CN111261939A

CN111261939A - Electrolyte solution and electrochemical device using the same

Info

Publication number: CN111261939A
Application number: CN202010064798.1A
Authority: CN
Inventors: 栗文强; 熊亚丽; 郑建明
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2020-01-20
Filing date: 2020-01-20
Publication date: 2020-06-09

Abstract

The present application relates to an electrolyte and an electrochemical device using the same. The electrolyte of the present application comprises a compound of formula I and LiPO₂F₂：

Description

Electrolyte solution and electrochemical device using the same

Technical Field

The present application relates to the technical field of electrochemical devices, and more particularly, to an electrolyte and an electrochemical device using the same.

Background

With the development of the times and the upgrade of intelligent equipment, the market has more and more requirements on the functions of batteries. With the incandescence of rapid market competition and the arrival of the 5G era, high-rate charge and discharge become inevitable trends. With a higher temperature rise. The impedance change of the battery during such high temperature and long-term use becomes a focus of increasing market attention. How to solve such problems also becomes a problem hindering the development of secondary batteries.

Disclosure of Invention

Embodiments of the present application provide an electrolyte and an electrochemical device using the same, in an attempt to solve at least one of the problems occurring in the related art to at least some extent. The embodiment of the application also provides an electrochemical device and an electronic device using the electrolyte.

According to the bookIn one aspect of the application, the application provides an electrolyte comprising a compound of formula I and LiPO₂F₂：

Wherein R is₁₁、R₁₂Each independently selected from H, halogen, cyano, substituted or unsubstituted C_1-20Alkyl, substituted or unsubstituted C_3-20Cycloalkyl, substituted or unsubstituted C_2-20Alkenyl, substituted or unsubstituted C_1-20Alkoxy, substituted or unsubstituted C_6-20Aryl or substituted or unsubstituted C_6-20A heteroaryl group;

R₁₃、R₁₄each independently selected from the group consisting of a single bond, -O-, -S-, and substituted or unsubstituted C_1-6Alkylene, substituted or unsubstituted C_1-6Alkenylene or substituted or unsubstituted C_1-6An alkyleneoxy group;

R₁₅selected from single bonds, -O-, -NR₁-、

Substituted or unsubstituted C_1-20Alkylene, substituted or unsubstituted C_1-6An alkyleneoxy group; wherein R is₁Is selected from C_1-20Alkyl radical, C_3-20Cycloalkyl radical, C_2-20Alkenyl radical, C_6-20Aryl or C_6-20A heteroaryl group;

wherein R is₁₁、R₁₂、R₁₃、R₁₄And R₁₅Each independently substituted, the substituents being selected from halogen, cyano, C_1-20Alkyl radical, C_3-20Cycloalkyl radical, C_1-20Alkoxy radical, C_2-20Alkenyl radical, C_6-20Aryl radical, C_6-20Heteroaryl, -R₀-S-R group, -R₀-an O-R group or any combination thereof; wherein R is₀Is selected from C_1-6Alkylene, and R is selected from C_1-20Alkyl radical, C_3-20Cycloalkyl radical, C_2-20Alkenyl radical, C_6-20Aryl or C_6-20A heteroaryl group.

According to some embodiments of the present application, the compound of formula I in the electrolyte comprises at least one of the following compounds:

according to some embodiments of the present application, wherein the weight percentage of the compound of formula I is awt%, awt% is 0.001 wt% to 3 wt%, based on the total weight of the electrolyte, and the LiPO₂F₂The weight percentage of the b is 0.01wt percent to 0.49wt percent, a and b satisfy the following relational expression: a + b is less than 3.4; and a/b.gtoreq. 1/5.

According to some embodiments of the present application, the electrolyte further comprises a fluorocarboxylate compound, the fluorocarboxylate compound comprising a compound of formula II:

wherein R is₂₁、R₂₂Each independently selected from substituted or unsubstituted C_1-20Alkyl, substituted or unsubstituted C_3-20Cycloalkyl, substituted or unsubstituted C_2-20Alkenyl, substituted or unsubstituted C_1-20Alkoxy, substituted or unsubstituted C_6-20Aryl or substituted or unsubstituted C_6-20A heteroaryl group;

wherein R is₂₁、R₂₂Each independently substituted, the substituents being selected from halogen, cyano, C_1-20Alkyl radical, C_3-20Cycloalkyl radical, C_1-20Alkoxy radical, C_2-20Alkenyl radical, C_6-20Aryl or any combination thereof; wherein R is₂₁And R₂₂At least one of which is substituted with F.

In some embodiments herein, the fluorocarboxylate compound comprises at least one of the following compounds:

in some embodiments of the present application, wherein the weight percentage of the fluorocarboxylic acid ester is between 0.5 and 70 wt%, based on the total weight of the electrolyte.

In some embodiments of the present application, the electrolyte further comprises a phosphate compound, the phosphate compound comprising a compound of formula III:

wherein R is₃₁、R₃₂、R₃₃Each independently selected from H, halogen, cyano, substituted or unsubstituted C_1-20Alkyl, substituted or unsubstituted C_3-20Cycloalkyl, substituted or unsubstituted C_2-20Alkenyl, substituted or unsubstituted C_2-20Alkynyl, substituted or unsubstituted C_1-20Alkoxy, substituted or unsubstituted C_6-20Aryl or substituted or unsubstituted C_6-20A heteroaryl group;

wherein R is₃₁、R₃₂、R₃₃Each independently substituted, the substituents are selected from halogen, cyano, nitro, carboxyl, C_1-20Alkyl radical, C_3-20Cycloalkyl radical, C_1-20Alkoxy radical, C_2-20Alkenyl radical, C_6-20Aryl radical, C_6-20Heteroaryl, or any combination thereof.

In some embodiments herein, the phosphate compound comprises at least one of the following compounds:

in some embodiments herein, the weight percentage of the phosphate ester compound is 0.1 wt% to 20 wt% based on the total weight of the electrolyte.

In another aspect of the present application, there is provided an electrochemical device comprising a positive electrode including a positive electrode active material layer containing a positive electrode active material; and an electrolyte according to embodiments of the present application.

In some embodiments of the present application, the electrolyte of the electrochemical device further comprises cobalt ions, wherein the content of the cobalt ions is less than or equal to 50ppm based on the total weight of the electrolyte.

In some embodiments of the present application, an Al element is included in a positive electrode active material of an electrochemical device in an amount of m × 10 based on the total weight of the positive electrode active material layer³ppm, m is 0.5-10, and (a + b)/m is less than or equal to 6.

In another embodiment, the present application provides an electronic device comprising an electrochemical device according to an embodiment of the present application.

Lithium ion batteries made from the electrolytes of the present application have reduced storage and cycling resistance as well as improved overcharge and hot box performance.

Additional aspects and advantages of embodiments of the present application will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of embodiments of the present application.

Detailed Description

Embodiments of the present application will be described in detail below. The embodiments of the present application should not be construed as limiting the present application.

In the detailed description and claims, a list of items connected by the terms "one of," "one of," or other similar terms may mean any one of the listed items. For example, if items a and B are listed, the phrase "one of a and B" means a alone or B alone. In another example, if items A, B and C are listed, the phrase "one of A, B and C" means only a; only B; or only C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.

In the detailed description and claims, a list of items linked by the term "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means a only; 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 a only; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.

As used herein, the term "alkyl" is intended to be a straight chain saturated hydrocarbon structure having from 1 to 20 carbon atoms. "alkyl" is also contemplated to be a branched or cyclic hydrocarbon structure having from 3 to 20 carbon atoms. For example, the alkyl group can be an alkyl group of 1 to 20 carbon atoms, an alkyl group of 1 to 10 carbon atoms, an alkyl group of 1 to 5 carbon atoms, an alkyl group of 5 to 20 carbon atoms, an alkyl group of 5 to 15 carbon atoms, or an alkyl group of 5 to 10 carbon atoms. When an alkyl group having a particular carbon number is specified, all geometric isomers having that carbon number are intended to be encompassed; thus, for example, "butyl" is meant to include n-butyl, sec-butyl, isobutyl, tert-butyl, and cyclobutyl; "propyl" includes n-propyl, isopropyl and cyclopropyl. Examples of alkyl groups 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, and the like. In addition, the alkyl group may be optionally substituted.

As used herein, the term "cycloalkyl" encompasses cyclic alkyl groups. The cycloalkyl group may be a cycloalkyl group of 3 to 20 carbon atoms, a cycloalkyl group of 6 to 20 carbon atoms, a cycloalkyl group of 3 to 12 carbon atoms, a cycloalkyl group of 3 to 6 carbon atoms. For example, cycloalkyl groups can be cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and the like. In addition, cycloalkyl groups may be optionally substituted.

The term "alkoxy" as used herein refers to a L-O-group, wherein L is alkyl. For example, the alkoxy group may be an alkoxy group of 1 to 20 carbon atoms, an alkoxy group of 1 to 12 carbon atoms, an alkoxy group of 1 to 5 carbon atoms, an alkoxy group of 5 to 20 carbon atoms, an alkoxy group of 5 to 15 carbon atoms or an alkoxy group of 5 to 10 carbon atoms. In addition, alkoxy groups may be optionally substituted.

As used herein, the term "alkyleneoxy" refers to-L₁-O-group, wherein L₁Is an alkylene group. For example, the alkyleneoxy group may be an alkyleneoxy group of 1 to 20 carbon atoms, an alkyleneoxy group of 1 to 12 carbon atoms, an alkyleneoxy group of 1 to 5 carbon atoms, an alkyleneoxy group of 5 to 20 carbon atoms, an alkyleneoxy group of 5 to 15 carbon atoms, or an alkyleneoxy group of 5 to 10 carbon atoms. In addition, the alkyleneoxy group may be optionally substituted.

The term "alkenyl" as used herein refers to a monovalent unsaturated hydrocarbon group that can be straight-chain 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 may be, for example, an alkenyl group of 2 to 20 carbon atoms, an alkenyl group of 6 to 20 carbon atoms, an alkenyl group of 2 to 12 carbon atoms, or an alkenyl group of 2 to 6 carbon atoms. Representative alkenyl groups include, by way of example, ethenyl, n-propenyl, isopropenyl, n-but-2-enyl, but-3-enyl, n-hex-3-enyl, and the like. In addition, the alkenyl group may be optionally substituted.

The term "alkynyl" refers to a monovalent unsaturated hydrocarbon group that can be straight-chain 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 may be, for example, an alkynyl group of 2 to 20 carbon atoms, an alkynyl group of 6 to 20 carbon atoms, an alkynyl group of 2 to 10 carbon atoms, or an alkynyl group of 2 to 6 carbon atoms. Representative alkynyl groups include, for example, ethynyl, prop-2-ynyl (n-propynyl), n-but-2-ynyl, n-hex-3-ynyl, and the like. In addition, the alkynyl group may be optionally substituted.

As used herein, the term "alkylene" means a straight or branched chain divalent saturated hydrocarbon group. For example, the alkylene group may be an alkylene group of 1 to 20 carbon atoms, an alkylene group of 1 to 15 carbon atoms, an alkylene group of 1 to 10 carbon atoms, an alkylene group of 1 to 5 carbon atoms, an alkylene group of 5 to 20 carbon atoms, an alkylene group of 5 to 15 carbon atoms or an alkylene group of 5 to 10 carbon atoms. Representative alkylene groups include, for example, methylene, ethane-1, 2-diyl ("ethylene"), propane-1, 2-diyl, propane-1, 3-diyl, butane-1, 4-diyl, pentane-1, 5-diyl, and the like. In addition, the alkylene group may be optionally substituted.

As used herein, the term "alkenylene" encompasses both straight-chain and branched alkenylene groups. When an alkenylene group having a particular carbon number is specified, all geometric isomers having that carbon number are intended to be encompassed. For example, the alkenylene group may be an alkenylene group of 2 to 20 carbon atoms, an alkenylene group of 2 to 15 carbon atoms, an alkenylene group of 2 to 10 carbon atoms, an alkenylene group of 2 to 5 carbon atoms, an alkenylene group of 5 to 20 carbon atoms, an alkenylene group of 5 to 15 carbon atoms, or an alkenylene group of 5 to 10 carbon atoms. Representative alkenylene groups include, for example, ethenylene, propenylene, butenylene, and the like. In addition, alkenylene may be optionally substituted.

As used herein, the term "aryl" encompasses monocyclic and polycyclic ring systems. Polycyclic rings can have two or more rings in which two carbons are common to two adjoining rings (the rings are "fused"), wherein at least one of the rings is aromatic, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryls, heterocyclics, and/or heteroaryls. For example, the aryl group may be C₆-C₅₀Aryl radical, C₆-C₄₀Aryl radical, C₆-C₃₀Aryl radical, C₆-C₂₀Aryl or C₆-C₁₀And (4) an aryl group. Representative aryl groups include, for example, phenyl, methylphenyl, propylphenyl, isopropylphenyl, benzyl, and naphthalen-1-yl, naphthalen-2-yl, and the like. In addition, the aryl group may be optionally substituted.

As used herein, the term "heteroaryl" encompasses monocyclic heteroaromatic groups that may include one to three heteroatoms, such as pyrrole, furan, thiophene, imidazole, oxazole, thiazole, triazole, pyrazole, pyridine, pyrazine, pyrimidine and the like. The term heteroaryl also includes polycyclic heteroaromatic systems having two or more rings in which two atoms are common to two adjoining rings (the rings are "fused"), wherein the rings areAt least one of which is heteroaryl, and the other rings can be cycloalkyl, cycloalkenyl, aryl, heterocyclic, and/or heteroaryl. The heteroatom in the heteroaryl group may be, for example, O, S, N, Se. For example, the heteroaryl group may be C₃-C₅₀Heteroaryl group, C₃-C₄₀Heteroaryl group, C₃-C₃₀Heteroaryl group, C₃-C₂₀Heteroaryl or C₃-C₁₀A heteroaryl group. In addition, heteroaryl groups may be optionally substituted.

As used herein, the term "heteroatom" encompasses O, S, P, N, B or an isostere thereof.

As used herein, the term "halogen" encompasses F, Cl, Br, I.

When the above substituents are substituted, their substituents may each be independently selected from the group consisting of: halogen, alkyl, alkenyl, aryl. As used herein, the term "substituted" or "substituted" means that it may be substituted with 1 or more (e.g., 2, 3) substituents.

As used herein, the content of each component is obtained based on the total weight of the electrolyte.

First, electrolyte

In some embodiments, the present application provides an electrolyte comprising a compound of formula I and LiPO₂F₂：

R₁₃、R₁₄each independently selected from the group consisting of a single bond, -O-, -S-, and substituted or unsubstituted C_1-6Alkylene, substituted or unsubstituted C_1-6Alkenylene radicalOr substituted or unsubstituted C_1-6An alkyleneoxy group;

R₁₅selected from single bonds, -O-, -NR₁-、

In some embodiments, the compound of formula I comprises or is selected from at least one of the following compounds:

a compound of formula I and LiPO₂F₂The combined action may improve the storage impedance and the cycling impedance of the electrochemical device. Although the detailed mechanism of action for obtaining this effect is not clear, the following is conceivable: a compound of formula I and LiPO₂F₂The combined action can form a protective film which is good in stability, rich in more organic components and good in film flexibility, the content of LiF in the organic protective film is increased, LiF has good stability, the high-temperature resistance of the organic protective film can be enhanced, and the consumption of the organic protective film in a long circulation process is reduced.

In some embodiments, the weight percent of the compound of formula I is awt%, and the a wt% is 0.001 wt% to 3 wt%, based on the total weight of the electrolyte. In some embodiments, the a wt% is 0.005 wt%, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, or a range consisting of any two of these values.

In some embodiments, the LiPO is based on the total weight of the electrolyte₂F₂The weight percentage of the component (b) is b wt percent, and the weight percentage of b is 0.01wt percent to 0.49wt percent. In some embodiments, b wt% is 0.01 wt%, 0.03 wt%, 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.5 wt%, or a range consisting of any two of these values.

In some embodiments, a and b satisfy the following relationship: a + b < 3.4, < 3.0, < 2.5, < 2.0, < 1.5, < 1.0, < 0.5, < 0.25, < 0.2, < 0.1, or < 0.05.

In some embodiments, a/b ≧ 1/5, ≧ 2/5, ≧ 3/5, ≧ 4/5, ≧ 5/5, ≧ 6/5, ≧ 2, ≧ 3, ≧ 4, ≧ 6, ≧ 8, or ≧ 10.

A compound of formula I and LiPO₂F₂The weight percentage of (b) in the above range enables the viscosity of the electrolyte, the thickness of the protective film and the composition of the protective film to be in appropriate ranges, resulting in further improvement of the storage resistance and cycle resistance of the electrochemical device.

In some embodiments, the electrolyte further comprises a fluorocarboxylate compound comprising a compound of formula II:

In some embodiments, the fluorocarboxylic acid ester is present in an amount ranging from 0.5% to 70% by weight, based on the total weight of the electrolyte. In some embodiments, the weight percent of the fluorocarboxylic acid ester is 0.5 wt%, 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 70 wt%, or a range consisting of any two of these values, based on the total weight of the electrolyte.

In some embodiments, the fluorocarboxylate compound comprises or is selected from at least one of the following compounds:

bound compound of formula I, LiPO₂F₂And the fluorocarboxylate can further improve the oxidation resistance of an electrolyte system, so that good interface protection is formed, the effect of improving the safety performance is achieved, and the safety performance of the electrochemical device can be further improved.

In some embodiments, the electrolyte further comprises a phosphate ester compound, a compound of formula I, LiPO₂F₂The free radicals can be effectively captured under the combined action of the phosphate compound, so that the safety performance of the electrochemical device is improved. In some embodiments, the phosphate ester compound comprises a compound of formula III:

In some embodiments, the weight percentage of the phosphate ester compound is 0.1 wt% to 20 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the phosphate compound is 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, or a range consisting of any two of these values, based on the total weight of the electrolyte.

In some embodiments, the phosphate compound comprises or is selected from at least one of the following compounds:

in some embodiments, the electrolyte further comprises a polynitrile compound, the polynitrile compound comprises at least one of 1,3, 5-pentane-trimethylnitrile, 1,2, 3-propane-trimethylnitrile, 1,3, 6-hexane-trimethylnitrile, 1,2, 3-tris (2-cyanoethoxy) propane, 1,2, 4-tris (2-cyanoethoxy) butane, 1,1, 1-tris (cyanoethoxymethylene) ethane, 1,1, 1-tris (cyanoethoxymethylene) propane, 3-methyl-1, 3, 5-tris (cyanoethoxy) pentane, 1,2, 7-tris (cyanoethoxy) heptane, 1,2, 6-tris (cyanoethoxy) hexane, and 1,2, 5-tris (cyanoethoxy) pentane.

In some embodiments, the electrolyte further comprises a dinitrile compound. The dinitrile compound can make up for the film forming defect of the polynitrile substance due to smaller steric hindrance, thereby enhancing the interface protection of the anode material.

In some embodiments, the dinitrile compounds include, but are not limited to: succinonitrile, glutaronitrile, adiponitrile, 1, 5-dicyanopentane, 1, 6-dicyanohexane, 1, 7-dicyanoheptane, 1, 8-dicyanooctane, 1, 9-dicyanononane, 1, 10-dicyanodecane, 1, 12-dicyanododecane, tetramethylsuccinonitrile, 2-methylglutaronitrile, 2, 4-dimethylglutaronitrile, 2,4, 4-tetramethylglutaronitrile, 1, 4-dicyanopentane, 2, 5-dimethyl-2, 5-hexanediocarbonitrile, 2, 6-dicyanoheptane, 2, 7-dicyanooctane, 2, 8-dicyanononane, 1, 6-dicyanodecane, 1, 2-dicyanobenzene, 1, 3-dicyanobenzene, 1, 4-dicyanobenzene, 3, 5-dioxa-pimelinitrile, 1, 4-bis (cyanoethoxy) butane, ethylene glycol di (2-cyanoethyl) ether, diethylene glycol di (2-cyanoethyl) ether, triethylene glycol di (2-cyanoethyl) ether, tetraethylene glycol di (2-cyanoethyl) ether, 3,6,9,12,15, 18-hexaoxaeicosanoic acid dinitrile, 1, 3-bis (2-cyanoethoxy) propane, 1, 4-bis (2-cyanoethoxy) butane, 1, 5-bis (2-cyanoethoxy) pentane and ethylene glycol di (4-cyanobutyl) ether, 1, 4-dicyano-2-butene, 1, 4-dicyano-2-methyl-2-butene, 1, 4-bis (cyanoethoxy) butane, 2-cyanoethyl-ethyl-ether, 1, 4-dicyano-2-ethyl-2-butene, 1, 4-dicyano-2, 3-dimethyl-2-butene, 1, 4-dicyano-2, 3-diethyl-2-butene, 1, 6-dicyano-3-hexene, 1, 6-dicyano-2-methyl-5-methyl-3-hexene.

In some embodiments, the weight percentage of the dinitrile compound is 0.1 wt% to 15 wt%, based on the total weight of the electrolyte. In some embodiments, the weight percentage of the dinitrile compound is not less than 0.1 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the dinitrile compound is not less than 0.5 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the dinitrile compound is not less than 2 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the dinitrile compound is not less than 4 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the dinitrile compound is no greater than 15 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the dinitrile compound is no greater than 10 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the dinitrile compound is no greater than 8 wt% based on the total weight of the electrolyte.

In some embodiments, the electrolyte further comprises a cyclic ether. The cyclic ether can form a film on the cathode and the anode simultaneously, and the reaction of the electrolyte and the active material is reduced.

In some embodiments, the 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, dimethoxypropane.

In some embodiments, the weight percentage of the cyclic ether is 0.1 wt% to 10 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the cyclic ether is not less than 0.1 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the cyclic ether is not less than 0.5 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the cyclic ether is no greater than 2 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the cyclic ether is no greater than 5 wt% based on the total weight of the electrolyte.

In some embodiments, the electrolyte further comprises a chain ether. In some embodiments, chain ethers include, but are not limited to: dimethoxymethane, 1-dimethoxyethane, 1, 2-dimethoxyethane, diethoxymethane, 1-diethoxyethane, 1, 2-diethoxyethane, ethoxymethoxymethane, 1-ethoxymethoxyethane, 1, 2-ethoxymethoxyethane.

In some embodiments, the weight percentage of the chain ether is 0.1 wt% to 10 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the chain ether is not less than 0.5 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the chain ether is not less than 2 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the chain ether is not less than 3 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the chain ethers is not greater than 10 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the chain ethers is not greater than 5 wt% based on the total weight of the electrolyte.

In some embodiments, the electrolyte further comprises an aromatic fluorine-containing solvent. The aromatic fluorine-containing solvent can quickly form a film to protect the active material, and the fluorine-containing substance can improve the wetting performance of the electrolyte on the active material. 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 weight percent of the aromatic fluorine-containing solvent is about 0.1 wt% to 10 wt% based on the total weight of the electrolyte. In some embodiments, the weight percent of the aromatic fluorine-containing solvent is not less than 0.5 wt% based on the total weight of the electrolyte. In some embodiments, the weight percent of the aromatic fluorine-containing solvent is not less than 2 wt% based on the total weight of the electrolyte. In some embodiments, the weight percent of the aromatic fluorine-containing solvent is not greater than 4 wt% based on the total weight of the electrolyte. In some embodiments, the weight percent of the aromatic fluorine-containing solvent is not greater than 8 wt% based on the total weight of the electrolyte.

In some embodiments, the electrolyte further comprises a lithium salt additive. In some embodiments, the lithium salt additive includes, but is not limited to, lithium trifluoromethanesulfonylimide LiN (CF)₃SO₂)₂(abbreviated as LiTFSI), lithium bis (fluorosulfonyl) imide Li (N (SO)₂F)₂) (abbreviated as LiFSI) and lithium LiB (C) bis (oxalato-borate₂O₄)₂(abbreviated as LiBOB) and tetrafluoroLithium oxalate phosphate (LiPF)₄C₂O₂) Lithium difluorooxalato borate LiBF₂(C₂O₄) (abbreviated as LiDFOB) and lithium hexafluorocaesium acid (LiCSF)₆)。

In some embodiments, the weight percentage of the lithium salt additive is 0.01 wt% to 10 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the lithium salt additive is 0.1 wt% to 5 wt% based on the total weight of the electrolyte. In some embodiments, the weight percentage of the lithium salt additive is 0.1 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt%, 10 wt%, or a range consisting of any two of these values, based on the total weight of the electrolyte.

II, electrolyte

The electrolyte used in the electrolyte of the embodiment of the present application may be an electrolyte known in the art, and the electrolyte includes, but is not limited to: inorganic lithium salts, e.g. LiClO₄、LiAsF₆、LiPF₆、LiBF₄、LiSbF₆、LiSO₃F、LiN(FSO₂)₂Etc.; organic lithium salts containing fluorine, e.g. LiCF₃SO₃、LiN(FSO₂)(CF₃SO₂)、LiN(CF₃SO₂)₂、LiN(C₂F₅SO₂)₂Cyclic 1, 3-hexafluoropropane disulfonimide lithium, cyclic 1, 2-tetrafluoroethane disulfonimide lithium, LiN (CF)₃SO₂)(C₄F₉SO₂)、LiC(CF₃SO₂)₃、LiPF₄(CF₃)₂、LiPF₄(C₂F₅)₂、LiPF₄(CF₃SO₂)₂、LiPF₄(C₂F₅SO₂)₂、LiBF₂(CF₃)₂、LiBF₂(C₂F₅)₂、LiBF₂(CF₃SO₂)₂、LiBF₂(C₂F₅SO₂)₂(ii) a Lithium salts containing dicarboxylic acid complexes, e.g. lithium bis (oxalato) borate, difluoroLithium oxalato borate, lithium tris (oxalato) phosphate, lithium difluorobis (oxalato) phosphate, lithium tetrafluoro (oxalato) phosphate, and the like. The electrolyte may be used alone or in combination of two or more. For example, in some embodiments, the electrolyte comprises LiPF₆And LiBF₄Combinations of (a) and (b). In some embodiments, the electrolyte comprises LiPF₆Or LiBF₄An inorganic lithium salt and LiCF₃SO₃、LiN(CF₃SO₂)₂、LiN(C₂F₅SO₂)₂And the like, a combination of fluorine-containing organic lithium salts. In some embodiments, the concentration of the electrolyte is in the range of 0.8 to 3mol/L, such as in the range of 0.8 to 2.5mol/L, in the range of 0.8 to 2mol/L, in the range of 1 to 2mol/L, 0.5 to 1.5mol/L, 0.8 to 1.3mol/L, 0.5 to 1.2mol/L, and again, such as 1mol/L, 1.15mol/L, 1.2mol/L, 1.5mol/L, 2mol/L, or 2.5 mol/L.

Electrochemical device

The electrochemical device of the present application includes any device in which electrochemical reactions occur, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. 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. In some embodiments, an electrochemical device according to the present application is an electrochemical device including a positive electrode having a positive electrode active material capable of occluding and releasing metal ions and a negative electrode having a negative electrode active material capable of occluding and releasing metal ions, and includes an electrolytic solution according to any one of the embodiments described above.

1. Electrolyte solution

The electrolyte used in the electrochemical device of the present application is the electrolyte of any of the embodiments described above in the present application.

In some embodiments, the electrolyte in the electrochemical device further comprises cobalt ions, wherein the content of the cobalt ions is less than or equal to 50ppm based on the total weight of the electrolyte. In some embodiments, the cobalt ion is present in an amount of 0.01ppm, 0.05ppm, 1ppm, 5ppm, 7ppm, 10ppm, 15ppm, 20ppm, 25ppm, 30ppm, 35ppm, 40ppm, 45ppm, 50ppm, or a range consisting of any two of these values, based on the total weight of the electrolyte.

In addition, the electrolyte used in the electrochemical device of the present application may further include other electrolytes within a range not departing from the gist of the present application.

2. Negative electrode

The material, composition, and manufacturing method of the negative electrode used in the electrochemical device of the present application may include any of the techniques disclosed in the prior art. In some embodiments, the negative electrode is the negative electrode described in U.S. patent application US9812739B, which is incorporated by reference in its entirety.

In some embodiments, the negative electrode includes a current collector and a negative active material layer on the current collector. The negative active material includes a material that reversibly intercalates/deintercalates lithium ions. In some embodiments, the material that reversibly intercalates/deintercalates lithium ions comprises a carbon material. In some embodiments, the carbon material may be any carbon-based negative active material commonly used in lithium ion rechargeable batteries. In some embodiments, carbon materials include, but are not limited to: crystalline carbon, amorphous carbon, or mixtures thereof. The crystalline carbon may be amorphous, flake, platelet, spherical or fibrous natural or artificial graphite. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or the like.

In some embodiments, the negative active material layer includes a negative active material. In some embodiments, the negative active material includes, but is not limited to: lithium metal, structured lithium metal, natural graphite, artificial graphite, mesophase micro carbon spheres (MCMB), hard carbon, soft carbon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO₂Spinel-structured lithiated TiO₂-Li₄Ti₅O₁₂A Li-Al alloy, or any combination thereof.

When the anode includes a silicon carbon compound, the silicon carbon is 1:10 to 10:1 based on the total weight of the anode active material, and the median particle diameter Dv50 of the silicon carbon compound is 0.1 μm to 100 μm. When the negative electrode includes an alloy material, the negative electrode active material layer can be formed by a method such as an evaporation method, a sputtering method, or a plating method. When the anode includes lithium metal, the anode active material layer is formed, for example, with a conductive skeleton having a spherical strand shape and metal particles dispersed in the conductive skeleton. In some embodiments, the spherical-stranded conductive skeleton may have a porosity of 5% -85%. In some embodiments, a protective layer may also be disposed on the lithium metal anode active material layer.

In some embodiments, the negative active material layer may include a binder, and optionally a conductive material. The binder improves the binding of the negative active material particles to each other and the binding of the negative active material to the current collector. In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

In some embodiments, the conductive material includes, but is not limited to: a carbon-based material, a metal-based material, a conductive polymer, or a mixture thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from the group consisting of metal powder, metal fiber, copper, nickel, aluminum, silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

In some embodiments, the current collector includes, but is not limited to: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymeric substrates coated with a conductive metal, and any combination thereof.

The negative electrode may be prepared by a preparation method well known in the art. For example, the negative electrode can be obtained by: the active material, the conductive material, and the binder are mixed in a solvent to prepare an active material composition, and the active material composition is coated on a current collector. In some embodiments, the solvent may include water, and the like, but is not limited thereto.

3. Positive electrode

The material of the positive electrode used in the electrochemical device of the present application may be prepared using materials, configurations, and manufacturing methods well known in the art. In some embodiments, the positive electrode of the present application can be prepared using the techniques described in US9812739B, which is incorporated by reference in its entirety.

In some embodiments, the positive electrode includes a current collector and a positive active material layer on the current collector. The positive electrode active material includes at least one lithiated intercalation compound that reversibly intercalates and deintercalates lithium ions. In some embodiments, the positive electrode active material includes a composite oxide. In some embodiments, the composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

In some embodiments, the positive active material is selected from lithium cobaltate (LiCoO)₂) Lithium Nickel Cobalt Manganese (NCM) ternary material, lithium iron phosphate (LiFePO)₄) Lithium manganate (LiMn)₂O₄) Or any combination thereof.

In some embodiments, the positive electrode active material may have a coating layer on a surface thereof, or may be mixed with another compound having a coating layer. The coating may comprise at least one coating element compound selected from the group consisting of an oxide of the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element and an oxycarbonate of the coating element. The compounds used for the coating may be amorphous or crystalline.

In some embodiments, the coating elements contained in the coating may include Mg, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, F, or any combination thereof. The coating layer may be applied by any method as long as the method does not adversely affect the properties of the positive electrode active material. For example, the method may include any coating method known to the art, such as spraying, dipping, and the like.

In some embodiments, the positive electrode active materialThe material contains Al element in an amount of m x 10 based on the total weight of the positive electrode active material layer³ppm, m is 0.5-10, (a + b)/m is less than or equal to 6.

In some embodiments, m is 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or a range consisting of any two of these values.

In some embodiments, (a + b)/m is 6, 5, 4, 3, 2,1, or a range consisting of any two of these values.

The positive active material layer further includes a binder, and optionally a conductive material. The binder improves the binding of the positive electrode active material particles to each other, and also improves the binding of the positive electrode active material to the current collector.

In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy, nylon, and the like.

In some embodiments, the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from the group consisting of metal powder, metal fiber, copper, nickel, aluminum, silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

In some embodiments, the current collector may be aluminum, but is not limited thereto.

The positive electrode may be prepared by a preparation method well known in the art. For example, the positive electrode can be obtained by: the active material, the conductive material, and the binder are mixed in a solvent to prepare an active material composition, and the active material composition is coated on a current collector. In some embodiments, the solvent may include, but is not limited to, N-methylpyrrolidone, and the like.

In some embodiments, the positive electrode is made by forming a positive electrode material on a current collector using a positive electrode active material layer including a lithium transition metal-based compound powder and a binder.

In some embodiments, the positive electrode active material layer may be generally fabricated by: the positive electrode active material and a binder (a conductive material, a thickener, and the like, which are used as needed) are dry-mixed to form a sheet, and the obtained sheet is pressure-bonded to a positive electrode current collector, or these materials are dissolved or dispersed in a liquid medium to form a slurry, which is applied to the positive electrode current collector and dried. In some embodiments, the material of the positive electrode active material layer includes any material known in the art.

4. 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 short circuit. The material and shape of the separation film used in the electrochemical device of the present application are not particularly limited, and may be any of the techniques disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance or the like formed of a material stable to the electrolyte of the present application.

For example, the release film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is at least one selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

At least one surface of the base material layer is provided with a surface treatment layer, the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance, the ratio of the thickness of the base material layer to the thickness of the surface treatment layer is 1: 1-20: 1, the thickness of the base material layer is 4-14 μm, and the thickness of the surface treatment layer is 1-5 μm.

The inorganic layer comprises inorganic particles and a binder, wherein the inorganic particles are selected from one or more of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is selected from one or a combination of more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer comprises a polymer, and the material of the polymer comprises at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

Fourth, application

The electrolyte according to the embodiment of the present application can be used to reduce the storage resistance and the cycle resistance of a battery and improve the overcharge performance and the hot box performance of the battery, and is suitable for use in an electronic device including an electrochemical device.

The use of the electrochemical device of the present application is not particularly limited, and the electrochemical device can be used for various known uses. Such as a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a cellular phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large-sized battery for home use, or a lithium ion capacitor.

While the following lithium ion battery is taken as an example and the specific examples for preparing the electrolyte and the test method for electrochemical devices are combined to illustrate the preparation and performance of the lithium ion battery, those skilled in the art will understand that the preparation method described in the present application is only an example, and any other suitable preparation method is within the scope of the present application.

Although illustrated as a lithium ion battery, one skilled in the art will appreciate after reading this application that the cathode materials of the present application may be used in other suitable electrochemical devices. Such an electrochemical device includes any device in which electrochemical reactions occur, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. 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.

Examples

The present application will be described in more detail below with reference to examples and comparative examples, but the present application is not limited to these examples as long as the gist thereof is not deviated.

1. Lithium ion battery preparation

1) Preparing an electrolyte:

at water content<In a 10ppm argon atmosphere glove box, Ethylene Carbonate (EC), diethyl carbonate (DEC) and Propylene Carbonate (PC) are uniformly mixed according to the weight ratio of 3:4:3, and then the fully dried lithium salt LiPF is added₆Dissolving the mixed solvent to obtain a basic electrolyte, wherein LiPF is contained in the basic electrolyte₆The concentration of (2) is 1 mol/L. The electrolytes of different examples and comparative examples were obtained by adding different contents of the substances shown in the following tables to the base electrolyte. The contents of each substance in the electrolyte described below were calculated based on the total weight of the electrolyte.

Examples of compounds of formula I are as follows:

examples of fluorocarboxylate compounds are as follows:

examples of phosphate compounds are as follows:

2) preparation of the positive electrode:

preparing a positive electrode active material lithium cobaltate (the molecular formula is LiCoO) containing Al element₂) Acetylene black and polyvinylidene fluoride (abbreviated as PVDF) are fully stirred and mixed in a proper amount of N-methyl pyrrolidone (abbreviated as NMP) solvent according to the weight ratio of 96:2:2 to form uniform anode slurry; coating the slurry on an Al foil of a positive current collector, drying, cold pressing to obtain a positive active material layer, and cutting and welding tabs to obtain the positive electrode. In the following examples and comparative examples, the content of Al element was 3000ppm based on the total weight of the positive electrode active material layer, unless otherwise specified.

The following illustrates a method for preparing a positive electrode active material lithium cobaltate satisfying a content of Al element of 3000ppm calculated based on the total weight of the positive electrode active material layer: adding CoCl₂And AlCl₃Respectively preparing aqueous solutions according to the molar ratio of active substances of 1: k (K is more than or equal to 0 and less than or equal to 0.01088221) and adding NH₃·HCO₃The solution adjusted the pH of the mixture to 10.5 to give a precipitated material. Calcining the obtained precipitate at 400 deg.C for 5h to obtain Al-containing C_O3O₄. The obtained C_O3O₄And Li₂CO₃According to a molar ratio of 2: 3.15, and calcining at 1000 ℃ for 8 hours to obtain LiCoO₂. The obtained LiCoO₂According to a molar ratio of 1: [ (0.01088221-K)/2]Adding Al according to the proportion₂O₃Mixing, and sintering at 800 deg.C for 8 hr to obtain anode active material lithium cobaltate (molecular formula is LiCoO) containing Al element₂)。

3) Preparation of a negative electrode:

fully stirring and mixing a negative electrode active material graphite, a conductive agent acetylene black, a binder Styrene Butadiene Rubber (SBR), and a thickener sodium carboxymethyl cellulose (CMC) in a proper amount of deionized water solvent according to a weight ratio of 95:2:2:1 to form uniform negative electrode slurry; coating the slurry on a Cu foil of a negative current collector, drying, cold pressing to obtain a negative active material layer, cutting and welding a tab to obtain a negative electrode.

4) And (3) isolation film: using a Polyethylene (PE) porous polymer film of 6.5-7.5 μm as a substrate, and Al is provided on the substrate₂O₃Particle layer of Al₂O₃The thickness of the particle layer is 2-4 μm.

5) Preparing a lithium ion battery: and sequentially stacking the anode, the isolating membrane and the cathode to enable the isolating membrane to be positioned between the anode and the cathode to play an isolating role, then winding and placing the isolating membrane into an outer packaging foil, injecting the prepared electrolyte into the dried battery, and carrying out vacuum packaging, standing, formation, shaping and other procedures to complete the preparation of the lithium ion battery. The electrolyte of the completed lithium ion battery was prepared to contain Co ions, and in the following examples and comparative examples, the content of Co ions was about 7ppm based on the total weight of the electrolyte, unless otherwise specified.

2. Lithium ion battery performance test method

1) And (3) testing the storage impedance:

the cells were discharged to 4.4V at 0.5C at 25C, charged to 4.4V at 0.5C, charged to 0.05C at constant voltage at 4.4V, placed in a 60℃ oven, stored at 60℃ for 21 days (21d), and the resistance value after storage was monitored using a resistivity meter and recorded.

2) And (3) testing the cyclic impedance:

the battery is charged to 4.4V at the temperature of 45 ℃ by 0.7C, charged to 0.05C at the constant voltage of 4.4V and discharged to 3.0V by the constant current of 1.0C, and then the battery is cycled for 400 circles (400cls) under the condition, and the impedance change condition under the condition of 100% charging State (SOC) in the battery cycling process is monitored by using a resistivity measuring instrument.

3) And (3) overcharging test:

the cell was discharged to 3.0V at 0.5C, left to rest for 5 minutes, then charged to 7V at a current of 3C, and charged at a constant voltage of 7V for 1 h. Pass the test without fire or explosion (pass). Five cells were tested each time and the number of cells that passed the test was recorded.

4) And (3) hot box testing:

the cell was discharged to 3.0V at 0.5C, left to rest for 5 minutes, and then charged to 4.4V at a current of 0.5C, with a constant voltage to 0.05C at a voltage of 4.4V. The fully charged battery was placed in a hot box at 140 ℃ and kept at constant temperature for 60 min. Pass the test without fire or explosion (pass). Five cells were tested at a time in the oven fixture position and the number of cells passing the test was recorded.

5) Lithium ion battery physical and chemical test method

a) Co ion content test

The cell was discharged to 2.8V at 0.5C, left for 5 minutes, to 2.8V at 0.05C, left for 5 minutes, and discharged to 2.8V with 0.01C. And removing the outer aluminum-plastic film of the discharged battery. And centrifuging the electrolyte in the lithium ion battery by using a centrifugal machine. And (3) taking the centrifuged electrolyte, putting the sample into a numbered digestion tank, weighing the sample by using an electronic balance to be accurate to 0.0001g, and recording the weight of the sample as c (c is less than or equal to 10) g. Slowly add 10mL concentrated HNO₃(mass fraction: 68%), the sample on the inner wall was flushed into the bottom of the pot and the digestion pot was gently shaken. Wiping the water drops outside the digestion tank with dust-free paper, and placing the water drops into an acid dispelling instrument for digestion at 180 ℃ for 20 minutes. When the solution is steamed to 1-2ml, taking down the digestion tank, cooling to room temperature, washing the digestion tank for 3 times by using ultrapure water, pouring the liquid into a 50ml plastic volumetric flask after washing, and shaking up after constant volume. The samples were tested using a standard curve method using a plasma emission spectrometer (ICP) and the concentration of the test samples was recorded as ρ₁g/ml. The calculation result of the Co ions is as follows: (ρ)₁×50)/c。

b) Al element content test

The cell was discharged to 2.8V at 0.5C current, left to rest for 5 minutes, discharged to 2.8V at 0.05C current, left to rest for 5 minutes, discharged to 2.8V with 0.01C current, left to rest for 5 minutes, and the discharge was repeated three times with 0.01C current. The battery is disassembled by wearing clean gloves, and the anode and the cathode are carefully separated and do not contact with each other. In glove box, use the heightPure DMC (dimethyl carbonate, the purity is more than or equal to 99.99%) is soaked in the anode for 10 minutes, then taken out and dried for 30 minutes. (DMC amount:>15ml/1540mm²area of the disc). In a dry environment, powder is scraped by using a ceramic scraper>0.4g, and wrapping with weighing paper. The weight is measured by an electronic balance to the nearest 0.0001g, and the weight of the sample is recorded as d (d is less than or equal to 0.4) g. Slowly adding 10mL of aqua regia with the mass ratio of concentrated nitric acid to concentrated hydrochloric acid being 1:1, flushing the sample on the inner wall into the bottom of the tank, and slightly shaking the digestion tank. Wiping the water drops outside the digestion tank with dust-free paper, assembling the digestion device, and placing the digestion device in a microwave digestion instrument for digestion. The digestion tank is detached, the cover is rinsed with ultrapure water for 2-3 times, and the flushing fluid is poured into the digestion tank. The sample solution was shaken, slowly poured into a funnel into the volumetric flask, and the digestion tank was rinsed 3 times with a constant volume of 100ml and shaken up. The samples were tested using a standard curve method using a plasma emission spectrometer (ICP) and the concentration of the test samples was recorded as ρ₂g/ml. The calculation result of the Al element content is as follows: (ρ)₂×100)/d。

A. The electrolytes of examples 1.1 to 1.16 and comparative examples 1.1 to 1.5 and lithium ion batteries, in which the compound of formula I and LiPO were mixed in the electrolyte, were prepared according to the above-mentioned preparation methods₂F₂The contents of (A) are shown in Table 1-1.

TABLE 1-1

Wherein "-" represents that the substance was not added.

Tables 1-2 show the results of the storage resistance test and the cycle resistance test for the lithium ion batteries of examples 1.1-1.16 and comparative examples 1.1-1.5.

Tables 1 to 2

As can be seen from the test results of examples 1.1 to 1.16 and comparative examples 1.1 to 1.5 in tables 1 to 1 and 1 to 2, appropriate amounts of the compound of formula I and LiPO were simultaneously added to the electrolyte₂F₂For lithium ion batteriesThe memory impedance and the circulating impedance have better improvement effect.

B. The electrolytes of example 1.4 and examples 2.1 to 2.9 in Table 2-1 and lithium ion batteries were prepared according to the above preparation methods, wherein the electrolyte was a compound of formula I, LiPO₂F₂The content of fluorocarboxylic acid ester is shown in Table 2-1.

TABLE 2-1

Wherein "-" represents that the substance was not added.

Table 2-2 shows the storage impedance test and overcharge test results for the lithium ion batteries of example 1.4 and examples 2.1-2.9.

Tables 2 to 2

Serial number	Storage impedance (m omega) for 60-21 days	3C/7V overcharge
			Example 1.4	29	1/5pass
Example 2.1	28.99	4/5pass
			Example 2.2	28.98	5/5pass
Example 2.3	28.96	5/5pass
			Example 2.4	28.97	5/5pass
Example 2.5	28.92	5/5pass
			Example 2.6	28.00	5/5pass
Example 2.7	29.00	5/5pass
			Example 2.8	29.10	5/5pass
Example 2.9	29.00	5/5pass

As can be seen from the test results of examples 2.1-2.9 and example 1.4, in the case of a composition containing a compound of formula I and LiPO₂F₂The electrolyte of the lithium ion battery is added with the fluorocarboxylate compound, so that the overcharge performance of the lithium ion battery can be obviously improved.

C. The electrolytes of example 1.4 and examples 3.1 to 3.8 in Table 3-1 and lithium ion batteries were prepared according to the above preparation methods, wherein the electrolyte was a compound of formula I, LiPO₂F₂The content of the phosphoric acid ester compound is shown in Table 3-1.

TABLE 3-1

Wherein "-" represents that the substance was not added.

Table 3-2 shows the storage impedance and hot box results for the lithium ion batteries of example 1.4 and examples 3.1-3.8.

TABLE 3-2

As can be seen from the test results of examples 3.1 to 3.8 and example 1.4, in the case of a composition containing a compound of the formula I and LiPO₂F₂The phosphate compound is added into the electrolyte, so that the hot box performance of the lithium ion battery can be obviously improved.

D. The electrolytes and lithium ion batteries of examples 1.4 and 4.1 to 4.8 were prepared according to the above preparation methods, wherein the contents of the relevant substances in the electrolytes are shown in table 4-1. Table 4-1 shows the results of the cycle impedance test for the lithium ion batteries of example 1.4 and examples 4.1-4.8 simultaneously.

TABLE 4-1

As can be seen from the test results of examples 4.1 to 4.8 and example 1.4, when a lithium ion battery is used containing a compound of formula I and LiPO₂F₂The amount of cobalt ions dissolved out of the positive electrode material is small, and the cycle impedance of the lithium ion battery is low.

E. The electrolytes and lithium ion batteries of examples 1.4 and 5.1 to 5.23 were prepared according to the above preparation methods, wherein the contents of the respective substances in the electrolytes are shown in table 5-1. Table 5-1 shows the content of Al element in the positive electrode active material layer in example 1.4 and examples 5.1 to 5.23 together with the storage resistance and the hot box test results of the lithium ion battery.

TABLE 5-1

Wherein "-" represents the absence of the substance.

The structure of the positive active material may change after lithium is removed, and the structure of the positive active material may collapse after transition metal ions are removed. The large amount of dissolved transition metal ions may catalytically react with the electrolyte, and the structurally damaged positive active material may also catalyze decomposition of the electrolyte, thereby deteriorating electrical properties. Al element doping can occupy certain space lattice, play the effect of stable positive pole active material structure, reduce the collapse of positive pole active material structure.

A compound of formula I and LiPO₂F₂A protective layer containing LiS and LiF can be formed on the positive electrode, the interface is protected, particularly, the number of surface active sites is large after the interface collapses, the LiS and LiF in the positive electrode protective layer can reduce the surface active sites, and the effect of reducing the side reaction of the positive electrode material and the electrolyte is achieved. Thereby realizing the effects of reducing the storage impedance and improving the hot box test. The compounds of the formula I, LiPO, can be seen from examples 1.4 and 5.1 to 5.23₂F₂And the content of Al element in a certain range can improve the storage resistance and the hot box performance.

F. The electrolytes and lithium ion batteries of examples 1.4 and 6.1 to 6.3 were prepared according to the above preparation methods, wherein the contents of the respective substances in the electrolytes and the content of Al element in the positive electrode active material layer are shown in table 6-1.

TABLE 6-1

Wherein "-" represents that the substance was not added.

Table 6-2 shows the storage impedance, cycling impedance, overcharge test and hot box test results for the lithium ion batteries of examples 1.4 and 6.1-6.3.

TABLE 6-2

As can be seen from the test results of examples 6.1 to 6.3 and example 1.4, in the case of a composition comprising a compound of the formula I and LiPO₂F₂The electrolyte is added with the fluorocarboxylate compound and the phosphate compound at the same time, the positive active material layer contains a proper amount of Al element, and the electrolyte has a proper amount of cobalt ions, so that the storage impedance and the circulation impedance of the lithium ion battery can be remarkably reduced, and the overcharge performance and the hot box performance of the lithium ion battery can be remarkably improved.

Reference throughout this specification to "some embodiments," "one embodiment," "another example," "an example," "a specific example," or "some examples" means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. Thus, throughout the specification, descriptions appear, for example: "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "by example," which do not necessarily refer to the same embodiment or example in this application. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

Although illustrative embodiments have been illustrated and described, it will be appreciated by those skilled in the art that the above embodiments are not to be construed as limiting the application and that changes, substitutions and alterations can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims

1. An electrolyte comprising a compound of formula I and LiPO₂F₂：

R₁₅selected from single bonds, -O-, -NR₁-、

2. The electrolyte of claim 1, wherein the compound of formula I comprises at least one of the following compounds:

3. the electrolyte of claim 1, wherein the weight percent of the compound of formula I is a wt%, a wt% is 0.001 wt% to 3 wt%, the LiPO is based on the total weight of the electrolyte₂F₂B wt%, and bwt% is 0.01 wt% to 0.49 wt%, and a and b satisfy the following relational expression: a + b is less than 3.4; and a/b.gtoreq. 1/5.

4. The electrolyte of claim 1, further comprising a fluorocarboxylate compound comprising a compound of formula II:

wherein R is₂₁、R₂₂Each independently substituted, the substituents being selected from halogen, cyano, C_1-20Alkyl radical, C_3-20A cycloalkyl group, a,C_1-20Alkoxy radical, C_2-20Alkenyl radical, C_6-20Aryl or any combination thereof; wherein R is₂₁And R₂₂Is substituted with F;

wherein the fluorocarboxylic acid ester is present in an amount of 0.5 to 70 wt%, based on the total weight of the electrolyte.

5. The electrolyte of claim 4, wherein the fluorocarboxylate compound comprises at least one of the following compounds:

6. the electrolyte of claim 1, further comprising a phosphate ester compound comprising a compound of formula III:

wherein R is₃₁、R₃₂、R₃₃Each independently substituted, the substituents are selected from halogen, cyano, nitro, carboxyl, C_1-20Alkyl radical, C_3-20Cycloalkyl radical, C_1-20Alkoxy radical, C_2-20Alkenyl radical, C_6-20Aryl radical, C_6-20Heteroaryl or any combination thereof;

wherein the weight percentage of the phosphate ester compound is 0.1 wt% to 20 wt% based on the total weight of the electrolyte.

7. The electrolyte of claim 6, wherein the phosphate ester compound comprises at least one of:

8. an electrochemical device comprising a positive electrode active material layer comprising a positive electrode active material; and an electrolyte as claimed in any one of claims 1 to 7.

9. The electrochemical device according to claim 8, wherein the electrolyte of the electrochemical device further comprises cobalt ions, wherein the content of the cobalt ions is less than or equal to 50ppm based on the total weight of the electrolyte.

10. The electrochemical device according to claim 8, wherein the Al element is contained in the positive electrode active material in an amount of m x 10 based on the total weight of the positive electrode active material layer³ppm, m is 0.5-10, wherein (a + b)/m is less than or equal to 6.

11. An electronic device, wherein the electronic device comprises the electrochemical device according to any one of claims 8-10.