Electrolyte, secondary battery, and device

Abstract

The invention provides an electrolyte, a secondary battery and a device. The electrolyte comprises fluorine-containing lithium sulfimide and a boron ring compound shown in a formula I, wherein # imgabs0 # n is 1, 2 or 3; r1 and R2 are selected from hydrogen, fluorine, alkyl with 1 to 6 carbon atoms, alkoxy with 1 to 6 carbon atoms, alkenyl with 2 to 6 carbon atoms, alkenyloxy with 2 to 6 carbon atoms, alkynyl with 2 to 6 carbon atoms, alkynyloxy with 2 to 6 carbon atoms, cycloalkyl with 3 to 6 carbon atoms, epoxy alkyl with 3 to 6 carbon atoms, aryl with 6 to 12 carbon atoms or heteroaryl with 6 to 12 carbon atoms; r3 and R4 are selected from fluorine, C1-C6 alkyl groups, C1-C6 alkoxy groups or C1-C6 ester alkyl groups; or, R3 and R4 are interconnected and are selected from the group consisting of a C1-C6 alkylene group, a C1-C6 alkyleneoxy group, and a C1-C6 alkenylidenealkyl group; m is selected from lithium or sodium; based on the mass of the electrolyte, the mass percentage content of the fluorine-containing lithium sulfimide is S%, the mass percentage content of the boron ring compound is R%, and S / R is greater than or equal to 1 and less than or equal to 35.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and in particular to an electrolyte, a secondary battery and a device. Background Art

[0002] At present, lithium hexafluorophosphate (LiPF 6 ) is a commonly used lithium salt in lithium-ion batteries due to its comprehensive advantages such as high ionic conductivity, wide electrochemical window and good film formation on the positive and negative electrode surfaces. 6 It is easy to decompose at high temperature and is extremely sensitive to moisture, producing highly toxic PF 5 In addition, for high-voltage and high-capacity cathode systems such as high-nickel ternary and lithium-rich manganese-based cathodes, the presence of HF in the electrolyte will cause Mn 2+ dissolves, thus destroying the structural integrity of the positive electrode material, accelerating the attenuation of battery capacity and the deterioration of cycle stability. 6 It is difficult to apply to special battery systems with high energy density.

[0003] In recent years, fluorinated lithium sulfonyl imide has been widely studied. 6 The price is similar, and it is more soluble in carbonate solvents than LiPF 6 It has higher ionic conductivity, and its thermal stability and water stability are better than LiPF 6 In addition, the interfacial protective film formed by the lithium salt on the surface of the positive and negative electrodes has lower impedance, which is conducive to improving the battery rate performance. Therefore, fluorinated sulfonyl imide lithium is expected to become LiPF 6 However, fluorinated lithium sulfonyl imide easily corrodes the positive electrode current collector aluminum foil under high voltage, which limits its application in high-voltage battery systems. To address this problem, existing reports show that the use of boron-based lithium salts such as lithium bis(oxalatoborate) (LiBOB) or lithium difluorooxalatoborate (LiDFOB), as well as LiPF 6 Although the problem of lithium fluoride sulfonyl imide corroding aluminum foil under high voltage can be improved to a certain extent by mixing lithium salts such as LiFSI with fluorine-containing sulfonyl imide, a large amount of these lithium salts (20% to 40%) need to be added, which will bring other problems. 6 If too much is added, the electrolyte will inherit LiPF 6 disadvantages; when the amount of boron lithium salts such as LiBOB or LiDFOB is added in large quantities, the battery impedance becomes larger and the gas production is serious.

[0004] Therefore, it is of great significance to develop a high-performance aluminum foil corrosion-resistant additive for electrolyte to prevent the corrosion of aluminum foil by fluorinated sulfonyl imide lithium, thereby realizing the application of fluorinated sulfonyl imide lithium in high-voltage battery systems and improving battery safety performance. Summary of the invention

[0005] In view of the above problems existing in the prior art, the present application provides an electrolyte, a secondary battery and a device.

[0006] The first aspect of the present application provides an electrolyte, comprising a fluorinated lithium sulfonyl imide and a boron ring compound represented by formula I;

[0007]

[0008] In Formula 1, n is 1, 2 or 3; R 1 and R 2 R is each independently selected from hydrogen, fluorine, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C2-C6 alkenyloxy, substituted or unsubstituted C2-C6 alkynyl, substituted or unsubstituted C2-C6 alkynyloxy, substituted or unsubstituted C3-C6 cycloalkyl, substituted or unsubstituted C3-C6 epoxyalkyl, substituted or unsubstituted C6-C12 aryl, or substituted or unsubstituted C6-C12 heteroaryl; 3 and R 4 are each independently selected from fluorine, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy or substituted or unsubstituted C1-C6 ester alkyl; or, R 3 and R 4 interconnected, and R 3 and R 4 Each independently selected from substituted or unsubstituted C1-C6 alkylene, substituted or unsubstituted C1-C6 alkyleneoxy, substituted or unsubstituted C1-C6 ester-based alkyl; the substituted substituents are each independently selected from fluorine, R 1 and R 2 At least one of them contains fluorine, R 3 and R 4 At least one of them contains fluorine; M is selected from lithium or sodium; based on the mass of the electrolyte, the mass percentage of the fluorinated sulfonyl imide lithium is S%, the mass percentage of the boron ring compound is R%, and the following is satisfied: 1≤S / R≤35.

[0009] The electrolyte of the present application includes a fluorinated lithium sulfonyl imide and a boron ring compound. By controlling the ratio of the content of the fluorinated lithium sulfonyl imide to the content of the boron ring compound, the boron ring compound can form a layer rich in AlF on the surface of the positive electrode current collector aluminum foil. 3The dense passivation film of organic-inorganic hybrid of lithium fluoride, lithium malonate derivatives, and boron-oxide can effectively avoid the continuous corrosion of the positive electrode current collector aluminum foil by the fluorinated lithium sulfonyl imide in the electrolyte at high voltage, reduce the impedance of the battery after formation, and reduce the gas production of the battery during the cycle, thereby significantly improving the cycle performance and rate performance of the high-voltage battery. At the same time, by adding fluorinated lithium sulfonyl imide, the electrolyte has excellent thermal stability, and the high temperature performance and safety performance of the battery are also greatly improved. In addition, by controlling the ratio of the content of fluorinated lithium sulfonyl imide and the content of boron ring compounds, the comprehensive performance of lithium batteries can be improved. The content of boron ring compounds is low, and the anti-corrosion effect is not very obvious. If the content of boron ring compounds is too high, the conductivity of the electrolyte will be reduced and the compatibility with the positive and negative electrodes will be poor. Although it does not corrode the aluminum foil, it affects the electrochemical performance of the battery.

[0010] A second aspect of the present application provides a secondary battery, which includes a positive electrode sheet, a negative electrode sheet and the aforementioned electrolyte.

[0011] A third aspect of the present application provides a device, which includes the aforementioned secondary battery. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as limiting the present application.

[0013] For simplicity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unspecified range.

[0014] In the description herein, unless otherwise specified, “above” and “below” include the number.

[0015] Unless otherwise specified, the terms used in this application have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0016] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0017] The term "C1-C6 alkyl" may be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl or n-hexyl, and the like.

[0018] The term "C1-C6 alkoxy" includes, but is not limited to, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, tert-butoxy, n-pentoxy, isopentyloxy or n-hexyloxy, etc.

[0019] The term "C2-C6 alkenyl" may be ethenyl, propenyl, butenyl, pentenyl or hexenyl.

[0020] The term "C2-C6 alkynyl" includes, but is not limited to, ethynyl, propynyl, butynyl, pentynyl or hexynyl and the like.

[0021] The term "C3-C6 cycloalkyl" includes, but is not limited to, cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl and the like.

[0022] The term "C3-C6 epoxyalkyl" includes, but is not limited to, cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl containing an epoxy group.

[0023] The term "C6-C12 aryl" may be phenyl or naphthyl, and the like.

[0024] The term "C6-C12 heteroaryl" refers to an aromatic group having 1-3 heteroatoms as ring atoms, the remaining ring atoms being carbon, and the heteroatoms including oxygen, sulfur or nitrogen, including but not limited to: furanyl, thienyl, pyridyl, pyrrolyl, pyrimidinyl, pyrazinyl or imidazolyl, etc.

[0025] The term "C1-C6 alkylene" may be methylene, ethylene, n-propylene, isopropylene, n-butylene, isobutylene, tert-butylene, n-pentylene, isopentylene or n-hexylene, or the like.

[0026] The term "C1-C6 alkyleneoxy" includes, but is not limited to, methyleneoxy, ethyleneoxy, n-propyloxy, isopropyloxy, n-butyloxy, isobutyloxy, tert-butyloxy, n-pentyloxy, isopentyloxy or n-hexyloxy, etc.

[0027] The term "C2-C6 alkenylene" can be vinylene, propenylene, butenylene, pentenylene or hexenylene. The present application is further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0028] 1. Electrolyte

[0029] One or more embodiments of the present application provide an electrolyte, including a fluorine-containing lithium sulfonyl imide and a boron ring compound shown in Formula I,

[0030]

[0031] In Formula 1, n is 1, 2 or 3; R 1 and R 2 R is each independently selected from hydrogen, fluorine, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C2-C6 alkenyloxy, substituted or unsubstituted C2-C6 alkynyl, substituted or unsubstituted C2-C6 alkynyloxy, substituted or unsubstituted C3-C6 cycloalkyl, substituted or unsubstituted C3-C6 epoxyalkyl, substituted or unsubstituted C6-C12 aryl, or substituted or unsubstituted C6-C12 heteroaryl; 3 and R 4 are each independently selected from fluorine, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy or substituted or unsubstituted C1-C6 ester alkyl; or, R 3 and R 4 interconnected, and R 3 and R 4 Each is independently selected from substituted or unsubstituted C1-C6 alkylene, substituted or unsubstituted C1-C6 alkyleneoxy, substituted or unsubstituted C1-C6 esterylalkyl; it is understood that various isomers of the groups satisfying the above number of carbon atoms are within the scope of protection claimed in the present application.

[0032] The substituted substituents are each independently selected from fluorine, R 1 and R 2 At least one of them contains fluorine, R 3 and R 4 At least one of them contains fluorine; M is selected from lithium or sodium.

[0033] In some embodiments, based on the mass of the electrolyte, the mass percentage of the fluorinated sulfonyl imide lithium is S%, and the mass percentage of the boron ring compound is R%, satisfying: 1≤S / R≤35. In some embodiments, S / R is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 35 or a range consisting of any two of the above values; in some embodiments, 2≤S / R≤25. In some embodiments, 5≤S / R≤15. Thus, by controlling the ratio of the content of the fluorinated sulfonyl imide lithium and the boron ring compound, the electrochemical performance and high temperature safety performance of the battery can be effectively improved. When S / R is too large, the corrosion of the current collector aluminum foil cannot be suppressed, resulting in a decline in battery performance; when S / R is too small, the conductivity of the battery electrolyte will decrease and the battery kinetic performance will decrease.

[0034] In some embodiments, based on the mass of the electrolyte, the mass percentage S% of the fluorinated sulfonyl imide lithium satisfies: 9≤S≤25. Exemplarily, based on the mass of the electrolyte, the mass percentage T% of the fluorinated sulfonyl imide lithium is 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25% or a range consisting of any two of the above values. In some embodiments, 12≤S≤17. When the mass percentage of the fluorinated sulfonyl imide lithium is too high, the viscosity of the electrolyte will increase, the conductivity will decrease, and the capacity and kinetic performance of the battery will be affected; when the mass percentage of the fluorinated sulfonyl imide lithium is too low, the corrosion of the current collector aluminum foil will not be effectively suppressed, and the battery performance will deteriorate.

[0035] In some embodiments, based on the mass of the electrolyte, the mass percentage R% of the boron ring compound satisfies: 0.01≤R≤10; illustratively, based on the mass of the electrolyte, the mass percentage R% of the boron ring compound is 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% or a range consisting of any two of the above values. In some embodiments, 0.5≤R≤5. When the mass percentage of the boron ring compound is too high, the conductivity of the electrolyte will decrease and the battery kinetic performance will decrease; when the mass percentage of the boron ring compound is too low, the corrosion of the current collector aluminum foil will not be suppressed, resulting in battery performance degradation.

[0036] It can be understood that the electrolyte of the above embodiment includes fluorinated lithium sulfonyl imide and boron ring compound. By controlling the ratio of the content of fluorinated lithium sulfonyl imide to the content of boron ring compound, the boron ring compound can form a layer rich in AlF on the surface of the positive electrode current collector aluminum foil. 3 The dense organic-inorganic hybrid passivation film of lithium malonate derivatives can effectively prevent the continuous corrosion of the positive electrode current collector aluminum foil by lithium salts such as lithium fluorinated sulfonyl imide (such as LiFSI) in the electrolyte at high voltage, reduce the impedance of the battery after formation, and reduce the gas production of the battery during the cycle, thereby significantly improving the cycle performance and rate performance of high-voltage batteries. At the same time, the electrolyte has excellent thermal stability, and has greatly improved the high temperature performance and safety performance of the battery.

[0037] In some embodiments, the fluorine-containing lithium sulfonyl imide includes at least one of lithium bisfluorosulfonyl imide, lithium bis(trifluoromethylsulfonyl)imide, lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, lithium (fluorosulfonyl)(perfluorobutylsulfonyl)imide, lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide, and lithium bis(pentafluoroethylsulfonyl)imide. In some embodiments, the fluorine-containing lithium sulfonyl imide includes lithium bisfluorosulfonyl imide (LiFSI).

[0038] In some embodiments, in Formula 1, n is 1, and the boron ring compound is a six-membered boron ring compound, and its structural formula is Therefore, the six-membered boron ring compound has more stable chemical properties and is easy to store and prepare.

[0039] In some embodiments, n is 1, and R 1 and R 2 One of fluorine, R 1 and R 2 The other one of them is selected from substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C1-C4 alkoxy, substituted or unsubstituted C2-C4 alkenyl, substituted or unsubstituted C2-C4 alkenyloxy, substituted or unsubstituted C2-C4 alkynyl, substituted or unsubstituted C2-C4 alkynyloxy or substituted or unsubstituted C6-C12 aryl; R 3 and R 4 All are fluorine; M is lithium.

[0040] In some embodiments, the boron ring compound includes at least one of Compound 1, Compound 2, Compound 3, and Compound 4:

[0041]

[0042] In some implementations, the electrode solution further includes a first lithium salt, the first lithium salt including lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4), at least one of trifluorosulfonyl lithium (LiOTf), lithium bis(oxalatoborate) (LiBOB), lithium bis(fluoromalonate)borate (LiBFMB), lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium (LiTDI) and lithium difluorooxalatoborate (LiDFOB).

[0043] In some embodiments, the concentration of the first lithium salt in the electrolyte is 0.01 mol / L to 2.0 mol / L. Exemplarily, the concentration of the first lithium salt in the electrolyte is 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L, 2.0 mol / L or a range consisting of any two of the above values.

[0044] In some embodiments, the electrolyte further includes a first additive, the first additive including vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), 1,3-propane sultone (PS), vinyl sulfate (DTD), 1,3-propene sultone (1,3-PST), vinyl sulfite (ES), tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB), methylene disulfonate (MMD S), succinonitrile, adiponitrile, glutaronitrile, hexanetrinitrile, ethyl disulfonate, 1-propylene-1,3-sultone (PST), 1,4-butane sultone (1,4-BS), 4-methylethylene sulfate (PCS), 4-ethylethylene sulfate (PES), 4-propylethylene sulfate (PEGLST), propylene sulfate (TS), ethylene sulfite (DTO), dimethyl sulfite (DMS) and diethyl sulfite (DES).

[0045] In some embodiments, based on the mass of the electrolyte, the mass percentage of the first additive satisfies 0.01% to 10%. Exemplarily, based on the mass of the electrolyte, the mass percentage of the first additive is 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% or a range consisting of any two of the above values.

[0046] In some embodiments, the electrolyte further includes a non-aqueous solvent, and the non-aqueous solvent includes at least one of a linear carbonate, a cyclic carbonate, and a carboxylic acid ester.

[0047] In some embodiments, the linear carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and fluorinated linear carbonate.

[0048] In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, and a fluorinated cyclic carbonate.

[0049] In some embodiments, the carboxylic acid ester includes at least one of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, and a fluorocarboxylic acid ester.

[0050] In some embodiments, the mass percentage of the non-aqueous solvent is 10% to 70% based on the mass of the electrolyte. Exemplarily, the mass percentage of the non-aqueous solvent is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or a range consisting of any two of the above values ​​based on the mass of the electrolyte.

[0051] 2. Secondary battery

[0052] One or more embodiments of the present application further provide a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, and the electrolyte of the aforementioned embodiment.

[0053] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0054] In some embodiments, the positive electrode active material includes lithium nickel transition metal oxide. The lithium nickel transition metal oxide includes LiNi x Co y M (1-x-y) O 2 At least one of the following, M includes at least one of manganese, iron, chromium, titanium, zinc, vanadium, aluminum, zirconium, cerium, magnesium, calcium, molybdenum, strontium, tungsten, copper, yttrium, lanthanum, gallium, silver and niobium, 0.5≤x≤1, 0≤y≤0.5, x+y≤1.

[0055] In some embodiments, the positive electrode current collector includes but is not limited to aluminum foil or a composite material containing aluminum. The electrolyte of the present application includes fluorinated lithium sulfonyl imide and a boron ring compound, which solves the problem that fluorinated lithium sulfonyl imide corrodes the aluminum foil as the positive electrode current collector under high voltage, and significantly improves the cycle performance and rate performance of the secondary battery under high voltage.

[0056] In some embodiments, the positive electrode active material layer further includes a conductive agent and a binder. The positive electrode active material, the conductive agent, and the binder are mixed in a solvent system (e.g., N-methylpyrrolidone) in a certain proportion, and then coated on an aluminum current collector, dried, and rolled to obtain a positive electrode sheet.

[0057] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0058] In some embodiments, the negative electrode active material includes at least one of a silicon-based material, a carbon-based material, a tin-based material, a phosphorus-based material, and metallic lithium.

[0059] In some embodiments, the silicon-based material includes at least one of silicon, silicon alloys, silicon-oxygen compounds, and silicon-carbon compounds.

[0060] In some embodiments, the carbon-based material includes at least one of graphite, soft carbon, hard carbon, carbon nanotubes, and graphene.

[0061] In some embodiments, the tin-based material includes at least one of tin, tin oxide, and tin alloy.

[0062] In some embodiments, the phosphorus-based material includes phosphorus and / or a phosphorus-carbon composite.

[0063] In some embodiments, the material of the negative electrode current collector includes but is not limited to copper, and can be any conventional negative electrode current collector material or a material that has the potential to become a negative electrode current collector, and the present application does not impose any specific limitation on this.

[0064] In some embodiments, the negative electrode active material layer further includes a conductive agent and a binder. The negative electrode active material, the conductive agent, and the binder are mixed in a solvent (e.g., deionized water) in a certain proportion, and then coated on a copper current collector, dried, and rolled to obtain a negative electrode sheet.

[0065] In some embodiments, the leakage current of the secondary battery is TμA / cm 2 Satisfies: 0.01≤T≤25. For example, the leakage current of the secondary battery is TμA / cm 2 0.01μA / cm 2 , 0.05μA / cm 2 , 0.1μA / cm 2 , 0.5μA / cm 2 , 1μA / cm 2 , 2μA / cm 2 , 4μA / cm 2 , 5μA / cm 2 , 6μA / cm 2 , 8μA / cm2 , 10μA / cm 2 , 12μA / cm 2 , 14μA / cm 2 , 15μA / cm 2 , 16μA / cm 2 , 18μA / cm 2 , 20μA / cm 2 , 21μA / cm 2 , 22μA / cm 2 , 24μA / cm 2 , 24.5μA / cm 2 Or a range consisting of any two of the above values. Therefore, when the leakage current is within the above range, the cycle stability of the battery will be improved. When the leakage current is too large, the current collector aluminum foil will be severely corroded, resulting in an increase in the irreversible capacity of the battery, serious gas production of the battery, and a deterioration in the cycle life.

[0066] In some embodiments, the leakage current of the secondary battery is TμA / cm 2 Satisfies: 10≤T≤15. Exemplarily, the leakage current of the secondary battery is TμA / cm 2 10.5μA / cm 2 , 11μA / cm 2 , 11.5μA / cm 2 , 12.5μA / cm 2 , 13μA / cm 2 , 13.5μA / cm 2 , 14.5μA / cm 2 Or a range consisting of any two of the above values.

[0067] In some embodiments, the secondary battery of the present application includes a separator, which includes a composite film composed of at least one or more of polyethylene, polypropylene, polyvinylidene fluoride, aramid and polyimide films, or a composite film modified by a ceramic material coating.

[0068] 3. Battery Module

[0069] One or more embodiments of the present application further provide a battery module, the battery module comprising the aforementioned secondary battery.

[0070] The battery module of the present application uses the above-mentioned secondary battery, and therefore has at least the same advantages as the secondary battery. The number of secondary batteries contained in the battery module of the present application can be one or more, and the specific number can be adjusted according to the application and capacity of the battery module.

[0071] 4. Battery Pack

[0072] One or more embodiments of the present application also provide a battery pack, which includes the aforementioned battery module.

[0073] The number of battery modules contained in a battery pack may be one or more, and the specific number may be adjusted according to the application and capacity of the battery pack.

[0074] 5. Device

[0075] One or more embodiments of the present application also provide a device, which includes at least one of the aforementioned secondary battery, battery module and battery pack.

[0076] In some embodiments, the device of the present application includes, but is not limited to: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, etc. In order to meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0077] In some embodiments, the device of the present application also includes: a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini CD, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, lighting fixtures, toys, a game console, a clock, a power tool, a flashlight, a camera, a large household battery or a lithium-ion capacitor, etc.

[0078] The technical solution of the present application will be further illustrated below with reference to specific embodiments and comparative examples.

[0079] Examples and Comparative Examples

[0080] Example 1

[0081] The steps of preparing the positive electrode sheet, the negative electrode sheet, the electrolyte, the separator and the battery are described as follows. 0.9 Co 0.05 Mn 0.05 O 2 ; The negative electrode active material is artificial graphite, and the coating surface density is determined according to the battery size, capacity design and the capacity of the positive and negative electrode materials.

[0082] The positive electrode preparation steps are: 0.9 Co 0.05 Mn 0.05 O 2 , conductive agent carbon nanotube / acetylene black, binder polyvinylidene fluoride (PVDF), by weight ratio LiNi0.9 Co 0.05 Mn 0.05 O 2 : CNT / Super-P: PVDF=95:2.0 / 1.0:2 was fully slurried in N-methylpyrrolidone (NMP) solvent system, coated on a 12 μm thick aluminum-coated current collector, dried, and roll-pressed to obtain a positive electrode sheet.

[0083] The negative electrode preparation steps are as follows: artificial graphite, a negative electrode active material, acetylene black, a binder, styrene butadiene rubber (SBR), a thickener, sodium carboxymethyl cellulose (CMCNa), and polyacrylic acid (PAA) are fully slurried in a deionized water solvent in a weight ratio of 95:2:1.5:1:0.5, and then coated on the surface of a 8μm thick copper current collector, and then dried, rolled, and slit to obtain a negative electrode sheet.

[0084] The diaphragm is a PP / PE / PP three-layer composite diaphragm.

[0085] Preparation of electrolyte: In a glove box filled with argon (H 2 O<0.1ppm,O 2 <0.1ppm), ethylene carbonate, propylene carbonate, diethyl carbonate and ethyl methyl carbonate are mixed in a mass ratio of EC:DEC:EMC=25:20:55, and then 17% of lithium bis(fluorosulfonyl)imide (LiFSI) based on the total weight of the electrolyte is slowly added to the mixed solution, and finally 0.5% of compound 1 based on the total weight of the electrolyte is added, and the lithium ion battery electrolyte of Example 1 is obtained after stirring.

[0086] Preparation of secondary battery: stack the prepared positive electrode sheet, separator and negative electrode sheet in order, make the separator between the positive and negative electrode sheets, and wind them to get bare battery cell; place the bare battery cell in an aluminum plastic film outer packaging, inject the prepared electrolyte into the fully dried artificial graphite / LiNi 0.9 Co 0.05 Mn 0.05 O 2 In the battery, the battery was placed at 45°C, formed in a high-temperature fixture (the formation conditions were: temperature 45°C, pressure 210kgf, 0.05C current charging to 4.25V and standing for 60min, then 0.1C charging to 4.25V, and then 0.2C discharge to 3.0V, and this was repeated three times) and secondary sealing before conventional capacity division.

[0087] It can be understood that the content of each component in the electrolyte of this embodiment refers to the mass percentage of each component based on the mass of the electrolyte.

[0088] Examples 2 to 13 and Comparative Examples 1 to 11

[0089] The only difference between Examples 2 to 13 and Comparative Examples 1 to 11 and Example 1 is that at least one of the type and mass percentage of the fluorinated sulfonic acid imide lithium, the type and mass percentage of the first lithium salt, the type and mass percentage of the boron ring compound, and the type and mass percentage of the first additive in the electrolyte is changed.

[0090] The rest of the preparation methods of Examples 2 to 17 and Comparative Examples 1 to 9 are the same as those of Example 1. Specific adjustment measures and detailed data are shown in Table 1.

[0091] Table 1

[0092]

[0093]

[0094]

[0095] Test method:

[0096] 1. Leakage current test

[0097] The battery after capacity conversion was float-charged at a constant voltage of 4.5 V using an electrochemical workstation to obtain a stable current-time It curve. The current value after 12 hours was read, which was the leakage current of the battery.

[0098] 2. Impedance test

[0099] Before the cycle capacity retention rate test, the lithium-ion battery was discharged to 2.5V at 1C constant current at 25±2℃, then charged to 4.25V at 0.5C constant current, and charged to 0.05C at 4.25V, and then discharged to 50% SOC at 1C constant current, and left to stand for 60 minutes, and the voltage U1 after the end of the standing was recorded, and then discharged at 2C constant current for 10s, and the voltage U2 after the discharge was recorded, and the 2C current was recorded as I, and left to stand for 60 minutes. According to the formula DCR = (U1-U2) / I, the discharge DCR (impedance) of the battery at 50% SOC is calculated.

[0100] 3. Cycle capacity retention rate test

[0101] At 25°C, the lithium-ion battery was charged to 4.25V at 1C constant current and constant voltage, and then discharged to 2.5V at 1C constant current. After 500 cycles of charge and discharge, the capacity retention rate after the 500th cycle at 25°C was calculated according to the following formula: discharge capacity after the 500th cycle / discharge capacity in the first cycle×100%.

[0102] At 25°C, the lithium-ion battery was charged to 4.25V at 2C constant current and constant voltage, and then discharged to 2.5V at 2C constant current. After 500 cycles of charge and discharge, the capacity retention rate after the 500th cycle at 25°C was calculated according to the following formula: discharge capacity after the 500th cycle / discharge capacity in the first cycle×100%.

[0103] At 45°C, the lithium-ion battery was charged to 4.25V at 1C constant current and constant voltage, and then discharged to 2.5V at 1C constant current. After 300 cycles of charge and discharge, the capacity retention rate after the 300th cycle at 45°C was calculated according to the following formula: discharge capacity after the 300th cycle / discharge capacity in the first cycle×100%.

[0104] 4. Expansion rate test

[0105] The battery was discharged at 0.5C to 3.0V at 25°C, then charged at 0.5C to 4.45V, and then charged at a constant voltage to 0.05C at 4.45V. The thickness of the battery at this time was measured using a PPG soft pack battery thickness gauge and recorded as a. The battery was placed in an oven and stored at a constant voltage of 4.45V at 45°C for 14 days. The thickness of the battery after 14 days was recorded as b. The thickness expansion rate was calculated as: (ba) / a×100%.

[0106] Table 2

[0107]

[0108]

[0109] From the experimental results, referring to the experimental data of Examples 1 to 11 and Comparative Example 1, after adding compound 1 to the electrolyte, the leakage current, the impedance after the secondary battery is formed, and the expansion rate are significantly reduced, and the cycle capacity retention rate of the secondary battery is also significantly improved. In addition, in conjunction with Comparative Example 2, when the mass percentage of compound 1 is too large, the S / R value does not meet the preset relationship, the improvement of the comprehensive performance of the secondary battery is not obvious, and the DCR is significantly increased, affecting the battery rate performance. Further, in conjunction with Comparative Example 3, the content of compound 1 is too low, and the S / R value does not meet the preset relationship, which will cause severe corrosion of the positive electrode current collector aluminum foil. This is because when the content of compound 1 is too low, the passivation film formed on the surface of the current collector is not enough to resist the corrosion of the electrolyte with a higher LiFSI content.

[0110] In addition, referring to the experimental data of Comparative Examples 1 and 4 to 7, when the first additive is added to the electrolyte alone without adding the boron ring compound, the cycle capacity retention rate of the secondary battery is further deteriorated and the aluminum foil is corroded; however, in combination with the experimental data of Examples 5 to 11, when Compound 1 and the first additive are added to the electrolyte at the same time, the impedance and expansion rate of the secondary battery after formation are further reduced, and the cycle capacity retention rate of the secondary battery is further improved; This indicates that Compound 1 and the first additive also have an obvious synergistic effect.

[0111] Further, referring to the experimental data of Examples 7 to 9, after using Compound 2, Compound 3 and Compound 4 to replace Compound 1, respectively, similar technical effects as Compound 1 can be achieved. It can be seen that the use of the boron ring compound of the present application to improve the comprehensive performance of the secondary battery is universal. However, referring to Comparative Examples 4 to 7, other types of boron ring compounds (for example, LiBOB or LiDFOB, as the first lithium salt) are used in combination with the first additive, and the above technical effects cannot be achieved. In addition, referring to Examples 12 and 13 and Comparative Examples 10 and 11, even if the S / R value satisfies the preset relationship, the content of LIFSI is too low, the improvement of the comprehensive performance of the secondary battery is still not obvious, and the capacity retention rate is poor, which further proves that LIFSI and Compound 1 have obvious synergistic effects.

[0112] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those skilled in the art will recognize that some modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. An electrolyte, characterized in that: It includes a fluorine-containing lithium sulfonyl imide and a boron ring compound shown in formula I; In formula 1, n is 1, 2 or 3; R1 and R2 are each independently selected from hydrogen, fluorine, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C2-C6 alkenyloxy, substituted or unsubstituted C2-C6 alkynyl, substituted or unsubstituted C2-C6 alkynyloxy, substituted or unsubstituted C3-C6 cycloalkyl, substituted or unsubstituted C3-C6 epoxyalkyl, substituted or unsubstituted C6-C12 aryl, or substituted or unsubstituted C6-C12 heteroaryl; R3 and R4 are each independently selected from fluorine, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, or substituted or unsubstituted C1-C6 esteralkyl; or, R3 and R4 are interconnected, and R3 and R4 are each independently selected from substituted or unsubstituted C1-C6 alkylene, substituted or unsubstituted C1-C6 alkyleneoxy, substituted or unsubstituted C1-C6 esteralkylene; The substituted substituents are each independently selected from fluorine, at least one of R1 and R2 contains fluorine, and at least one of R3 and R4 contains fluorine; M is selected from lithium or sodium; Based on the mass of the electrolyte, the mass percentage of the fluorinated sulfonyl imide lithium is S%, the mass percentage of the boron ring compound is R%, and the following conditions are satisfied: 1≤S / R≤35.

2. The electrolyte according to claim 1, characterized in that The fluorine-containing lithium sulfonyl imide comprises at least one of lithium bisfluorosulfonyl imide, lithium bis(trifluoromethylsulfonyl)imide, lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, lithium (fluorosulfonyl)(perfluorobutylsulfonyl)imide, lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide and lithium bis(pentafluoroethylsulfonyl)imide; and / or In formula I, n is 1; one of R1 and R2 is selected from fluorine, the other of R1 and R2 is selected from substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C1-C4 alkoxy, substituted or unsubstituted C2-C4 alkenyl, substituted or unsubstituted C2-C4 alkenyloxy, substituted or unsubstituted C2-C4 alkynyl, substituted or unsubstituted C2-C4 alkynyloxy or substituted or unsubstituted C6-C12 aryl, R3 and R4 are both fluorine, and M is lithium.

3. The electrolyte according to claim 1 or 2, characterized in that The fluorine-containing lithium sulfonyl imide comprises lithium bis(fluorosulfonyl)imide; and / or The boron ring compound includes at least one of the following compounds:

4. The electrolyte according to claim 1, characterized in that 2≤S / R≤25; and / or, 9≤S≤25; and / or, 0.01≤R≤10.

5. The electrolyte according to claim 4, characterized in that 5≤S / R≤15; and / or, 12≤S≤17; and / or, 0.5≤R≤5.

6. The electrolyte according to claim 1, characterized in that The electrolyte further includes a first lithium salt, the first lithium salt including at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, trifluorosulfonyl lithium, lithium bis(oxalatoborate), lithium bis(fluoromalonate)borate, 4,5-dicyano-2-(trifluoromethyl)imidazole lithium and lithium difluorooxalatoborate; the concentration of the first lithium salt is 0.01 mol / L to 2.0 mol / L; and / or The electrolyte further includes a first additive, the first additive including at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, vinyl sulfate, 1,3-propene sultone, vinyl sulfite, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, methylene disulfonate, succinonitrile, adiponitrile, glutaronitrile, hexanetrinitrile, ethyl disulfonate, 1-propylene-1,3-sultone, 1,4-butane sultone, 4-methyl ethylene sulfate, 4-ethyl ethylene sulfate, 4-propyl ethylene sulfate, propylene sulfate, ethylene sulfite, dimethyl sulfite and diethyl sulfite; based on the mass of the electrolyte, the mass percentage of the first additive is 0.01% to 10%; and / or The electrolyte also includes a non-aqueous solvent, which includes at least one of a chain carbonate, a cyclic carbonate and a carboxylic acid ester; the chain carbonate includes at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate and a fluorinated chain carbonate; the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate and a fluorinated cyclic carbonate; the carboxylic acid ester includes at least one of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone and a fluorinated carboxylic acid ester; based on the mass of the electrolyte, the mass percentage of the non-aqueous solvent is 10% to 70%.

7. A secondary battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and the electrolyte according to any one of claims 1 to 6.

8. The secondary battery according to claim 7, characterized in that: The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, wherein the positive electrode active material comprises a lithium nickel transition metal oxide; the lithium nickel transition metal oxide comprises LiNi x Co y M (1-x-y) O2, M includes at least one of manganese, iron, chromium, titanium, zinc, vanadium, aluminum, zirconium, cerium, magnesium, calcium, molybdenum, strontium, tungsten, copper, yttrium, lanthanum, gallium, silver and niobium, 0.5≤x≤1, 0≤y≤0.5, x+y≤1; the material of the positive electrode current collector includes aluminum; and / or The negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material, the negative electrode active material comprises at least one of a silicon-based material, a carbon-based material, a tin-based material, a phosphorus-based material and metallic lithium; the silicon-based material comprises at least one of silicon, a silicon alloy, a silicon oxide compound and a silicon-carbon compound, the carbon-based material comprises at least one of graphite, soft carbon, hard carbon, carbon nanotubes and graphene, the tin-based material comprises at least one of tin, tin oxide and a tin alloy, the phosphorus-based material comprises phosphorus and / or a phosphorus-carbon composite; and / or The leakage current of the secondary battery is TμA / cm 2 Satisfies: 0.01≤T≤25.

9. The secondary battery according to claim 8, characterized in that: The leakage current of the secondary battery is TμA / cm 2 Satisfies: 10≤T≤15.

10. A device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 7 to 9.

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