WO2024183543A1

WO2024183543A1 - Electrochemical device and electronic device

Info

Publication number: WO2024183543A1
Application number: PCT/CN2024/078234
Authority: WO
Inventors: 刘俊飞; 周邵云
Original assignee: 宁德新能源科技有限公司
Priority date: 2023-03-07
Filing date: 2024-02-23
Publication date: 2024-09-12
Also published as: WO2024182992A1

Abstract

Provided are an electrochemical device and an electronic device. The electrochemical device comprises a negative electrode and an electrolyte, wherein the negative electrode comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector. The negative electrode current collector contains chromium, and the content of chromium is 0.001% to 0.5% based on the mass of the negative electrode current collector. The electrolyte comprises a compound based on oxalic acid, and the content of the compound based on oxalic acid is 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. The electrochemical device has significantly reduced self-discharge.

Description

Electrochemical devices and electronic devices

This application claims the priority of the Chinese patent application filed with the China Patent Office on March 7, 2023, with international application number PCT/CN2023/080022 and invention name “Electrochemical Device and Electronic Device”, the entire contents of which are incorporated by reference in this application.

Technical Field

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

Background Art

Electrochemical devices (e.g., lithium-ion batteries) have the advantages of high energy density, stable operating 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, notebooks, cameras and other electronic products), electric vehicles, power tools, drones, intelligent robots, and large-scale energy storage. However, with the rapid development of information and communication technology and the diversity of market demand, people have put forward more requirements and challenges for the power supply of electronic products, such as thinner, lighter, more diverse in appearance, higher volume energy density and mass energy density, higher safety and higher power.

The positive electrode active materials, negative electrode active materials and electrolyte contained in the electrochemical device are sensitive to moisture. Therefore, during the preparation of the battery, it is necessary to keep it in an environment with as low humidity as possible, which has a great impact on the battery preparation process control, battery performance, production cost, etc.

In view of this, it is indeed necessary to provide an electrochemical device that is compatible with the influence of humidity in the battery production environment.

Summary of the invention

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

According to one aspect of the present application, the present application provides an electrochemical device, which includes 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, wherein the negative electrode current collector contains a chromium element, and the content of the chromium element is 0.001% to 0.5% based on the mass of the negative electrode current collector;

The electrolyte comprises an oxalic acid-based compound, wherein 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 includes 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:

in:

A ⁺ are 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 are each independently selected from H, Li, Na, K, Cs, NH ₄ , 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 be optionally combined together with the atoms to which they are attached to form a ring.

According to an embodiment of the present application, the compound of formula I comprises at least one of the following compounds: lithium bisoxalatoborate (LiBOB), sodium bisoxalatoborate (NaBOB), cesium bisoxalatoborate (CsBOB) or potassium bisoxalatoborate (KBOB);

The compound of formula II includes at least one of the following compounds:

The compound of formula III includes at least one of the following compounds:

The compound of formula IV comprises at least one of the following compounds:

The compound of formula V comprises at least one of the following compounds:

H ₂ C ₂ O ₄ , Li ₂ C ₂ O ₄ , Na ₂ C ₂ O ₄ , K ₂ C ₂ O ₄ , Cs ₂ C ₂ O ₄ , NH ₄ C ₂ O ₄ , CH ₃ C ₂ O ₄ Li,

According to an embodiment of the present application, the content of the oxalic acid-based compound is 0.01% to 3% based on the mass of the electrolyte.

According to an embodiment of the present application, the content of the oxalic acid-based compound is 0.01% to 1% based on the mass of the electrolyte.

According to an embodiment of the present application, based on the mass of the negative electrode current collector, the content of the chromium element is 0.001% to 0.1%.

According to an embodiment of the present application, based on the mass of the negative electrode current collector, the content of the chromium element is 0.001% to 0.05%.

According to an embodiment of the present application, the negative electrode current collector is copper foil.

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

According to an embodiment of the present application, S1 is in the range of 15 to 50.

According to an embodiment of the present application, the electrolyte further comprises an additive, the additive is selected from at least one of 1,3-propane sultone (PS), diethylene sulfate (DTD), lithium difluorophosphate (LiPO ₂ F ₂ ) or vinylene carbonate (VC), and the content of the additive is 0.01 wt % to 5 wt % based on the mass of the electrolyte.

According to another aspect of the present application, the present application provides an electronic device, which includes the electrochemical device according to the present application.

The present application provides an electrochemical device and an electronic device, which uses an electrolyte containing an oxalic acid-based compound on the basis of a negative electrode current collector containing chromium elements. On the one hand, the oxalic acid-based compound 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 radicals produced by the hydrolysis of the oxalic acid-based compound 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 electrode current collector to form a protective layer, thereby avoiding the metal ions of the negative electrode current collector from dissolving and then being reduced to form a single metal at the negative electrode. Under the combined effect of these factors, the electrochemical device of the present application has significantly reduced self-discharge.

Additional aspects and advantages 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

In order to make the purpose, technical scheme, and advantages of the present application more clearly understood, the present application is further described in detail with reference to the accompanying drawings and examples. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

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.

In the detailed description and claims, a 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, 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 can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

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.

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, _-C2-4 alkenyl, _-C2-6 alkenyl and _-C2-10 alkenyl. Representative alkenyl groups include, for example, vinyl, n-propenyl, isopropenyl, n-but-2-enyl, but-3-enyl, n-hex-3-enyl, and the like.

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 alkynyl. Representative alkynyl groups include, for example, ethynyl, prop-2-ynyl (n-propynyl), n-but-2-ynyl, n-hex-3-ynyl, and the like.

The term "halogen" may be F, Cl, Br or I.

The positive electrode active materials, negative electrode active materials and electrolytes in electrochemical devices (e.g., lithium-ion batteries) are sensitive to moisture. For example, in an environment with high humidity, the negative electrode current collector (e.g., copper foil) is prone to corrosion, which can have many adverse effects on the electrochemical device. The use of chromium-containing copper current collectors can delay the oxidation of the copper current collector in the air and the corrosion of the copper current collector by the electrolyte to a certain extent, but the oxide protective layer formed by chromium will still be destroyed by the hydrofluoric acid in the electrolyte, resulting in copper dissolution, which in turn leads to increased self-discharge of the electrochemical device.

In order to solve the above problems, the present application provides an electrochemical device, which uses an electrolyte containing an oxalic acid-based compound on the basis of a negative electrode current collector containing chromium elements. On the one hand, the oxalic acid-based compound can react with water in the electrolyte, consume excess water, avoid the production of hydrofluoric acid, and thus avoid the destruction of the oxide protective layer formed by chromium. On the other hand, the oxalate radicals produced by the hydrolysis of the oxalic acid-based compound 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 electrode current collector to form a protective layer, thereby avoiding the metal ions of the negative electrode current collector from being dissolved and then reduced to form a single metal at the negative electrode. Under the combined effect of these factors, the electrochemical device of the present application has significantly reduced self-discharge.

Electrolyte

The electrolyte in the electrochemical device of the present application comprises an oxalic acid-based compound, wherein 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:

in:

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

In some embodiments, the compound of Formula I comprises at least one of the following compounds: lithium bisoxalatoborate (LiBOB), sodium bisoxalatoborate (NaBOB), cesium bisoxalatoborate (CsBOB), or potassium bisoxalatoborate (KBOB).

In some embodiments, the compound of formula II includes at least one of the following compounds:

In some embodiments, the compound of formula III includes at least one of the following compounds:

In some embodiments, the compound of formula IV comprises at least one of the following compounds:

In some embodiments, the compound of formula V comprises at least one of the following compounds:

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

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

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 consisting of any two of the foregoing values.

In some embodiments, S1 is in the range of 15 to 50. In some embodiments, S1 is 15, 30, 40, 50, or in the range of any two of the above values.

In some embodiments, S2 is in the range of 15 to 75. In some embodiments, S2 is 15, 25, 35, 45, 55, 65, 75 or in the range consisting of any two of the above values.

When the electrolyte contains the above-mentioned content of cyclic esters and chain esters, the mixed solvent forms a suitable coordination relationship with the electrolyte salt (such as LiPF ₆ ) and exists in the form of ion clusters, which weakens the redox reaction activity of the single solvent, helps to reduce the chemical self-discharge caused by side reactions, and maintain a stable self-discharge evaluation parameter K value; at the same time, it ensures the full dissociation of the electrolyte salt and the relatively low viscosity of the electrolyte as a whole, improves the electrolyte conductivity, and thus improves the low-temperature discharge performance of the battery.

In some embodiments, the electrolyte further comprises an additive, the additive is selected from at least one of 1,3-propane sultone (PS), diethylene sulfate (DTD), lithium difluorophosphate (LiPO ₂ F ₂ ) or vinylene carbonate (VC), and the content of the additive is 0.01 wt % to 5 wt % based on the mass of the electrolyte.

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 the range of any two of the above values based on the mass of the electrolyte.

The addition of additives can not only further reduce the self-discharge of electrochemical devices, but also significantly improve the storage gas generation problem caused by the low oxidation potential of oxalic acid-based compounds. This is because the additives 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 additives can reduce the oxidation and decomposition of oxalic acid-based compounds at the positive electrode and improve the high-temperature storage performance of the electrochemical device.

The electrolyte that can be used in the present application includes LiPF _6. In some embodiments, the concentration of LiPF ₆ is in the range of 0.8 mol/L to 3 mol/L, 0.8 mol/L to 2.5 mol/L, 0.8 mol/L to 2 mol/L, or 1 mol/L to 2 mol/L. In some embodiments, the concentration of the 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.

The solvents that can be used in the electrolyte of the embodiments of the present application include, but are not limited to: 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.

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.

In some embodiments, the linear carbonates include, but are not limited to: methyl n-propyl carbonate, ethyl n-propyl carbonate, di-n-propyl carbonate and the like; as the fluorine-substituted linear carbonates, for example, 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.

In some embodiments, the cyclic carboxylic acid ester includes, but is not limited to, γ-valerolactone. In some embodiments, part of the hydrogen atoms of the cyclic carboxylic acid ester may be substituted with fluorine.

In some embodiments, the chain carboxylic acid ester includes, but is 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, part of the hydrogen atoms of the chain carboxylic acid ester can be substituted by fluorine. In some embodiments, the fluorine-substituted chain carboxylic acid ester includes, but is not limited to: methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate and 2,2,2-trifluoroethyl trifluoroacetate.

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.

In some embodiments, the chain ethers include, but are not limited to, dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxymethane, 1,1-ethoxymethoxyethane, and 1,2-ethoxymethoxyethane.

In some embodiments, the phosphorus-containing organic solvent includes, but is not limited to, trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, diethyl methyl phosphate, ethylidene methyl phosphate, ethylidene phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(2,2,3,3,3-pentafluoropropyl) phosphate.

In some embodiments, the sulfur-containing organic solvent includes, but is 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 hydrogen atoms of the sulfur-containing organic solvent may be substituted by fluorine.

In some embodiments, the aromatic fluorine-containing solvent includes, but is not limited to, fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, and trifluoromethylbenzene.

In some embodiments, the solvent used in the electrolyte of the present application includes one or more of the above. 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 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.

negative electrode

The negative electrode in the electrochemical device of the present 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, wherein the negative electrode current collector contains a chromium element, and the content of the chromium element is 0.001% to 0.5% based on the mass of the negative electrode current collector. In some embodiments, the content of the chromium element is 0.001% to 0.1% based on the mass of the negative electrode current collector. In some embodiments, the content of the chromium element is 0.001% to 0.05% based on the mass of the negative electrode current collector. In some embodiments, the content of the chromium element is 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% or within the range of any two of the above values based on the mass of the negative electrode current collector.

In some embodiments, the negative electrode current collector is a copper foil. Copper foil containing chromium can be recorded 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 can substantially contain only Cu and Cr.

In some embodiments, the negative electrode active material layer includes a negative electrode active material, and the specific types of the negative electrode active material are not subject to specific restrictions and can be selected according to needs. Specifically, the negative electrode active material is selected from one or more of natural graphite, artificial graphite, mesophase microcarbon beads (MCMB for short), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO ₂ , spinel-structured lithiated TiO ₂ -Li ₄ Ti ₅ O ₁₂ , Li metal, and Li-Al alloy. The silicon-carbon composite refers to a silicon-carbon negative electrode active material containing at least about 5wt% silicon based on the weight of the silicon-carbon negative electrode active material.

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, fluorine-based rubber, and ethylene-propylene-diene.

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 metal material and a conductive polymer having conductivity. 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.

In some embodiments, a negative electrode current collector has a negative electrode active material layer on one surface. In some embodiments, a negative electrode current collector has a negative electrode active material layer on both surfaces. In some embodiments, at least one surface of the negative electrode current collector includes an area where no negative electrode active material layer is provided, also referred to as an empty foil area.

positive electrode

The positive electrode includes a positive electrode current collector and a positive electrode active material disposed on the positive electrode current collector. The specific types of the positive electrode active material are not subject to specific restrictions and can be selected according to needs.

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

Specifically, the chemical formula of lithium cobalt oxide may be as shown in Chemical Formula 1:
Li _x Co _a M1 _b O _2-c Chemical formula 1

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 the values of x, a, b and c are respectively in the following ranges: 0.8≤x≤1.2, 0.8≤a≤1, 0≤b≤0.2, -0.1≤c≤0.2.

The chemical formula of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide may be as shown in Chemical Formula 2:
Li _y Ni _d M2 _e O _2-f Chemical formula 2

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 the values of y, d, e and f are respectively in the following ranges: 0.8≤y≤1.2, 0.3≤d≤0.98, 0.02≤e≤0.7, -0.1≤f≤0.2.

The chemical formula of lithium manganate can be as shown in Chemical Formula 3:
Li _z Mn _2-g M3 _g O _4-h Chemical formula 3

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 the values of z, g and h are respectively in the following ranges: 0.8≤z≤1.2, 0≤g<1.0 and -0.2≤h≤0.2.

In some embodiments, the positive electrode active material layer may have a coating on the surface, or may be mixed with another compound having a coating. The coating may include at least one coating element compound selected from an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. The compound used for the coating may be amorphous or crystalline. The coating element contained in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, F, or a mixture thereof. The coating may be applied by any method as long as the method As long as the performance of the positive electrode active material is not adversely affected, the method may include any coating method well known to those skilled in the art, such as spraying, dipping, and the like.

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

The binder can improve the bonding between the positive electrode active material particles and also improve the bonding between the positive electrode active material and the current collector. Non-limiting examples of binders 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, etc.

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

The positive electrode current collector used in the electrochemical device according to the present application may be aluminum (Al), but is not limited thereto.

Isolation film

In some embodiments, the electrochemical device of the present application is provided with a separator between the positive electrode and the negative electrode to prevent the current short circuit caused by the contact between the two pole pieces, while allowing lithium ions to pass through.

The material and shape of the isolation membrane used in the electrochemical device of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the isolation membrane includes a polymer (e.g., a synthetic resin) or an inorganic substance (e.g., a ceramic) formed from a material that is stable to the electrolyte of the present application. In some embodiments, the isolation membrane includes a porous membrane made of the polymer or the inorganic substance. In some embodiments, the isolation membrane includes a laminated membrane in which two or more porous membranes are laminated. In some embodiments, the polymer includes, but is not limited to, polytetrafluoroethylene, polypropylene, and polyethylene.

In some embodiments, the separator includes the above-mentioned porous film (base material layer) and a polymer compound layer disposed on one or both surfaces of the base material layer, which can improve the adhesion of the separator relative to the positive electrode and the negative electrode, inhibit the deflection when the electrode sheet is wound, thereby inhibiting the decomposition reaction of the electrolyte and inhibiting the liquid leakage of the electrolyte impregnated with the base material layer. By using such a separator, the resistance of the electrochemical device will not increase significantly even in the case of repeated charge/discharge, thereby inhibiting the expansion of the electrochemical device.

In some embodiments, the polymer compound layer includes, but is not limited to, polyvinylidene fluoride. Polyvinylidene fluoride has excellent physical strength and electrochemical stability. The polymer compound layer can be formed by the following method: after preparing a solution containing a polymer material, coating a substrate material layer with the solution or soaking the substrate material layer in water. In solution, drying is finally performed.

application

The electrochemical device of the present application includes any device that generates an electrochemical reaction, and its specific examples include all kinds of primary batteries or secondary batteries. 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.

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 prior art. In one embodiment, 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.

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.

Example

The following describes the performance evaluation of the examples and comparative examples of the lithium-ion battery according to the present application.

1. Preparation of lithium-ion batteries

1. Preparation of negative electrode

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

The negative electrode active material artificial graphite, the conductive agent Super P, sodium carboxymethyl cellulose (CMC), and the binder styrene butadiene rubber (SBR) were mixed in a weight ratio of 96.4:1.5:0.5:1.6, deionized water was added, and stirred evenly to obtain a negative electrode slurry, wherein the solid content of the negative electrode slurry was 54wt%. The negative electrode slurry was evenly coated on both surfaces of a Cu (Cr) foil with a thickness of 8μm to form a negative electrode material layer, dried at 85°C, and then cold pressed, die-cut, slit, and wound, and dried under vacuum conditions at 120°C for 12 hours to obtain a negative electrode. Among them, the thickness of the single-sided negative electrode material layer is 52μm.

2. Preparation of positive electrode

The positive electrode active material LiCoO ₂ , the conductive agent conductive carbon black (Super-P) and polyvinylidene fluoride were mixed at a ratio of 97:1.4:1.6. The positive electrode slurry was mixed with N-methylpyrrolidone (NMP) in a mass ratio of 100 wt % and stirred evenly to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry was 72 wt %. The positive electrode slurry was coated on both surfaces of an aluminum foil with a thickness of 10 μm to form a positive electrode material layer, dried at 85°C, and then cold pressed, die-cut, slit, and welded to the pole ear, and then dried at 85°C under vacuum conditions for 4 hours to obtain a positive electrode. The thickness of the single-sided positive electrode material layer was 35.6 μm.

3. Preparation of electrolyte

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

In a dry argon environment, based on the total mass of the electrolyte, 20% EC, 25% PC, 20% DEC and 20% EMC are first mixed according to the mass ratio, dissolved and fully stirred, and then additives are added according to the required content and type in the table, and stirring is continued. Finally, lithium salt LiPF ₆ with a corresponding percentage content (so that the total content of each component of the electrolyte is 100%) is added, and mixed evenly to obtain an electrolyte.

The electrolyte preparation process of Examples 2-1 to 2-11 is as follows:

Under dry argon environment, the solvents were first mixed according to the percentages in the table based on the total mass of the electrolyte, then 0.10% II-1 of the additive in Example 1-6 was added, and finally corresponding percentages (so that the total content of each component of the electrolyte was 100%) of lithium salt LiPF ₆ were added and mixed uniformly to obtain an electrolyte.

The abbreviations of the components used in the electrolyte and their corresponding compound names are shown in the following table:

4. Preparation of isolation membrane

A polyethylene (PE) film with a thickness of 7 μm was selected, PVDF slurry was coated on both surfaces, dried, and then inorganic particles (the mass ratio of flake boehmite and Al ₂ O ₃ was 70:30) slurry was continuously coated on one surface, dried, and the total thickness of the polyethylene film and the coating was 12 μm to obtain an isolation membrane. Among them, the single layer 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.

5. Preparation of lithium-ion batteries

The obtained positive electrode, separator and negative electrode are wound in order and placed in the outer packaging foil, leaving a liquid injection port. The electrolyte is poured from the liquid injection port, packaged, and then subjected to formation (charged to 3.3V at a constant current of 0.02C, and then charged to 3.8V at a constant current of 0.1C) and capacity processes to obtain a lithium-ion battery (thickness of about 9.1mm, width of about 49mm, and length of about 74mm). Among them, the layer formed by the inorganic particle slurry faces the positive electrode.

2. Test Method

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

The Cr content in Cu(Cr) can be obtained by inductively coupled plasma (ICP) testing.

2. Self-discharge test method of lithium-ion batteries

Place the lithium-ion battery in a 25°C constant temperature box and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Then charge the lithium-ion battery at a constant current of 0.5C to 4.2V, charge it at a constant voltage of 4.2V to a current of 0.025C, let it stand for 5 minutes, then discharge it at a constant current of 0.5C to 3.0V, let it stand for 5 minutes, and then charge it at a constant current of 0.5C for 60 minutes. Record the open circuit voltage OCV1 (V) of the lithium-ion battery at this time, then let it stand at 25°C for 48±0.5h, and test the open circuit voltage OCV2 (V) of the lithium-ion battery. Calculate the self-discharge evaluation parameter K (mV/h) of the lithium-ion battery by the following formula:
K = 1000 x (OCV1 - OCV2)/48.

3. Test method for high temperature storage performance of lithium-ion batteries

Place the lithium-ion battery in a 25°C thermostat and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Then charge the lithium-ion battery at a constant current of 0.5C to 4.2V, and charge it at a constant voltage of 4.2V to a current of 0.025C, and test the initial thickness H0 of the lithium-ion battery. After storing the lithium-ion battery in an 80°C high-temperature furnace for 24 hours, record the thickness H1 of the lithium-ion battery. Calculate the storage thickness expansion rate of the lithium-ion battery by the following formula:
Storage thickness expansion ratio = (H1 - H0)/H0 x 100%.

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

Place the lithium-ion battery in a temperature-adjustable high and low temperature box, first set the temperature to 25°C, let it stand for 60 minutes, then charge it at a constant current of 0.5C to 4.2V, charge it at a constant voltage of 4.2V to a current of 0.025C, let it stand for 10 minutes, then discharge it at a constant current of 0.5C to 3.0V, and record the discharge capacity at this time as D0. At 25°C, charge it at a constant current of 0.5C to 4.2V, charge it at a constant voltage of 4.2V to a current of 0.025C, adjust the temperature to -10°C, let it stand for 60 minutes, then discharge it at a constant current of 0.5C to 3.0V, and obtain the discharge capacity D1. The low-temperature discharge capacity retention rate D of the lithium-ion battery is calculated by the following formula:
D=D1/D0×100%.

3. Test Results

Table 1 shows the effects of the chromium content in the negative electrode current collector and the oxalic acid-based compounds and their content in the electrolyte on the self-discharge of lithium-ion batteries.

Table 1

Note: “—” in Table 1 means there is no corresponding parameter.

In Comparative Example 1-1, the electrolyte does not contain oxalic acid-based compounds and the negative electrode current collector does not contain Cr. In Comparative Example 1-2, the negative electrode current collector contains a certain amount of Cr but the electrolyte does not contain oxalic acid-based compounds. In Comparative Example 1-3, the electrolyte contains a certain amount of oxalic acid-based compounds but the negative electrode current collector does not contain Cr. In Comparative Example 1-4, the electrolyte does not contain oxalic acid-based compounds and the negative electrode current collector contains excessive Cr. These lithium-ion batteries have high self-discharge and are difficult to meet usage requirements.

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 electrode current collector contains 0.001% to 0.5% of the chromium element, the self-discharge of the lithium ion battery can be significantly reduced.

Since the cost of oxalic acid-based compounds is higher than other substances in the electrolyte, considering the self-discharge of lithium-ion batteries Performance and cost, when the content of oxalic acid-based compounds in the electrolyte is in the range of 0.01% to 3%, the improvement effect on the self-discharge of lithium-ion batteries is more excellent and the cost is reasonable. When the content of oxalic acid-based compounds in the electrolyte is in the range of 0.01% to 1%, the improvement effect on the self-discharge of lithium-ion batteries is particularly outstanding and the cost is more reasonable.

Since the increase of chromium content will increase the cost of negative electrode current collector, considering the self-discharge performance and cost of lithium-ion batteries, when the content of chromium in the negative electrode current collector is 0.001% to 0.1%, the improvement effect on the self-discharge of lithium-ion batteries is more excellent and the cost is reasonable. When the content of chromium in the negative electrode current collector is 0.001% to 0.05%, the improvement effect on the self-discharge of lithium-ion batteries is particularly prominent and the cost is more reasonable.

Table 2 shows the effects of cyclic esters and chain esters and their contents in the electrolyte on the self-discharge and low-temperature discharge performance of lithium-ion batteries. Except for the parameters listed in Table 2, the configurations of Examples 2-1 to 2-11 are consistent with those of Example 1-6.

Table 2

The results show that when the electrolyte also includes cyclic esters and chain esters and the ratio S1/S2 of the content of cyclic esters (S1%) to the content of chain esters (S2%) is in the range of 0.2 to 1, the lithium-ion battery can not only maintain a low self-discharge, but also has a low-temperature discharge capacity retention rate of at least 80%. This is because within this range, the mixed solvent forms a suitable coordination relationship with the electrolyte salt (such as LiPF ₆ ) and exists in the form of ion clusters, which weakens the redox reaction activity of the single solvent, helps to reduce the chemical self-discharge caused by side reactions, and maintains a stable K value; at the same time, it ensures the full dissociation of the electrolyte salt and the relatively low viscosity of the electrolyte as a whole, improves the electrolyte conductivity, and thus improves the low-temperature discharge performance of the battery.

Table 3 shows the effects of additives in the electrolyte on the self-discharge and high temperature storage performance of lithium-ion batteries. Except for the parameters listed in Table 3, the configurations of Examples 3-1 to 3-10 are consistent with those of Example 1-6.

Table 3

Note: “—” in Table 3 indicates that there is no corresponding parameter.

The results show that when the electrolyte further contains 0.01wt% to 5wt% of additives (at least one of PS, DTD, LiPO ₂ F ₂ and VC), the self-discharge of lithium-ion batteries can be further reduced, and the high-temperature storage thickness expansion rate of lithium-ion batteries can be significantly reduced. This is mainly because the operating voltage range of lithium batteries has basically exceeded the electrochemical window of the solvent in the electrolyte. The solvent will continue to react on the electrode surface to produce chemical self-discharge. Further adding a certain amount of additives to the electrolyte can form a protective layer on the electrode surface, further slowing down the side reactions of the solvent on the electrode surface, thereby improving the K value and gas production.

References throughout the specification to “embodiments,” “partial embodiments,” “one embodiment,” “another example,” “example,” “specific example,” or “partial example” 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 referred to in any suitable manner. One or more embodiments or examples may be combined.

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.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

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, wherein the negative electrode current collector contains a chromium element, and the content of the chromium element is 0.001% to 0.5% based on the mass of the negative electrode current collector;

The electrolyte comprises an oxalic acid-based compound, wherein 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 includes 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:

in:

A + are 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 are each independently selected from H, Li, Na, K, Cs, NH 4 , 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 be optionally combined together with the atoms to which they are attached to form a ring.
The electrochemical device according to claim 1, wherein the electrochemical device satisfies at least one of the following conditions:

The compound of formula I comprises at least one of the following compounds: lithium bis(oxalatoborate), sodium bis(oxalatoborate), Cesium dioxalatoborate or potassium dioxalatoborate;

The compound of formula II includes at least one of the following compounds:

The compound of formula III includes at least one of the following compounds:

The compound of formula IV comprises at least one of the following compounds:

The compound of formula V comprises at least one of the following compounds:

H 2 C 2 O 4 , Li 2 C 2 O 4 , Na 2 C 2 O 4 , K 2 C 2 O 4 , Cs 2 C 2 O 4 , NH 4 C 2 O 4 , CH 3 C 2 O 4 Li,
The electrochemical device according to claim 1, wherein the content of the oxalic acid-based compound is 0.01% to 3% based on the mass of the electrolyte.
The electrochemical device according to claim 1, wherein the content of the oxalic acid-based compound is 0.01% to 1% based on the mass of the electrolyte.
The electrochemical device according to claim 1, wherein the content of the chromium element is 0.001% to 0.1% based on the mass of the negative electrode current collector.
The electrochemical device according to claim 1, wherein the content of the chromium element is 0.001% to 0.05% based on the mass of the negative electrode current collector.
The electrochemical device according to claim 1, wherein the negative electrode current collector is copper foil.
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, and fluoroethylene carbonate, and the chain ester comprises at least one of diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, ethyl acetate, ethyl propionate, and propyl propionate, and

Based on the mass of the electrolyte, the content of the cyclic ester is S1%, the content of the chain ester is S2%, and S1/S2 is in the range of 0.20 to 1.00.
The electrochemical device according to claim 8, wherein S1 is in the range of 15 to 50.
The electrochemical device according to claim 1, wherein the electrolyte further comprises an additive selected from at least one of 1,3-propane sultone, vinyl sulfate, lithium difluorophosphate or vinylene carbonate, and the content of the additive is 0.01 wt% to 5 wt% based on the mass of the electrolyte.
An electronic device comprising the electrochemical device according to any one of claims 1 to 10.