Electrochemical devices and electronic devices

Abstract

The present application relates to an electrochemical device and an electronic device. Specifically, the present application provides an electrochemical device, which includes: a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, wherein: the negative electrode active material layer includes a nonionic surfactant, and the electrolyte includes alkyl lithium sulfate. The electrochemical device of the present application has improved floating charge performance and safety.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and in particular to an electrochemical device and an electronic device, in particular a lithium-ion battery. Background Art

[0002] In recent years, electrochemical devices (e.g., lithium-ion batteries) have been widely used in the fields of mobile phones, tablet computers, electric vehicles, etc. as a green secondary battery with high energy density and power density. However, the electrolyte used in existing lithium-ion batteries usually includes ethylene carbonate, dimethyl carbonate, diethyl carbonate and other flammable organic solvents, which are prone to violent combustion and even battery explosion when thermal runaway occurs. Therefore, the safety of lithium-ion batteries has attracted more and more attention.

[0003] Although battery manufacturers, raw material suppliers and research institutes have done a lot of work on improving the performance of lithium-ion batteries, existing methods are still unable to effectively improve the floating charge performance of lithium-ion batteries and fundamentally control the thermal runaway of lithium-ion batteries.

[0004] In view of the above, there is a real need to provide an electrochemical device and an electronic device with improved floating charge performance and safety. Summary of the invention

[0005] The embodiments of the present application solve the problems existing in the prior art to some extent by providing an electrochemical device and an electronic device with improved floating charge performance and safety.

[0006] In one aspect of the present application, the present application provides an electrochemical device comprising: a positive electrode, a negative electrode and an electrolyte, the negative electrode comprising a negative electrode collector and a negative electrode active material layer formed on the negative electrode collector, wherein: the negative electrode active material layer comprises a non-ionic surfactant, and the electrolyte comprises alkyl lithium sulfate.

[0007] According to an embodiment of the present application, based on the weight of the negative electrode active material layer, the content of the nonionic surfactant is a%; based on the weight of the electrolyte, the content of the alkyl lithium sulfate is b%; and a and b satisfy: 0.1≤a / b≤2.

[0008] According to an embodiment of the present application, the value range of a is 0.01 to 5.

[0009] According to an embodiment of the present application, the value range of b is 0.01 to 5.

[0010] According to an embodiment of the present application, the nonionic surfactant has a chain segment formed by an ethylene oxide structure.

[0011] According to an embodiment of the present application, the hydrophile-lipophile balance value of the nonionic surfactant is in the range of 8 to 19.

[0012] According to an embodiment of the present application, the nonionic surfactant includes at least one of polyoxyethylene alkyl ether, sorbitan fatty acid ester, glycerol fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene resin hardened castor oil or polyoxyethylene alkylamine.

[0013] According to an embodiment of the present application, the alkyl lithium sulfate includes a compound of formula I:

[0014]

[0015] in:

[0016] R is selected from the following groups which are unsubstituted or substituted with one or more halogens: C1-20 alkyl, C2-20 alkoxy, C6-12 aryl, C2-10 alkenyl, C2-10 alkynyl, C3-18 chain ester, C3-18 cyclic ester, C4-10 silane or C2-10 alkyl containing a cyano group.

[0017] According to an embodiment of the present application, the alkyl lithium sulfate includes methyl lithium sulfate, ethyl lithium sulfate, propyl lithium sulfate, butyl lithium sulfate, pentyl lithium sulfate, hexyl lithium sulfate, heptyl lithium sulfate, octyl lithium sulfate, isopropyl lithium sulfate, sec-butyl lithium sulfate, trifluoromethyl lithium sulfate, 2,2,2-trifluoroethyl lithium sulfate, 2,2,3,3-tetrafluoropropyl lithium sulfate, 1,1,1,3,3,3-hexafluoro-2-propyl lithium sulfate, methoxyethyl lithium sulfate, ethoxyethyl lithium sulfate, methoxypropyl At least one of lithium sulfate, phenyl lithium sulfate, 4-methylphenyl lithium sulfate, 4-fluorophenyl lithium sulfate, perfluorophenyl lithium sulfate, vinyl lithium sulfate, allyl lithium sulfate, propargyl lithium sulfate, 1-oxo-1-(2-propynyloxy)propane-2-yl lithium sulfate, 2-(trimethylsilyl)ethyl lithium sulfate, 2-cyanoethyl lithium sulfate or 1,3-dicyanopropynyl-2-yl lithium sulfate; preferably at least one of hexyl lithium sulfate, trifluoromethyl lithium sulfate or 2-cyanoethyl lithium sulfate.

[0018] According to an embodiment of the present application, the electrolyte further comprises a fluorine- and phosphorus-containing compound, wherein the fluorine- and phosphorus-containing compound comprises at least one of lithium difluorophosphate, lithium monofluorophosphate or a compound of formula II:

[0019]

[0020] Wherein R is a C1-10 hydrocarbon group or a C1-10 hydrocarbon group substituted by halogen.

[0021] According to an embodiment of the present application, the compound of formula II comprises at least one of the following compounds:

[0022]

[0023] According to an embodiment of the present application, based on the weight of the electrolyte, the content of the alkyl lithium sulfate is b%, and the content of the fluorine- and phosphorus-containing compound is c%, and b and c satisfy: 0.5≤b+c≤5 and 0.4≤b / c≤5.

[0024] According to an embodiment of the present application, based on the weight of the electrolyte, the content of the fluorine- and phosphorus-containing compound is c%, and the value range of c is 0.1 to 5.

[0025] According to an embodiment of the present application, the value range of c is 0.2 to 3.

[0026] In another aspect of the present application, the present application provides an electronic device, which includes the electrochemical device according to the present application.

[0027] The specific combination of the negative electrode active material layer including the nonionic surfactant and the electrolyte including the alkyl lithium sulfate used in the present application can significantly improve the floating performance and safety of the electrochemical device.

[0028] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the subsequent description through implementation of the embodiments of the present application. DETAILED DESCRIPTION

[0029] The embodiments of the present application will be described in detail below. The embodiments of the present application should not be interpreted as limiting the present application.

[0030] Unless expressly stated otherwise, the following terms used herein have the meanings indicated below.

[0031] In the detailed description and claims, a list of items connected by the term "at least one of" 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 include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements. The term "at least one of" has the same meaning as the term "at least one of."

[0032] The term "hydrocarbyl" encompasses alkyl, alkenyl, alkynyl.

[0033] The term "alkyl" is expected to be a straight chain saturated hydrocarbon structure with 1 to 20 carbon atoms. "Alkyl" is also expected to be a branched or cyclic hydrocarbon structure with 3 to 20 carbon atoms. When specifying an alkyl with a specific carbon number, it is expected to cover all geometric isomers with that carbon number; therefore, for example, "butyl" means including n-butyl, sec-butyl, isobutyl, tert-butyl and cyclobutyl; "propyl" includes n-propyl, isopropyl and cyclopropyl. Alkyl examples include, but are not limited to methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornyl, etc.

[0034] The term "alkenyl" refers to a monovalent unsaturated hydrocarbon group which may be straight or branched and has at least one and typically 1, 2 or 3 carbon-carbon double bonds. Unless otherwise defined, the alkenyl group typically contains 2 to 20 carbon atoms and includes, for example, -C 2-4 Alkenyl, -C 2-6 Alkenyl and -C 2-10 Representative alkenyl groups include, for example, ethenyl, n-propenyl, isopropenyl, n-but-2-enyl, but-3-enyl, n-hex-3-enyl, and the like.

[0035] The term "alkynyl" refers to a monovalent unsaturated hydrocarbon group which may be straight or branched and has at least one and typically 1, 2 or 3 carbon-carbon triple bonds. Unless otherwise defined, the alkynyl group typically contains 2 to 20 carbon atoms and includes, for example, -C 2-4 Alkynyl, -C 3-6 Alkynyl and -C 3-10 Representative alkynyl groups include, for example, ethynyl, prop-2-ynyl (n-propynyl), n-but-2-ynyl, n-hex-3-ynyl, and the like.

[0036] The term "aryl" means a monovalent aromatic hydrocarbon having a single ring (e.g., phenyl) or fused rings. Fused ring systems include those that are fully unsaturated (e.g., naphthalene) as well as those that are partially unsaturated (e.g., 1,2,3,4-tetrahydronaphthalene). Unless otherwise defined, the aryl group typically contains 6 to 26 carbon ring atoms and includes, for example, -C 6-10 Aryl. Representative aryl groups include, for example, phenyl, methylphenyl, propylphenyl, isopropylphenyl, benzyl, and naphth-1-yl, naphth-2-yl, and the like.

[0037] The term "cycloalkyl" encompasses cyclic alkyl groups. The cycloalkyl group may be a cycloalkyl group of 3-20 carbon atoms, a cycloalkyl group of 6-20 carbon atoms, a cycloalkyl group of 3-12 carbon atoms, a cycloalkyl group of 3-6 carbon atoms. For example, the cycloalkyl group may be a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, etc. In addition, the cycloalkyl group may be optionally substituted.

[0038] The term "halogen" refers to elements of Group VIIA of the periodic table of chemical elements, including fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At).

[0039] Overcharging is one of the causes of thermal runaway of lithium-ion batteries. When overcharging occurs, metallic lithium is deposited at the negative electrode. When the negative electrode is embedded with more and more lithium and reaches saturation, the excess lithium will form lithium dendrites on the surface of the negative electrode in the form of metallic lithium. The growth of lithium dendrites will pierce the isolation membrane and cause an internal short circuit in the battery cell. In addition, the voltage of the lithium-ion battery will continue to increase as the overcharge progresses, and then reach the electrolyte decomposition voltage, causing the electrolyte to decompose and produce gas. The increase in gas production will cause the internal gas pressure of the lithium-ion battery to increase to exceed the valve opening pressure, causing the battery cell explosion-proof valve to open, creating a safety hazard. Methods to prevent lithium-ion batteries from overcharging mainly include adding external protection devices and adding new electrolyte additives. However, the addition of external devices to prevent overcharging will increase the cost of battery cell production, and the introduction of new electrolyte additives may cause new side reactions.

[0040] The present application solves the above-mentioned problems by using a combination of a negative electrode active material layer including a nonionic surfactant and an electrolyte including alkyl lithium sulfate. The nonionic surfactant contributes greatly to the surface flatness of the negative electrode and can reduce the risk of lithium dendrites. However, when the electrochemical device is under high temperature and high pressure, the nonionic surfactant will increase the floating charge thickness of the lithium-ion battery. Adding alkyl lithium sulfate to the electrolyte can effectively improve the floating charge performance of the lithium-ion battery, because alkyl lithium sulfate can reduce the ionic conductivity and electronic conductivity inside the negative electrode. At the same time, the combination of the negative electrode active material layer including a nonionic surfactant and the electrolyte including alkyl lithium sulfate can also significantly improve the overcharge safety of the lithium-ion battery.

[0041] I ,negative electrode

[0042] The negative electrode includes a negative electrode current collector and a positive electrode active material layer disposed on one or both surfaces of the negative electrode current collector, and the negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer can be one or more layers, and each layer of the multi-layer negative electrode active material can contain the same or different negative electrode active materials. The negative electrode active material is any substance that can reversibly embed and deintercalate metal ions such as lithium ions. In some embodiments, the chargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material to prevent lithium metal from being accidentally precipitated on the negative electrode during charging.

[0043] A main feature of the electrochemical device of the present application is that the negative electrode active material layer includes a nonionic surfactant.

[0044] In some embodiments, the nonionic surfactant has a segment formed of an oxyethylene structure.

[0045] In some embodiments, the nonionic surfactant has a hydrophile-lipophile balance (HLB) value in the range of 8-19.

[0046] In some embodiments, the nonionic surfactant includes at least one of polyoxyethylene alkyl ether, sorbitan fatty acid ester, glycerol fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene resin hardened castor oil or polyoxyethylene alkylamine.

[0047] In some embodiments, the content of the nonionic surfactant is a%, based on the weight of the negative electrode active material layer, and the value of a ranges from 0.01 to 5. In some embodiments, the value of a ranges from 0.1 to 3. In some embodiments, a is 0.1, 0.3, 0.5, 1, 2, 2.5, 3, 3.5, 4, 4.5, 5 or in a range consisting of any two of the above values. When the content of the nonionic surfactant in the negative electrode active material layer is within the above range, the floating charge performance and safety of the electrochemical device can be further improved.

[0048] As a current collector for holding the negative electrode active material, any known current collector can be used. Examples of negative electrode current collectors include, but are not limited to, metal materials such as aluminum, copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is copper.

[0049] In the case where the negative electrode current collector is a metal material, the negative electrode current collector may include, but is not limited to, metal foil, metal cylinder, metal strip, metal plate, metal film, metal mesh, stamped metal, foamed metal, etc. In some embodiments, the negative electrode current collector is a metal film. In some embodiments, the negative electrode current collector is a copper foil. In some embodiments, the negative electrode current collector is a rolled copper foil based on a rolling method or an electrolytic copper foil based on an electrolytic method.

[0050] In some embodiments, the thickness of the negative electrode current collector is greater than 1 μm or greater than 5 μm. In some embodiments, the thickness of the negative electrode current collector is less than 100 μm or less than 50 μm. In some embodiments, the thickness of the negative electrode current collector is within the range of any two of the above values.

[0051] There is no particular limitation on the negative electrode active material, as long as it can reversibly absorb and release lithium ions. Examples of negative electrode active materials may include, but are not limited to, carbon materials such as natural graphite and artificial graphite; metals such as silicon (Si) and tin (Sn); or oxides of metal elements such as Si and Sn. Negative electrode active materials may be used alone or in combination.

[0052] The negative electrode active material layer may further include a negative electrode binder. The negative electrode binder can improve the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. The type of negative electrode binder is not particularly limited, as long as it is a material that is stable to the solvent used in the electrolyte or electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluororesins, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, and the like. When an aqueous solvent is used to prepare the negative electrode mixture slurry, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salt, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salt, polyvinyl alcohol, and the like.

[0053] The negative electrode can be prepared by applying a negative electrode mixture slurry containing a negative electrode active material, a resin binder, etc. on a negative electrode current collector, drying it, and then rolling it to form a negative electrode active material layer on both sides of the negative electrode current collector, thereby obtaining a negative electrode.

[0054] II. Electrolyte

[0055] The electrolytic solution used in the electrochemical device of the present application includes an electrolyte and a solvent that dissolves the electrolyte.

[0056] Another main feature of the electrochemical device of the present application is that the electrolyte includes alkyl lithium sulfate.

[0057] In some embodiments, the alkyl lithium sulfate comprises a compound of formula I:

[0058]

[0059] in:

[0060] R is selected from the following groups which are unsubstituted or substituted with one or more halogens: C1-20 alkyl, C2-20 alkoxy, C6-12 aryl, C2-10 alkenyl, C2-10 alkynyl, C3-18 chain ester, C3-18 cyclic ester, C4-10 silane or C2-10 alkyl containing a cyano group.

[0061] In some embodiments, the alkyl lithium sulfate includes at least one of methyl lithium sulfate, ethyl lithium sulfate, propyl lithium sulfate, butyl lithium sulfate, pentyl lithium sulfate, hexyl lithium sulfate, heptyl lithium sulfate, octyl lithium sulfate, isopropyl lithium sulfate, sec-butyl lithium sulfate, trifluoromethyl lithium sulfate, 2,2,2-trifluoroethyl lithium sulfate, 2,2,3,3-tetrafluoropropyl lithium sulfate, 1,1,1,3,3,3-hexafluoro-2-propyl lithium sulfate, methoxyethyl lithium sulfate, ethoxyethyl lithium sulfate, methoxypropyl lithium sulfate, phenyl lithium sulfate, 4-methylphenyl lithium sulfate, 4-fluorophenyl lithium sulfate, perfluorophenyl lithium sulfate, vinyl lithium sulfate, allyl lithium sulfate, propargyl lithium sulfate, 1-oxo-1-(2-propynyloxy)propane-2-yl lithium sulfate, 2-(trimethylsilyl)ethyl lithium sulfate, 2-cyanoethyl lithium sulfate, or 1,3-dicyanopropynyl-2-yl lithium sulfate.

[0062] In some embodiments, the alkyl lithium sulfate includes at least one of lithium hexyl sulfate, lithium trifluoromethyl sulfate, or lithium 2-cyanoethyl sulfate.

[0063] In some embodiments, based on the weight of the electrolyte, the content of the alkyl lithium sulfate is b%, and a and b satisfy: 0.1≤a / b≤2. In some embodiments, a and b satisfy: 0.1≤a / b≤1. In some embodiments, a and b satisfy the following relationship: 0.2≤a / b≤0.5. In some embodiments, a / b is 0.1, 0.2, 0.5, 1, 1.2, 1.5, 1.8, 2 or within the range consisting of any two of the above values. When the content of the nonionic surfactant in the positive electrode active material layer and the content of the alkyl lithium sulfate in the electrolyte satisfy the above relationship, the floating performance and safety of the electrochemical device can be further improved.

[0064] In some embodiments, b is in the range of 0.01 to 5. In some embodiments, b is in the range of 0.1 to 3. In some embodiments, b is 0.1, 0.3, 0.5, 1, 2, 2.5, 3, 3.5, 4, 4.5, 5 or in the range consisting of any two of the above values. When the content of lithium alkyl sulfate in the electrolyte is within the above range, the floating charge performance and safety of the electrochemical device can be further improved.

[0065] In some embodiments, the electrolyte further comprises a fluorine- and phosphorus-containing compound, wherein the fluorine- and phosphorus-containing compound comprises at least one of lithium difluorophosphate, lithium monofluorophosphate, or a compound of formula II:

[0066]

[0067] Wherein R is a C1-10 hydrocarbon group or a C1-10 hydrocarbon group substituted by halogen.

[0068] In some embodiments, the compound of formula II comprises at least one of the following compounds:

[0069]

[0070] Compounds containing fluorine and phosphorus can further reduce the ionic conductivity and electronic conductivity inside the electrode, thereby further improving the floating charge performance and safety of the electrochemical device.

[0071] In some embodiments, based on the weight of the electrolyte, the content of the alkyl lithium sulfate is b%, and the content of the fluorine- and phosphorus-containing compound is c%, and b and c satisfy: 0.5≤b+c≤5 and 0.4≤b / c≤5. In some embodiments, 1≤b+c≤3. In some embodiments, b+c is 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or within the range consisting of any two of the above values. In some embodiments, 0.5≤b / c≤3. In some embodiments, 1≤b / c≤2. When the contents of the alkyl lithium sulfate and the fluorine- and phosphorus-containing compound in the electrolyte satisfy the above relationship, the floating charge performance and safety of the electrochemical device can be further improved.

[0072] In some embodiments, c is in the range of 0.1 to 5. In some embodiments, c is in the range of 0.2 to 3. In some embodiments, c is in the range of 0.5 to 2. In some embodiments, c is in the range of 1 to 1.5. In some embodiments, c is 0.1, 0.3, 0.5, 1, 2, 2.5, 3, 3.5, 4, 4.5, 5 or in the range consisting of any two of the above values. When the content of fluorine- and phosphorus-containing compounds in the electrolyte satisfies the above relationship, the ionic conductivity and electronic conductivity inside the electrode can be further reduced, thereby further improving the floating charge performance and safety of the electrochemical device.

[0073] In some embodiments, the electrolyte further comprises any non-aqueous solvent known in the prior art that can be used as a solvent for the electrolyte.

[0074] In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, cyclic ethers, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorine-containing solvents.

[0075] In some embodiments, examples of the cyclic carbonate may include, but are not limited to, one or more of the following: ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate. In some embodiments, the cyclic carbonate has 3-6 carbon atoms.

[0076] In some embodiments, examples of the linear carbonates may include, but are not limited to, one or more of the following: dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate (DEC), methyl n-propyl carbonate, ethyl n-propyl carbonate, di-n-propyl carbonate, etc. Examples of fluorine-substituted linear carbonates may include, but are not limited to, one or more of the following: bis(fluoromethyl) carbonate, bis(difluoromethyl) carbonate, bis(trifluoromethyl) carbonate, bis(2-fluoroethyl) carbonate, bis(2,2-difluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) carbonate, 2-fluoroethyl methyl carbonate, 2,2-difluoroethyl methyl carbonate, and 2,2,2-trifluoroethyl methyl carbonate, etc.

[0077] In some embodiments, examples of the cyclic carboxylic acid ester may include, but are not limited to, one or more of the following: one or more of γ-butyrolactone and γ-valerolactone. In some embodiments, part of the hydrogen atoms of the cyclic carboxylic acid ester may be substituted with fluorine.

[0078] In some embodiments, examples of the chain carboxylic acid esters may include, but are not limited to, one or more of the following: methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate and ethyl pivalate, etc. In some embodiments, some hydrogen atoms of the chain carboxylic acid ester may be substituted by fluorine. In some embodiments, examples of fluorine-substituted chain carboxylic acid esters may include, but are not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate and 2,2,2-trifluoroethyl trifluoroacetate, etc.

[0079] In some embodiments, examples of the cyclic ether may include, but are not limited to, one or more of the following: tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 2-methyl1,3-dioxolane, 4-methyl1,3-dioxolane, 1,3-dioxane, 1,4-dioxane and dimethoxypropane.

[0080] In some embodiments, examples of the chain ether may include, but are not limited to, one or more of the following: dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxymethane, 1,1-ethoxymethoxyethane and 1,2-ethoxymethoxyethane, etc.

[0081] In some embodiments, examples of the phosphorus-containing organic solvent may include, but are not limited to, one or more of the following: trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, diethyl methyl phosphate, ethylidene methyl phosphate, ethylidene ethyl phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(2,2,3,3,3-pentafluoropropyl) phosphate, etc.

[0082] In some embodiments, examples of the sulfur-containing organic solvent may include, but are not limited to, one or more of the following: sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, methyl propyl sulfone, dimethyl sulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate, and dibutyl sulfate. In some embodiments, some hydrogen atoms of the sulfur-containing organic solvent may be substituted by fluorine.

[0083] In some embodiments, the aromatic fluorine-containing solvent includes, but is not limited to, one or more of the following: fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, and trifluoromethylbenzene.

[0084] In some embodiments, the solvent used in the electrolyte of the present application includes cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, and combinations thereof. In some embodiments, the solvent used in the electrolyte of the present application includes an organic solvent selected from the group consisting of the following substances: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, n-propyl acetate, ethyl acetate, and combinations thereof. In some embodiments, the solvent used in the electrolyte of the present application includes: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, γ-butyrolactone, and combinations thereof.

[0085] In some embodiments, the electrolyte is not particularly limited, and any substance known as an electrolyte can be used arbitrarily. In the case of a lithium secondary battery, a lithium salt is generally used. Examples of electrolytes may include, but are not limited to, inorganic lithium salts such as LiPF6, LiBF4, LiClO4, LiAlF4, LiSbF6, LiWF7; lithium tungstates such as LiWOF5; lithium carboxylates such as HCO2Li, CH3CO2Li, CH2FCO2Li, CHF2CO2Li, CF3CO2Li, CF3CH2CO2Li, CF3CF2CO2Li, CF3CF2CF2CO2Li, CF3CF2CF2CF2CO2Li; lithium salts such as FSO3Li, CH3SO3Li 、CH2FSO3Li、CHF2SO3Li、CF3SO3Li、CF3CF2SO3Li、CF3CF2CF2SO3Li、CF3CF2CF2CF2SO3Li and other lithium sulfonate salts; LiN(FCO)2、LiN(FCO)(FSO2)、LiN(FSO2)2、LiN(FSO2)(CF3SO2)、LiN(CF3SO2)2、LiN(C2F5SO2)2、Cyclic 1,2-perfluoroethane bissulfonyl imide lithium、Cyclic 1,3-perfluoropropane bissulfonyl imide Lithium, LiN(CF3SO2)(C4F9SO2) and other imide lithium salts; LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3 and other methylated lithium salts; (malonate) borate lithium salts such as bis(malonate) borate and difluoro(malonate) borate lithium salts; (malonate) phosphate lithium salts such as tris(malonate) phosphate, difluorobis(malonate) phosphate, tetrafluoro(malonate) phosphate; and LiPF4(CF3)2, LiPF4(C2F5)2, Fluorine-containing organic lithium salts such as LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2; lithium oxalate borate salts such as lithium difluorooxalatoborate and lithium bis(oxalato)borate; lithium oxalate phosphate salts such as lithium tetrafluorooxalato phosphate, lithium difluorobis(oxalato) phosphate and lithium tris(oxalato) phosphate, etc.

[0086] In some embodiments, the electrolyte is selected from LiPF6, LiSbF6, FSO3Li, CF3SO3Li, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethane bissulfonyl imide lithium, cyclic 1,3-perfluoropropane bissulfonyl imide lithium, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3, lithium difluorooxalatoborate, lithium bis(oxalate)borate or lithium difluorobis(oxalato)phosphate, which helps to improve the output power characteristics, high-rate charge and discharge characteristics, high-temperature storage characteristics and cycle characteristics of the electrochemical device.

[0087] The content of the electrolyte is not particularly limited as long as it does not impair the effect of the present application. In some embodiments, the total molar concentration of lithium in the electrolyte is greater than 0.3 mol / L, greater than 0.4 mol / L or greater than 0.5 mol / L. In some embodiments, the total molar concentration of lithium in the electrolyte is less than 3 mol / L, less than 2.5 mol / L or less than 2.0 mol / L. In some embodiments, the total molar concentration of lithium in the electrolyte is within the range formed by any two of the above values. When the electrolyte concentration is within the above range, there will not be too little lithium as a charged particle, and the viscosity can be kept within an appropriate range, thereby easily ensuring good conductivity.

[0088] When more than two electrolytes are used, the electrolyte includes at least one salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate. In some embodiments, the electrolyte includes a salt selected from the group consisting of monofluorophosphate, oxalate and fluorosulfonate. In some embodiments, the electrolyte includes a lithium salt. In some embodiments, based on the weight of the electrolyte, the content of the salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate is greater than 0.01% or greater than 0.1%. In some embodiments, based on the weight of the electrolyte, the content of the salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate is less than 20% or less than 10%. In some embodiments, the content of the salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate is within the range of any two of the above values.

[0089] In some embodiments, the electrolyte comprises one or more substances selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate and one or more salts other than this. As salts other than this, the lithium salts exemplified above can be cited, and in some embodiments, they are LiPF6, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethane bissulfonyl imide lithium, cyclic 1,3-perfluoropropane bissulfonyl imide lithium, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3. In some embodiments, the salt other than this is LiPF6.

[0090] In some embodiments, the content of the other salt is greater than 0.01% or greater than 0.1% based on the weight of the electrolyte. In some embodiments, the content of the other salt is less than 20%, less than 15%, or less than 10% based on the weight of the electrolyte. In some embodiments, the content of the other salt is within the range formed by any two of the above values. The other salt having the above content helps to balance the conductivity and viscosity of the electrolyte.

[0091] III. Positive electrode

[0092] The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The positive electrode active material layer may be one or more layers. The positive electrode active material layer includes a positive electrode active material, and each layer of the multi-layer positive electrode active material may contain the same or different positive electrode active materials. The positive electrode active material is any substance that can reversibly embed and de-embed metal ions such as lithium ions.

[0093] There is no particular limitation on the type of positive electrode active material, as long as it can electrochemically absorb and release metal ions (e.g., lithium ions). In some embodiments, the positive electrode active material is a material containing lithium and at least one transition metal. Examples of positive electrode active materials may include, but are not limited to, lithium transition metal composite oxides and lithium-containing transition metal phosphate compounds.

[0094] In some embodiments, the transition metal in the lithium transition metal composite oxide includes V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. In some embodiments, the lithium transition metal composite oxide includes lithium cobalt composite oxides such as LiCoO2, lithium nickel composite oxides such as LiNiO2, lithium manganese composite oxides such as LiMnO2, LiMn2O4, Li2MnO4, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2、LiNi0.5 Mn 0.3 Co 0.2 O2 and the like, wherein a portion of the transition metal atoms serving as the main body of these lithium transition metal composite oxides are replaced by other elements such as Na, K, B, F, Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, Nb, Mo, Sn, W, etc. Examples of lithium transition metal composite oxides may include, but are not limited to, LiNi 0.5 Mn 0.5 O2、LiNi 0.85 Co 0.10 Al 0.05 O2、LiNi 0.33 Co 0.33 Mn 0.33 O2、LiNi 0.45 Co 0.10 Al 0.45 O2、LiMn 1.8 Al 0.2 O4 and LiMn 1.5 Ni 0.5 O4, etc. Examples of combinations of lithium transition metal composite oxides include, but are not limited to, combinations of LiCoO2 and LiMn2O4, wherein a portion of the Mn in LiMn2O4 can be replaced by a transition metal (e.g., LiNi 0.33 Co 0.33 Mn 0.33 O2), part of the Co in LiCoO2 can be replaced by transition metals.

[0095] In some embodiments, the transition metal in the lithium-containing transition metal phosphate compound includes V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. In some embodiments, the lithium-containing transition metal phosphate compound includes iron phosphates such as LiFePO4, Li3Fe2(PO4)3, LiFeP2O7, and cobalt phosphates such as LiCoPO4, wherein a portion of the transition metal atoms as the main body of these lithium transition metal phosphate compounds are replaced by other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si, etc.

[0096] In some embodiments, a substance with a different composition from that of the positive electrode active material may be attached to the surface of the above-mentioned positive electrode active material. Examples of surface-attached substances may include, but are not limited to: oxides such as aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, etc.; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, aluminum sulfate, etc.; carbonates such as lithium carbonate, calcium carbonate, magnesium carbonate, etc.; carbon, etc. By attaching substances to the surface of the positive electrode active material, the oxidation reaction of the electrolyte on the surface of the positive electrode active material can be suppressed, and the life of the electrochemical device can be improved. When the amount of surface-attached substances is too small, the effect cannot be fully manifested; when the amount of surface-attached substances is too much, it will hinder the entry and exit of lithium ions, so that the resistance sometimes increases. In this application, the positive electrode active material having a substance with a different composition attached to the surface of the positive electrode active material is also referred to as a "positive electrode active material."

[0097] In some embodiments, the shape of the positive electrode active material particles includes, but is not limited to, block, polyhedron, sphere, ellipsoid, plate, needle and column, etc. In some embodiments, the positive electrode active material particles include primary particles, secondary particles or a combination thereof. In some embodiments, the primary particles can be agglomerated to form secondary particles.

[0098] There is no limitation on the type of positive electrode conductive material, and any known conductive material can be used. Examples of positive electrode conductive materials may include, but are not limited to, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; carbon materials such as amorphous carbon such as needle coke; carbon nanotubes; graphene, etc. The above positive electrode conductive materials may be used alone or in any combination.

[0099] There is no particular restriction on the type of positive electrode binder used in the manufacture of the positive electrode active material layer. In the case of a coating method, any material that can be dissolved or dispersed in the liquid medium used in the manufacture of the electrode can be used. Examples of positive electrode binders may include, but are not limited to, one or more of the following: resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; styrene-butadiene-styrene block copolymers or their hydrogenates, ethylene-propylene-diene terpolymers (EPDM), Thermoplastic elastomer polymers such as styrene·ethylene·butadiene·ethylene copolymers, styrene·isoprene·styrene block copolymers or their hydrogenated products; soft resin polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene·vinyl acetate copolymers, propylene·α-olefin copolymers; fluorine-based polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene·ethylene copolymers; polymer compositions having ion conductivity of alkali metal ions (especially lithium ions), etc. The above positive electrode binders can be used alone or in any combination.

[0100] There is no limitation on the type of solvent used to form the positive electrode slurry, as long as it is a solvent that can dissolve or disperse the positive electrode active material, the conductive material, the positive electrode binder and the thickener used as needed. Examples of solvents used to form the positive electrode slurry may include any of aqueous solvents and organic solvents. Examples of aqueous media may include, but are not limited to, water and mixed media of alcohol and water. Examples of organic media may include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide, etc.

[0101] Thickeners are generally used to adjust the viscosity of the slurry. In the case of using an aqueous medium, a thickener and a styrene-butadiene rubber (SBR) emulsion can be used for slurrying. The type of thickener is not particularly limited, and examples thereof may include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. The above thickeners may be used alone or in any combination.

[0102] The type of positive electrode current collector is not particularly limited, and it can be any material known to be suitable for use as a positive electrode current collector. Examples of positive electrode current collectors may include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metal material. In some embodiments, the positive electrode current collector is aluminum.

[0103] In order to reduce the electronic contact resistance between the positive electrode current collector and the positive electrode active material layer, the surface of the positive electrode current collector may include a conductive additive. Examples of the conductive additive may include, but are not limited to, carbon and precious metals such as gold, platinum, and silver.

[0104] The positive electrode can be made by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector. The manufacture of a positive electrode using a positive electrode active material can be carried out by a conventional method, that is, the positive electrode active material and the binder, as well as the conductive material and the thickener as required, are dry-mixed to form a sheet, and the obtained sheet is pressed onto the positive electrode current collector; or these materials are dissolved or dispersed in a liquid medium to form a slurry, and the slurry is applied to the positive electrode current collector and dried to form a positive electrode active material layer on the current collector, thereby obtaining a positive electrode.

[0105] IV. Isolation membrane

[0106] In order to prevent short circuit, a separator is usually provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application is usually used by infiltrating the separator.

[0107] There is no particular restriction on the material and shape of the isolation membrane, as long as the effect of the present application is not significantly impaired. The isolation membrane may be a resin, glass fiber, inorganic substance, etc. formed of a material that is stable to the electrolyte of the present application. In some embodiments, the isolation membrane includes a porous sheet or a non-woven fabric-like material with excellent liquid retention. Examples of materials for resin or glass fiber isolation membranes may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyether sulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above isolation membranes may be used alone or in any combination.

[0108] The isolation film may also be a material formed by laminating the above materials, and examples thereof include, but are not limited to, a three-layer isolation film formed by laminating polypropylene, polyethylene, and polypropylene in this order.

[0109] Examples of inorganic materials may include, but are not limited to, oxides such as aluminum oxide and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.) The form of the inorganic material may include, but is not limited to, granular or fibrous.

[0110] The separator may be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous films, etc. In the thin film form, the separator has a pore size of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-mentioned independent thin film separators, the following separators may also be used: a separator formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or the negative electrode using a resin-based adhesive, for example, a separator formed by using a fluororesin as an adhesive to form a porous layer on both sides of the positive electrode with aluminum oxide particles having a particle size of 90% less than 1 μm.

[0111] The thickness of the isolation membrane is arbitrary. In some embodiments, the thickness of the isolation membrane is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the isolation membrane is less than 50 μm, less than 40 μm, or less than 30 μm. In some embodiments, the thickness of the isolation membrane is within the range formed by any two of the above values. When the thickness of the isolation membrane is within the above range, the insulation and mechanical strength can be ensured, and the rate characteristics and energy density of the electrochemical device can be ensured.

[0112] When a porous material such as a porous sheet or non-woven fabric is used as an isolation membrane, the porosity of the isolation membrane is arbitrary. In some embodiments, the porosity of the isolation membrane is greater than 10%, greater than 15%, or greater than 20%. In some embodiments, the porosity of the isolation membrane is less than 60%, less than 50%, or less than 45%. In some embodiments, the porosity of the isolation membrane is within the range formed by any two of the above values. When the porosity of the isolation membrane is within the above range, insulation and mechanical strength can be ensured, and membrane resistance can be suppressed, so that the electrochemical device has good safety characteristics.

[0113] The average pore size of the isolation membrane is also arbitrary. In some embodiments, the average pore size of the isolation membrane is less than 0.5 μm or less than 0.2 μm. In some embodiments, the average pore size of the isolation membrane is greater than 0.05 μm. In some embodiments, the average pore size of the isolation membrane is within the range formed by any two of the above values. If the average pore size of the isolation membrane exceeds the above range, short circuit is likely to occur. When the average pore size of the isolation membrane is within the above range, the electrochemical device has good safety characteristics.

[0114] V. Electrochemical Device Components

[0115] The electrochemical device assembly includes an electrode group, a current collecting structure, an outer casing and a protective element.

[0116] The electrode group may be any of a laminated structure formed by laminating the above-mentioned positive electrode and the negative electrode with the above-mentioned separator, and a structure formed by spirally winding the above-mentioned positive electrode and the negative electrode with the above-mentioned separator. In some embodiments, the proportion of the mass of the electrode group in the internal volume of the battery (electrode group occupancy) is greater than 40% or greater than 50%. In some embodiments, the electrode group occupancy is less than 90% or less than 80%. In some embodiments, the electrode group occupancy is within the range formed by any two of the above values. When the electrode group occupancy is within the above range, the capacity of the electrochemical device can be ensured, and at the same time, the reduction of characteristics such as repeated charge and discharge performance and high temperature storage associated with the increase in internal pressure can be suppressed.

[0117] There is no particular limitation on the current collection structure. In some embodiments, the current collection structure is a structure that reduces the resistance of the wiring portion and the joint portion. When the electrode group is the above-mentioned stacked structure, it is suitable to use a structure formed by bundling the metal core portions of each electrode layer and welding them to the terminal. When the electrode area of ​​a sheet increases, the internal resistance increases, so it is also suitable to set more than two terminals in the electrode to reduce the resistance. When the electrode group is the above-mentioned winding structure, the internal resistance can be reduced by setting more than two lead structures at the positive electrode and the negative electrode respectively, and bundling them at the terminal.

[0118] The material of the outer casing is not particularly limited, as long as it is a material that is stable to the electrolyte used. The outer casing can be made of, but not limited to, nickel-plated steel, stainless steel, aluminum or aluminum alloy, magnesium alloy and other metals, or a laminated film of resin and aluminum foil. In some embodiments, the outer casing is a metal or laminated film of aluminum or aluminum alloy.

[0119] The metal outer casing includes, but is not limited to, a packaged closed structure formed by welding metals to each other by laser welding, resistance welding, and ultrasonic welding; or a riveted structure formed by using the above-mentioned metals through a resin gasket. The outer casing using the above-mentioned laminated film includes, but is not limited to, a packaged closed structure formed by thermally bonding resin layers to each other. In order to improve the sealing performance, a resin different from the resin used in the laminated film can also be sandwiched between the above-mentioned resin layers. When the resin layer is thermally bonded to form a closed structure through the collector terminal, due to the bonding between the metal and the resin, a resin with a polar group or a modified resin into which a polar group is introduced can be used as the sandwiched resin. In addition, the shape of the outer casing is also arbitrary, for example, it can be any of cylindrical, square, laminated, button-shaped, large, etc.

[0120] The protection element may be a positive temperature coefficient (PTC) whose resistance increases when abnormal heat is released or excessive current flows, a temperature fuse, a thermistor, or a valve (current cutoff valve) that cuts off the current flowing in the circuit by causing the internal pressure or internal temperature of the battery to rise sharply when abnormal heat is released. The above protection element may be selected to be an element that does not work in normal use of high current, or may be designed in a form that does not cause abnormal heat release or thermal runaway even if the protection element is not present.

[0121] The electrochemical device of the present application includes any device that generates an electrochemical reaction, and specific examples thereof include a lithium metal secondary battery or a lithium ion secondary battery.

[0122] The present application further provides an electronic device, which includes the electrochemical device according to the present application.

[0123] The use of the electrochemical device of the present application is not particularly limited, and it can be used for any electronic device known in the prior art. In some embodiments, the electrochemical device of the present application can be used for, but not limited to, laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0124] The preparation of lithium-ion batteries is described below by taking lithium-ion batteries as an example and combining specific embodiments. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0125] Example

[0126] 1. Preparation of lithium-ion batteries

[0127] 1. Preparation of negative electrode

[0128] Artificial graphite, styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed with deionized water in a mass ratio of 96%:2%:2%, and nonionic surfactant is added as needed, and stirred evenly to obtain negative electrode slurry. The negative electrode slurry is coated on a 9μm copper foil, dried, cold pressed, cut into pieces, and welded to the pole ears to obtain a negative electrode.

[0129] 2. Preparation of positive electrode

[0130] Lithium cobalt oxide, Super-P and polyvinylidene fluoride were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 97:1:2 and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was coated on a 12μm aluminum foil, dried, cold pressed, cut into pieces, and welded to the tabs to obtain a positive electrode.

[0131] 3. Preparation of electrolyte

[0132] In a dry argon environment, EC, PC and DEC (weight ratio 1:1:1) were mixed, and LiPF6 was added and mixed evenly to form a basic electrolyte, wherein the concentration of LiPF6 was 12.5%. Different amounts of additives were added to the basic electrolyte to obtain electrolytes of different embodiments and comparative examples.

[0133] The abbreviations and names of the components in the electrolyte are shown in the following table:

[0134] Material Name abbreviation Material Name abbreviation Ethylene carbonate EC Propylene carbonate PC Diethyl carbonate DEC Compound of formula II-1 Formula II-1 Compound of formula II-2 Formula II-2 Compound of formula II-3 Formula II-3

[0135] 4. Preparation of isolation membrane

[0136] A polyethylene porous polymer film is used as the isolation membrane.

[0137] 5. Preparation of lithium-ion batteries

[0138] The obtained positive electrode, separator and negative electrode are wound in order and placed in an outer packaging foil, leaving a liquid injection port. The electrolyte is poured from the liquid injection port, packaged, and then subjected to formation, capacity and other processes to obtain a lithium-ion battery.

[0139] 2. Test Method

[0140] 1. Test method for overcharge deformation rate of lithium-ion batteries

[0141] At 25°C, let the lithium-ion battery stand for 30 minutes, then charge it to 4.7V at a constant current rate of 0.5C, then charge it to 0.05C at a constant voltage rate at 4.7V, let it stand for 60 minutes, and measure the thickness T1 of the lithium-ion battery. Then charge the lithium-ion battery at a constant current rate of 0.1C for 60 minutes, let it stand for 30 minutes, repeat this step 5 times, so that the lithium-ion battery reaches 150% state of charge (SOC), and measure the thickness T2 of the lithium-ion battery. The overcharge deformation rate of the lithium-ion battery is calculated by the following formula:

[0142] Overcharge deformation rate = [(T2-T1) / T1]×100%.

[0143] 2. Test method for floating charge performance of lithium-ion batteries

[0144] At 25°C, the lithium-ion battery is charged to 4.7V at a constant current of 0.5C, and then charged to 0.05C at a constant voltage of 4.7V. The lithium-ion battery is then placed in a 50°C oven and continuously charged at a constant voltage of 4.7V (with a cut-off current of 20mA), and the change in the thickness of the lithium-ion battery is monitored. The thickness of the lithium-ion battery at the initial 50% state of charge (SOC) is used as a benchmark, and when the thickness of the lithium-ion battery increases by more than 20%, it is recorded as a failure. The time from floating charge to failure of the lithium-ion battery at 50°C is recorded, with hours (h) as the statistical unit.

[0145] 3. Test Results

[0146] Table 1 shows the effects of the negative electrode active material layer and the electrolyte on the floating charge performance and safety of lithium-ion batteries, wherein the nonionic surfactant in the negative electrode active material layer is polyoxyethylene alkyl ether, and the alkyl lithium sulfate in the electrolyte is lithium trifluoromethyl sulfate.

[0147] Table 1

[0148]

[0149] As shown in Comparative Example 1-1, although the electrolyte includes alkyl lithium sulfate, the negative electrode active material layer does not include a non-ionic surfactant, and the overcharge deformation rate of the lithium ion battery is high and the floating charge failure time is short. As shown in Comparative Example 1-2, although the negative electrode active material layer includes a non-ionic surfactant, the electrolyte does not include alkyl lithium sulfate, and the overcharge deformation rate of the lithium ion battery is high and the floating charge failure time is short.

[0150] As shown in Examples 1-1 to 1-15, when the negative electrode active material layer includes a nonionic surfactant and the electrolyte includes lithium alkyl sulfate, the overcharge deformation rate of the lithium ion battery can be significantly reduced and the floating charge failure time thereof can be significantly increased.

[0151] In addition, when the content a% of the nonionic surfactant in the negative electrode active material layer and the content b% of the alkyl lithium sulfate in the electrolyte satisfy 0.1≤a / b≤2, the overcharge deformation rate of the lithium-ion battery can be further reduced and its floating charge failure time can be increased.

[0152] When the content of the nonionic surfactant in the negative electrode active material layer is in the range of 0.01%-5%, the overcharge deformation rate of the lithium-ion battery can be further reduced and its floating charge failure time can be increased.

[0153] When the content of lithium alkyl sulfate in the electrolyte is in the range of 0.01% to 5%, the overcharge deformation rate of the lithium-ion battery can be further reduced and its floating charge failure time can be increased.

[0154] Table 2 shows the effects of 1% alkyl lithium sulfate compounds with different structures on the floating charge performance and safety of lithium ion batteries. Except for the parameters listed in Table 2, the configurations of Examples 2-1 to 2-8 are the same as those of Example 1-1.

[0155] Table 2

[0156] Lithium alkyl sulfate Overcharge deformation rate (%) Float charge failure time (h) Example 1-1 Lithium trifluoromethyl sulfate 20.8 1125 Example 2-1 Lithium Propyl Sulfate 25.1 903 Example 2-2 Lithium hexyl sulfate 23.2 917 Example 2-3 1,1,1,3,3,3-Hexafluoro-2-propyl lithium sulfate 16.1 1227 Embodiment 2-4 2-Cyanoethyl Lithium Sulfate 15.1 1348 Embodiment 2-5 Lithium Ethoxyethyl Sulfate 13.5 1531 Embodiment 2-6 Lithium Perfluorophenyl Sulfate 15.3 1279 Embodiment 2-7 Allyl lithium sulfate 13.9 1467 Embodiment 2-8 2-(Trimethylsilyl)ethyllithium sulfate 12.9 1206

[0157] The results show that alkyl lithium sulfates with different structures can achieve basically equivalent effects. When alkyl lithium sulfates contain fluorine substituents, silane groups, oxygen-containing alkyl groups, alkenyl groups or cyano groups, the overcharge deformation rate of lithium-ion batteries can be further reduced and their floating charge failure time can be increased.

[0158] Table 3 shows the effects of fluorine- and phosphorus-containing compounds on the floating charge performance and safety of lithium-ion batteries, wherein the content of fluorine- and phosphorus-containing compounds in the electrolyte is 0.5%. Except for the parameters listed in Table 3, the configurations of Examples 3-1 to 3-5 are the same as those of Example 1-1.

[0159] Table 3

[0160] Sulfur-oxygen double bond compounds Overcharge deformation rate (%) Float charge failure time (h) Example 1-1 — 20.8 1125 Example 3-1 Lithium difluorophosphate 15.7 1205 Example 3-2 Lithium Monofluorophosphate 16.3 1198 Example 3-3 Formula II-1 14.2 1325 Embodiment 3-4 Formula II-2 13.1 1569 Embodiment 3-5 Formula II-3 12.8 1632

[0161] The results show that when the electrolyte further includes a fluorine- and phosphorus-containing compound (at least one of lithium difluorophosphate, lithium monofluorophosphate or a compound of formula II), the overcharge deformation rate of the lithium-ion battery can be further reduced and its floating charge failure time can be increased.

[0162] Table 4 shows the influence of the content relationship of lithium alkyl sulfate and fluorine- and phosphorus-containing compounds in the electrolyte on the floating charge performance and safety of lithium-ion batteries. Except for the parameters listed in Table 4, the configuration of Examples 4-1 to 4-8 is the same as that of Example 1-1.

[0163] Table 4

[0164]

[0165] The results show that when the content b% of alkyl lithium sulfate and the content c% of fluorine- and phosphorus-containing compounds in the electrolyte meet 0.5≤b+c≤5 and 0.4≤b / c≤5, the overcharge deformation rate of the lithium-ion battery can be further reduced and its floating charge failure time can be increased.

[0166] References to "embodiments", "partial embodiments", "one embodiment", "another example", "example", "specific example" or "partial example" throughout the specification mean that at least one embodiment or example in the present application includes the specific features, structures, materials or characteristics described in the embodiment or example. Therefore, descriptions appearing in various places throughout the specification, such as: "in some embodiments", "in an embodiment", "in one embodiment", "in another example", "in an example", "in a specific example" or "example", do not necessarily refer to the same embodiment or example in the present application. In addition, the specific features, structures, materials or characteristics herein may be combined in one or more embodiments or examples in any suitable manner.

[0167] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions and modifications may be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. An electrochemical device comprising: A positive electrode, a negative electrode and an electrolyte, wherein the negative electrode comprises a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, wherein: The negative electrode active material layer includes a nonionic surfactant, The electrolyte comprises lithium alkyl sulfate, Based on the weight of the negative electrode active material layer, the content of the nonionic surfactant is a%; Based on the weight of the electrolyte, the content of the alkyl lithium sulfate is b%; a and b satisfy: 0.1≤a / b≤2, The value of a ranges from 0.1 to 2, and The value range of b is 1 to 5. 2 . The electrochemical device according to claim 1 , wherein the nonionic surfactant has a segment formed of an ethylene oxide structure. 3 . The electrochemical device according to claim 2 , wherein the hydrophilic-lipophilic balance value of the nonionic surfactant is in the range of 8 to 19.

4. The electrochemical device according to claim 2, wherein the nonionic surfactant comprises at least one of polyoxyethylene alkyl ether, sorbitan fatty acid ester, glycerol fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene resin hardened castor oil or polyoxyethylene alkylamine.

5. The electrochemical device of claim 1, wherein the lithium alkyl sulfate comprises a compound of formula I: (Formula I) in: R is selected from the following groups which are unsubstituted or substituted with one or more halogens: C1-20 alkyl, C2-20 alkoxy, C6-12 aryl, C2-10 alkenyl, C2-10 alkynyl, C3-18 chain ester, C3-18 cyclic ester, C4-10 silane or C2-10 alkyl containing a cyano group.

6. The electrochemical device of claim 1 , wherein the alkyl lithium sulfate comprises at least one of methyl lithium sulfate, ethyl lithium sulfate, propyl lithium sulfate, butyl lithium sulfate, pentyl lithium sulfate, hexyl lithium sulfate, heptyl lithium sulfate, octyl lithium sulfate, isopropyl lithium sulfate, sec-butyl lithium sulfate, trifluoromethyl lithium sulfate, 2,2,2-trifluoroethyl lithium sulfate, 2,2,3,3-tetrafluoropropyl lithium sulfate, 1,1,1,3,3,3-hexafluoro-2-propyl lithium sulfate, methoxyethyl lithium sulfate, ethoxyethyl lithium sulfate, methoxypropyl lithium sulfate, phenyl lithium sulfate, 4-methylphenyl lithium sulfate, 4-fluorophenyl lithium sulfate, perfluorophenyl lithium sulfate, vinyl lithium sulfate, allyl lithium sulfate, propargyl lithium sulfate, 1-oxo-1-(2-propynyloxy)propan-2-yl lithium sulfate, 2-(trimethylsilyl)ethyl lithium sulfate, 2-cyanoethyl lithium sulfate, or 1,3-dicyanopropynyl-2-yl lithium sulfate.

7. The electrochemical device according to claim 6, wherein the alkyl lithium sulfate comprises at least one of lithium hexyl sulfate, lithium trifluoromethyl sulfate, or lithium 2-cyanoethyl sulfate.

8. The electrochemical device according to claim 1, wherein the electrolyte further comprises a fluorine- and phosphorus-containing compound, wherein the fluorine- and phosphorus-containing compound comprises at least one of lithium difluorophosphate, lithium monofluorophosphate, or a compound of formula II: (Formula II), Wherein R is a C1-10 hydrocarbon group or a C1-10 hydrocarbon group substituted by halogen.

9. The electrochemical device according to claim 8, wherein the compound of formula II comprises at least one of the following compounds: (Formula II-1), (Formula II-2) or (Formula II-3).

10. The electrochemical device according to claim 8, wherein the content of the alkyl lithium sulfate is b%, and the content of the fluorine- and phosphorus-containing compound is c%, based on the weight of the electrolyte, and b and c satisfy: 0.5≤b+c≤5 and 0.4≤b / c≤5.

11. The electrochemical device according to claim 8, wherein the content of the fluorine- and phosphorus-containing compound is c%, based on the weight of the electrolyte, and the value of c ranges from 0.1 to 5.

12. The electrochemical device according to claim 11, wherein the value of c ranges from 0.2 to 3.

13. An electronic device comprising the electrochemical device according to any one of claims 1 to 12.

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