CN112886062B - Electrolyte solution, electrochemical device, and electronic apparatus - Google Patents
Electrolyte solution, electrochemical device, and electronic apparatus Download PDFInfo
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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
- H01M10/056—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
- H01M10/0566—Liquid materials
- H01M10/0567—Liquid materials characterised by the additives
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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
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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
- H01M10/42—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
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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
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0025—Organic electrolyte
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- 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
Abstract
The present application relates to the technical field of secondary batteries, and particularly to an electrolyte, an electrochemical device, and an electronic apparatus. The electrolyte solution includes an organic solvent, a lithium salt, a first compound, and a fluoroether. This application is through adding first compound and fluoroether in electrolyte, and first compound reduction potential is higher, and oxidation potential is lower simultaneously, can form the SEI membrane at electrochemical device's negative pole, protects the negative pole, reduces negative pole side reaction, promotes electrolyte, efficiency to improve the cyclicity ability of battery.
Description
Technical Field
The present disclosure relates to the field of electrolyte solutions, and particularly, to an electrolyte solution, an electrochemical device, and an electronic apparatus.
Background
The lithium ion battery has the advantages of high energy density, good cycle performance, environmental protection, safety, no memory effect and the like, and is widely applied to the fields of portable electronic products, electric transportation, national defense aviation, energy storage and the like. Conventional lithium ion batteries use graphite as the negative electrode material, and their actual energy density is approaching the theoretical upper limit more and more. Lithium metal batteries, however, have an extremely high theoretical energy density and are therefore gaining increasing attention.
At present, lithium metal in the lithium metal battery can generate continuous side reaction with electrolyte, so that the electrolyte and the lithium metal can be rapidly consumed, the battery capacity is rapidly attenuated, and sustainable cyclic charge and discharge capacity is unavailable. And in the process of charge and discharge cycle of the lithium metal battery, because a solid electrolyte interface film (SEI) is unstable and the concentration of lithium ions is not uniform, the deposition of lithium metal is not uniform, and a large amount of lithium dendrites grow, so that the safety risk of short circuit of the battery exists.
In order to realize long cycle of a lithium metal battery with high energy density, it is urgently needed to develop a lithium metal battery liquid electrolyte which can realize high-current density charging and discharging under different operating temperature conditions and has a long cycle life.
Disclosure of Invention
In view of this, the application provides an electrolyte, an electrochemical device and an electronic device, which can meet the requirements of large-current density long-cycle charge and discharge under the high and low temperature conditions of a lithium ion battery, and the electrolyte has the advantages of high ionic conductivity, good electrochemical stability, high voltage tolerance, good safety performance, and can remarkably improve the cycle performance; the electrolyte provided by the application can also be used in lithium ion batteries.
In a first aspect, the present application provides an electrolyte, including a first compound and a fluoroether, where the first compound is a compound represented by formula I,
wherein R is 1 、R 2 、R 3 、R 4 Each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C12 alkynyl, ester group; when substituted, the substituents are selected from halogen or cyano;
m is selected from any one of Na, K or Cs.
With reference to the first aspect, in one possible embodiment, the compound of formula I is selected from at least one of the following compounds:
in one possible embodiment in combination with the first aspect, the fluoroether is a compound of formula II,
wherein R is 5 And R 6 Each independently selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C12 alkynyl, substituted or unsubstituted C6-C26 aryl, nitro, sulfonic acid group, aldehyde group, carboxyl group, and R 5 And R 6 At least one of them containing a fluoroalkyl group。
In one possible embodiment in combination with the first aspect, the fluoroether comprises at least one of the following compounds:
in one possible embodiment in combination with the first aspect, the electrolyte further includes at least one of fluoroethylene carbonate, methyl trifluoroethyl carbonate, ethylene glycol dimethyl ether, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, or γ -butyrolactone.
With reference to the first aspect, in one possible embodiment, the electrolyte solution further includes a second compound, and the second compound includes at least one of an alkaline earth metal salt, a cyclic carbonate compound having a carbon-carbon unsaturated bond, a halogen-substituted cyclic carbonate compound, a nitrile compound, an acid anhydride compound, a phosphorus-containing compound, and a sulfur-containing compound;
with reference to the first aspect, the second compound is present in the electrolyte in an amount of 0.1% to 10% by mass.
With reference to the first aspect, in a possible embodiment, at least one of a to d is satisfied, where (1) the mass percentage of the first compound in the electrolyte is a%, and a is in a range from 0.1 to 2; b. the mass percentage of the fluoroether in the electrolyte is b percent, and the value range of b is 5 to 50; preferably, b ranges from 17 to 30; c. the mass percentage of the first compound in the electrolyte is a%, the mass percentage of the fluoroether in the electrolyte is b%, the mass ratio of the fluoroether to the first compound is b/a, and the value range of b/a is 2.5-250; d. the electrolyte also comprises at least one of fluoroethylene carbonate, methyl trifluoroethyl carbonate, ethylene glycol dimethyl ether, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or gamma-butyrolactone; the electrolytic solution further includes at least one of lithium hexafluorophosphate, lithium bistrifluoromethanesulfonylimide, lithium bis (fluorosulfonyl) imide, lithium tetrafluoroborate, lithium difluorooxalato borate, lithium dioxalate borate, or lithium difluorophosphate. The electrolyte also comprises an organic solvent, wherein the mass percentage of the organic solvent in the electrolyte is c percent, and the value range of c is 40-94.9; the mass ratio of the organic solvent to the first compound is c/a, and the value range of c/a is 20-800; the concentration of the lithium salt in the electrolyte is 0.3mol/L to 2mol/L.
In a second aspect, the present application provides an electrochemical device comprising: the positive electrode comprises a positive electrode current collector and a positive electrode active material layer which is arranged on the surface of the positive electrode current collector and contains a positive electrode active material; 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; a separator provided between the positive electrode and the negative electrode; and an electrolytic solution according to the first aspect.
In combination with the second aspect, in one possible embodiment, the positive active material includes at least one of a lithium nickel cobalt manganese ternary material, lithium iron phosphate, lithium manganate, or lithium cobaltate; and/or the negative active material is selected from at least one of lithium metal or lithium metal alloy compound, carbon material, silicon material, or silicon oxygen material.
In combination with the second aspect, in one possible embodiment, at least one of (1) to (4), (1) the positive electrode active material includes at least one of a lithium nickel cobalt manganese ternary material, lithium iron phosphate, lithium manganate, or lithium cobaltate; (2) The negative electrode active material is selected from at least one of a lithium metal or lithium metal alloy compound, a carbon material, a silicon material, or a silicon oxygen material. (3) The negative active material surface has a protective film comprising lithium fluoride; the thickness of the protective film is less than 50nm. (4) Detecting M metal ions on the surface of the negative active material by using X-ray photoelectron spectroscopy or X-ray spectroscopy, wherein M is at least one selected from Na, K and Cs.
In a third aspect, the present application provides an electronic device comprising the electrochemical device of the second aspect.
Compared with the prior art, the method has the following beneficial effects:
the application provides an electrolyte adds first compound in electrolyte, and first compound can form the SEI membrane at electrochemical device's negative pole, protects the negative pole, reduces negative pole side reaction, obviously promotes electrolyte coulomb efficiency to improve the cycling stability of battery. The first compound can also form a CEI film on the anode of the electrochemical device, so that the side reaction of the anode is reduced, and the cycling stability of the battery is improved. Furthermore, a second compound is added into the electrolyte, and the second compound can be a positive electrode or negative electrode protective agent such as vinylene carbonate, methylene methyl disulfonate, an acid anhydride compound, a nitrile compound, a boron compound, a phosphorus compound, a sulfur compound and the like, so that the cycling stability of the battery is improved.
Compared with the prior art, the electrolyte provided by the application has the advantages of high ionic conductivity, good electrochemical stability, high voltage tolerance, good safety performance and capability of remarkably improving the cycle performance.
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.
The following terms used herein have the meanings indicated below, unless explicitly indicated otherwise.
In the detailed description and claims, a list of items connected by the terms "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, B are listed, the phrase "at least one of a, B" means a only; only B; or A and B. In another example, if 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 all of 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 disclosure, unless otherwise expressly stated or limited, the terms "first," "second," "third," "formula I," "formula II," "formula I-1," and the like are used for illustrative 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.
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 to C10", "C6 to C26", etc., the number 1, 10, 6 or 26 following "C" represents the number of carbon atoms in a specific functional group. That is, the functional groups may include 1 to 10 carbon atoms and 6 to 26 carbon atoms, respectively.
Herein, the term "halogen" encompasses fluorine (F), chlorine (Cl), bromine (Br), iodine (I); preferably, the halogen is selected from F or Cl.
First aspect
The embodiment of the application provides an electrolyte, which comprises a first compound, wherein the first compound is a compound shown as a formula I,
wherein R is 1 、R 2 、R 3 、R 4 Each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C12 alkynyl, ester group; the substituent is selected from halogen and cyano;
m is selected from any one of Na, K or Cs.
In the above scheme, because the first compound is added into the electrolyte, the reduction potential of the first compound is higher, and the oxidation potential is lower, so that an SEI (solid electrolyte interphase) film can be formed on the negative electrode of the electrochemical device, the negative electrode of the lithium metal is protected, the side reaction of the negative electrode is reduced, the coulomb efficiency of the lithium metal electrolyte is improved, and the cycling stability of the lithium metal battery is further improved. In addition, the first compound can also form a CEI film on the positive electrode, so that the side reaction of the positive electrode is reduced, and the cycle stability of the lithium metal battery is further improved.
As an alternative embodiment of the present application, in the compounds represented by formula I:
the C1-C10 alkyl can be chain alkyl or cyclic alkyl, the chain alkyl can be straight-chain alkyl or branched-chain alkyl, and hydrogen on the ring of the cyclic alkyl can be further substituted by alkyl. The number of carbon atoms in the C1-C10 alkyl group is preferably lower than 1,2, 3, 4,5, and more preferably upper than 3, 4,5, 6, 8, 10. Preferably, a C1-C6 chain alkyl group, a C3-C8 cyclic alkyl group is selected; more preferably, a C1-C4 chain alkyl group or a C5-C7 cyclic alkyl group is selected. Examples of C1-C10 alkyl groups include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, hexyl, 2-methyl-pentyl, 3-methyl-pentyl, 1, 2-trimethyl-propyl, 3-dimethyl-butyl, heptyl, 2-heptyl, 3-heptyl, 2-methylhexyl, 3-methylhexyl, isoheptyl, octyl, nonyl, decyl.
When the aforementioned C1-C10 alkyl group contains an oxygen atom, it may be a C1-C10 alkoxy group. Preferably, C1-C6 alkoxy is selected; further preferably, a C1-C4 alkoxy group is chosen. Specific examples of the C1-C10 alkoxy group include: methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, n-pentoxy, isopentoxy, cyclopentoxy, cyclohexoxy.
The C2-C10 alkenyl group may be a cyclic alkenyl group or a chain alkenyl group, and the chain alkenyl group may be a linear alkenyl group or a branched alkenyl group. In addition, the number of double bonds in the C2-C10 alkenyl group is preferably 1. The number of carbon atoms in the C2-C10 alkenyl group preferably has a lower limit of 2, 3, 4,5 and an upper limit of 3, 4,5, 6, 8, 10. Preferably, a C2-C6 alkenyl group is selected; further preferably, a C2-C5 alkenyl group is chosen. Examples of C2-C10 alkenyl groups include: vinyl, allyl, isopropenyl, pentenyl, cyclohexenyl, cycloheptenyl, cyclooctenyl.
C2-C12 alkynyl may be cyclic alkynyl, chain alkynyl, linear alkynyl or branched alkynyl. In addition, the number of triple bonds in C2-C12 alkynyl is preferably 1. The number of carbon atoms in the C2-C12 alkynyl group preferably has a lower limit of 2, 3, 4,5 and a higher limit of 3, 4,5, 6, 8, 10, 12. Preferably, C2-C6 alkynyl is selected; further preferably, C2-C5 alkynyl is chosen. Specific examples of C2-C10 alkynyl groups include: ethynyl, propargyl, isopropynyl, pentynyl, cyclohexynyl, cycloheptynyl, cyclooctynyl.
Preferably, R2, R3 are hydrogen atoms; further preferably, R1, R2, R3 and R4 are all hydrogen atoms, or R2 and R3 are all hydrogen atoms and R1 and R4 are selected from fluorine atom, chlorine atom, bromine atom, substituted or unsubstituted C1-C6 straight or branched alkyl group, and substituted or unsubstituted C1-C6 alkoxy group. Wherein, the substituent is selected from one or more of halogen atoms, preferably, the substituent is selected from fluorine atoms.
As an optional technical scheme of the present application, the mass percentage of the first compound in the electrolyte is a%, and the value range of a is 0.1 to 2;
when the content of the first compound in the electrolyte is lower than 0.1%, the first compound is not enough to form a stable SEI film, the protection of the negative electrode is not enough, the occurrence of negative electrode side reaction is difficult to inhibit, and the cycle performance of the battery is difficult to effectively improve. When the content of the first compound in the electrolyte is higher than 2%, the first compound is difficult to dissolve in the electrolyte, increasing the cost and making it difficult to improve the anode protection effect.
Alternatively, the content of the first compound in the electrolyte may be specifically 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0% by mass, and the like, and may be other values within the above range, which is not limited herein.
As an alternative solution, the first compound is selected from at least one of the following compounds:
further, the electrolyte also comprises a diluent, wherein the diluent is fluoroether, the structure of which is shown in a formula II,
wherein R is 5 And R 6 Each independently selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C12 alkynyl, substituted or unsubstituted C6-C12 aryl, nitro, sulfonic acid group, aldehyde group, carboxyl group, and R 5 And R 6 At least one of which has a fluorine substituent.
As an alternative embodiment of the present application, in the compound represented by formula II:
the C1-C10 alkyl can be chain alkyl or cyclic alkyl, the chain alkyl can be straight-chain alkyl or branched-chain alkyl, and hydrogen on the ring of the cyclic alkyl can be further substituted by alkyl. The number of carbon atoms in the C1-C10 alkyl group is preferably lower than 1,2, 3, 4,5, and more preferably upper than 3, 4,5, 6, 8, 10. Preferably, a C1-C6 chain alkyl group, a C3-C8 cyclic alkyl group is selected; more preferably, a C1-C4 chain alkyl group or a C5-C7 cyclic alkyl group is selected. Examples of C1-C10 alkyl groups include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, hexyl, 2-methyl-pentyl, 3-methyl-pentyl, 1, 2-trimethyl-propyl, 3-dimethyl-butyl, heptyl, 2-heptyl, 3-heptyl, 2-methylhexyl, 3-methylhexyl, isoheptyl, octyl, nonyl, decyl.
When the aforementioned C1-C10 alkyl group contains an oxygen atom, it may be a C1-C10 alkoxy group. Preferably, a C1-C6 alkoxy group is selected; further preferably, a C1-C4 alkoxy group is chosen. Specific examples of the C1-C10 alkoxy group include: methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, n-pentoxy, isopentoxy, cyclopentoxy, cyclohexoxy.
The C2-C10 alkenyl group may be a cyclic alkenyl group or a chain alkenyl group, and the chain alkenyl group may be a linear alkenyl group or a branched alkenyl group. In addition, the number of double bonds in the C2-C10 alkenyl group is preferably 1. The number of carbon atoms in the C2-C10 alkenyl group is preferably 2, 3, 4,5 in the lower limit, and 3, 4,5, 6, 8, 10 in the upper limit. Preferably, a C2-C6 alkenyl group is selected; further preferably, a C2-C5 alkenyl group is chosen. Examples of C2-C10 alkenyl groups include: vinyl, allyl, isopropenyl, pentenyl, cyclohexenyl, cycloheptenyl, cyclooctenyl.
C2-C12 alkynyl can be cyclic alkynyl, also can be chain alkynyl, chain alkynyl can be straight chain alkynyl or branched chain alkynyl. In addition, the number of triple bonds in C2-C10 alkynyl is preferably 1. The number of carbon atoms in the C2-C12 alkynyl group preferably has a lower limit of 2, 3, 4,5 and a higher limit of 3, 4,5, 6, 8, 10, 12. Preferably, C2-C6 alkynyl is selected; further preferably, C2-C5 alkynyl is chosen. Specific examples of C2-C10 alkynyl groups include: ethynyl, propargyl, isopropynyl, pentynyl, cyclohexynyl, cycloheptynyl, cyclooctynyl.
The C6-C26 aryl group can be phenyl, phenylalkyl, biphenyl, fused ring aromatic hydrocarbon groups (e.g., naphthyl, anthryl, phenanthryl), biphenyl and fused ring aromatic hydrocarbon groups can be further substituted with alkyl or alkenyl groups. Preferably, a C6-C16 aryl group is selected; further preferably, a C6-C14 aryl group is selected; even more preferably, a C6-C9 aryl group is chosen. Specific examples of the C6-C26 aryl group include: phenyl, benzyl, biphenyl, p-tolyl, o-tolyl, m-tolyl, naphthyl, anthryl, phenanthryl.
It should be noted that the main function of the fluoroether compound in the electrolyte of the present application is a diluent that stabilizes the negative electrode, and does not participate in the dissociation of the lithium salt, but the viscosity of the electrolyte can be reduced, so that a good solid electrolyte membrane (abbreviated as SEI) is formed on the negative electrode, and the coulombic efficiency is improved.
The fluorine ether can be used as a diluent to reduce the viscosity of the electrolyte, is beneficial to the infiltration of the electrolyte and the exertion of the battery capacity, has better oxidation resistance and can improve the high-voltage cycling stability of the battery.
As an alternative solution, the fluoroether comprises at least one of the following compounds:
as an optional technical solution of the present application, the mass percentage of the fluoroether in the electrolyte is b%, and the value range of b is 5 to 50. When the content of fluoroether in the electrolyte is lower than 5%, the local lithium salt concentration cannot be increased, so that excessive lithium salt needs to be added to the electrolyte to maintain the oxidation resistance of the electrolyte and maintain good film-forming performance on a lithium metal cathode, and the cost is rapidly increased. When the content of fluoroether in the electrolyte is higher than 50%, the dissolution capacity of the electrolyte to lithium salt is reduced, and the lithium salt cannot be dissolved, so that the electrolyte cannot normally conduct lithium ions, and the rate performance and the cycle performance of the battery are influenced.
Alternatively, the content of the fluoroether in the electrolyte solution by mass may be specifically 5%, 8%, 10%, 12%, 15%, 17%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 45%, or 50%, and the like, and may be other values within the above range, which is not limited herein. Preferably, the mass percentage of the fluoroether in the electrolyte is b%, and the value of b ranges from 17 to 30.
As an optional technical solution of the present application, the mass percentage content of the first compound in the electrolyte is a%, the mass percentage content of the fluoroether in the electrolyte is b%, the mass ratio of the fluoroether in the electrolyte to the first compound is b/a, and the value range of b/a is 2.5 to 250. When the above mass ratio is less than 2.5, it means that the first compound in the electrolyte is excessive, and it is difficult to completely dissolve in the electrolyte, increasing the cost and making it difficult to improve the negative electrode protection effect. When the mass ratio is higher than 250, the first compound in the electrolyte is insufficient, a stable SEI film is difficult to form, the protection of the negative electrode is insufficient, the occurrence of negative side reaction is difficult to inhibit, and the cycle performance of the battery is difficult to effectively improve.
Optionally, the mass ratio of the fluoroether to the first compound in the electrolyte may be specifically 2.5, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200, 230 or 250, etc., or may be other values within the above range, which is not limited herein.
As an alternative embodiment of the present application, the organic solvent is selected from fluoro carbonate compounds, ether compounds, and the like.
As an alternative embodiment of the present invention, the organic solvent includes at least one of fluoroethylene carbonate (abbreviated as FEC), methyltrifluoroethyl carbonate (abbreviated as FEMC), ethylene glycol dimethyl ether (abbreviated as DME), ethylene carbonate (abbreviated as EC), propylene carbonate (abbreviated as PC), dimethyl carbonate (abbreviated as DMC), diethyl carbonate (abbreviated as DEC), ethyl methyl carbonate (abbreviated as EMC), or γ -butyrolactone (abbreviated as BL).
As an optional technical scheme of the present application, the mass percentage of the organic solvent in the electrolyte is c%, the value range of c is 40 to 94.9, and when the content of the organic solvent in the electrolyte is lower than 40%, the dissolving capacity of the electrolyte for lithium salt is reduced, and the lithium salt is difficult to completely dissolve, so that the capacity of conducting lithium ions by the electrolyte is reduced, and the rate capability and the cycle performance of the battery are affected.
Optionally, the content of the organic solvent in the electrolyte solution by mass percentage may be specifically 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 94.9%, and the like, and may also be other values within the above range, which is not limited herein. Preferably, the mass percentage of the organic solvent in the electrolyte is 47% to 82%.
As an optional technical solution of the present application, a mass ratio of the organic solvent to the first compound is c/a, and a value range of c/a is 20 to 800. The value range of c/a may be specifically 20, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, or 800, etc., and may also be other values within the above range, which is not limited herein. When the mass ratio of the organic solvent to the first compound is less than 20, it means that the first compound in the electrolyte is too much to be completely dissolved in the electrolyte, increasing the cost and making it difficult to improve the anode protection effect. When the mass ratio of the organic solvent to the first compound is higher than 800, the first compound in the electrolyte is insufficient, a stable SEI film is difficult to form, the protection of the negative electrode is insufficient, the occurrence of a negative electrode side reaction is difficult to inhibit, and the cycle performance of the battery is difficult to effectively improve.
As an optional technical solution of the present application, the electrolyte may further include a second compound, and the second compound includes at least one of an alkaline earth metal salt, a cyclic carbonate compound having a carbon-carbon unsaturated bond, a halogen-substituted cyclic carbonate compound, a nitrile compound, an acid anhydride compound, a phosphorus-containing compound, and a sulfur-containing compound.
The mass percentage of the second compound in the electrolyte is 0.1-10%. When the second compound is present in an amount of more than 10% by mass, the cycle performance improving effect on the electrochemical device is reduced, the manufacturing cost is increased, and there is a possibility that the dc resistance of the battery is increased, which affects the cycle performance.
As an alternative solution, the alkaline earth metal salt includes at least one of beryllium salt, calcium salt, magnesium salt, and strontium salt.
As an alternative solution, the cyclic carbonate compound containing carbon-carbon unsaturated bonds may be specifically selected from one or more of the following compounds, but the present application is not limited thereto:
preferably, the cyclic carbonate compound having a carbon-carbon unsaturated bond is vinylene carbonate (abbreviated as VC). The electrolyte is added with a proper amount of vinylene carbonate (VC for short), so that the film forming stability of an electrochemical device at a high voltage on a negative electrode can be improved, the impedance increase is inhibited, and the cycle performance of a lithium ion battery at the high voltage is improved.
As an alternative embodiment of the present application, the halogen-substituted cyclic carbonate compound may be at least one selected from fluoroethylene carbonate (hereinafter, abbreviated as FEC), propylene fluorocarbonate (hereinafter, abbreviated as FPC), propylene carbonate trifluoride (hereinafter, abbreviated as TFPC), trans-or cis-4, 5-difluoro-1, 3-dioxolan-2-one (hereinafter, both of them are collectively referred to as "DFEC").
As the optional technical scheme of the application, a proper amount of nitrile compounds are added into the electrolyte, and because the carbon-nitrogen triple bond energy in the cyano group is very high, the nitrile compounds have very strong oxidation resistance, and the nitrile compounds can form an organic protective layer on the surface of the anode, organic molecules on the surface of the anode can well separate easily-oxidized components in the electrolyte from the surface of the anode, so that the oxidation effect of the surface of the anode on the electrolyte under high voltage is greatly reduced, and the cycle performance of the lithium ion battery under high voltage is improved.
Optionally, the nitrile compound may also be selected from at least one of the nitrile compounds shown in the following structures;
as an optional technical scheme of the application, a proper amount of anhydride compound is added into the electrolyte, so that the electrolyte is superior to a basic electrolyte in a small amount of oxidative decomposition, the battery impedance is inhibited, and the normal-temperature and high-temperature capacity retention rate of an electrochemical device is improved.
The acid anhydride compound may be a linear acid anhydride or a cyclic acid anhydride. Specifically, the acid anhydride compound may be at least one selected from the group consisting of acetic anhydride, propionic anhydride, succinic anhydride, maleic anhydride, 2-allyl succinic anhydride, glutaric anhydride, itaconic anhydride, and 3-sulfo-propionic anhydride.
As an alternative technical scheme, the phosphorus-containing compound comprises at least one of a phosphazene compound, a phosphite compound and a phosphate compound.
Alternatively, the phosphazene compound may be specifically selected from at least one of methoxy pentafluorocyclotriphosphazene, ethoxy pentafluorocyclotriphosphazene, phenoxy pentafluorocyclotriphosphazene, and ethoxy heptafluorocyclotetraphosphazene.
As an alternative embodiment of the present application, the sulfur-containing compound includes at least one of sulfolane, a sulfate compound, a sultone compound, and a disulfonate compound.
Alternatively, the sulfate compound may be specifically selected from at least one of the following compounds, but the present application is not limited thereto:
alternatively, the sultone sulfonate compound may be specifically selected from at least one of the following compounds, but the present application is not limited thereto:
alternatively, the disulfonate compound may be specifically selected from at least one of the following compounds, but the present application is not limited thereto:
preferably, the disulfonate compound is methylene methyldisulfonate (abbreviated as MMDS), which is effective in improving the cycle stability of the electrochemical device at high temperatures.
As an alternative embodiment of the present invention, the lithium salt includes lithium hexafluorophosphate (chemical formula LiPF) 6 ) Lithium bistrifluoromethanesulfonylimide (abbreviated to LiTFSI), lithium bistrifluoromethanesulfonylimide (abbreviated to LiFSI), and lithium tetrafluoroborate (chemical formula of LiBF) 4 ) Lithium difluorooxalato borate (abbreviated as LiDFOB), lithium dioxaoxalato borate (abbreviated as LiBOB), or lithium difluorophosphate (chemical formula LiPO) 2 F 2 ) At least one of (a).
The concentration of the lithium salt in the electrolyte is 0.3mol/L to 2mol/L. The lithium salt mainly serves to provide lithium ions, and can provide organic anions to react with a lithium metal negative electrode to form a good negative electrode protective film SEI. When the concentration of the lithium salt is less than 0.3mol/L, the lithium ion concentration of the electrolyte is low, and the ionic conductivity is too low, so that the rate performance and the cycle performance of the battery are reduced. When the concentration of the lithium salt is more than 2mol/L, the lithium salt may have a phenomenon of difficult dissolution, or a crystallization phenomenon may occur during low-temperature storage after dissolution, the viscosity of the electrolyte is too high, the conductivity of lithium ions is reduced, the use window of the electrolyte is narrow, the wettability is poor, and the electrochemical performance of the battery is affected.
Optionally, the concentration of the lithium salt may specifically be 0.3mol/L, 0.5mol/L, 0.8mol/L, 1.0mol/L, 1.3mol/L, 1.5mol/L, 1.8mol/L, or 2.0mol/L, and may also be other values within the above range, which is not limited herein.
In a second aspect, the present application provides an electrochemical device comprising:
the positive electrode comprises a positive electrode current collector and a positive electrode active material layer which is arranged on the surface of the positive electrode current collector and contains a positive electrode active material;
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;
a separator provided between the positive electrode and the negative electrode;
and an electrolytic solution according to the first aspect.
As an optional technical solution of the present application, the specific type of the positive electrode active material is not limited, and may be selected according to requirements. What is needed isThe positive active material comprises lithium nickel cobalt manganese ternary material (NCM), lithium iron phosphate (LiFePO) 4 ) Lithium manganate (LiMn) 2 O 4 ) Or lithium cobaltate (LiCoO) 2 ) At least one of (1).
As an alternative solution, the negative electrode active material is selected from at least one of lithium metal or lithium metal alloy compound, carbon material, silicon material or silicon oxygen material.
As an alternative solution, the capacity of the negative active material is in the range of 1mAh/cm 2 To 20mAh/cm 2 . Alternatively, the capacity range of the negative electrode active material may specifically be 1mAh/cm 2 、3mAh/cm 2 、5mAh/cm 2 、8mAh/cm 2 、10mAh/cm 2 、12mAh/cm 2 、15mAh/cm 2 、18mAh/cm 2 Or 20mAh/cm 2 And the like, and other values within the above range are also possible, without limitation.
Specifically, the anode active material may be a pure lithium metal anode; the lithium metal and the carbon material may be compounded, and the carbon material may be one or more of hard carbon, graphite, graphene, carbon nanotube, and the like; the negative electrode active material can also be a simple silicon material, a simple silicon-oxygen negative electrode material, a composite of a silicon negative electrode material and a carbon material, a composite of a silicon negative electrode material and lithium metal, an alloy of lithium metal and other metal materials or non-metal materials, a physical composite of lithium metal and other metal materials or non-metal materials, and the like. Illustratively, lithium metal may be deposited in other metals having a three-dimensional framework, such as in the three-dimensional pores of nickel foam to form a lithium metal negative electrode.
As an optional technical solution of the present application, the first compound in the electrolyte may react with lithium ions or metal lithium during the circulation process to generate lithium fluoride (LiF), and LiF is deposited on the particle surface of the negative electrode active material to form a protective film, which can effectively isolate the electrolyte; and the lithium fluoride is used as a lithium ion conductor material, so that a lithium ion transmission channel can be provided, the side reaction of lithium metal and electrolyte is reduced, the coulombic efficiency is improved, the growth of lithium dendrite is inhibited, and the cycling stability is improved. The thickness of the protective film is less than 50nm, specifically, it may be 5nm, 8nm, 10nm, 15nm, 18nm, 20nm, 25nm, 28nm, 30nm, 38nm, 40nm, 45nm or 50nm, and the like, and it may be other values within the above range, which is not limited herein.
As an optional technical solution of the present application, the surface of the negative active material contains a protective film of LiF. In one embodiment, the recycled cell is disassembled in a drying room, a small amount of negative electrode is cut, and after the surface is cleaned by a solvent (such as dimethyl ether), the particle surface of the negative electrode active material is detected by using X-ray photoelectron spectroscopy analysis.
In another embodiment, the recycled battery is disassembled in a drying room, a small amount of negative electrodes are cut, the surface of the battery is cleaned by a solvent (for example, dimethyl ether), and then the surface of the negative electrode active material is analyzed by using X-ray photoelectron spectroscopy or X-ray spectroscopy, wherein M is selected from any one of Na, K and Cs.
As an optional technical solution of the present application, the separator is selected from one or more of a polyethylene film, a polypropylene film, and a polyvinylidene fluoride film, and of course, an inorganic or organic coating may be coated on the surface of the separator substrate according to actual needs to enhance the hardness of the battery cell or to improve the adhesion between the separator and the cathode/anode interface.
In a third aspect, embodiments of the present application further provide an electronic device, including the electrochemical device according to the second aspect.
The present application is further illustrated below with reference to examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present application.
(1) Preparation of positive electrode
High nickel-three positive electrode active material lithium nickel cobalt manganese (abbreviated as NCM 811), conductive agent (Super p), binder polyvinylidene fluoride (abbreviated as PVDF) according to weight ratio of about 97:1.4:1.6 dissolving in N-methyl pyrrolidone (NMP) solvent, fully stirring and mixing to obtain anode slurry; then coating the positive electrode slurry on a positive electrode current collector aluminum foil; and drying the aluminum foil, cold pressing, cutting into pieces, slitting and drying to obtain the anode.
(2) Preparation of negative electrode
a. Lithium metal negative electrode: compounding metal lithium on a current collector copper foil with the thickness of about 12 mu m, and coating lithium on one side or two sides of the copper current collector, wherein the thickness of the lithium is controlled to be about 30 mu m, so as to obtain a lithium-copper composite belt; and cutting, cutting and drying to obtain the lithium metal negative electrode.
b. Silicon oxide composite graphite negative electrode: artificial graphite and SiOz (z is more than or equal to 0.5 and less than or equal to 1.5) coated with alumina are mixed according to the weight ratio of 30:70 to obtain a negative electrode active material, and then mixing the negative electrode active material, conductive carbon black, sodium carboxymethylcellulose (abbreviated as CMC), and styrene butadiene rubber (abbreviated as SBR) as a binder according to a weight ratio of 96.2:1.5:0.5:1.8 dissolving the mixture in water, fully stirring and mixing to obtain negative electrode slurry, wherein the solid content of the negative electrode slurry is about 54wt%; subsequently, the negative electrode slurry was coated on a negative electrode current collector copper foil provided with a carbon layer having a thickness of 1 μm on the surface; and drying, cold pressing, cutting, slitting and drying the copper foil to obtain the cathode.
(3) Preparation of the separator
Polyethylene (PE) having a thickness of about 15 μm was used as the separator.
(4) Preparation of electrolyte
In an argon atmosphere glove box with the water content of less than 10ppm, the substances shown in table 1 are uniformly mixed, and lithium salt LiPF6 is added to be dissolved and uniformly stirred to obtain the electrolyte. Table 1 shows the compositions of the electrolytes in each example and comparative example, in which the contents of each substance in the electrolytes were calculated based on the total weight of the electrolytes.
The fluorinated carbonate in the electrolyte is selected from compounds A, B or C,
the fluoroether in the electrolyte is selected from the group consisting of formula II-1 or II-3,
the compound shown in the formula I in the electrolyte is selected from formula I-2, formula I-5 or formula I-8,
the nitrile compound in the electrolyte is selected from the formula D or E,
the sulfur compound in the electrolyte is selected from F or G,
for comparison with I-2, I-5 and I-8, the conductive lithium salt of formula H was added as a comparison with the first compound
Table 1 shows the composition, effect of the first compound and fluoroether of the electrolytic solutions in examples and comparative examples
In the table of the present application, "/" indicates that the substance was not added, the wt% was the mass percentage calculated based on the mass of the electrolyte, and the remaining substance was the conductive lithium salt LiPF 6 。
TABLE 2 respective electrolyte composition, second Compound influence
In the tables of the present application, "/" means notThe weight percent of the material is calculated based on the mass of the electrolyte, and the rest material is conductive lithium salt LiPF 6 。
TABLE 3 differentiation of the first Compound from the related conductive lithium salt additive
In the table of the present application, "/" indicates that the substance was not added, the wt% was the mass percentage calculated based on the mass of the electrolyte, and the remaining substance was the conductive lithium salt LiPF 6 。
(5) Preparation of lithium metal battery:
in table 4, the negative electrode is a lithium metal negative electrode, and the preparation process is as follows: sequentially stacking the anode, the isolating membrane and the lithium copper composite belt cathode, and then stacking according to the requirement; and welding the tabs, placing the welded tabs into an aluminum plastic film for battery external packaging, injecting the prepared electrolyte into the dried bare cell, sequentially carrying out vacuum packaging, standing, formation (charging to 3.3V at a constant current of 0.02C and then charging to 3.6V at a constant current of 0.1C), shaping, capacity testing and other processes, and finally obtaining the soft-package laminated lithium metal battery.
(6) Preparing a silicon-oxygen compound composite carbon cathode lithium ion battery:
stacking the 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) placing the bare cell in an outer packaging foil aluminum-plastic film after welding a tab, drying, injecting the prepared electrolyte into the dried bare cell, 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 (with the thickness of 3.3mm, the width of 39mm and the length of 96 mm).
The lithium ion batteries of the examples and comparative examples of the present application were prepared according to the above-described method.
And (3) testing the performance of the lithium metal battery: (in Table 4, the negative electrode is a lithium metal negative electrode)
(1) Lithium metal battery 25 ℃ cycle performance test
And (3) placing the prepared lithium metal battery in a constant temperature box at 25 ℃, and standing for 30 minutes to keep the temperature of the lithium metal battery constant. The lithium metal battery was then charged at a constant current of 0.1C to a voltage of 4.3V, then charged at a constant voltage of 4.3V to a current of 0.05C, and then discharged at a constant current of 0.5C to a voltage of 2.8V, which was a charge-discharge cycle. And (3) taking the initial discharge capacity as a reference 100%, repeatedly carrying out a charge-discharge cycle test, stopping the charge-discharge cycle test when the discharge capacity is attenuated to 80% of the reference, and recording the number of cycles.
(2) 45 ℃ cycle performance test of lithium metal battery
And (3) placing the prepared lithium metal battery in a constant temperature box at 45 ℃, and standing for 30 minutes to keep the temperature of the lithium metal battery constant. The lithium metal battery was then constant-current charged at 0.1C to a voltage of 4.3V, then constant-voltage charged at 4.3V to a current of 0.05C, and then constant-current discharged at 0.5C to a voltage of 2.8V, which was a charge-discharge cycle. And (4) taking the volume of the first discharge as the reference 100%, repeatedly carrying out the charge-discharge cycle test, stopping the charge-discharge cycle test when the discharge capacity is attenuated to 80% of the reference, and recording the number of cycles. The cycle performance test data for each lithium metal battery is shown in table 2.
(3) High-rate (1C) discharge performance test of lithium metal battery
The lithium metal battery was charged to 4.3V at 0.1C at room temperature, then charged at 4.3V at a constant voltage to a current of 0.05C, left to stand for 5 minutes, discharged at a constant current of 0.2C to a voltage of 2.8V, and the discharge capacity was recorded with the discharge capacity of 0.2C as a reference. Test 1C capacity of discharge: the lithium metal battery was charged to 4.3V at 0.1C, then charged at constant voltage to a current of 0.05C at 4.3V, left to stand for 5 minutes, discharged at constant current of 1C to a voltage of 2.8V, and the discharge capacity was recorded. And the capacity retention was calculated as follows: capacity retention =1C discharge capacity/0.2C discharge capacity × 100%.
The cycle performance test data and the discharge performance test data of each lithium metal battery are shown in table 2.
Table 4 lithium metal batteries of examples 1 to 18 and comparative examples 1 to 6
By combining table 1 and table 2, the first compound is added in examples 1 to 5, and the first compound is not added in comparative example 1, and it can be seen by comparison that when the first compound is added to the electrolyte, the cycle performance of the lithium metal battery at 25 ℃ and 45 ℃ can be significantly improved, and the high-rate discharge can be maintained at a higher level. In contrast, the electrolyte of the lithium metal battery provided in comparative example 1, in which the first compound was not added, was insufficient in protection of the negative electrode, and the cycle performance at 25 ℃ and 45 ℃ was significantly reduced.
Examples 3 to 5 each add a different first compound, wherein the cycle performance of the lithium metal battery at 25 ℃ and 45 ℃ can be significantly improved when the metal cation M in the first compound is K + or Cs +. Comparative example 6 shows that if M is a common lithium salt, the cycle performance is not significantly improved. This is mainly because of K + 、Na + 、Cs + The alkali metal ions can form an alloying protective layer on the surface of the lithium metal, and the deposition of the lithium metal can be improved.
In comparison with the case that the first compound is added in an amount of 0.1wt% in example 1, 0.2wt% in example 2 and 0.05wt% in comparative example 3, it can be seen that when the first compound is added in an appropriate amount in example 1 and example 2, the first compound has a higher reduction potential and a lower oxidation potential, and can form an SEI film on a negative electrode of an electrochemical device, protect a lithium metal negative electrode and reduce side reactions of the negative electrode; and a CEI film can be formed on the positive electrode, so that the side reaction of the positive electrode is reduced, and the cycle performance of the lithium metal battery at 25 ℃ and 45 ℃ is improved. When the first compound is added to the electrolyte in an amount of less than 0.1%, it is insufficient to form a stable SEI film, the protection of the negative electrode is insufficient, it is difficult to suppress the occurrence of negative side reactions, and the cycle performance of the lithium metal battery at 25 ℃ and 45 ℃ is degraded.
As can be seen from table 2, the cycle performance of the lithium metal battery at 25 ℃ and 45 ℃ can be further improved, but the high rate discharge performance of the lithium metal battery is slightly reduced.
The content of cyclic fluoro carbonate in the organic solvent fluoro carbonate in comparative example 2 and comparative example 6 was gradually increased and the content of chain fluoro carbonate was gradually decreased, and it can be seen from table 2 that the cycle performance of the lithium metal battery at 25 ℃ and 45 ℃ can be further improved, but the large rate discharge performance of the lithium metal battery is slightly decreased.
As can be seen from table 2, the cycle performance of the lithium metal battery at 25 ℃ and 45 ℃ increases first and then decreases as the fluoroether content increases gradually from 5% to 50%, with respect to the electrolyte of example 6 having a fluoroether content of 17%, the electrolyte of example 9 having a fluoroether content of 25%, the electrolyte of example 10 having a fluoroether content of 30%, the electrolyte of example 11 having a fluoroether content of 50%, and the electrolyte of example 12 having a fluoroether content of only 5%. The film forming of the negative electrode can be realized by the cooperation of the appropriate amount of the fluoroether and the first compound, so that the coulomb efficiency of the electrolyte is improved, and the cycle performance of the electrolyte is improved. However, if the content of fluoroether is too much or too little, the capability of the electrolyte to dissociate lithium salt is reduced, and conductive lithium ions in the electrolyte are reduced, so that the electrolyte cannot normally conduct the lithium ions, and the cycle capability and the discharge performance of the battery are affected. Therefore, the fluorine ether is preferably contained in the electrolyte in an amount of 17 to 30% by mass.
In examples 9 and 14 to 18, the electrolyte solution contains 62% of fluoro carbonate, 25% of fluoroether and 0.2% of the first compound, but examples 14 to 18 also contain a second compound compared with example 9, and it can be seen from table 2 that the cycle performance of the lithium metal batteries of examples 14 to 18 is further improved, and the second compound is a positive electrode protection additive, so that the negative electrode and the positive electrode of the lithium metal battery are effectively protected, and the cycle stability of the battery is improved.
The electrolyte of comparative example 5 was added with the second compound in an amount of 15% without adding the first compound, and the electrolyte of example 5 was added with the first compound in an amount of 0.2% without adding the second compound; as can be seen from table 2, comparative example 5 does not protect the negative electrode of the battery with the first compound, the amount of the second compound added is too large, the stability of the second compound to the negative electrode is poor, and the cycle stability is reduced; an excessive amount of the second compound added results in an increase in battery impedance, resulting in a decrease in high-rate discharge performance.
For the mechanism, the first compound is added into the electrolyte, and the first compound can form an SEI film on the negative electrode of the electrochemical device, so that the negative electrode is protected, the negative electrode side reaction is reduced, the coulombic efficiency of the electrolyte is obviously improved, and the cycling stability of the battery is improved. Specifically, F can react on the surface of the negative electrode to form LiF, an ethylenic bond can polymerize to form a polymer, and meanwhile, alkali metal ions and lithium can form an alloy compound, so that the three synergistically act to form good SEI protected by the negative electrode. The first compound can also form a CEI film on the anode of the electrochemical device, so that the side reaction of the anode is reduced, and the cycling stability of the battery is improved.
Silicon cathode lithium ion battery performance test process (in table 5, the cathode adopts silica compound composite graphite cathode)
(1) And (3) testing the 45 ℃ cycle performance of the lithium ion battery:
and (3) placing the prepared lithium ion battery in a constant temperature box at 45 ℃, and standing for 30 minutes to keep the temperature of the lithium ion battery constant. The lithium ion battery was then charged at 0.5C constant current to a voltage of 4.25V, then charged at 4.25V at constant voltage to a current of 0.05C, and then discharged at 0.5C constant current to a voltage of 3.0V, which is a charge-discharge cycle. And (4) taking the volume of the first discharge as the reference 100%, repeatedly carrying out the charge-discharge cycle test, stopping the charge-discharge cycle test when the discharge capacity is attenuated to 80% of the reference, and recording the number of cycles. The cycle performance test data for each lithium ion cell is shown in table 3.
(2) And (3) testing the 25 ℃ cycle performance of the lithium ion battery:
and (3) placing the prepared lithium ion battery in a constant temperature box at 25 ℃, and standing for 30 minutes to keep the temperature of the lithium ion battery constant. The lithium ion battery was then charged at a constant current of 0.5C to a voltage of 4.25V, then charged at a constant voltage of 4.25V to a current of 0.05C, and then discharged at a constant current of 0.5C to a voltage of 3.0V, which is a charge-discharge cycle. And (3) taking the initial discharge capacity as a reference 100%, repeatedly carrying out a charge-discharge cycle test, stopping the charge-discharge cycle test when the discharge capacity is attenuated to 80% of the reference, and recording the number of cycles. The cycle performance test data for each lithium ion cell is shown in table 3.
Table 5 lithium ion batteries of examples 1 to 22 and comparative examples 1 to 6
By combining table 1 and table 3, the first compound is added in examples 1 to 5, and the first compound is not added in comparative example 1, and it can be seen by comparison that when the first compound is added to the electrolyte, the cycle performance of the lithium ion battery at 25 ℃ and 45 ℃ can be remarkably improved, and the high-rate discharge can be maintained at a higher level. In contrast, the first compound was not added to the electrolyte of the lithium ion battery provided in comparative example 1, the protection of the negative electrode was insufficient, and the cycle performance at 25 ℃ and 45 ℃ was significantly reduced.
Examples 3 to 5 each add a different first compound, wherein when the metal cation M in the first compound is K + or Cs +, the cycle performance of the lithium ion battery at 25 ℃ and 45 ℃ can be significantly improved. Comparative example 6 shows that if M is a normal lithium salt, the cycle performance is not significantly improved. This is mainly because of K + 、Na + 、Cs + The alkali metal ions can form an alloying protective layer on the surface of the lithium metal, and the deposition of the lithium metal can be improved.
Example 1 is added with the first compound with the content of 0.1wt%, example 2 is added with the first compound with the content of 0.2wt%, and comparative example 3 is added with the first compound with the content of 0.05wt%, and the comparison shows that the first compound with the proper amount is added in example 1 and example 2, the reduction potential of the first compound is higher, and the oxidation potential is lower, so that an SEI film can be formed on the negative electrode of an electrochemical device, the negative electrode of a lithium ion battery can be protected, and the side reaction of the negative electrode can be reduced; and a CEI film can be formed on the anode, so that the side reaction of the anode is reduced, and the cycle performance of the lithium ion battery at 25 ℃ and 45 ℃ is improved. When the first compound added to the electrolyte is less than 0.1%, a stable SEI film is not sufficiently formed, the protection of the negative electrode is insufficient, the occurrence of negative electrode side reactions is difficult to inhibit, and the cycle performance of the lithium ion battery at 25 ℃ and 45 ℃ is reduced.
It is understood that the cyclic fluorocarbonate content in the organic solvent fluorocarbonate in examples 5 to 7 gradually increases and the chain fluorocarbonate content gradually decreases, and table 3 shows that the cycle performance of the lithium ion battery at 25 ℃ and 45 ℃ can be further improved
The content of cyclic fluoro carbonate in the organic solvent fluoro carbonate in comparative example 2 and comparative example 6 is gradually increased, and the content of chain fluoro carbonate is gradually decreased, and it can be known from table 3 that the cycle performance of the lithium ion battery at 25 ℃ and 45 ℃ can be further improved.
As can be seen from table 3, the cycle performance of the lithium ion battery at 25 ℃ and 45 ℃ increases first and then decreases as the fluoroether content increases gradually from 5% to 50%, with the contents of 17% and 25% in the electrolyte of example 6, 25% and 30% in the electrolyte of example 9, 30% and 50% in the electrolyte of example 10, 50% and 5% in the electrolyte of example 11, respectively. The film forming of the negative electrode can be realized by the cooperation of the appropriate amount of the fluoroether and the first compound, so that the coulomb efficiency of the electrolyte is improved, and the cycle performance of the electrolyte is improved. However, if the content of fluoroether is too much or too little, the capability of the electrolyte to dissociate lithium salt is reduced, and conductive lithium ions in the electrolyte are reduced, so that the electrolyte cannot normally conduct the lithium ions, and the cycle capability and the discharge performance of the battery are affected. Therefore, the fluorine ether is preferably contained in the electrolyte in an amount of 17 to 30% by mass.
In examples 9 and 14 to 18, the electrolyte solution contains 62% of the fluoro-carbonate, 25% of the fluoroether and 0.2% of the first compound, but examples 14 to 18 also contain a second compound compared with example 9, and it can be seen from table 3 that the cycle performance of the lithium ion batteries of examples 14 to 18 is further improved, and the second compound is a positive electrode protection additive, so that the negative electrode and the positive electrode of the lithium ion battery are both effectively protected, and the cycle stability of the battery is improved.
The electrolyte of comparative example 5 was added with the second compound in an amount of 15% without adding the first compound, and the electrolyte of example 5 was added with the first compound in an amount of 0.2% without adding the second compound; as can be seen from table 3, in comparative example 5, the first compound does not protect the negative electrode of the battery, the second compound is added in an excessive amount, the second compound has poor stability to the negative electrode, and the cycle stability is reduced; an excessive amount of the second compound added results in an increase in battery impedance, resulting in a decrease in high-rate discharge performance.
The reason concrete analysis that the first compound and the fluoroether have synergistic effect to improve the performance is that the first compound is added into the electrolyte, and the first compound can form an SEI (solid electrolyte interface) film on the cathode of the electrochemical device, so that the cathode is protected, the side reaction of the cathode is reduced, the coulomb efficiency of the electrolyte is obviously improved, and the cycling stability of the battery is improved. Specifically, F can react on the surface of the negative electrode to form LiF, an ethylenic bond can polymerize to form a polymer, and meanwhile, alkali metal ions can form an alloy compound on the surface of the silicon, so that the three synergistically act to form good SEI (solid electrolyte interphase) protected by the negative electrode. The first compound can also form a CEI film on the anode of the electrochemical device, so that the side reaction of the anode is reduced, and the cycling stability of the battery is improved.
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.
Although the present application has been described with reference to preferred embodiments, it is not intended to limit the scope of the claims, and many possible variations and modifications may be made by one skilled in the art without departing from the spirit of the application.
Claims (9)
1. An electrolyte is characterized by comprising a first compound, a second compound and fluoroether, wherein the first compound is a compound shown as a formula I,
wherein R is 1 、R 2 、R 3 、R 4 Each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C12 alkynyl, ester group; when substituted, the substituents are selected from halogen or cyano;
m is selected from any one of Na, K or Cs;
the second compound comprises at least one of a nitrile compound or a sulfur-containing compound;
the mass percentage content of the first compound in the electrolyte is 0.1-2%;
the second compound accounts for 0.1 to 10 percent of the electrolyte by mass.
2. The electrolyte of claim 1, wherein the compound of formula I is selected from at least one of the following compounds:
3. the electrolyte of claim 1, wherein the fluoroether is a compound of formula II,
wherein R is 5 And R 6 Each independently selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C12 alkynyl, substituted or unsubstituted C6-C26 aryl, nitro, sulfonic acid group, aldehyde group, carboxyl group, and R 5 And R 6 At least one of which contains a fluoroalkyl group.
4. The electrolyte of claim 3, wherein the fluoroether comprises at least one of the following compounds:
5. the electrolyte as claimed in any one of claims 1 to 4, wherein the electrolyte satisfies at least one of the following characteristics a to c:
a. the mass percentage of the fluoroether in the electrolyte is b percent, and the value range of b is 5 to 50;
b. the mass percentage of the first compound in the electrolyte is a%, the mass percentage of the fluoroether in the electrolyte is b%, the mass ratio of the fluoroether to the first compound is b/a, and the value range of b/a is 2.5-250;
c. the electrolyte also comprises at least one of fluoroethylene carbonate, methyl trifluoroethyl carbonate, ethylene glycol dimethyl ether, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or gamma-butyrolactone.
6. The electrolyte of any one of claims 1 to 4, wherein the electrolyte satisfies:
the mass percentage of the fluoroether in the electrolyte is b%, and the value range of b is 17-30.
7. An electrochemical device, comprising:
the positive electrode comprises a positive electrode current collector and a positive electrode active material layer which is arranged on the surface of the positive electrode current collector and contains a positive electrode active material;
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;
a separator provided between the positive electrode and the negative electrode;
and an electrolyte as claimed in any one of claims 1 to 6.
8. The electrochemical device according to claim 7, wherein at least one of the following features (1) to (4) is satisfied:
(1) The positive active material comprises at least one of a lithium nickel cobalt manganese ternary material, lithium iron phosphate, lithium manganate or lithium cobaltate;
(2) The negative active material is selected from at least one of lithium metal or lithium metal alloy compound, carbon material, silicon material, or silicon oxygen material;
(3) The negative active material surface has a protective film comprising lithium fluoride; the thickness of the protective film is less than 50nm;
(4) Detecting M metal ions on the surface of the negative active material by using X-ray photoelectron spectroscopy or X-ray spectroscopy, wherein M is at least one selected from Na, K and Cs.
9. An electronic device characterized by comprising the electrochemical device according to claim 7 or 8.
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| CN107431245A (en) * | 2015-02-04 | 2017-12-01 | 斯泰拉化工公司 | Non-aqueous electrolyte for secondary battery and the secondary cell for possessing it |
| CN110233289A (en) * | 2019-04-04 | 2019-09-13 | 李秀艳 | A kind of high voltage additive and electrolyte and battery containing the additive |
| CN112151865A (en) * | 2020-10-19 | 2020-12-29 | 珠海冠宇电池股份有限公司 | Electrolyte for lithium ion battery and lithium ion battery comprising same |
| CN112186190A (en) * | 2020-10-09 | 2021-01-05 | 西安科技大学 | High-voltage lithium ion battery |
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| JP6772834B2 (en) * | 2014-09-30 | 2020-10-21 | 三菱ケミカル株式会社 | Non-aqueous electrolyte solution and non-aqueous electrolyte solution secondary battery using it |
| CN105742713B (en) * | 2014-12-12 | 2020-08-28 | 东莞新能源科技有限公司 | All-solid-state polymer lithium battery |
| JP2017117686A (en) * | 2015-12-25 | 2017-06-29 | 株式会社日立製作所 | Lithium ion secondary battery |
| JP2022516205A (en) * | 2018-12-14 | 2022-02-24 | キューバーグ、インク． | System for ionic liquid-based electrolytes for high energy batteries |
| CN111916815B (en) * | 2019-05-08 | 2022-01-07 | 宁德时代新能源科技股份有限公司 | Lithium metal battery |
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| CN107431245A (en) * | 2015-02-04 | 2017-12-01 | 斯泰拉化工公司 | Non-aqueous electrolyte for secondary battery and the secondary cell for possessing it |
| CN110233289A (en) * | 2019-04-04 | 2019-09-13 | 李秀艳 | A kind of high voltage additive and electrolyte and battery containing the additive |
| CN112186190A (en) * | 2020-10-09 | 2021-01-05 | 西安科技大学 | High-voltage lithium ion battery |
| CN112151865A (en) * | 2020-10-19 | 2020-12-29 | 珠海冠宇电池股份有限公司 | Electrolyte for lithium ion battery and lithium ion battery comprising same |
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