mV, and the test frequency is 0.1 Hz to 100 KHz.

[0186] In order to ensure the reliability of the test results, each of the above tests should be performed 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-mentioned performance test method.

[0188] Table 3 shows the production parameters for the nonaqueous electrolytes of Examples 36 to 51, and Table 4 shows the test results for Examples 36 to 51 according to the above-mentioned performance test method. [Table 1] JPEG0007689582000010.jpg218128 [Table 2] JPEG0007689582000012.jpg221128 [Table 3] [Table 4]

[0189] As can be seen from the test results of Examples 1 to 35, when the first lithium salt, the second lithium salt, and the third lithium salt of the present application are used as auxiliary lithium salts in a nonaqueous electrolyte solution to control the total content thereof 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 conditions A1 / A2 being 0.016 to 40 and A1 / (A2+A3) being 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 non-aqueous electrolyte does not use the auxiliary lithium salt of the present invention or uses only a part of the auxiliary lithium salt of the present invention, and the secondary batteries produced have low capacity retention, high volume expansion rate and high internal resistance. Comparative Example 10 uses LiBOB as the auxiliary lithium salt, and the volume expansion rate of the secondary battery produced is improved to some extent, but the capacity retention rate is still low and the internal resistance is still high.

[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 has the same effect 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 in the embodiments are also included in the scope of the present application, as long as they do not deviate from the gist of the present application.

Claims

1. A non-aqueous electrolyte solution containing 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, R １ represents a fluorine atom or a partially or fully fluorinated C1-C10 alkyl, and its mass content in the nonaqueous electrolyte is A1, calculated based on the total mass of the nonaqueous electrolyte; The second lithium salt has a structure represented by Formula 2, 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, 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, and the mass content thereof in the nonaqueous electrolyte is A2 when calculated based on the total mass of the nonaqueous electrolyte, the third lithium salt is selected from lithium tetrafluoroborate, and its mass content in the nonaqueous electrolyte is A3, calculated based on the total mass of the nonaqueous electrolyte; The nonaqueous electrolyte satisfies the following requirements: A1+A2+A3 is 1% or less; A1 / A2 is 0.016 to 40; and A1 / (A2+A3) is 0.006 to 13.

5. 【Chemistry 1】 【Chemistry 2】

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

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

4. The nonaqueous electrolyte according to any one of claims 1 to 3, wherein the nonaqueous electrolyte satisfies at least one of the following conditions (1) to (3): (1) A1 is 0.005% to 0.2%. (2) A2 is 0.005% to 0.3%. (3) A3 is 0.01% to 0.5%.

5. The first lithium salt includes at least one of the following compounds: 【Chemistry 3】 and / or The nonaqueous electrolyte solution 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 nonaqueous electrolyte is A4, calculated based on the total mass of the nonaqueous electrolyte; the fifth lithium salt is lithium bisfluorosulfonylimide, and its mass content in the nonaqueous electrolyte is A5, calculated based on the total mass of the nonaqueous electrolyte; The nonaqueous electrolyte satisfies that A4+A5 is 10% to 20%. The nonaqueous electrolyte according to claim 1 .

7. (A4+A5) / (A1+A2+A3) is 10 to 200; The nonaqueous electrolyte according to claim 6.

8. the non-aqueous solvent includes a first solvent, a second solvent, and a third solvent; The first solvent contains at least one of ethylene carbonate, propylene carbonate, and butylene carbonate, and the mass content of the first solvent in the nonaqueous solvent is B1, calculated based on the total mass of the nonaqueous 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 nonaqueous electrolyte 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, calculated based on the total mass of the non-aqueous electrolyte, and C1 is 0.05% to 2%. The nonaqueous electrolyte according to claim 1 .

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

8. The nonaqueous electrolyte 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 nonaqueous electrolyte according to claim 1 .

12. A secondary battery including an electrode assembly, a non-aqueous electrolyte, and an exterior body, The nonaqueous electrolyte solution is the nonaqueous electrolyte solution according to any one of claims 1 to 3. Secondary battery.

13. 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, the electrochemical impedance spectrum is measured using an electrochemical AC impedance method of 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 set 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 of 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 the charge transfer resistance Rct2 of the negative electrode sheet. The secondary battery according to claim 12.

14. the non-aqueous 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 electrolyte 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 electrode assembly is centrifuged, and the liquid obtained by the centrifugal treatment is the first electrolyte solution. The secondary battery according to claim 12.

15. The positive electrode sheet has a molecular formula of Li ａ Ni ｂ Co ｃ Mn ｄ A 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, b+c+d+e+f=1, g+h=2; The secondary battery according to claim 12.

16. 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 15, which satisfies at least one of the above conditions (1) to (8).

17. A battery module comprising the secondary battery according to claim 12.

18. A battery pack comprising the secondary battery according to claim 12 and one of the battery modules according to claim 17.

19. An electric device comprising at least one of the secondary battery according to claim 12, the battery module according to claim 17, and the battery pack according to claim 18.

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