CN112701349B - Electrolyte solution, electrochemical device and electronic apparatus including the same - Google Patents

Electrolyte solution, electrochemical device and electronic apparatus including the same Download PDF

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CN112701349B
CN112701349B CN202011576415.5A CN202011576415A CN112701349B CN 112701349 B CN112701349 B CN 112701349B CN 202011576415 A CN202011576415 A CN 202011576415A CN 112701349 B CN112701349 B CN 112701349B
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lithium
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CN112701349A (en
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张水蓉
张丽兰
唐超
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Ningde Amperex Technology Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0565—Polymeric materials, e.g. gel-type or solid-type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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Abstract

The application relates to the technical field of energy storage, in particular to an electrolyte, an electrochemical device comprising the electrolyte and electronic equipment comprising the electrolyte. An electrolyte is provided that includes a cyclic dicarboxylate; and compounds containing 2 to 4 cyano groups. The electrolyte can form a stable and effective solid electrolyte interface film on a positive electrode and a negative electrode through the synergistic cooperation effect of the cyclic dicarboxylate and the compound containing 2 to 4 cyano groups, and side reactions of the electrolyte and the positive electrode and the negative electrode are reduced. When the electrochemical device of the present application is stored and circulated at high temperature, the electrolyte can effectively improve the high-temperature cycle performance and high-temperature storage performance of the electrochemical device.

Description

Electrolyte solution, electrochemical device and electronic apparatus including the same
Technical Field
The present disclosure relates to the field of energy storage technologies, and more particularly, to an electrolyte, and an electrochemical device and an electronic apparatus including the same.
Background
Electrochemical devices (such as lithium ion batteries) have the advantages of high energy density, long cycle life, light weight, high working voltage, large output power, environmental friendliness and the like, are widely applied to various fields such as mobile phones, computers, wearable devices, consumer-grade unmanned aerial vehicles, electric tools, electric motorcycles, electric vehicles, large-scale energy storage devices and the like, and are particularly more widely applied to electronic consumer products. The mobile phone or the notebook computer is an important direction of electronic consumer products, and the phenomenon that the notebook computer is charged while being used is common in practical use, but the battery performance is easily deteriorated due to the use condition. How to improve the performance of the battery in the high-temperature cycle process is an industry difficult problem which is urgently needed to be solved or improved at present.
Disclosure of Invention
An object of the present invention is to provide an electrolyte solution, and an electrochemical device and an electronic apparatus including the same, which can improve an electrode/electrolyte interface, improve high-temperature cycle performance of the electrochemical device, and solve at least one of the problems existing in the related art to at least some extent.
According to a first aspect of the present application, there is provided an electrolyte comprising, a cyclic dicarboxylate; and compounds containing 2 to 4 cyano groups.
In some embodiments herein, the cyclic dicarboxylate includes at least one of the compounds of formula I below:
Figure BDA0002864174670000011
wherein R is1、R2、R3And R4Each independently selected from hydrogen, halogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C1-C12 alkoxy, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl; wherein R is1、R2、R3、R4When substituted, the substituents include at least one of halogen or haloalkyl.
In some embodiments of the present application, the compound of formula I comprises at least one of the following compounds:
Figure BDA0002864174670000021
in some embodiments of the present application, the compound comprising 2 to 4 cyano groups comprises at least one of the compounds of formula ii or iii below:
Figure BDA0002864174670000022
in formula II, R5Selected from the group consisting of substituted or unsubstituted C1-C9 alkylene, substituted or unsubstituted C1-C5 alkyleneoxy, substituted or unsubstituted C2-C10 alkenylene; in formula III, R6、R7And R8Each independently selected from a covalent bond, a substituted or unsubstituted C1-C5 alkylene group, a substituted or unsubstituted C1-C5 alkyleneoxy group; wherein R is5、R6、R7、R8When substituted, the substituents include at least one of halogen or cyano.
In some embodiments of the present application, the compound of formula ii or iii comprises at least one of the following compounds:
Figure BDA0002864174670000031
in some embodiments of the present application, the cyclic dicarboxylate is present in an amount of 0.01 to 2% by mass, based on the mass of the electrolyte; the mass percentage of the compound containing 2 to 4 cyano groups is 0.5 to 10 percent. Preferably, the content of the cyclic dicarboxylate is 0.05% to 1.5% by mass based on the mass of the electrolyte; the mass percentage of the compound containing 2 to 4 cyano groups is 0.5 to 8 percent.
In some embodiments of the present application, the cyclic dicarboxylate is present in an amount of a% by mass, the compound containing 2 to 4 cyano groups is present in an amount of b% by mass, and b and a have a relationship of: b/a is more than or equal to 0.1 and less than or equal to 200.
In some embodiments of the present application, the relationship of b to a satisfies: b/a is more than or equal to 1 and less than or equal to 40.
In some embodiments of the present application, the electrolyte further comprises at least one of a cyclic ether additive or a lithium salt additive. The cyclic ether additive comprises at least one of 1, 3-dioxolane, 1, 3-dioxane or 1, 4-dioxane; the lithium salt additive includes at least one of lithium bis oxalate borate, lithium difluoro oxalate borate, or lithium difluoro phosphate. Based on the mass of the electrolyte, the mass percentage of the cyclic ether additive is 0.01-2%, and the mass percentage of the lithium salt additive is 0.01-2%.
According to a second aspect of the present application, there is provided an electrochemical device comprising: a positive electrode; a negative electrode; a separator provided between the positive electrode and the negative electrode; and an electrolyte according to the above embodiments of the present application. The negative electrode comprises a negative electrode current collector and a negative electrode active material layer which is arranged on the surface of the negative electrode current collector and contains a negative electrode active material; wherein the negative active material includes a silicon-based material. At least one part of the surface of the silicon-based material is provided with a protective layer, and the protective layer has at least one of the following characteristics: (a) the protective layer comprises a metal oxide MexOyWherein Me comprises at least one of Al, Mg, Ti, Si, Mn, V, Cr, Co or Zr, x is more than or equal to 1 and less than or equal to 2, and y is more than or equal to 1 and less than or equal to 3; (b) the protective layer comprises a carbon material; (c) the protectionThe thickness of the layer is 1.0nm to 100 nm.
According to a third aspect of the present application, there is provided an electronic device comprising an electrochemical device according to the above-described embodiments of the present application.
The technical scheme of the application has at least the following beneficial effects:
the electrolyte provided by the application can form a stable and effective solid electrolyte interface film on both the positive electrode and the negative electrode through the synergistic cooperation effect of the cyclic dicarboxylate and the compound containing 2 to 4 cyano groups, so that the side reactions of the electrolyte and the positive electrode and the negative electrode are reduced, the stability of the positive electrode/electrolyte interface and the stability of the negative electrode/electrolyte interface can be improved, and the protection of the electrolyte on the surfaces of the positive electrode and the negative electrode can be improved. When the electrochemical device is stored and circulated at high temperature, the electrolyte can effectively improve the high-temperature circulation performance and the high-temperature storage performance of the electrochemical device.
Detailed Description
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. 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 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 item A, B is listed, the phrase "at least one of A, B" means only a; only B; or A and B. In another example, if the items A, B, C are listed, the phrase "at least one of A, B, 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.
In the description of the present application, unless otherwise expressly specified or limited, the terms "formula I", "formula II", "formula III", "formula I-1", "formula I-2", and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or relationship to one another.
Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity, and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. Further, "about" as used herein is used to describe and illustrate minor variations.
Herein, unless otherwise specified, the functional groups of all compounds may be substituted or unsubstituted.
In the embodiments and claims, the expression of the number of carbon atoms (also referred to as carbon number), i.e., the number following the capital letter "C", for example, "C1-C12", "C2-C12", etc., the numbers 1,2, 12 following "C" represent the number of carbon atoms in a specific functional group. That is, the functional groups may include 1 to 12 carbon atoms and 2 to 12 carbon atoms, respectively. For example, "C1-C4 alkyl" or "C1-4Alkyl "means an alkyl group having 1 to 4 carbon atoms, e.g. CH3-、CH3CH2-、CH3CH2CH2-、(CH3)2CH-、CH3CH2CH2-and the like.
As used herein, the term "alkyl" contemplates alkyl groups having 1 to 12 carbon atoms, which may be chain alkyl groups, as well as cycloalkyl groups. "alkyl" is also contemplated to be a branched or cyclic hydrocarbon structure having 2 to 10 carbon atoms. For example, the alkyl group may be an alkyl group of 1 to 12 carbon atoms, an alkyl group of 1 to 10 carbon atoms, an alkyl group of 1 to 8 carbon atoms, an alkyl group of 1 to 6 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 "alkoxy" refers to an L-O-group, wherein L is alkyl. The alkoxy group herein may be an alkoxy group of 1 to 12 carbon atoms, and may also be an alkoxy group of 1 to 10 carbon atoms, an alkoxy group of 1 to 6 carbon atoms, an alkoxy group of 3 to 6 carbon atoms, or an alkoxy group of 5 to 9 carbon atoms.
As used herein, the term "alkenyl" 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 12 carbon atoms, and may be, for example, an alkenyl group of 2 to 10 carbon atoms, an alkenyl group of 2 to 8 carbon atoms, an alkenyl group of 2 to 6 carbon atoms, or an alkenyl group of 6 to 12 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.
As used herein, 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 12 carbon atoms, and may be, for example, an alkynyl group of 2 to 10 carbon atoms, an alkynyl group of 2 to 8 carbon atoms, an alkynyl group of 2 to 6 carbon atoms, or an alkynyl group of 6 to 10 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 can be an alkylene group of 1 to 9 carbon atoms, an alkylene group of 1 to 7 carbon atoms, an alkylene group of 1 to 5 carbon atoms, or an alkylene group of 1 to 4 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.
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 2-10 carbon atoms, an alkenylene group of 2-8 carbon atoms, an alkenylene group of 2-6 carbon atoms, or an alkenylene group of 2-4 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 "alkyleneoxy" encompasses both straight-chain and branched-chain alkenylenealkyleneoxy. When an alkyleneoxy group having a particular carbon number is specified, all geometric isomers having that carbon number are intended to be encompassed. For example, the alkyleneoxy group may be an alkyleneoxy group of 1 to 5 carbon atoms, and may also be an alkyleneoxy group of 1 to 6 carbon atoms, an alkyleneoxy group of 2 to 5 carbon atoms, or an alkyleneoxy group of 2 to 4 carbon atoms. In addition, the alkyleneoxy group may be optionally substituted.
Herein, the term "halogen" encompasses fluorine (F), chlorine (Cl), bromine (Br), iodine (I). Preferably, in some embodiments, the halogen is selected from F or Cl.
As used herein, the term "cyano" encompasses organic species containing an organic group-CN.
As used herein, the term "substituted or unsubstituted" means that the specified group is unsubstituted or substituted with one or more substituents.
When the above substituents are substituted, the substituents may be selected from the group consisting of: halogen, haloalkyl; or halogen, cyano.
As used herein, the content of each component in the electrolyte is calculated based on the mass of the electrolyte.
[ electrolyte ]
In some embodiments, an electrolyte is provided, the electrolyte comprising, a cyclic dicarboxylate; and compounds containing 2 to 4 cyano groups.
The electrolyte can improve the high-temperature cycle performance of an electrochemical device by combining the cyclic dicarboxylate with a compound containing 2 to 4 cyano groups, and has a high practical application value. Specifically, the cyclic dicarboxylate serving as an additive in the electrolyte easily obtains electrons at a negative electrode due to the fact that the cyclic dicarboxylate contains two strong electron-withdrawing groups-C (═ O) O-during charging, the cyclic dicarboxylate forms a polymer layer at the negative electrode through ring opening, the polymer layer protects a negative electrode/electrolyte interface, and the polymer layer has good stability and can reduce side reactions between the electrolyte and the negative electrode. The compound containing 2 to 4 cyano groups in the electrolyte can coordinate and stabilize the transition metal in the positive electrode through lone pair electrons of the cyano groups, and the improvement efficiency of a plurality of cyano functional groups, particularly 2 to 4 cyano functional groups, is higher; meanwhile, a plurality of cyano groups can form a space effect to limit the movement of transition metal and simultaneously prevent other components in the electrolyte from contacting with the anode; therefore, the polynitrile compound can further stabilize the anode through the coordination of the two aspects, separate the electrolyte and reduce the oxidative decomposition of the electrolyte on the surface of the anode. In high-temperature circulation, the time of the anode at high temperature and high voltage is long, side reaction is easy to occur with electrolyte, and transition metal is dissolved out; the negative electrode participates in high-temperature circulation, the repair of an SEI film is continuously carried out along with the circulation, the electrolyte is consumed, meanwhile, the transition metal of the positive electrode is easily deposited on the negative electrode, and the SEI of the negative electrode is damaged; through the synergistic cooperation of the cyclic dicarboxylate and the compound containing 2 to 4 cyano groups, a better protective layer can be formed on the positive electrode to reduce the side reaction of EL and the positive electrode and reduce the dissolution of transition metal ions, a stable macromolecular SEI film can be formed on the negative electrode to reduce the consumption of the negative electrode on electrolyte, and meanwhile, the macromolecular SEI is not easily damaged by the transition metal ions, so that the high-temperature cycle performance can be improved, and an electrochemical device using the electrolyte has excellent cycle, storage and/or float charge performance.
In some embodiments, the cyclic dicarboxylate includes at least one of the compounds of formula I below:
Figure BDA0002864174670000071
wherein R is1、R2、R3And R4Each independently selected from hydrogen, halogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C1-C12 alkoxy, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl; wherein R is1、R2、R3、R4When substituted, the substituent includes at least one of halogen and haloalkyl.
In some embodiments, R1、R2、R3And R4Each independently selected from hydrogen, halogen, substituted or unsubstituted C1-C10 alkyl. Preferably, in some embodiments, R1、R2、R3And R4Each independently selected from hydrogen, halogen, substituted or unsubstituted C1-C6 alkyl.
In some embodiments, the compound of formula I comprises at least one of the following compounds:
Figure BDA0002864174670000072
Figure BDA0002864174670000081
in some embodiments, the cyclic dicarboxylate is present in an amount of 0.01 to 2% by mass based on the mass of the electrolyte. In some embodiments, the cyclic dicarboxylate is present in an amount of 0.1% to 1.5% by weight. In some embodiments, the cyclic dicarboxylate is present in an amount of 0.5% to 1% by weight. In some embodiments, the lower limit of the content range of the cyclic dicarboxylate may be selected from 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, 0.5%, 0.6%, 0.7%, the upper limit of the content range of the cyclic dicarboxylate may be selected from 2%, 1.8%, 1.6%, 1.5%, 1.4%, 1.2%, 1%, and the content range of the cyclic dicarboxylate by mass percentage may be composed of any value of the upper limit or the lower limit. When the mass percentage of the cyclic dicarboxylate is less than 0.01%, the formed negative electrode SEI is insufficient, the protection of the negative electrode is weakened, and the performance of the electrochemical device is not obviously improved; when the content of the cyclic dicarboxylate is more than 2% by mass, the formed resistance is large, which may affect the electrochemical performance of the electrochemical device. Therefore, the mass content of the cyclic dicarboxylate in the electrolyte is within the range of 0.01-2%, a film can be effectively formed on an electrode, the interface stability of a positive electrode and a negative electrode can be effectively improved, the increase of the internal resistance of a battery caused by the overgrowth of an SEI film can be effectively inhibited, and the high-temperature cycle performance of an electrochemical device can be effectively improved.
In some embodiments, the compound comprising 2 to 4 cyano groups comprises at least one of a compound of formula ii or formula iii below:
Figure BDA0002864174670000082
in formula II, R5Selected from substituted or unsubstituted C1-C9 alkylene, substituted or unsubstituted C1-C5 alkyleneoxy, substituted or unsubstituted C2-C10 alkenylene; in the formula III, R6、R7And R8Each independently selected from a covalent bond (e.g., a single bond), a substituted or unsubstituted C1-C5 alkylene, a substituted or unsubstituted C1-C5 alkyleneoxy group; wherein R is5、R6、R7、R8When substituted, the substituent group includes at least one of halogen and cyano.
In some embodiments, the compound of formula ii or formula iii comprises at least one of the following compounds:
Figure BDA0002864174670000083
Figure BDA0002864174670000091
in some embodiments, the compound including 2 to 4 cyano groups is contained in an amount of 0.5 to 10% by mass based on the mass of the electrolyte. In some embodiments, the compound comprising 2 to 4 cyano groups is present in an amount of 0.5 to 8% by weight. In some embodiments, the compound comprising 2 to 4 cyano groups is present in an amount of 1 to 6% by weight. In some embodiments, the lower limit of the range of the content of the compound having 2 to 4 cyano groups may be any selected from 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, the upper limit of the range of the content of the compound having 2 to 4 cyano groups may be any selected from 10%, 9%, 8%, 7%, 6.5%, 6%, 5.5%, and the range of the content of the compound having 2 to 4 cyano groups may be composed of any value of the upper limit or the lower limit. When the mass percentage of the compound containing 2 to 4 cyano groups is higher than 0.5%, the transition metal dissolved out from the surface of the positive electrode can be effectively isolated from the easily-oxidized components in the electrolyte by the compound containing 2 to 4 cyano groups, so that the positive electrode is effectively protected, and the oxidation side reaction of the electrolyte on the surface of the positive electrode at high temperature is reduced. When the content of the compound including 2 to 4 cyano groups is less than 10% by mass, it is possible to reduce or prevent the electrochemical device from being affected due to the large resistance formed. Therefore, the mass content of the compound containing 2 to 4 cyano groups in the electrolyte is in the range of 0.5 to 10 percent, so that a film can be effectively formed on an electrode, the interface stability of a positive electrode and a negative electrode can be effectively improved, the increase of the internal resistance of a battery caused by the overgrowth of a protective film can be effectively inhibited, and the high-temperature cycle performance of an electrochemical device can be effectively improved.
It should be understood that in the above embodiments, the polynitrile compounds with different structural formulas have different complexing and adsorbing forces, so that they have different isolating effects on the electrolyte and the surface of the positive electrode. In some embodiments, as the number of cyano (-CN) groups in the polynitrile compound increases, the more significant the separation effect of the electrolyte from the surface of the positive electrode can be achieved.
In some embodiments, the cyclic dicarboxylate is present in an amount of a% by mass, the compound including 2 to 4 cyano groups is present in an amount of b% by mass, and b satisfies the following relationship with a: b/a is more than or equal to 0.1 and less than or equal to 200. In some embodiments, the relationship of b to a satisfies: b/a is more than or equal to 0.5 and less than or equal to 100. In some embodiments, the relationship of b to a satisfies: b/a is more than or equal to 1 and less than or equal to 40. Illustratively, the lower limit of b/a may be 0.1, 0.5, 1,2, 5, 10, 15, 20, 30, 40, 50, the upper limit of b/a may be 200, 180, 160, 150, 140, 120, 100, 90, 80, 70, and the range of b/a may be any value of the upper limit or the lower limit.
In some embodiments, the electrolyte further comprises at least one of a cyclic ether additive or a lithium salt additive. That is, in some embodiments, the electrolyte may include a cyclic dicarboxylate, a compound including 2 to 4 cyano groups, and a cyclic ether additive. In some embodiments, the electrolyte may include a cyclic dicarboxylate, a compound including 2 to 4 cyano groups, and a lithium salt additive. In some embodiments, the electrolyte may include a cyclic dicarboxylate, a compound including 2 to 4 cyano groups, a cyclic ether additive, and a lithium salt additive. By using the above cyclic dicarboxylate and the compound containing 2 to 4 cyano groups in combination with one or more of a cyclic ether additive or a lithium salt additive, the protection of the active material can be enhanced, the electrode/electrolyte interface can be further improved, and the high-temperature cycle performance can be further improved.
In some embodiments, the cyclic ether additive includes, but is not limited to, at least one of 1, 3-dioxolane, 1, 3-dioxane, or 1, 4-dioxane, as shown below.
Figure BDA0002864174670000101
After the cyclic ether additive, the cyclic dicarboxylate and the compound combination containing 2 to 4 cyano groups are added into the electrolyte together, a film can be formed on a positive electrode and a negative electrode more easily, and a complete, compact and uniform protective film can be formed on the surface of an active material, so that the high-temperature cycle performance can be further improved, and the high-temperature storage performance of an electrochemical device can be improved.
In some embodiments, the cyclic ether additive is present in an amount of 0.01 to 2% by mass, based on the mass of the electrolyte. In some embodiments, the cyclic ether additive is present in an amount of 0.2 to 1.5 percent by weight. In some embodiments, the lower limit of the content range of the cyclic ether additive may be selected from 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, 0.5%, 0.6%, 0.8%, the upper limit of the content range of the cyclic ether additive may be selected from 2%, 1.8%, 1.6%, 1.5%, 1.4%, 1.2%, and the range of the content of the cyclic ether additive by mass may be composed of any value of the upper limit or the lower limit.
When the mass percentage of the cyclic ether additive is in the range of 0.01-2%, a complete and effective organic film can be formed on the surface of the electrode, the stability of the electrolyte is enhanced, and the high-temperature cycle performance of the electrochemical device is improved. When the mass percentage of the cyclic ether additive is less than 0.01%, the protective film formed on the surface of the positive electrode is insufficient, and the high-temperature cycle performance of the electrochemical device is not obviously improved; when the cyclic ether is present in an amount of more than 2% by mass, the formed film is thick and has a high resistance, which may reduce the cycle performance of the electrochemical device.
In some embodiments, the lithium salt additive includes, but is not limited to, lithium bis (oxalato) borate (LiBOB), lithium difluoro (oxalato) borate (lidob), or lithium difluoro (hpo) phosphate (LiPO)2F2) At least one of (1). The lithium salts have higher reduction potential, can preferentially form a film on the negative electrode, and the formed SEI film is stable in the circulation process of the electrochemical device, so that the reaction of a solvent and the negative electrode in the circulation process can be reduced, and the circulation performance is improved.
In some embodiments, the lithium salt additive is present in an amount of 0.01 to 2% by mass, based on the mass of the electrolyte. In some embodiments, the lithium salt additive is present in an amount of 0.2 to 1.5% by weight. In some embodiments, the lower limit of the range of the lithium salt additive may be selected from 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, 0.5%, 0.6%, 0.8%, the upper limit of the range of the lithium salt additive may be selected from 2%, 1.8%, 1.6%, 1.5%, 1.4%, 1.2%, and the range of the lithium salt additive may be composed of any value of the upper limit or the lower limit.
When the mass percentage of the lithium salt additive is in the range of 0.01-2%, a complete and effective organic film can be formed on the surface of the electrode, the stability of the electrolyte is enhanced, and the high-temperature cycle performance of the electrochemical device is improved. When the mass percentage of the lithium salt additive is less than 0.01%, a protective film formed on the surface of the negative electrode is insufficient, and the high-temperature cycle performance of the electrochemical device is not obviously improved; when the lithium salt additive is present in an amount of more than 2% by mass, the formed film is thick and has a high resistance, which may seriously degrade the dynamic performance of the electrochemical device.
In some embodiments, the electrolyte may further include other types of additives, which may be additives known in the art that can be used to improve the electrochemical performance of a battery, such as SEI film forming additives. Exemplary such additives include, but are not limited to, fluoroethylene carbonate (FEC), 1, 3-Propane Sultone (PS), 1,4 butane sultone, Vinylene Carbonate (VC), and vinyl sulfate (DTD).
In some embodiments, the electrolyte further comprises a non-aqueous solvent and an electrolyte salt. The nonaqueous solvent may be any of those conventionally used in electrochemical devices known in the art, and may be, for example, a nonaqueous organic solvent. In the electrolyte of the embodiment of the present application, the kind of the nonaqueous solvent is not particularly limited, and may be selected according to actual requirements. The electrolyte salt is well known to those skilled in the art and can be used for an electrochemical device. For different electrochemical devices, suitable electrolyte salts may be selected. For example, for a lithium ion battery, a lithium salt is generally used as the electrolyte salt. The lithium salt may be a lithium salt known in the art that may be used in a lithium ion battery.
In some embodiments, the non-aqueous solvent may include at least one of any kind of carbonate, carboxylate. The carbonate ester may include chain carbonate and cyclic carbonate ester. The non-aqueous solvent may also include halogenated compounds of carbonates.
It is to be understood that the carbonate may be any kind of carbonate, and the carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.
In some embodiments, the non-aqueous solvent used in the electrolyte according to the embodiments of the present disclosure may include cyclic carbonates and chain carbonates, which may further improve the cycle performance and the storage performance under high temperature and high voltage conditions, and may easily adjust the conductivity of the electrolyte to a suitable range, thereby facilitating each additive to achieve a better film forming effect.
The nonaqueous solvent used in the electrolyte solution of the embodiment of the present application may further include a carboxylic acid ester, that is, the nonaqueous solvent according to the present application may include a mixture of cyclic carbonate, chain carbonate, and carboxylic acid ester, whereby the electrolyte solution may be provided with good ion conductive characteristics.
In some embodiments, the cyclic carbonate may be selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, vinyl ethylene carbonate, γ -butyrolactone, pentylene carbonate, fluoroethylene carbonate, but is not limited thereto, and may be a halogenated derivative thereof.
The chain carbonate may be at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate, methyl propyl carbonate, and methyl butyl carbonate, but is not limited thereto, and may be a halogenated derivative thereof.
The carboxylic acid ester may be at least one selected from methyl pivalate, ethyl pivalate, propyl pivalate, ethyl butyrate, methyl butyrate, propyl butyrate, butyl butyrate, propyl propionate, ethyl propionate, methyl propionate, ethyl acetate, methyl acetate, and butyl acetate.
In some embodiments, the non-aqueous solvent comprises at least one of diethyl carbonate (DEC), Ethylene Carbonate (EC), Propylene Carbonate (PC), Propyl Propionate (PP).
According to the embodiment of the present application, the non-aqueous organic solvent in the electrolyte may be a single non-aqueous organic solvent or a mixture of a plurality of non-aqueous organic solvents, and when a mixed solvent is used, the mixing ratio is controlled according to the desired performance of the electrochemical device.
In some embodiments, the electrolyte salt comprises a lithium salt, which includes a lithium salt additive. The lithium salt is selected from one or more of inorganic lithium salt and organic lithium salt. Preferably, according to some embodiments of the present application, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF)6) Lithium difluorophosphate (LiPO)2F2) Lithium tetrafluoroborate (LiBF)4) Lithium hexafluoroarsenate, lithium perchlorate, lithium bis (fluorosulfonylimide) (LiFSI), lithium bis (trifluoromethanesulfonylimide) (LiTFSI), and lithium bis (oxalato) borate LiB (C)2O4)2(abbreviated as LiBOB) and lithium difluorooxalato borate LiBF2(C2O4) (abbreviated as LiDFOB).
The content of the electrolyte salt is not particularly limited as long as the effect of the present application is not impaired. In some embodiments, the molar concentration of the electrolyte salt is about 0.5M to about 2.5M, based on the total volume of the electrolyte. Preferably, according to some embodiments of the present application, the electrolyte salt is at a molar concentration of about 0.5M to about 1.5M. Preferably, according to some embodiments of the present application, the electrolyte salt has a molarity of about 0.8M to about 1.3M. The electrolyte salt concentration is too low, the conductivity of the electrolyte is low, and the multiplying power and the cycle performance of the whole battery system can be influenced; and the electrolyte salt concentration is too high, the viscosity of the electrolyte is too high, and the multiplying power of the whole battery system is also influenced. Therefore, when the concentration of the electrolyte salt is within the above range, the content of lithium as charged particles in the electrolytic solution can be made more appropriate, the viscosity of the electrolytic solution can be made more appropriate, and the electrolytic solution can have good conductivity.
The preparation method of the electrolyte in the embodiment of the application is not limited, and the electrolyte can be prepared in a conventional electrolyte mode. In some embodiments, the electrolytes of the present application can be prepared by mixing the components.
[ electrochemical device ]
The electrochemical device of the present application includes any device in which an electrochemical reaction occurs, 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, but not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. The electrochemical device of 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 is mainly characterized by including any of the above-described electrolytic solutions of the present application.
In some embodiments, an electrochemical device of the present application comprises a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte as described herein.
Electrolyte solution
The electrolyte used in the electrochemical device of the present application is any of the electrolytes described above in the present application. 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.
Positive electrode
The positive electrode of the electrochemical device according to the embodiment of the present application includes a positive electrode current collector and a positive electrode active material layer disposed on a surface of the positive electrode current collector and including a positive electrode active material.
In some embodiments, among others, the positive electrode active material includes a compound that reversibly intercalates and deintercalates lithium ions (i.e., a lithiated intercalation compound).
In some embodiments, the positive active material may include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel. The specific kind of the positive electrode active material is not particularly limited and may be selected as desired.
In some embodiments, the positive electrode active material is selected from at least one of: lithium cobaltate (LiCoO)2) Lithium nickel manganese cobalt ternary material (NCM) and lithium iron phosphate (LiFePO)4) Lithium manganate (LiMn)2O4) Lithium nickel manganese oxide (LiNi)0.5Mn1.5O4)。
In some embodiments, the positive active material layer further includes a binder, and optionally further includes a conductive material. The binder may improve binding of the positive electrode active material particles to each other and may improve binding of the positive electrode active material to the positive electrode current collector. In some embodiments, the binder 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 positive active material layer includes a conductive material, thereby imparting conductivity to the electrode. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the conductive material 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.
In some embodiments, the positive current collector is a metal, for example including, but not limited to, aluminum foil.
In some embodiments, the structure of the positive electrode is a positive electrode sheet structure that can be used in electrochemical devices as is known in the art.
In some embodiments, the method of preparing the positive electrode is a method of preparing a positive electrode that can be used in an electrochemical device, which is 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.
Negative electrode
The negative electrode of the electrochemical device according to the embodiment of the present application includes a negative electrode current collector and a negative electrode active material layer disposed on a surface of the negative electrode current collector and including a negative electrode active material.
In some embodiments, the negative active material comprises a silicon-based material. The electrochemical device uses the electrolyte provided by the embodiment of the application and uses the silicon-based material as the negative electrode active material, so that the electrochemical device is more favorable for improving the high-temperature cycle performance of the battery.
In some embodiments, the silicon-based material has a protective layer on at least a portion of the surface. The surface of the silicon-based material is covered with the protective layer, so that the cycle performance of the electrochemical device can be improved, and the impedance increase in the cycle process can be inhibited.
In some embodiments, the protective layer comprises a carbon material.
In some embodiments, the protective layer comprises a metal oxide MexOyWherein Me comprises at least one of Al, Mg, Ti, Si, Mn, V, Cr, Co or Zr, x is more than or equal to 1 and less than or equal to 2, and y is more than or equal to 1 and less than or equal to 3.
In some embodiments, the protective layer has a thickness of 1.0nm to 100 nm. By making the thickness of the protective layer in the range of 1.0nm to 100nm, both the cycle performance and the impedance of the electrochemical device can be further improved.
In some embodiments, the negative active material layer further comprises a binder. The binder may include various binder polymers such as 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-difluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy, nylon, and the like.
In some embodiments, the negative active material layer further includes a conductive material to improve electrode conductivity. Any conductive material may be used as the conductive material as long as it does not cause a chemical change. Examples of conductive materials include, but are not limited to: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, and the like; metal-based materials such as metal powders or metal fibers including copper, nickel, aluminum, silver, and the like; conductive polymers such as polyphenylene derivatives and the like; or mixtures thereof.
In some embodiments, the negative current collector may be a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.
In some embodiments, the negative electrode 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. In some embodiments, the negative current collector is a copper foil.
In some embodiments, the structure of the negative electrode is a negative electrode tab structure known in the art that can be used in electrochemical devices.
In some embodiments, the method of preparing the negative electrode is a method of preparing a negative electrode that can be used in an electrochemical device, which is well known in the art. Illustratively, the negative electrode may 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.
Isolation film
In some embodiments, a separator is provided between the positive and negative electrodes to prevent short circuits. The material and shape of the separator 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, in some embodiments, the isolation film comprises a substrate layer. The substrate layer is a non-woven fabric, a membrane or a composite membrane with a porous structure. The material of the substrate layer may be selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, the material of the substrate layer can be selected from polypropylene porous membrane, polyethylene porous membrane, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite membrane.
At least one surface of the substrate layer is provided with a surface treatment layer. The surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. Specifically, the inorganic layer includes inorganic particles and a binder. The inorganic particles can be selected from one or more of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder can be 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.
[ electronic apparatus ]
In some embodiments, the present application provides an electronic device comprising the aforementioned electrochemical device.
According to the electrolyte of the embodiment of the application, the high-temperature cycle performance of the electrochemical device can be improved, and the electrochemical device has higher safety, so that the electrochemical device manufactured by the electrolyte is suitable for electronic equipment in various fields.
The use of the electrochemical device of the present application is not particularly limited, and it can be used for any electronic apparatus known in the art. For example, the electronic devices include, but are not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copiers, portable printers, headphones, video recorders, liquid crystal televisions, portable cleaners, portable CDs, mini-discs, transceivers, electronic organizers, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, lighting fixtures, toys, game machines, clocks, electric tools, flashlights, cameras, large household batteries, lithium ion capacitors, and the like. In addition, the electrochemical device of the present application is applicable to an energy storage power station, a marine vehicle, and an air vehicle, in addition to the above-exemplified electronic devices. The air transport carrier device comprises an air transport carrier device in the atmosphere and an air transport carrier device outside the atmosphere.
The present application will be described in more detail with reference to specific examples and comparative examples, taking a lithium ion battery as an example, but the present application is not limited to these examples as long as the gist thereof is not deviated. In the following examples and comparative examples, reagents, materials and instruments used therefor were commercially available or synthetically available, unless otherwise specified.
The lithium ion batteries in the examples and comparative examples were prepared as follows.
Preparation of lithium ion battery
1. Preparation of the electrolyte
In a dry argon atmosphere glove box, Ethylene Carbonate (EC), Propylene Carbonate (PC) diethyl carbonate (DEC) were mixed according to 2: 2: 6, 5 wt% of fluoroethylene carbonate (FEC) was added, dissolved and sufficiently stirred, and then lithium salt lithium hexafluorophosphate (LiPF) was added6) Mixing uniformly to form a basic electrolyte, wherein LiPF6The concentration of (2) was 1.05 mol/L. To the base electrolyte, substances (additives) were added in different amounts as shown in the following tables (tables 1 to 5) to obtain electrolytes of different examples and comparative examples.
Wherein, the content of each additive is calculated based on the mass of the electrolyte and is the mass percentage.
2. Preparation of the Positive electrode
The positive electrode active material lithium cobaltate (LiCoO)2) The conductive agent Super-P and the binder polyvinylidene fluoride (PVDF) are mixed according to the mass ratio of 97: 1.4: 1.6 mixing the mixture in a solvent N-methyl pyrrolidone (NMP), and stirring the mixture in a vacuum stirrer until the system is uniform and transparent to obtain anode slurry; wherein the solid content of the positive electrode slurry is 72 wt%. Coating the anode material on an anode current collector aluminum foil, drying the aluminum foil at 85 ℃, then carrying out cold pressing, cutting, slitting and drying for 4 hours at 85 ℃ under a vacuum condition to obtain an anode.
3. Preparation of the negative electrode
Preparation of negative electrodes of examples 1 to 40 and comparative examples 1 to 3:
preparing a negative electrode active material artificial graphite, sodium carboxymethyl cellulose (CMC) and a binder Styrene Butadiene Rubber (SBR) according to a mass ratio of about 97: 1: 2, mixing the mixture in deionized water, and fully mixing and uniformly stirring to obtain cathode slurry; wherein the solid content of the anode slurry is 54 wt%. And uniformly coating the negative electrode slurry on a copper foil of a negative electrode current collector, drying the copper foil at 85 ℃, then carrying out cold pressing, cutting, slitting and drying for 12 hours at 120 ℃ under a vacuum condition to obtain the negative electrode.
Preparation of negative electrodes of examples 41 to 43 and comparative examples 4 to 6:
the negative active material of artificial graphite and the silicon-oxygen negative active material SiO coated with metal oxide are mixedx(x is more than or equal to 0.5 and less than or equal to 1.5) (wherein the silica material accounts for 10 wt% of the negative active material), a conductive agent Super P, a thickening agent sodium carboxymethyl cellulose (CMC), and a binder Styrene Butadiene Rubber (SBR) according to the weight ratio of about 96.2: 1.5: 0.5: 1.8, mixing the mixture in deionized water, fully mixing and uniformly stirring to obtain cathode slurry; wherein the solid content of the anode slurry is 54 wt%. And uniformly coating the negative electrode slurry on a copper foil of a negative electrode current collector, drying the copper foil at 85 ℃, then carrying out cold pressing, cutting into pieces, slitting, and drying for 12 hours at 120 ℃ under a vacuum condition to obtain the negative electrode.
4. Preparation of the separator
A Polyethylene (PE) film of 10 microns was used as the separator.
5. Preparation of lithium ion battery
Stacking the obtained anode, the isolating membrane and the cathode in sequence to enable the isolating membrane to be positioned between the anode and the cathode to play an isolating role, and then winding to obtain a bare cell; and (3) after welding a tab, placing the bare cell in an outer packaging foil aluminum-plastic film, injecting the prepared electrolyte into the dried cell, and performing vacuum packaging, standing, formation (charging to 3.5V at a constant current of 0.02C and then charging to 3.9V at a constant current of 0.1C), shaping, capacity testing and other processes to obtain the soft package lithium ion battery, wherein the lithium ion battery has the thickness of about 3.3mm, the width of about 39mm and the length of about 96 mm.
The measurement methods of the respective performance parameters of the examples and comparative examples are as follows.
Second, testing method
1. High temperature cycle performance testing of lithium ion batteries
The formed battery of each example or each comparative example is charged to 4.45V at 40 ℃ by a constant current of 0.5C, then charged to 0.05C by a constant voltage, the first full-charge thickness is recorded as W0, and the battery is placed still for 19.5C and then discharged to 3.0V at a constant current of 0.5C; such as 75 cycles; the fully charged cell thickness after the 75 th cycle was recorded as W1.
The high temperature cycle thickness growth rate of the lithium ion battery was calculated by the following formula:
the high-temperature cycle thickness growth rate (%) - (W1-W0)/W0 × 100%.
2. High temperature storage performance testing of lithium ion batteries
The battery after formation of each example or comparative example was tested with a micrometer and the thickness of the battery was recorded as W2. Then the lithium ion battery is subjected to constant current charging to 4.45V at a constant charging rate of 0.5C at 25 ℃, then is subjected to constant voltage charging to 0.05C, then is transferred into an incubator at 85 ℃ for storage for 24 hours, and the thickness of the lithium ion battery is tested after the test is finished and is recorded as W3.
The thickness expansion rate of the high-temperature storage of the lithium ion battery was calculated by the following formula:
the thickness expansion rate (%) in high-temperature storage was (W3-W2)/W2 × 100%.
3. Normal temperature cycle performance test of lithium ion battery
And (3) placing the formed battery in a constant temperature box at 25 ℃, and standing for 30 minutes to keep the temperature of the lithium ion battery constant. Charging a lithium ion battery reaching a constant temperature to 4.45V at a constant current of 0.5C at 25 ℃, then charging at a constant voltage until the current is 0.05C, standing for 5min, and then discharging at a constant current of 0.5C until the voltage is 3.0V, which is a charge-discharge cycle; the charge and discharge cycle was repeated 500 times. The first discharge capacity was designated as D0, and the 500 th cycle discharge capacity was designated as D1.
The capacity retention after cycling of the lithium ion battery was calculated by the following formula:
the cycle capacity retention (%) of the lithium ion battery was D1/D0 × 100%.
4. High temperature cycle performance testing of lithium ion batteries
And (3) placing the formed battery in a constant temperature box at 45 ℃, and standing for 30 minutes to keep the temperature of the lithium ion battery constant. Charging the lithium ion battery reaching the constant temperature to 4.45V at a constant current of 0.5C at 45 ℃, then charging at a constant voltage until the current is 0.05C, standing for 5min, and then discharging at a constant current of 0.5C until the voltage is 3.0V, which is a charge-discharge cycle; the charge and discharge cycle was repeated 500 times. The first discharge capacity was designated as D2, and the 500 th cycle discharge capacity was designated as D3.
The capacity retention after high temperature cycling of the lithium ion battery was calculated by the following formula:
the retention ratio (%) of the high-temperature cycle capacity of the lithium ion battery was D3/D2 × 100%.
Third, test results
The electrolytes of examples 1 to 21 and comparative examples 1 to 3 and the lithium ion batteries were prepared according to the above-described methods. Table 1 shows the kinds and contents of additives used in the electrolytes of examples 1 to 21 and comparative examples 1 to 3, and the test results of the high temperature cycle thickness growth rate of the lithium ion battery.
TABLE 1
Figure BDA0002864174670000181
Note: "/" indicates no addition (same below).
As can be seen from the data analysis of table 1, when the cyclic dicarboxylate and the compound including 2 to 4 cyano groups are combined and applied to a lithium ion battery, the high temperature cycle thickness increase rate can be reduced, and the high temperature cycle performance of the lithium ion battery can be effectively improved. Wherein the high temperature cycle performance of the lithium ion battery can be significantly improved, compared to comparative examples 2 and 3 in which the cyclic dicarboxylate and the compound including 2 to 4 cyano groups are not added at all, in comparison to comparative example 1 in which the cyclic dicarboxylate and the compound including 2 to 4 cyano groups are added only, while the high temperature cycle decay of the lithium ion batteries of comparative examples 1 to 3 is faster. The reason is that the addition of the cyclic dicarboxylate additive and the compound containing at least 2 cyano groups stabilizes the positive electrode/electrolyte interface and the negative electrode/electrolyte interface, reduces the side reaction of the electrolyte, and thus effectively improves the high-temperature storage performance of the lithium ion battery.
It can be seen from comparison of examples 1 to 7 that examples 5 to 7, in which the compound having 2 to 4 cyano groups is the compound represented by formula iii, are more effective in reducing the thickness growth rate in the high temperature cycle test than the compounds represented by formula ii used in examples 1 to 4. Example 6 also shows a significant improvement in high temperature cycle performance with the addition of a different type of compound of formula I compared to examples 8 to 11. Example 6 compared with examples 12 to 16, the compound of formula I was added in different amounts, and the content of the compound of formula I was between 0.05% and 1.5%, which also significantly improved the high temperature cycle performance. Example 6 compared with examples 19 to 21, the addition of different amounts of different compounds of formula II and III also significantly improves the high temperature cycle performance, so that different compounds of formula II and III can be used not only alone but also in combination.
In some embodiments herein, the electrolyte of the present application can further comprise other additives to further enhance the electrochemical performance of a lithium ion battery comprising the electrolyte. In the following examples 22 to 28, the same procedure as in example 6 was conducted except that at least one of the compounds represented by the following structural formulae was further added to the preparation of the electrolytes in examples 22 to 28:
Figure BDA0002864174670000191
1, 3-dioxolane (cyclic ether 1),
Figure BDA0002864174670000192
1, 3-dioxane (cyclic ether 2),
Figure BDA0002864174670000193
1, 4-dioxane (cyclic ether 3).
Table 2 shows the kinds and contents of additives used in the electrolytes of examples 6 and 22 to 28, table 2 shows cyclic dicarboxylic acid ester as represented by structural formula I-7, and the contents are all 0.5%, and the compound containing 2 to 4 cyano groups is formula iii-2, and the contents are all 1.5%, and table 2 shows the test results of the high temperature cycle thickness growth rate and the high temperature storage thickness expansion rate of the lithium ion battery.
TABLE 2
Figure BDA0002864174670000194
As can be seen from the data analysis in table 2, the cyclic dicarboxylate, the compound containing 2 to 4 cyano groups, and the cyclic ether additive cooperate with each other to form a composite interfacial film, which can further reduce the high-temperature cycle thickness growth rate, effectively improve the high-temperature cycle performance of the lithium ion battery, reduce the high-temperature storage thickness growth rate, and improve the high-temperature storage performance of the lithium ion battery.
Examples 22 to 28 based on example 6 in which a cyclic dicarboxylate and a compound including 2 to 4 cyano groups were added, a cyclic ether additive compound was further added, and the content of the added cyclic ether additive compound was in the range of 0.02% to 1.5%, and it was possible to form a complete and effective organic film on the surface of an electrode, enhance the stability of an electrolyte, and improve the high-temperature cycle performance and high-temperature storage performance of a lithium ion battery.
In other embodiments herein, the electrolyte solution of the present application can further comprise other additives. In the following examples 29 to 36, the same manner as in example 6 was conducted except that at least one of the following compounds was further added in the preparation of the electrolytes in examples 29 to 36: lithium bis (oxalato) borate (LiBOB), lithium difluoro (oxalato) borate (lidob), lithium difluoro (opho)2F2)。
Table 3 lists the types and contents of the additives used in the electrolytes of example 6 and examples 29 to 36, table 3 shows that the cyclic dicarboxylic acid ester is represented by structural formula I-7 and the contents are all 0.5%, and table 3 lists the test results of the high-temperature cycle thickness growth rate and the cycle capacity retention rate of the lithium ion battery.
TABLE 3
Figure BDA0002864174670000201
As can be seen from the data analysis in table 3, the cyclic dicarboxylate, the compound containing 2 to 4 cyano groups, and the lithium salt additive are synergistically combined to form a composite interfacial film, which can further reduce the high-temperature cycle thickness growth rate, effectively improve the high-temperature cycle performance of the lithium ion battery, and improve the cycle performance of the lithium ion battery. As can be seen from comparing example 6 with examples 29 to 36, the capacity retention rate of the lithium ion battery in examples 29 to 36, which passes the (normal temperature) cycle performance test, can reach 73.6% to 88.4%, because the reduction potential of the lithium salt additives is higher and the lithium salt additives preferentially form a film on the negative electrode, and the formed SEI film is stable in the battery cycle process, so that the reaction between the solvent and the negative electrode in the cycle process is reduced, and the cycle performance of the lithium ion battery is improved.
Table 4 lists the types and contents of the additives used in the electrolytes of examples 6, 22, 29, 37 to 40, table 4 shows that the cyclic dicarboxylic acid ester is represented by the structural formula I-7 and the contents are all 0.5%, and table 4 lists the test results of the high temperature cycle thickness growth rate and the high temperature cycle capacity retention rate of the lithium ion battery.
TABLE 4
Figure BDA0002864174670000211
From the data analysis in table 4, it can be seen that the cyclic dicarboxylate and the compound containing 2 to 4 cyano groups are combined with the lithium salt additive and the cyclic ether additive, so that the high-temperature cycle thickness growth rate can be further reduced, the high-temperature cycle performance of the lithium ion battery can be effectively improved, and the high-temperature cycle performance of the lithium ion battery can be improved. As can be seen by comparing examples 6, 22, 29 and 37 to 40, the capacity retention rate of the lithium ion battery in examples 37 to 40, which passes the high temperature cycle performance test, can reach 80.5% to 83.2%, and the thickness growth rate of the battery passing the high temperature cycle performance reaches 12.4% to 13.1%, which indicates that the high temperature cycle performance and the high temperature cycle performance of the lithium ion battery can be further improved by adding a lithium salt additive and a cyclic ether additive together on the basis of adding a cyclic dicarboxylate and a compound containing 2 to 4 cyano groups.
In other embodiments of the present application, the application of an electrolyte comprising the above cyclic dicarboxylate and a compound comprising 2 to 4 cyano groups to a lithium ion battery comprising a silicon-containing anode can significantly improve the high temperature cycle thickness growth rate of silicon systems.
Table 5 shows the kinds and contents of additives used in the electrolytes of examples 41 to 43 and comparative examples 4 to 6, the types of negative active materials, and the test results of the high temperature cycle thickness growth rate of the lithium ion battery.
TABLE 5
Figure BDA0002864174670000212
Figure BDA0002864174670000221
As can be seen from the data analysis of table 5 above, in comparison with comparative examples 4 to 6, examples 41 to 43 of the present application provide a lithium ion battery capable of reducing the high temperature cycle thickness growth rate by adding the above cyclic dicarboxylate and the combination of compounds containing 2 to 4 cyano groups to an electrolyte, and at the same time, coating a silicon material can further reduce the high temperature cycle thickness growth rate, and can more effectively improve the high temperature cycle performance of the lithium ion battery.
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 (10)

1. An electrolyte for a lithium ion battery, comprising a cyclic dicarboxylate and a compound containing 2 to 4 cyano groups;
the cyclic dicarboxylate includes at least one of the compounds of formula I:
Figure FDA0003556414900000011
wherein R is1、R2、R3And R4Each independently selected from hydrogen, halogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C1-C12 alkoxy, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl; wherein R is1、R2、R3、R4When substituted, the substituents include at least one of halogen or haloalkyl;
the compound containing 2 to 4 cyano groups includes at least one of compounds represented by the following formula II or formula III:
Figure FDA0003556414900000012
in formula II, R5Selected from substituted or unsubstituted C1-C9 alkylene, substituted or unsubstituted C1-C5 alkyleneoxy, substituted or unsubstituted C2-C10 alkenylene;
in formula III, R6、R7And R8Each independently selected from a covalent bond, a substituted or unsubstituted C1-C5 alkylene group, a substituted or unsubstituted C1-C5 alkyleneoxy group;
wherein R is5、R6、R7、R8When substituted, the substituents include at least one of halogen or cyano.
2. The electrolyte of claim 1, wherein the compound of formula I comprises at least one of the following compounds:
Figure FDA0003556414900000013
Figure FDA0003556414900000021
3. the electrolyte of claim 1, wherein the compound of formula ii or iii comprises at least one of the following compounds:
Figure FDA0003556414900000022
Figure FDA0003556414900000031
4. the electrolyte of any one of claims 1 to 3, wherein the cyclic dicarboxylate is present in an amount of 0.01 to 2% by mass, based on the mass of the electrolyte; the mass percentage of the compound containing 2 to 4 cyano groups is 0.5 to 10 percent.
5. The electrolyte of claim 4, wherein the cyclic dicarboxylate is present in an amount of 0.05 to 1.5% by weight; the mass percentage of the compound containing 2 to 4 cyano groups is 0.5 to 8 percent.
6. The electrolyte according to any one of claims 1 to 3, wherein the cyclic dicarboxylate is present in an amount of a% by mass, the compound containing 2 to 4 cyano groups is present in an amount of b% by mass, and b and a satisfy the following relationship: b/a is more than or equal to 0.1 and less than or equal to 200.
7. The electrolyte of claim 6, wherein the relationship of b to a satisfies: b/a is more than or equal to 1 and less than or equal to 40.
8. The electrolyte of any one of claims 1 to 3, wherein the electrolyte further comprises at least one of a cyclic ether additive or a lithium salt additive;
the cyclic ether additive comprises at least one of 1, 3-dioxolane, 1, 3-dioxane or 1, 4-dioxane, and the content of the cyclic ether additive in percentage by mass is 0.01-2% based on the mass of the electrolyte;
the lithium salt additive comprises at least one of lithium bis (oxalate) borate, lithium difluoro (oxalate) borate or lithium difluoro (phosphate), and the mass percentage of the lithium salt additive is 0.01-2%.
9. A lithium ion battery, comprising:
a positive electrode;
a negative electrode;
a separator provided between the positive electrode and the negative electrode;
and, the electrolyte of any one of claims 1 to 8;
the negative electrode comprises a negative electrode current collector and a negative electrode active material layer which is arranged on the surface of the negative electrode current collector and contains a negative electrode active material;
wherein the negative active material comprises a silicon-based material, at least one part of the surface of the silicon-based material is provided with a protective layer, and the protective layer has at least one of the following characteristics:
(a) the protective layer comprises a metal oxide MexOyWherein Me comprises Al, Mg, Ti, Si,X is more than or equal to 1 and less than or equal to 2, and y is more than or equal to 1 and less than or equal to 3;
(b) the protective layer comprises a carbon material;
(c) the thickness of the protective layer is 1.0nm to 100 nm.
10. An electronic device comprising the lithium ion battery according to claim 9.
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