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 comprising a negative electrode and an electrolyte, wherein: the negative electrode comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode current collector contains a chromium element, the content of the chromium element is 0.001% to 0.5% based on the mass of the negative electrode current collector; the electrolyte contains an oxalic acid-based compound, the content of the oxalic acid-based compound is 0.01% to 5% based on the mass of the electrolyte; and the oxalic acid-based compound comprises at least one of a compound of formula I, a compound of formula II, a compound of formula III, a compound of formula IV, or a compound of formula V. The electrochemical device of the present application has significantly reduced self-discharge.

Description

[0001] This application claims priority to the Chinese patent application No. PCT / CN2023 / 080022 filed on March 7, 2023, and entitled “Electrochemical device and electronic device”, the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the field of energy storage, in particular to an electrochemical device and an electronic device. BACKGROUND

[0003] Electrochemical devices (e.g., lithium ion batteries) have advantages of high energy density, stable working voltage, low self-discharge rate, long cycle life, no memory effect, and environmental friendliness, and have been widely used in consumer electronics (including mobile phones, laptops, cameras, and other electronic products), electric vehicles, power tools, drones, intelligent robots, and large-scale energy storage fields and industries. However, with the rapid development of information and communication technology and the diversification of market demand, people have put forward more requirements and challenges for the power supply of electronic products, such as thinner, lighter, more diversified shape, higher volume and mass energy density, higher safety, and higher power, etc.

[0004] The positive electrode active material, negative electrode active material, and electrolyte contained in the electrochemical device are sensitive to moisture, so it is necessary to maintain a low humidity environment as much as possible during the preparation of the battery, which has a great impact on the preparation process control, battery performance, production cost, etc.

[0005] Therefore, it is necessary to provide an electrochemical device that can be compatible with the influence of humidity in the battery production environment. SUMMARY

[0006] The present application attempts to solve at least one problem existing in the related art, at least to some extent, by providing an electrochemical device and an electronic device.

[0007] According to one aspect of the present application, the present application provides an electrochemical device, comprising a negative electrode and an electrolyte, wherein:

[0008] The negative electrode comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode current collector contains chromium element, the content of the chromium element is 0.001% to 0.5% based on the mass of the negative electrode current collector;

[0009] The electrolyte contains a compound based on oxalic acid, the content of the compound based on oxalic acid is 0.01% to 5% based on the mass of the electrolyte; and

[0010] The oxalate-based compounds include at least one of a compound of Formula I, a compound of Formula II, a compound of Formula III, a compound of Formula IV, or a compound of Formula V:

[0011]

[0012] wherein:

[0013] A+are each independently selected from Li+, Na+, K+, or Cs+;

[0014] R 11 , R 12 , R 21 , R 22 , R 31 , R 32 , R 33 , and R 34 are each independently selected from halogen, unsubstituted or halogen-substituted C 1-4 alkyl, unsubstituted or halogen-substituted C 2-4 alkenyl, or unsubstituted or halogen-substituted C 2-4 alkynyl;

[0015] R 41 and R 42 are each independently selected from H, Li, Na, K, Cs, NH4, unsubstituted or halogen-substituted C 1-4 alkyl, unsubstituted or fluorine-substituted C 2-4 alkenyl, or unsubstituted or fluorine-substituted C 2-4 alkynyl, and R 41 and R 42 may optionally be bound together with the atoms to which they are attached to form a ring.

[0016] According to embodiments of the present application, the compound of Formula I includes at least one of lithium bis(oxalato)borate (LiBOB), sodium bis(oxalato)borate (NaBOB), cesium bis(oxalato)borate (CsBOB), or potassium bis(oxalato)borate (KBOB);

[0017] The compound of Formula II includes at least one of:

[0018]

[0019] The compound of Formula III includes at least one of:

[0020]

[0021] The compound of Formula IV includes at least one of:

[0022]

[0023] The compound of Formula V includes at least one of the following compounds:

[0024] H2C2O4, Li2C2O4, Na2C2O4, K2C2O4, Cs2C2O4, NH4C2O4, CH3C2O4Li,

[0025]

[0026] According to embodiments of the present application, the content of the oxalate-based compound is 0.01% to 3% based on the mass of the electrolyte.

[0027] According to embodiments of the present application, the content of the oxalate-based compound is 0.01% to 1% based on the mass of the electrolyte.

[0028] According to embodiments of the present application, the content of the chromium element is 0.001% to 0.1% based on the mass of the negative current collector.

[0029] According to embodiments of the present application, the content of the chromium element is 0.001% to 0.05% based on the mass of the negative current collector.

[0030] According to embodiments of the present application, the negative current collector is a copper foil.

[0031] According to embodiments of the present application, the electrolyte further includes a cyclic ester and a chain ester, the cyclic ester includes at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), fluoroethylene carbonate (FEC), the chain ester includes at least one of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), and the content of the cyclic ester is S1%, the content of the chain ester is S2% based on the mass of the electrolyte, and S1 / S2 is in the range of 0.20 to 1.00.

[0032] According to embodiments of the present application, S1 is in the range of 15 to 50.

[0033] According to embodiments of the present application, the electrolyte further includes an additive selected from at least one of 1,3-propane sultone (PS), vinyl sulfate (DTD), lithium difluorophosphate (LiPO2F2), or vinylene carbonate (VC), and the content of the additive is 0.01wt% to 5wt% based on the mass of the electrolyte.

[0034] According to another aspect of the present application, the present application provides an electronic device including the electrochemical device according to the present application.

[0035] This application provides an electrochemical device and an electronic device that utilizes an electrolyte containing an oxalic acid-based compound on top of a chromium-containing negative electrode current collector. On one hand, the oxalic acid-based compound reacts with water in the electrolyte, consuming excess water and preventing the formation of hydrofluoric acid, thereby avoiding damage to the chromium oxide protective layer. On the other hand, the oxalate ions produced by the hydrolysis of the oxalic acid-based compound can react with dissolved chromium ions to form a substance insoluble in the electrolyte, which deposits on the surface of the negative electrode current collector to form a protective layer, thus preventing the metal ions in the negative electrode current collector from dissolving and then being reduced to elemental metal at the negative electrode. Under the combined effect of these factors, the electrochemical device of this application exhibits significantly reduced self-discharge.

[0036] Additional aspects and advantages of this application will be described, shown, or illustrated in part by way of implementation of embodiments thereof in the following description. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0038] The embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application.

[0039] In the detailed description and claims, the list of items connected by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, then 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, then 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 element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0040] The term "alkyl" is intended to mean a straight-chain saturated hydrocarbon structure having from one to twenty carbon atoms. "Alkyl" is also intended to mean a branched or cyclic hydrocarbon structure having from three to twenty carbon atoms. When an alkyl group is designated with a specific number of carbons, it is intended to encompass all geometric isomers having that number of carbons; thus, for example, "butyl" is intended to include n-butyl, sec-butyl, iso-butyl, t-butyl, and cyclobutyl; "propyl" includes n-propyl, iso-propyl, and cyclopropyl. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, iso-propyl, cyclopropyl, n-butyl, iso-butyl, sec-butyl, t-butyl, cyclobutyl, n-pentyl, iso-pentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, iso-hexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornyl, and the like.

[0041] The term "alkenyl" refers to a monovalent unsaturated hydrocarbon group that can be straight- chain or branched and that has at least one and usually 1, 2, or 3 carbon-carbon double bonds. Unless otherwise defined, the alkenyl group typically contains from 2 to 20 carbon atoms and includes, for example, -C 2-4 alkenyl, -C 2-6 alkenyl, and -C 2-10 alkenyl. Representative alkenyl groups include, for example, ethenyl, n-propenyl, iso- propenyl, n-but-2-enyl, but-3-enyl, n-hex-3-enyl, and the like.

[0042] The term "alkynyl" refers to a monovalent unsaturated hydrocarbon group that can be straight- chain or branched and that has at least one and usually 1, 2, or 3 carbon-carbon triple bonds. Unless otherwise defined, the alkynyl group typically contains from 2 to 20 carbon atoms and includes, for example, -C 2-4 alkynyl, -C 3-6 alkynyl, and -C 3-10 alkynyl. Representative alkynyl groups include, for example, ethynyl, prop-2-ynyl (n- propynyl), n-but-2-ynyl, n-hex-3-ynyl, and the like.

[0043] The term "halogen" can be F, Cl, Br, or I.

[0044] Positive active materials, negative active materials, and electrolytes, etc. in electrochemical devices (e.g., lithium ion batteries) are sensitive to moisture. For example, in a high humidity environment, the negative current collector (e.g., copper foil) is prone to corrosion, which can have many adverse effects on the electrochemical device. The use of a copper current collector containing chromium can slow the oxidation of the copper current collector in air and the corrosion of the copper current collector by the electrolyte to some extent, but the oxide protective layer formed by chromium is still destroyed by the hydrofluoric acid in the electrolyte, leading to copper dissolution and, in turn, an increase in self-discharge of the electrochemical device.

[0045] To solve the above problems, the present application provides an electrochemical device which uses an electrolyte containing oxalic acid-based compounds on the basis of a negative current collector containing chromium elements. On the one hand, the oxalic acid-based compounds can react with water in the electrolyte, consume excess water, avoid the generation of hydrofluoric acid, and thus avoid the destruction of the oxide protective layer formed by chromium. On the other hand, the oxalate generated by the hydrolysis of the oxalic acid-based compounds can form a substance that is difficult to dissolve in the electrolyte with the dissolved chromium ions, and deposit on the surface of the negative current collector to form a protective layer, thereby avoiding the reduction of the metal ions dissolved from the negative current collector to form elemental metal at the negative electrode. Under the combined action of these factors, the electrochemical device of the present application has significantly reduced self-discharge.

[0046] Electrolyte

[0047] The electrolyte in the electrochemical device of the present application contains oxalic acid-based compounds, the content of the oxalic acid-based compounds is 0.01% to 5% based on the mass of the electrolyte, and the oxalic acid-based compounds include at least one of the following compounds:

[0048]

[0049] wherein:

[0050] A+is each independently selected from Li+, Na+, K+or Cs+;

[0051] R 11 , R 12 , R 21 , R 22 , R 31 , R 32 , R 33 and R 34 are each independently selected from halogen, unsubstituted or halogen-substituted C 1-4 alkyl, unsubstituted or halogen-substituted C 2-4 alkenyl or unsubstituted or halogen-substituted C 2-4 alkynyl;

[0052] R 41 and R 42 are each independently selected from H, Li, Na, K, Cs, NH4, unsubstituted or halogen-substituted C 1-4 alkyl, unsubstituted or halogen-substituted C 2-4 alkenyl or unsubstituted or halogen-substituted C 2-4 alkynyl, and R 41 and R 42 may optionally be combined with the atoms to which they are attached to form a ring.

[0053] In some embodiments, the compound of Formula I includes at least one of lithium bis(oxalato)borate (LiBOB), sodium bis(oxalato)borate (NaBOB), cesium bis(oxalato)borate (CsBOB), or potassium bis(oxalato)borate (KBOB).

[0054] In some embodiments, the compound of Formula II includes at least one of:

[0055]

[0056] In some embodiments, the compound of Formula III includes at least one of:

[0057]

[0058] In some embodiments, the compound of Formula V includes at least one of:

[0059] H2C2O4, Li2C2O4, Na2C2O4, K2C2O4, Cs2C2O4, NH4C2O4, CH3C2O4Li,

[0060]

[0061] In some embodiments, the content of the oxalate-based compound is 0.01% to 3% based on the mass of the electrolyte. In some embodiments, the content of the oxalate-based compound is 0.01% to 1% based on the mass of the electrolyte. In some embodiments, the content of the oxalate-based compound is 0.1% to 0.5% based on the mass of the electrolyte. In some embodiments, the content of the oxalate-based compound is 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or within a range between any two of the aforementioned values, based on the mass of the electrolyte. When the content of the oxalate-based compound in the electrolyte is within the aforementioned range, it helps to further reduce the self-discharge of the electrochemical device.

[0062] In some embodiments, the electrolyte further includes a cyclic ester and a chain ester, the cyclic ester includes at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), fluoroethylene carbonate (FEC), the chain ester includes at least one of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), and the content of the cyclic ester is S1%, the content of the chain ester is S2%, S1 / S2 is within a range of 0.2 to 1, based on the mass of the electrolyte.

[0063] In some embodiments, S1 / S2 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or within a range between any two of the aforementioned values.

[0064] In some embodiments, S1 is within a range of 15 to 50. In some embodiments, S1 is 15, 30, 40, 50, or within a range between any two of the aforementioned values.

[0065] In some embodiments, S2 is within a range of 15 to 75. In some embodiments, S2 is 15, 25, 35, 45, 55, 65, 75, or within a range between any two of the aforementioned values.

[0066] When the electrolyte contains the aforementioned cyclic ester and chain ester in the aforementioned amounts, the mixed solvent forms a suitable coordination relationship with the electrolyte salt (such as LiPF6) to exist in the form of ion clusters, which weakens the redox reactivity of the individual solvent, is conducive to reducing the chemical self-discharge caused by side reactions, and maintains a stable self-discharge evaluation parameter K value; at the same time, it also ensures the sufficient dissociation of the electrolyte salt and the relatively low viscosity of the overall electrolyte, improves the electrolyte conductivity, and thus improves the low-temperature discharge performance of the battery.

[0067] In some embodiments, the electrolyte further contains an additive selected from at least one of 1,3-propane sultone (PS), vinyl sulfate (DTD), lithium difluorophosphate (LiPO2F2), or vinylene carbonate (VC), and the content of the additive is 0.01wt% to 5wt% based on the mass of the electrolyte.

[0068] In some embodiments, the content of the additive is 0.05wt% to 3wt% based on the mass of the electrolyte. In some embodiments, the content of the additive is 0.1wt% to 1wt% based on the mass of the electrolyte. In some embodiments, the content of the additive is 0.01wt%, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, or within a range between any two of the aforementioned values based on the mass of the electrolyte.

[0069] The addition of the additive not only can further reduce the self-discharge of the electrochemical device, but also can significantly improve the storage gas production problem of the oxalic acid-based compound due to the low oxidation potential. This is because the additive can form a protective layer on the electrode surface, reduce the occurrence of side reactions, and play a role in reducing chemical self-discharge. At the same time, the additive can reduce the oxidative decomposition gas of the oxalic acid-based compound at the positive electrode, and improve the high-temperature storage performance of the electrochemical device.

[0070] LiPF6, in some embodiments, the concentration of LiPF6is in the range of 0.8 mol / L to 3 mol / L, in the range of 0.8 mol / L to 2.5 mol / L, in the range of 0.8 mol / L to 2 mol / L, or in the range of 1 mol / L to 2 mol / L. In some embodiments, the concentration of lithium salt is about 1 mol / L, about 1.15 mol / L, about 1.2 mol / L, about 1.5 mol / L, about 2 mol / L, or about 2.5 mol / L.

[0071] Solvents that can be used in electrolytes of embodiments of the present application include, but are not limited to, cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, cyclic ethers, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorine-containing solvents.

[0072] In some embodiments, cyclic carbonates include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate. In some embodiments, cyclic carbonates have 3-6 carbon atoms.

[0073] In some embodiments, chain carbonates include, but are not limited to, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, di-n-propyl carbonate, and the like, chain carbonates substituted with fluorine, such as 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.

[0074] In some embodiments, cyclic carboxylic acid esters include, but are not limited to, γ-valerolactone. In some embodiments, some of the hydrogen atoms of cyclic carboxylic acid esters can be substituted with fluorine.

[0075] In some embodiments, chain carboxylic acid esters include, but are not limited to, methyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate, and ethyl pivalate. In some embodiments, some of the hydrogen atoms of chain carboxylic acid esters can be substituted with fluorine. In some embodiments, fluorine-substituted chain carboxylic acid esters include, but are not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, and 2,2,2-trifluoroethyl trifluoroacetate.

[0076] In some embodiments, cyclic ethers include, but are not limited to, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 2-methyl 1,3-dioxolane, 4-methyl 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, and dimethoxypropane.

[0077] In some embodiments, chain ethers include, but are not limited to, dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxy methane, 1,1-ethoxymethoxyethane, and 1,2-ethoxymethoxyethane.

[0078] In some embodiments, phosphorus-containing organic solvents include, but are not limited to, trimethyl phosphate, triethyl phosphate, dimethylethyl phosphate, methyldiethyl phosphate, ethylene methyl phosphate, ethylene 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.

[0079] In some embodiments, sulfur-containing organic solvents include, but are not limited to, 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 of the hydrogen atoms of the sulfur-containing organic solvents can be substituted with fluorine.

[0080] In some embodiments, aromatic fluorine-containing solvents include, but are not limited to, fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, and trifluoromethylbenzene.

[0081] In some embodiments, the solvent used in the electrolyte of the present application includes one or more as described above. In some embodiments, the solvent used in the electrolyte of the present application includes cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, and combinations thereof. In some embodiments, the solvent used in the electrolyte of the present application comprises an organic solvent selected from the group consisting of 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 comprises ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, γ-butyrolactone, or combinations thereof.

[0082] Negative electrode

[0083] The negative electrode in the electrochemical device of this application includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode current collector contains chromium, and the chromium content is from 0.001% to 0.5% based on the mass of the negative electrode current collector. In some embodiments, the chromium content is from 0.001% to 0.1% based on the mass of the negative electrode current collector. In some embodiments, the chromium content is from 0.001% to 0.05% based on the mass of the negative electrode current collector. In some embodiments, the chromium content is 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or within any two of the above values, based on the mass of the negative electrode current collector.

[0084] In some embodiments, the negative current collector is copper foil. Copper foil containing chromium can be denoted as Cu(Cr). Cu(Cr) is an alloy with copper as the main component and a small amount of Cr, wherein Cr can be a protective film formed on the surface of the current collector or a crystalline phase embedded in Cu. Cu(Cr) can contain components other than Cu and Cr, or it can substantially contain only Cu and Cr.

[0085] In some embodiments, the negative electrode active material layer includes a negative electrode active material. The specific type of negative electrode active material is not limited and can be selected according to requirements. Specifically, the negative electrode active material is selected from natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 One or more of Li metal and Li-Al alloy. Among them, silicon-carbon composite refers to silicon-carbon anode active material containing at least about 5 wt% silicon by weight.

[0086] In some embodiments, the negative electrode active material layer further comprises a negative electrode binder. In some embodiments, the negative electrode binder comprises one or more of styrene-butadiene rubber, fluororubber, and ethylene propylene diene.

[0087] In some embodiments, the negative electrode active material layer further comprises a negative electrode conductive agent. In some embodiments, the negative electrode conductive agent comprises one or more of a conductive metallic material and a conductive polymer. In some embodiments, the negative electrode conductive agent comprises one or more of a carbon material, etc. In some embodiments, the carbon material includes, but is not limited to, graphite, carbon black, acetylene black, and Ketjen black.

[0088] In some embodiments, the negative electrode current collector has a negative active material layer on one surface thereof. In some embodiments, the negative electrode current collector has a negative active material layer on both surfaces thereof. In some embodiments, at least one surface of the negative electrode current collector includes a region where no negative active material layer is disposed, also referred to as a bare foil region.

[0089] Positive electrode

[0090] The positive electrode includes a positive electrode current collector and a positive active material disposed on the positive electrode current collector. The specific kind of positive active material is not particularly limited and can be selected as needed.

[0091] In some embodiments, the positive active material includes a positive electrode material capable of absorbing and releasing lithium (Li). Examples of the positive electrode material capable of absorbing / releasing lithium (Li) can include lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganese oxide, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium iron phosphate, lithium titanate, and lithium-rich manganese-based materials.

[0092] Specifically, the chemical formula of lithium cobaltate can be as Chemical Formula 1:

[0093] Li x Co a M1 b O 2-c Chemical Formula 1

[0094] wherein M1 represents at least one element selected from nickel (Ni), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), tungsten (W), yttrium (Y), lanthanum (La), zirconium (Zr), silicon (Si), fluorine (F), or sulfur (S), and x, a, b, and c values are in the following ranges, respectively: 0.8 ≤ x ≤ 1.2, 0.8 ≤ a ≤ 1, 0 ≤ b ≤ 0.2, -0.1 ≤ c ≤ 0.2.

[0095] The chemical formula of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminate can be as Chemical Formula 2:

[0096] Li y Ni d M2 e O 2-f Chemical Formula 2

[0097] wherein M2 represents at least one element selected from cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), tungsten (W), zirconium (Zr), silicon (Si), fluorine (F), or sulfur (S), and y, d, e, and f values are in the following ranges, respectively: 0.8≤y≤1.2, 0.3≤d≤0.98, 0.02≤e≤0.7, -0.1≤f≤0.2.

[0098] The chemical formula of the lithium manganate can be as Chemical Formula 3:

[0099] Li z Mn 2-g M3 g O 4-h Chemical Formula 3

[0100] wherein M3 represents at least one element selected from cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), niobium (Nb), tantalum (Ta), or tungsten (W), and z, g, and h values are in the following ranges, respectively: 0.8≤z≤1.2, 0≤g<1.0, and -0.2≤h≤0.2.

[0101] In some embodiments, the positive electrode active material layer can have a coating layer on the surface, or can be mixed with another compound having a coating layer. The coating layer can include at least one coating element compound selected from oxides of a coating element, hydroxides of a coating element, oxyhydroxides of a coating element, oxycarbonates of a coating element, and hydroxycarbonates of a coating element. The compound used for the coating layer can be amorphous or crystalline. The coating element contained in the coating layer can include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, F, or mixtures thereof. The coating layer can be applied by any method, as long as the method does not adversely affect the performance of the positive electrode active material. For example, the method can include any coating method well known to one of ordinary skill in the art, such as spraying, dipping, etc.

[0102] In some embodiments, the positive electrode active material layer further includes a binder, and optionally further includes a positive electrode conductive material.

[0103] The binder can improve the binding between the positive active material particles and also improve the binding between the positive active material and the current collector. Non-limiting examples of the binder include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon, and the like.

[0104] The positive active material layer includes a positive electrode conductive material, thereby imparting conductivity to the electrode. The positive electrode conductive material can include any conductive material, as long as it does not cause chemical changes. Non-limiting examples of the positive electrode conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, and the like), metal-based materials (e.g., metal powder, metal fiber, and the like, including, for example, copper, nickel, aluminum, silver, and the like), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0105] The positive current collector for the electrochemical device according to the present application can be aluminum (Al), but is not limited thereto.

[0106] Separator membrane

[0107] In some embodiments, the electrochemical device of the present application is provided with a separator film between the positive electrode and the negative electrode to prevent short circuiting of the current caused by contact between the two electrode sheets, while allowing the passage of lithium ions.

[0108] The material and shape of the separator film used in the electrochemical device of the present application are not particularly limited and can be any of the techniques disclosed in the prior art. In some embodiments, the separator film includes a polymer (e.g., synthetic resin) or inorganic substance (e.g., ceramic) formed of a material stable to the electrolyte of the present application, and the like. In some embodiments, the separator film includes a porous film made of the polymer or the inorganic substance. In some embodiments, the separator film includes a laminated film in which two or more porous films are laminated. In some embodiments, the polymer includes, but is not limited to, polytetrafluoroethylene, polypropylene, and polyethylene.

[0109] In some embodiments, the separator film includes the above-mentioned porous film (base material layer) and a layer of a high molecular compound provided on one or both surfaces of the base material layer, which can improve the adhesion of the separator film to the positive and negative electrodes, inhibit the generation of distortion when the electrode sheets are wound, thereby inhibiting the decomposition reaction of the electrolyte and inhibiting the leakage of the liquid electrolyte impregnated in the base material layer. By using such a separator film, even in the case of repeated charging / discharging, the electrical resistance of the electrochemical device does not significantly increase, thereby inhibiting the swelling of the electrochemical device.

[0110] In some embodiments, the high molecular compound layer includes, but is not limited to, polyvinylidene fluoride. Polyvinylidene fluoride has excellent physical strength and electrochemical stability. The high molecular compound layer can be formed by the following method: after preparing a solution in which a high molecular material is dissolved, coating a substrate material layer with the solution or immersing the substrate material layer in the solution, and finally drying.

[0111] Application

[0112] The electrochemical device of the present application includes any device in which an electrochemical reaction occurs, and specific examples thereof include primary or secondary batteries of all kinds. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0113] The use of the electrochemical device of the present application is not particularly limited, and it can be used for any use known in the art. In one embodiment, the electrochemical device of the present application can be used for, but is not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, hand-held cleaners, portable CD players, mini-disc players, transceivers, electronic organizers, calculators, memory cards, portable audio players, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting appliances, toys, game machines, timepieces, power tools, flashlights, cameras, home-use large storage batteries, and lithium ion capacitors, etc.

[0114] The preparation of lithium ion batteries will be described below with lithium ion batteries as an example and in connection with specific embodiments, and those skilled in the art will understand that the preparation methods described in the present application are only examples, and any other suitable preparation method is within the scope of the present application.

[0115] Examples

[0116] The following describes performance evaluation of the examples and comparative examples of lithium ion batteries according to the present application.

[0117] I. Preparation of lithium ion batteries

[0118] 1. Preparation of the negative electrode

[0119] The negative electrode current collector Cu(Cr) involved in the examples and comparative examples is essentially a copper foil containing a chromium element, but the Cu(Cr) that can actually serve as a current collector is not limited to one containing only Cu and Cr. The Cr element content in Cu(Cr) can be controlled by any conventional method in the art, for example, by adjusting the temperature, current density, and plating bath concentration, etc. for electroplating chromium.

[0120] The negative active material artificial graphite, conductive agent Super P, sodium carboxymethyl cellulose (CMC), binder styrene-butadiene rubber (SBR) were mixed according to the weight ratio of 96.4:1.5:0.5:1.6, deionized water was added, and stirred uniformly to obtain a negative electrode slurry, wherein the solid content of the negative electrode slurry was 54wt%. The negative electrode slurry was uniformly coated on both surfaces of a Cu(Cr) foil with a thickness of 8μm to form a negative electrode material layer, dried at 85℃, and then subjected to cold pressing, die cutting, slitting, and winding, and dried at 120℃ under vacuum conditions for 12 hours to obtain a negative electrode. The thickness of the single-sided negative electrode material layer was 52μm.

[0121] 2. Preparation of the positive electrode

[0122] The positive active material LiCoO2, conductive agent conductive carbon black (Super-P) and polyvinylidene fluoride were mixed with N-methyl pyrrolidone (NMP) according to the mass ratio of 97:1.4:1.6, and stirred uniformly to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry was 72wt%. The positive electrode slurry was coated on both surfaces of an aluminum foil with a thickness of 10μm to form a positive electrode material layer, dried at 85℃, and then subjected to cold pressing, die cutting, slitting, and welding of the tabs, and dried at 85℃ under vacuum conditions for 4 hours to obtain a positive electrode. The thickness of the single-sided positive electrode material layer was 35.6μm.

[0123] 3. Preparation of the electrolyte

[0124] The preparation process of the electrolyte of Comparative Examples 1-1 to 1-4, Examples 1-1 to 1-20, and Examples 3-1 to 3-10 is as follows:

[0125] Under a dry argon environment, 20% EC, 25% PC, 20% DEC and 20% EMC were mixed according to the mass ratio, dissolved and stirred thoroughly, then the additives required according to the table were added, and the stirring was continued, finally the lithium salt LiPF6 of the corresponding percentage content (so that the content of each component of the electrolyte adds up to 100%) was added, and mixed uniformly to obtain the electrolyte.

[0126] The preparation process of the electrolyte of Examples 2-1 to 2-11 is as follows:

[0127] Under a dry argon environment, the solvents were first mixed according to the percentage content in the table, then the additive 0.10% II-1 in Example 1-6 was added, and finally the lithium salt LiPF6 of the corresponding percentage content (so that the content of each component of the electrolyte adds up to 100%) was added, and mixed uniformly to obtain the electrolyte.

[0128] The abbreviations of each component used in the electrolyte and the corresponding compound names are shown in the following table:

[0129] Abbreviation Compound Abbreviation Compound EC Ethylene carbonate PC Propylene carbonate DEC Diethyl carbonate EMC Ethyl methyl carbonate PP Propyl propionate EP Ethyl propionate GBL Gamma-butyrolactone FEC Fluoroethylene carbonate DMC Dimethyl carbonate DTD Vinylene sulfate PS 1,3-Propane sulfone lactone VC Vinylene carbonate LiBOB Lithium bis(oxalato)borate NaBOB Sodium bis(oxalato)borate KBOB Potassium bis(oxalato)borate CsBOB Cesium bis(oxalato)borate

[0130] 4. Preparation of separator film

[0131] A polyethylene (PE) film with a thickness of 7 μm was selected, PVDF slurry was coated on both surfaces of the film, dried, and then inorganic particle (mass ratio of flaky boehmite and AI2O3 was 70:30) slurry was further coated on one of the surfaces, dried, and the total thickness of the polyethylene film and coating was 12 μm to obtain a separator film. The thickness of the layer formed by the PVDF slurry was 1.25 μm and the thickness of the layer formed by the inorganic particle slurry was 2.5 μm.

[0132] 5. Preparation of lithium ion battery

[0133] The obtained positive electrode, separator film and negative electrode were wound in order and placed in an outer packaging foil, leaving a liquid injection port. Electrolyte was poured from the liquid injection port, packaged, and then subjected to formation (charged to 3.3 V at 0.02 C constant current and then charged to 3.8 V at 0.1 C constant current) and capacity process to obtain a lithium ion battery (thickness of about 9.1 mm, width of about 49 mm, length of about 74 mm). The layer formed by the inorganic particle slurry was oriented toward the positive electrode.

[0134] II. Test methods

[0135] 1. Test method for chromium content in negative electrode current collector

[0136] The Cr content in Cu(Cr) can be obtained by inductively coupled plasma (ICP) test.

[0137] 2. Test method for self-discharge of lithium ion battery

[0138] The lithium ion battery was placed in a 25°C constant temperature oven and allowed to stand for 30 minutes to allow the lithium ion battery to reach a constant temperature. Then the lithium ion battery was charged at 0.5 C constant current to 4.2 V, charged at 4.2 V constant voltage to a current of 0.025 C, allowed to stand for 5 minutes, discharged at 0.5 C constant current to 3.0 V, allowed to stand for 5 minutes, and then charged at 0.5 C constant current for 60 minutes. The open circuit voltage OCV1 (V) of the lithium ion battery at this time was recorded. Then the lithium ion battery was allowed to stand at 25°C for 48±0.5 h, and the open circuit voltage OCV2 (V) of the lithium ion battery was tested. The self-discharge evaluation parameter K (mV / h) of the lithium ion battery was calculated by the following formula:

[0139] K = 1000 x (OCV1-OCV2) / 48.

[0140] 3. Test method for high temperature storage performance of lithium ion battery

[0141] The lithium ion battery was placed in a 25°C constant temperature oven and allowed to stand for 30 minutes to allow the lithium ion battery to reach a constant temperature. Then the lithium ion battery was charged at 0.5C to 4.2V, and charged at 4.2V to a current of 0.025C, and the initial thickness H0 of the lithium ion battery was tested. After the lithium ion battery was stored in an 80°C high-temperature furnace for 24 hours, the thickness H1 of the lithium ion battery was recorded. The storage thickness expansion rate of the lithium ion battery was calculated by the following formula:

[0142] Storage thickness expansion rate = (H1-H0) / H0 x 100%.

[0143] 4. Test method for low-temperature discharge performance of lithium ion batteries

[0144] The lithium ion battery was placed in a temperature-adjustable high-low temperature oven, the temperature was first set to 25°C, and allowed to stand for 60 minutes, then charged at 0.5C to 4.2V, and charged at 4.2V to a current of 0.025C, and allowed to stand for 10 minutes, then discharged at 0.5C to 3.0V, and the discharge capacity at this time was recorded as D0. At 25°C, the lithium ion battery was again charged at 0.5C to 4.2V, and charged at 4.2V to a current of 0.025C, the temperature was adjusted to -10°C, and allowed to stand for 60 minutes, then discharged at 0.5C to 3.0V, and the discharge capacity D1 was obtained. The low-temperature discharge capacity retention rate D of the lithium ion battery was calculated by the following formula:

[0145] D = D1 / D0 x 100%.

[0146] III. Test results

[0147] Table 1 shows the effect of the content of chromium in the negative electrode current collector and the oxalate-based compound and its content in the electrolyte on the self-discharge of the lithium ion battery.

[0148] Table 1

[0149]

[0150] Note: “—” in Table 1 indicates that the corresponding parameter does not exist.

[0151] In Comparative Example 1-1, the electrolyte did not contain an oxalate-based compound and the negative electrode current collector did not contain Cr. In Comparative Example 1-2, the negative electrode current collector contained a certain amount of Cr but the electrolyte did not contain an oxalate-based compound. In Comparative Example 1-3, the electrolyte contained a certain amount of an oxalate-based compound but the negative electrode current collector did not contain Cr. In Comparative Example 1-4, the electrolyte did not contain an oxalate-based compound and the negative electrode current collector contained an excess of Cr. The self-discharge of these lithium ion batteries was high and difficult to meet the use requirements.

[0152] As shown in Examples 1-1 to 1-20, when the electrolyte contains 0.01% to 5% of the oxalic acid-based compound and the negative current collector contains 0.001% to 0.5% of the chromium element, the self-discharge of the lithium ion battery can be significantly reduced.

[0153] Since the oxalic acid-based compound is more expensive than other substances in the electrolyte, in consideration of the self-discharge performance and cost of the lithium ion battery, when the content of the oxalic acid-based compound in the electrolyte is in the range of 0.01% to 3%, the improvement effect on the self-discharge of the lithium ion battery is more excellent and the cost is reasonable. When the content of the oxalic acid-based compound in the electrolyte is in the range of 0.01% to 1%, the improvement effect on the self-discharge of the lithium ion battery is particularly outstanding and the cost is more reasonable.

[0154] Since the increase of the content of the chromium element increases the cost of the negative current collector, in consideration of the self-discharge performance and cost of the lithium ion battery, when the content of the chromium element in the negative current collector is 0.001% to 0.1%, the improvement effect on the self-discharge of the lithium ion battery is more excellent and the cost is reasonable. When the content of the chromium element in the negative current collector is 0.001% to 0.05%, the improvement effect on the self-discharge of the lithium ion battery is particularly outstanding and the cost is more reasonable.

[0155] Table 2 shows the influence of the cyclic ester and the chain ester and their contents in the electrolyte on the self-discharge and low-temperature discharge performance of the lithium ion battery. Except for the parameters listed in Table 2, Examples 2-1 to 2-11 are consistent with the settings of Example 1-6.

[0156] Table 2

[0157]

[0158] The results show that when the electrolyte further includes the cyclic ester and the chain ester and the ratio S1 / S2 of the content (S1%) of the cyclic ester to the content (S2%) of the chain ester is in the range of 0.2 to 1, the lithium ion battery not only can maintain a low self-discharge, but also has a low-temperature discharge capacity retention rate of at least 80%. This is because in this range, the mixed solvent and the electrolyte salt (such as LiPF6) form a suitable coordination relationship to exist in the form of ion clusters, which weakens the redox reaction activity of the single solvent, is conducive to reducing the chemical self-discharge caused by side reactions, and maintains a stable K value; at the same time, it also ensures the full dissociation of the electrolyte salt and the relatively low viscosity of the overall electrolyte, improves the electrolyte conductivity, and thus improves the low-temperature discharge performance of the battery.

[0159] Table 3 shows the influence of the additives in the electrolyte on the self-discharge and high-temperature storage performance of the lithium ion battery. Except for the parameters listed in Table 3, Examples 3-1 to 3-10 are consistent with the settings of Example 1-6.

[0160] Table 3

[0161]

[0162] Note: "-" in Table 3 means that there is no corresponding parameter.

[0163] The results show that when the electrolyte further contains 0.01wt% to 5wt% of the additive (at least one of PS, DTD, LiPO2F2 and VC), the self-discharge of the lithium ion battery can be further reduced, and the high-temperature storage thickness expansion rate of the lithium ion battery is also significantly reduced. Mainly because the working voltage range of the lithium battery has basically exceeded the electrochemical window of the solvent in the electrolyte, the solvent will generate chemical self-discharge through continuous side reactions on the electrode surface, and further increase of a certain amount of additive in the electrolyte can form a protective layer on the electrode surface, further slow down the side reactions of the solvent on the electrode surface, thereby improving the K value and gas production.

[0164] Throughout this specification, the use of “example,” “exemplary,” “one example,” “another example,” “some examples,” “one embodiment,” “another embodiment,” “various embodiments,” or “some embodiments” means that the described feature, structure, material, or characteristic is included in at least one embodiment or example of the present application. Therefore, the appearance of such phrases in various places throughout this specification are not necessarily referring to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples.

[0165] While the illustrative embodiments have been described and illustrated, it will be understood by those skilled in the art that the above-described embodiments are not the only ways in which the present application can be practiced. Changes can be made to the embodiments in light of the teachings of the present application, and it is understood that well-known equivalents exist and are within the scope of the present application. Therefore, changes in the details of the application are intended to be covered by the application.

[0166] The above description is merely illustrative of the application and is not to be taken in a limiting sense. Rather, various modifications and / or changes can be made to the application without departing from the spirit and scope of the application.

Claims

1. An electrochemical device comprising a negative electrode and an electrolyte, wherein: the negative electrode comprises a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, the negative electrode current collector contains a chromium element at a content of 0.001% to 0.5% based on the mass of the negative electrode current collector; the electrolyte contains a compound based on oxalic acid at a content of 0.01% to 5% based on the mass of the electrolyte; and the compound based on oxalic acid comprises at least one of a compound of Formula I, a compound of Formula II, a compound of Formula III, a compound of Formula IV, or a compound of Formula V: wherein: A + each independently selected from Li + , Na + , K + , or Cs + ; R 11 , R 12 , R 21 , R 22 , R 31 , R 32 , R 33 and R 34 are each independently selected from halogen, unsubstituted or halogen-substituted C 1-4 alkyl, unsubstituted or halogen-substituted C 2-4 alkenyl or unsubstituted or halogen-substituted C 2-4 alkynyl; R 41 and R 42 each independently is selected from H, Li, Na, K, Cs, NH4, unsubstituted or halogen-substituted C 1-4 alkyl, unsubstituted or fluorine-substituted C 2-4 alkenyl or unsubstituted or fluorine-substituted C 2-4 alkynyl, and R 41 and R 42 may optionally be bound together with the atoms to which they are attached to form a ring.

2. The electrochemical device of claim 1, wherein, the electrochemical device satisfies at least one of the following conditions: the compound of Formula I comprises at least one of lithium bis(oxalato)borate, sodium bis(oxalato)borate, cesium bis(oxalato)borate, or potassium bis(oxalato)borate; the compound of Formula II comprises at least one of: the compound of Formula III comprises at least one of: the compound of Formula IV comprises at least one of: the compound of Formula V comprises at least one of: H2C2O4, Li2C2O4, Na2C2O4, K2C2O4, Cs2C2O4, NH4C2O4, CH3C2O4Li, 3.The electrochemical device according to claim 1, wherein the compound based on oxalic acid is contained at a content of 0.01% to 3% based on the mass of the electrolyte. 4.The electrochemical device according to claim 1, wherein the compound based on oxalic acid is contained at a content of 0.01% to 1% based on the mass of the electrolyte. 5.The electrochemical device according to claim 1, wherein the chromium element is contained at a content of 0.001% to 0.1% based on the mass of the negative electrode current collector. 6.The electrochemical device according to claim 1, wherein the chromium element is contained at a content of 0.001% to 0.05% based on the mass of the negative electrode current collector. 7.The electrochemical device according to claim 1, wherein the negative electrode current collector is a copper foil. 8.The electrochemical device according to claim 1, wherein the electrolyte further comprises a cyclic ester and a chain ester, the cyclic ester comprises at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone, fluoroethylene carbonate, the chain ester comprises at least one of diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, and the cyclic ester is contained at a content of S1% and the chain ester is contained at a content of S2% based on the mass of the electrolyte, S1 / S2 is in a range of 0.20 to 1.

00. 9.The electrochemical device according to claim 8, wherein S1 is in a range of 15 to 50. 10.The electrochemical device according to claim 1, wherein the electrolyte further contains an additive selected from at least one of 1,3-propane sultone, ethylene sulfate, lithium difluorophosphate, or vinylene carbonate, and the additive is contained at a content of 0.01wt% to 5wt% based on the mass of the electrolyte.

11. An electronic device comprising the electrochemical device according to any one of claims 1 to 10.

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