CN110854433A - Electrolyte and electrochemical device - Google Patents
Electrolyte and electrochemical device Download PDFInfo
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- CN110854433A CN110854433A CN201911122010.1A CN201911122010A CN110854433A CN 110854433 A CN110854433 A CN 110854433A CN 201911122010 A CN201911122010 A CN 201911122010A CN 110854433 A CN110854433 A CN 110854433A
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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
- H01M10/05—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
- 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
An electrolyte and an electrochemical device are disclosed. The electrolyte of the present application includes an organic solvent, a lithium salt, and an additive, wherein the additive includes a cyclic sulfate, lithium difluorooxalato borate, and a fluorosilane. The low-temperature direct-current impedance, the low-temperature discharge performance and the battery core low-temperature charging lithium precipitation window of the battery can be effectively improved through the synergistic effect of the additive cyclic sulfate, the lithium difluoro-oxalato-borate and the fluoro-silane, and therefore the low-temperature electrochemical performance of the electrochemical device is improved.
Description
Technical Field
The application relates to the technical field of energy storage, in particular to electrolyte and an electrochemical device.
Background
Compared with the traditional lead-acid battery, the lithium ion battery has the advantages of small volume, light weight, high specific energy, long cycle life and the like, and plays an increasingly important role in the production and life processes of human beings. However, in regions with higher latitude or altitude, the temperature is lower in winter, the lithium battery works in the environment, the viscosity of the electrolyte is increased, the ion mobility is reduced, the internal resistance of the battery is increased rapidly, the window for lithium precipitation during battery charging is reduced, the lithium precipitation can be caused by a slightly large charging current, the precipitated lithium metal forms lithium dendrites which can pierce through the diaphragm to influence the safety performance of the battery core, and meanwhile, the low temperature can cause the problems of battery discharge capacity attenuation and the like, thereby seriously restricting the application of the lithium ion battery.
Disclosure of Invention
In order to solve the above technical problem, embodiments of the present application provide an electrolyte and an electrochemical device. The electrolyte provided by the embodiment of the application has good cycle performance, lower internal resistance at low temperature, excellent low-temperature discharge performance and wider low-temperature charging lithium precipitation window, and improves the electrochemical performance of an electrochemical device at low temperature.
In one embodiment, the present application provides an electrolyte comprising an organic solvent, a lithium salt, and an additive, wherein the additive comprises a cyclic sulfate, lithium difluorooxalato borate, and a fluorosilane.
According to the embodiment of the application, the cyclic sulfate is selected from at least one of the compounds with the structural formula I,
wherein R is selected from C2-3Straight-chain alkylene, C substituted by substituent A2-3Straight chain alkylene group, C2-3Straight-chain alkenylene and C substituted by substituent A2-3One of linear alkenylene;
the substituent A is at least one selected from halogen atoms, alkoxy, carboxyl, sulfonic acid groups, alkyl groups with 1-20 carbon atoms, halogenated alkyl groups with 1-20 carbon atoms, unsaturated hydrocarbon groups with 2-20 carbon atoms and halogenated unsaturated hydrocarbon groups with 2-20 carbon atoms.
According to embodiments herein, the cyclic sulfate is selected from at least one of the following compounds:
according to the embodiments herein, the fluorosilane of the present application is selected from at least one compound of formula II,
wherein R is1、R2、R3、R4Each independently selected from hydrogen, halogen, C1-10Alkyl, C substituted by substituent B1-10Alkyl radical, C1-10Alkoxy, C substituted by substituent B1-10Alkoxy radical, C2-10Alkenyl, C substituted by substituent B2-10Alkenyl radical, C2-10Alkynyl, C substituted by substituent B2-10One of alkynyl and silicon-containing group; and R is1、R2、R3、R4At least one of which is a fluorine atom substituent;
wherein the substituent B is at least one selected from the group consisting of halogen, alkoxy, carboxyl, sulfonic acid group, alkyl group having 1 to 20 carbon atoms, haloalkyl group having 1 to 20 carbon atoms, unsaturated hydrocarbon group having 2 to 20 carbon atoms and halogenated unsaturated hydrocarbon group having 2 to 20 carbon atoms.
According to embodiments herein, the fluorosilane of the present application is selected from at least one of the following compounds:
according to the embodiment of the application, the mass percentage of the lithium difluoro (oxalato) borate in the electrolyte is 0.1-3.0%;
according to the embodiment of the application, the mass percentage of the lithium difluoro (oxalato) borate in the electrolyte is 0.1-2.0%.
According to the embodiment of the application, the content of the cyclic sulfate in the electrolyte is 0.1-4.0% by mass;
according to the embodiment of the application, the content of the cyclic sulfate in the electrolyte is 0.5-3.0% by mass.
According to the embodiment of the application, the mass percentage of the fluoro silane in the electrolyte is 0.1-4.0%;
according to the embodiment of the application, the mass percentage of the fluorosilane in the electrolyte is 0.3% -2.0%.
According to embodiments herein, the additive further comprises at least one of vinylene carbonate, 1, 3-propane sultone, 1-propene-1, 3-sultone, methylene methanedisulfonate, ethylene carbonate, tris (trimethylsilyl) phosphate, tris (trimethylsilyl) phosphite, adiponitrile, and fumaronitrile.
According to an embodiment of the present application, the additive further comprises a lithium salt additive, wherein the lithium salt additive comprises at least one of lithium tetrafluoroborate, lithium difluorophosphate, and lithium bis-fluorosulfonylimide.
According to the embodiment of the application, the content of the lithium salt additive in the electrolyte is less than 3% by mass.
The invention also provides an electrochemical device which comprises a positive plate, a negative plate, a diaphragm and any one of the electrolytes.
According to the invention, the additives of cyclic sulfate, lithium difluoro-oxalato-borate and fluoro-silane are added into the electrolyte, so that the low-temperature direct-current impedance, the low-temperature discharge performance and the low-temperature charging lithium precipitation window of the battery can be effectively improved.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the technical solutions of the present application will be described clearly and completely in conjunction with the embodiments of the present application. It should be apparent that the described embodiments are only some of the embodiments of the present application, not all of the embodiments, and the embodiments of the present application should not be construed as limiting the present application. All other embodiments obtained by those skilled in the art without any creative effort based on the technical solutions and the given embodiments provided in the present application belong to the protection scope of the present application.
The following terms used herein have the meanings indicated below, unless explicitly indicated otherwise.
The term "about" is used to describe and illustrate minor variations. When used in conjunction with an event or circumstance, the terms can refer to instances where the event or circumstance occurs precisely as well as instances where the event or circumstance occurs in close proximity. For example, when used in connection with data, the terms may refer to a range of variation of less than or equal to ± 10% of the stated value, such as less than or equal to ± 5%, less than or equal to ± 4%, less than or equal to ± 3%, less than or equal to ± 2%, less than or equal to ± 1%, less than or equal to ± 0.5%, less than or equal to ± 0.1%, or less than or equal to ± 0.05%. 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 ranges encompassed within that range as if each numerical value and subrange is explicitly recited.
The term "halogen" encompasses fluorine (F), chlorine (Cl), bromine (Br), iodine (I).
The term "hydrocarbyl" encompasses alkyl, alkenyl, alkynyl.
The term "alkyl" is intended to be a straight chain saturated hydrocarbon structure having from 1 to 20 carbon atoms. "alkyl" is also contemplated to be a branched or cyclic hydrocarbon structure having from 3 to 20 carbon atoms. 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-ethyl, hexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornyl, and the like. In addition, the alkyl group may be optionally substituted.
The term "alkenyl" refers to a monovalent unsaturated hydrocarbon that may be branched or branched and has at least one and typically 1,2, or 3 carbon-carbon double bondsA group. Unless otherwise defined, the alkenyl groups typically contain 2 to 20 carbon atoms and include, for example, -C2-4Alkynyl, -C3-6Alkynyl and-C3-10Alkynyl. Representative alkynyl groups include, for example, ethynyl, prop-2-ynyl (n-propynyl), n-but-2-ynyl, n-hex-3-ynyl, and the like.
The term "alkylene" means a divalent saturated hydrocarbon group that may be straight-chain or branched. Unless otherwise defined, the alkylene groups typically contain 2 to 10 carbon atoms and include, for example, -C2-3Alkylene and-C2-6An alkylene group. Representative alkylene groups include, for example, methylene, ethane-1, 2-diyl ("ethylene"), propane-1, 2-diyl, butane-1, 4-diyl, pentane-1, 5-diyl, and the like.
The term "alkenylene" is a straight-chain or branched alkenylene group, and the number of double bonds in the alkenyl group is preferably 1. Examples of alkenylene groups include: vinylidene, allylidene, isopropenylidene, alkenylidene butyl, alkenylidene pentyl.
The term "aryl" means a monovalent aromatic hydrocarbon having a single ring (e.g., phenyl) or a fused ring. Fused ring systems include those that are fully unsaturated (e.g., naphthalene) as well as those that are partially unsaturated (e.g., 1,2,3, 4-tetrahydronaphthalene). Unless otherwise defined, the aryl group typically contains 6 to 26 carbon ring atoms and includes, for example, -C6-10And (4) an aryl group. Representative aryl groups include, for example, phenyl, methylphenyl, propylphenyl, isopropylphenyl, benzyl, and naphthalen-1-yl, naphthalen-2-yl, and the like.
In the detailed description and claims, a list of items joined by the term "at least one of may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means a only; only B; or A and B. In another example two, if items A, B and C are listed, the phrase "at least one of A, B and C" means only a; only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.
As used herein, the relative amounts of the components are based on the total mass of the electrolyte.
The application relates to an electrolyte comprising an organic solvent, a lithium salt and an additive, the additive comprising a cyclic sulfate, lithium difluorooxalato borate and a fluorosilane. Because the cyclic sulfate and the lithium difluoro oxalato borate are used together, an SEI (Solid Electrolyte Interface) which is more rich in organic components can be formed after the battery cell is formed, the permeability of lithium ions on the Interface of a pole piece and an Electrolyte is increased, and the Interface impedance of the battery cell is reduced. The fluorosilane does not participate in the formation of an SEI film, the low-temperature conductivity of electrolyte in the battery cell can be improved, and the conduction of lithium ions between a positive electrode and a negative electrode is improved through the synergistic effect of the cyclic sulfate, the lithium difluoro oxalate borate and the fluorosilane, so that the low-temperature Direct Current Resistance (DCR) of the battery cell is reduced, the low-temperature charging lithium precipitation window and the low-temperature discharging performance of the battery cell are improved, and the cycle performance is improved.
In some embodiments, the lithium difluorooxalato borate is present in the electrolyte in an amount of about 0.1% to about 3.0% by weight. When the content of the lithium difluoro (oxalato) borate is lower than 0.1%, the film forming capability is insufficient, so that the improvement on the performance of the battery cell is limited; when the content of lithium difluoroborate is more than 3%, the permeability of lithium ions is reduced and the impedance is increased due to too thick film formation. When the content of the lithium difluoro (oxalato) borate is in the range of about 0.1-3.0%, the lithium difluoro (oxalato) borate and cyclic sulfate can form a compact SEI film rich in organic components in the battery cell formation stage, so that the side reaction of a pole piece and electrolyte is inhibited, the gas generation is improved, and the impedance performance and the cycle performance of the battery cell are improved.
In some embodiments, the lithium difluorooxalato borate is present in the electrolyte in an amount of about 0.1% to about 2.0% by weight.
In some embodiments, the cyclic sulfate herein is selected from at least one compound of formula I,
wherein R is selected from C2-3Straight-chain alkylene, C substituted by substituent A2-3Straight chain alkylene group, C2-3Straight-chain alkenylene and C substituted by substituent A2-3One of linear alkenylene;
wherein the substituent A is at least one selected from the group consisting of a halogen atom, an alkoxy group, a carboxyl group, a sulfonic acid group, an alkyl group having 1 to 20 carbon atoms, a halogenated alkyl group having 1 to 20 carbon atoms, an unsaturated hydrocarbon group having 2 to 20 carbon atoms and a halogenated unsaturated hydrocarbon group having 2 to 20 carbon atoms.
In some embodiments the cyclic sulfate of the present application is selected from at least one of the following compounds:
in some embodiments, the cyclic sulfate is present in the electrolyte in an amount of about 0.1% to about 4.0% by weight.
In some embodiments, the content of the cyclic sulfate in the electrolyte is about 0.5% to 3.0% by mass, which is probably due to insufficient film forming ability when the content of the cyclic sulfate is less than 0.5%, resulting in limited improvement in cell performance, and when the content of the cyclic sulfate is more than 3.0%, too thick film formation results in decreased permeability of lithium ions and increased impedance.
In some embodiments the fluorosilane of the present application is selected from at least one compound of formula II,
wherein R is1、R2、R3、R4Each independently selected from hydrogen, halogen, C1-10Alkyl, C substituted by substituent B1-10Alkyl radical, C1-10Alkoxy, C substituted by substituent B1-10Alkoxy radical, C2-10Alkenyl, C substituted by substituent B2-10Alkenyl radical, C2-10Alkynyl, C substituted by substituent B2-10Alkynyl radicalAnd a silicon-containing group; and R is1、R2、R3、R4At least one of which is a fluorine atom substituent;
wherein the substituent B is at least one selected from the group consisting of a halogen, an alkoxy group, a carboxyl group, a sulfonic acid group, an alkyl group having 1 to 20 carbon atoms, a halogenated alkyl group having 1 to 20 carbon atoms, an unsaturated hydrocarbon group having 2 to 20 carbon atoms and a halogenated unsaturated hydrocarbon group having 2 to 20 carbon atoms.
In some embodiments, the fluorosilanes of the present application are selected from at least one of the following compounds:
in some embodiments, the fluorosilane of the present application is present in the electrolyte in an amount of about 0.1% to about 4.0% by weight.
In some embodiments, the fluorosilane is present in an amount of about 0.3% to about 2.0% by weight. When the content of the fluoro-silane is less than 0.3%, the influence of the fluoro-silane on the low-temperature conductivity of the electrolyte is not obvious, and when the content of the fluoro-silane in percentage by mass is more than 2.0%, the boiling point of the fluoro-silane is generally low, so that the vapor pressure of the electrolyte is too high in the use process of the battery, and the safety problem is easily caused.
In some embodiments the additive of the present application further comprises at least one of Vinylene Carbonate (VC), 1, 3-Propane Sultone (PS), 1-propene-1, 3-sultone (PST), Methylene Methanedisulfonate (MMDS), ethylene carbonate (VEC), tris (trimethylsilyl) phosphate (TMSP), and tris (trimethylsilyl) phosphite additives. The addition of the additive can further optimize the characteristics of the electrode-electrolyte interfacial film, thereby improving the performance of the battery cell.
In some embodiments, the additive further comprises a lithium salt additive, wherein the lithium salt additive comprises at least one of lithium tetrafluoroborate, lithium difluorophosphate, and lithium bis-fluorosulfonylimide. Furthermore, the lithium salt additive in the electrolyte solution has a mass percentage of less than 3.0%. The introduction of the lithium salt additive can further optimize the characteristics of an electrode-electrolyte interfacial film, thereby improving the performance of a battery cell.
In some embodiments the organic solvent herein may be selected from at least one of cyclic carbonates and chain carbonates. The cyclic carbonate comprises at least one of ethylene carbonate, fluoroethylene carbonate and propylene carbonate, and the chain ethylene carbonate comprises at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and dipropyl carbonate. The organic solvent herein may also be selected from other solvents, and the present application is not particularly limited.
In some embodiments, the lithium salt herein is selected from at least one of organic lithium salts and inorganic lithium salts. Further, the lithium salt herein may contain at least one of fluorine, boron and phosphorus. Further, the lithium salt herein may be selected from lithium hexafluorophosphate (LiPF)6) Lithium tetrafluoroborate (LiBF)4) Lithium bis (oxalato) borate (LiBOB), lithium hexafluoroarsenate (LiAsF)6) Lithium difluorophosphate (LiPO)2F2) Lithium bis (trifluoromethylsulfonyl) imide (LiN (CF)3SO2)2) Lithium trifluoromethanesulfonate (LiCF)3SO3) Lithium perchlorate (LiClO)4) At least one of (1).
The application also relates to an electrochemical device which comprises a positive plate, a negative plate and any electrolyte. The electrochemical device of the present application includes any device in which electrochemical reactions occur, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, and capacitors. In particular, the electrochemical device includes a lithium secondary battery, and specifically, it includes a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery. In the following specific embodiments of the present application, only an embodiment of a lithium ion battery is shown, but the present application is not limited thereto.
The application also provides a lithium ion battery, which comprises a positive plate, a negative plate, a diaphragm arranged between the positive plate and the negative plate at intervals, electrolyte and packaging foil; the positive plate comprises a positive current collector and a positive diaphragm coated on the positive current collector, and the negative plate comprises a negative current collector and a negative diaphragm coated on the negative current collector; the electrolyte is any one of the above electrolytes.
The positive electrode membrane of the present application includes a positive electrode active material, a binder, and a conductive agent in some embodiments. Furthermore, the positive active material is selected from at least one of lithium cobaltate, lithium nickel manganese cobalt ternary material, lithium iron phosphate and lithium manganate.
In some embodiments, the negative electrode membrane of the present application includes a negative electrode active material, a binder, and a conductive agent. Further, the negative active material of the present application may be selected from any one of graphite, silicon, or a silicon-carbon composite. The silicon-carbon composite material is a negative electrode active material obtained by doping silicon and carbon in any proportion.
The technical solution of the present application is exemplarily described below by specific embodiments:
preparing an electrolyte: in an argon atmosphere glove box (H)2O<0.1ppm,O2<0.1ppm), mixing ethylene carbonate (abbreviated as EC), diethyl carbonate (DEC) and Ethyl Methyl Carbonate (EMC) uniformly according to the mass ratio of 40:30:30 to obtain a non-aqueous solvent, and drying the lithium salt LiPF sufficiently6Dissolving in the non-aqueous solvent to prepare LiPF6And the concentration of the basic electrolyte is 1.3 mol/L.
Cyclic sulfate ester, lithium difluoroborate and fluorosilane were added to the base electrolyte as shown in table 1.
Examples of cyclic sulfates are: ethylene glycol episulfide (S), 1, 2-propylene glycol episulfide (S1), 2, 3-butylene glycol episulfide (S2), 1-fluoroethylene glycol episulfide (S3), 1-trifluoromethylethylene glycol episulfide (S4), 1, 3-propylene glycol episulfide (S5), 2-methyl-1, 3-propylene glycol episulfide (S6), 2-fluoro-1, 3-propylene glycol episulfide (S7).
Examples of fluorosilanes are: trimethylfluorosilane (F), triethylfluorosilane (F1), dimethylethylfluorosilane (F2), trimethylsilyl-dimethylfluorosilane (F3), trimethoxyfluorosilane (F4), dimethyldifluorosilane (F5), methyltrifluorosilane (F6), ethyltrifluorosilane (F7).
TABLE 1 electrolyte additives and addition amounts for examples 1-32 and comparative examples 1-7
Preparing a lithium ion battery:
1) preparing a positive plate: mixing lithium nickel cobalt manganese (LiNi) as positive electrode active material0.8Co0.1Mn0.1O2) The conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in a proper amount of N-methyl pyrrolidone (NMP) solvent according to the weight ratio of 97:2:1 to form uniform anode slurry; and coating the slurry on an aluminum foil of a positive current collector, and drying, rolling and cutting into pieces to obtain the positive plate.
2) Preparing a negative plate: fully stirring and mixing a negative active material graphite, a conductive agent acetylene black and a binder Styrene Butadiene Rubber (SBR) in a proper amount of deionized water solvent according to a weight ratio of 96:1:3 to form uniform negative slurry; and coating the slurry on a copper foil of a negative current collector, and drying, rolling and cutting into pieces to obtain the negative plate.
3) Preparing a lithium ion battery: stacking the positive plate, the diaphragm and the negative plate in sequence to enable the isolating film to be positioned between the positive plate and the negative plate to play an isolating role, and then winding, hot-pressing and shaping, and welding tabs to obtain a bare cell; and placing the bare cell in an outer packaging foil, injecting the prepared electrolyte into the dried battery, and performing vacuum packaging, standing, formation, shaping and other processes to complete the preparation of the lithium ion battery.
The electrolytes and lithium ion batteries of examples 1 to 32 and comparative examples 1 to 7 were prepared according to the above preparation methods; the additives in the electrolyte and the respective amounts added are shown in table 1.
The lithium ion batteries of the comparative examples and examples of the present application were tested for performance by experiment as follows.
Test first, cycle experiment
The lithium ion batteries obtained by the preparation were subjected to the following tests, respectively:
and (2) carrying out charge-discharge cycle test in a voltage range of 2.8-4.3V at the condition of 25 ℃ by using the charge-discharge rate of 1C/1C, respectively recording the first charge-discharge capacity of the battery and the discharge capacity after each cycle, cycling 500 times, and calculating the capacity retention rate of each lithium battery, wherein the capacity retention rate is the discharge capacity per cycle/the first discharge capacity of the battery and is 100%. The electrolyte selected for each lithium ion battery and the data of the capacity retention rate after 500 cycles are shown in table 2.
TABLE 2 Capacity Retention rates for lithium ion batteries of examples 1-32 and comparative examples 1-7
Test two, low temperature DCR test
The lithium ion batteries obtained by the preparation were subjected to the following tests, respectively:
charging to 4.3V at constant current and constant voltage of 1C, stopping current at 0.05C, discharging at 1C for 30min, adjusting to 50% SOC, standing at-20 deg.C for 2h, executing pulse program, discharging at constant current of 0.3C for 10s, standing for 1min, charging at constant current of 0.3C for 10s, and standing for 5min to complete the test. DCR (voltage before pulse discharge-voltage after pulse discharge)/discharge current 100%, the reported results are shown in table 3.
TABLE 3 Low temperature DCR for lithium ion batteries of examples 1-32 and comparative examples 1-7
| Group of | -20℃DCR(mΩ) |
| Example 1 | 280.1 |
| Example 2 | 267.4 |
| Example 3 | 251.2 |
| Example 4 | 238.5 |
| Example 5 | 279.8 |
| Example 6 | 309.2 |
| Example 7 | 271.4 |
| Example 8 | 260.6 |
| Example 9 | 246.1 |
| Example 10 | 249.1 |
| Example 11 | 262.7 |
| Example 12 | 296.0 |
| Example 13 | 257.8 |
| Example 14 | 243.6 |
| Example 15 | 231.7 |
| Example 16 | 219.9 |
| Example 17 | 208.2 |
| Example 18 | 204.1 |
| Example 19 | 267.7 |
| Example 20 | 256.9 |
| Example 21 | 272.1 |
| Example 22 | 258.3 |
| Example 23 | 264.1 |
| Example 24 | 259.1 |
| Example 25 | 252.9 |
| Example 26 | 245.6 |
| Example 27 | 241.9 |
| Example 28 | 246.2 |
| Example 29 | 251.9 |
| Example 30 | 245.3 |
| Example 31 | 241.0 |
| Example 32 | 244.9 |
| Comparative example 1 | 359.7 |
| Comparative example 2 | 298.1 |
| Comparative example 3 | 321.3 |
| Comparative example 4 | 329.8 |
| Comparative example 5 | 278.2 |
| Comparative example 6 | 271.9 |
| Comparative example 7 | 306.1 |
Experiment three, low temperature discharge capacity test
The lithium ion batteries obtained by the preparation were subjected to the following tests, respectively:
charging to 4.3V at constant current and constant voltage of 1C, stopping current at 0.05C, standing for 5min, discharging the cell 1C to 3.0V, standing for 5min, and recording the discharge capacity as C0(ii) a Charging the battery cell to 4.3V at a constant current and a constant voltage of 1C, stopping the current to 0.05C, and standing for 5 min; placing the cell in a-20 ℃ incubator, standing for 120min (ensuring that the cell temperature reaches-20 ℃); then discharging the battery cell 1C to 3.0V, standing for 5min, and recording the discharge capacity as C1(ii) a Capacity retention rate ═ C1/C0100%, the results are reported in table 4.
TABLE 4 Low temperature discharge Capacity of lithium ion batteries of examples 1-32 and comparative examples 1-7
Experiment four, low temperature lithium extraction test
The lithium ion batteries obtained by the preparation were subjected to the following tests, respectively:
① discharging at 1C to 3.0V, standing for 5 min;
② standing the battery cell at-10 deg.C for 120min, charging to 4.3V at constant current and constant voltage of k C with cutoff current of 0.05C, standing for 5min, discharging to 3.0V at 1C, and standing for 5 min;
③ repeat step ②, loop 5 times;
④ charging to 4.3V with constant current and voltage of k C and cutoff current of 0.05C, standing for 5min, standing for 2h at 25 deg.C, charging to 4.3V with constant current and voltage of 1C and cutoff current of 0.05C;
wherein k is 0.25, 0.45, 0.65, 0.85;
⑤, the cell is disassembled in a drying room (dew point is lower than-35 ℃) with lower water content in the air, the obtained negative plate is photographed, the area of the lithium precipitation part is recorded, and the test is completed.
The percentage of area of lithium extracted is 100% of the area of the lithium extracted portion/the total area of the negative plate, and the recorded results are shown in table 5.
TABLE 5 area ratios of low-temperature lithium deposition for lithium ion batteries of examples 1 to 32 and comparative examples 1 to 7
Experiment five, high temperature storage thickness expansion rate test
The lithium ion batteries obtained by the preparation were subjected to the following tests, respectively:
respectively taking 5 branches, charging to 4.3V at constant current with 1C rate at normal temperature, further charging to current lower than 0.05C at constant voltage of 4.3V, and making it in 4.3V full charge state. The fully charged cell thickness before storage was measured and recorded as D0(ii) a Then the fully charged battery is placed in an oven at 85 ℃, after 3 days, the battery is taken out, the thickness after storage is immediately tested and recorded as D1(ii) a According to the formula ∈ ═ D1-D0)/D0X 100% the thickness expansion before and after storage of the cell was calculated and the average of 5 sets of experimental data was taken and recorded as epsilon and the results are shown in table 6.
TABLE 6 lithium ion batteries of examples 1-32 and comparative examples 1-7 having high temperature storage thickness expansion rates
The following conclusions can be drawn in conjunction with the data in tables 1-6:
1) from the experimental results of comparative example 1 and comparative example 2, it can be seen that only adding ethylene glycol cyclic sulfate can improve the cycle performance of the battery cell, reduce the gas generation of the battery cell, improve the low-temperature impedance of the battery cell, improve the low-temperature discharge performance of the battery cell and the low-temperature charging lithium precipitation window, because it can form an SEI film on the surface of the electrode, which can inhibit the side reaction of the electrode-electrolyte and is beneficial to the permeation of lithium ions, improve the cycle performance of the battery cell, and inhibit the gas generation of the battery cell. From examples 1 to 6, it can be seen that when the mass percentage content is less than 2%, the improvement of each performance of the battery cell is positively correlated with the increase of the content thereof as the concentration thereof increases, and when the mass percentage content is more than 2%, the content continues to increase and even causes the deterioration of the performance of the battery cell. This is because when the concentration is low, the film forming ability is insufficient, resulting in limited improvement of the cell performance, and with the increase of the concentration, an SEI film more favorable for permeation of lithium ions and inhibition of electrode-electrolyte side reactions is formed, enhancing the cell cycle improvement effect, and when the content is higher than 2.0%, the film forming is too thick, resulting in decrease of the lithium ion permeability, increase of impedance, and deterioration of the cycle performance. In combination with the above, the ethylene glycol episulfide is contained in an amount of 0.1 to 4.0% by mass, and preferably 0.5 to 3.0% by mass.
2) From comparative examples 1 and 3, it can be seen that the cycle performance of the battery cell can be slightly improved by only adding lithium difluorooxalato borate, but the improvement on other performances of the battery cell is limited, which indicates that the side reaction of the pole piece and the electrolyte solvent cannot be effectively inhibited by only relying on lithium difluorooxalato borate to form the film. From comparative example 5, it can be seen that when lithium difluorooxalato borate is used in combination with ethylene glycol cyclic sulfate, the cycle performance of the cell, low temperature DCR, low temperature discharge capacity and low temperature charging lithium deposition window can be further improved, but the gas generation performance is not greatly affected, compared with the case where only ethylene glycol cyclic sulfate is added. The reason is that the ethylene glycol episulfide can form a film together with the lithium difluorooxalato borate, and compared with the SEI film which is only added with the ethylene glycol episulfide, the content of organic components is higher, the SEI film which is more beneficial to lithium ion permeability is formed, and the performance of the battery cell is improved, but the formed SEI film has the same degree of compactness as the SEI film which is only added with the ethylene glycol episulfide, so that the gas production performance of the battery cell cannot be further improved. From comparative examples 2 and 3, and examples 4 and 7 to 12, it can be seen that in the presence of ethylene glycol cyclic sulfate, when the concentration of lithium difluoroborate is low, the effect of improving the cycle performance of the battery cell increases with the increase of the concentration, and when the concentration is further increased, the low-temperature resistance of the battery cell increases, and the cycle performance is reduced. The reason is that when the concentration of lithium difluorooxalato borate is low, the film forming capability is insufficient, so that the improvement on the performance of the battery cell is limited, an SEI film which is more beneficial to the permeation of lithium ions and the inhibition of electrode-electrolyte side reactions is formed along with the increase of the concentration of lithium difluorooxalato borate, the cycle improvement effect on the battery cell is enhanced, and when the content is too high, the film forming thickness causes the permeability of lithium ions to be reduced, the impedance is increased, and the cycle performance is reduced, and in combination with the above situation, the preferable mass percentage content of lithium difluorooxalato borate is 0.1-2.0%.
3) It can be seen from comparative examples 1 and 4 that the single trimethyl fluorosilane does not affect the cycle performance of the cell, and the low-temperature performance of the battery is improved to a certain extent. It can be seen from comparative examples 2 and 6 that trimethylfluorosilane can further improve the low-temperature performance of the cell on the basis of ethylene glycol episulfide. It can be seen from examples 4 and 13 to 18 that the low-temperature performance of the battery can be further improved along with the increase of the content of the trimethyl fluorosilane, and the influence on the cycle performance is not large. However, when the content of the trimethyl fluorosilane is higher than 1%, gas generation of the battery cell is aggravated as the content is further increased, because when the concentration of the trimethyl fluorosilane is lower, the trimethyl fluorosilane can be dissolved in the electrolyte, and when the concentration is too high, the trimethyl fluorosilane with the boiling point of only 16 ℃ can volatilize from the electrolyte, so that the gas generation is increased, and the concentration is too high, which is easy to bring about safety hazards, and in summary, the preferable mass percentage content of the trimethyl fluorosilane is 0.3% -2.0%.
4) From comparative examples 1 to 7 and example 4, it can be seen that the combined use of ethylene glycol cyclic sulfate, lithium difluoroborate and trimethylfluorosilane can better improve the cell gassing, cycling, low temperature impedance, low temperature discharge and low temperature charge lithium precipitation windows, because the ethylene glycol cyclic sulfate forms a film on the electrode surface, when the combined use with lithium difluoroborate, an SEI film is formed, which has higher organic component content compared with the case of only adding ethylene glycol cyclic sulfate, is more beneficial to lithium ion permeation, increases the permeability of lithium ions at the interface of the electrode and the electrolyte, and the trimethylfluorosilane can improve the low temperature conductivity of the electrolyte though not participating in the formation of the electrode surface SEI film. The conduction of lithium ions between the positive electrode and the negative electrode is improved through the synergistic effect of the ethylene glycol episulfide, the lithium difluoro-oxalato-borate and the trimethyl fluorosilane, so that the low-temperature impedance of the battery cell, the low-temperature charging lithium precipitation window and the low-temperature discharge performance are obviously improved, and the battery has better cycle performance.
5) From comparative example 7, example 4 and examples 19 to 24, it can be seen that the cyclic sulfate can improve gas generation, cycle and low-temperature performance of the battery cell to some extent, because the compound having the cyclic sulfate structure can form a film on the surface of the electrode, and an SEI film which is beneficial to permeation of lithium ions and can inhibit side reactions of the electrode-electrolyte is formed, so that the performance of the battery cell is improved.
6) From comparative example 5, example 4 and examples 25 to 31, it can be seen that, compared with other types of fluoro silanes, the methyl trifluoro silane and the ethyl trifluoro silane in the fluoro silane can accelerate the gas generation of the battery cell, and the other silanes have little influence on the gas generation performance of the battery cell, because the methyl trifluoro silane and the ethyl trifluoro silane have lower boiling points and are more easily volatilized from the electrolyte, so that the gas generation amount is increased. The fluorosilane has no obvious influence on the cycle performance of the battery cell, and can improve the low-temperature DCR (direct current resistance), the low-temperature discharge performance and the low-temperature charging lithium precipitation window of the battery cell to a certain extent, because the fluorosilane structure can have a certain action with lithium ions, the low-temperature conductivity of the electrolyte is reduced, and the low-temperature performance of the battery cell is improved.
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 (12)
1. An electrolyte comprising an organic solvent, a lithium salt and an additive, wherein the additive comprises a cyclic sulfate, lithium difluorooxalato borate and a fluorosilane.
2. The electrolyte of claim 1, wherein the cyclic sulfate is selected from at least one of the compounds of formula I,
wherein R is selected from C2-3Straight-chain alkylene, C substituted by substituent A2-3Straight chain alkylene group, C2-3Straight-chain alkenylene and C substituted by substituent A2-3One of linear alkenylene;
the substituent A is at least one selected from halogen atoms, alkoxy, carboxyl, sulfonic acid groups, alkyl groups with 1-20 carbon atoms, halogenated alkyl groups with 1-20 carbon atoms, unsaturated hydrocarbon groups with 2-20 carbon atoms and halogenated unsaturated hydrocarbon groups with 2-20 carbon atoms.
3. The electrolyte of claim 3, wherein the cyclic sulfate is selected from at least one of the following compounds:
4. the secondary battery electrolyte as claimed in claim 1, wherein the fluorosilane is at least one selected from the group consisting of compounds represented by the formula II,
wherein R is1、R2、R3、R4Each independently selected from hydrogen, halogen, C1-10Alkyl, C substituted by substituent B1-10Alkyl radical, C1-10Alkoxy, C substituted by substituent B1-10Alkoxy radical, C2-10Alkenyl, C substituted by substituent B2-10Alkenyl radical, C2-10Alkynyl, C substituted by substituent B2-10One of alkynyl and silicon-containing group; and R is1、R2、R3、R4At least one of which is a fluorine atom substituent;
the substituent B is at least one selected from halogen, alkoxy, carboxyl, sulfonic group, alkyl with 1-20 carbon atoms, halogenated alkyl with 1-20 carbon atoms, unsaturated hydrocarbon with 2-20 carbon atoms and halogenated unsaturated hydrocarbon with 2-20 carbon atoms.
5. The electrolyte of claim 4, wherein the fluoro silane is selected from at least one of the following compounds:
6. the electrolyte solution of claim 1, wherein the lithium difluorooxalato borate is present in the electrolyte solution in an amount of 0.1-3.0% by weight; preferably 0.1% to 2.0%.
7. The electrolyte of claim 1, wherein the cyclic sulfate is present in the electrolyte in an amount of 0.1-4.0% by weight; preferably 0.5% to 3.0%.
8. The electrolyte of claim 1, wherein the mass percentage of the fluorosilane in the electrolyte is 0.1-4.0%; preferably 0.3% to 2.0%.
9. The electrolyte of any one of claims 1-8, wherein the additive further comprises at least one of vinylene carbonate, 1, 3-propane sultone, 1-propene-1, 3-sultone, methylene methanedisulfonate, ethylene carbonate, tris (trimethylsilyl) phosphate, tris (trimethylsilyl) phosphite, adiponitrile, and fumaronitrile.
10. The electrolyte of claim 1, wherein the additive further comprises a lithium salt additive comprising at least one of lithium tetrafluoroborate, lithium difluorophosphate, and lithium bis-fluorosulfonylimide.
11. The electrolyte of claim 10, wherein the lithium salt additive is present in the electrolyte at less than 3% by weight.
12. An electrochemical device comprising a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1 to 11.
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| CN111900476A (en) * | 2020-07-27 | 2020-11-06 | 欣旺达电动汽车电池有限公司 | Electrolyte solution and electrochemical device |
| CN112216867A (en) * | 2020-09-29 | 2021-01-12 | 中国科学院成都有机化学有限公司 | Electrolyte additive, lithium ion high-voltage electrolyte and lithium ion battery |
| WO2021093265A1 (en) * | 2019-11-15 | 2021-05-20 | 欣旺达电动汽车电池有限公司 | Electrolyte and electrochemical device |
| CN113948770A (en) * | 2021-10-12 | 2022-01-18 | 远景动力技术(江苏)有限公司 | Electrolyte for improving high-temperature storage characteristics of battery and lithium ion battery |
| CN115588779A (en) * | 2022-11-11 | 2023-01-10 | 广州天赐高新材料股份有限公司 | High-temperature nonaqueous electrolyte solution and secondary battery |
| CN117712488A (en) * | 2024-02-04 | 2024-03-15 | 深圳海辰储能科技有限公司 | Electrolyte, secondary battery containing same, battery pack and electric equipment |
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| CN108933294B (en) * | 2017-05-26 | 2020-08-28 | 宁德时代新能源科技股份有限公司 | Lithium ion battery and electrolyte thereof |
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| CN105406126A (en) * | 2014-09-05 | 2016-03-16 | Sk新技术株式会社 | Electrolyte For Lithium Secondary Battery And Lithium Secondary Battery Containing The Same |
| CN110112464A (en) * | 2019-04-17 | 2019-08-09 | 欣旺达电动汽车电池有限公司 | A kind of electrolyte of lithium-ion secondary battery containing Trimethlyfluorosilane |
Cited By (8)
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| WO2021093265A1 (en) * | 2019-11-15 | 2021-05-20 | 欣旺达电动汽车电池有限公司 | Electrolyte and electrochemical device |
| CN111900476A (en) * | 2020-07-27 | 2020-11-06 | 欣旺达电动汽车电池有限公司 | Electrolyte solution and electrochemical device |
| CN112216867A (en) * | 2020-09-29 | 2021-01-12 | 中国科学院成都有机化学有限公司 | Electrolyte additive, lithium ion high-voltage electrolyte and lithium ion battery |
| CN113948770A (en) * | 2021-10-12 | 2022-01-18 | 远景动力技术(江苏)有限公司 | Electrolyte for improving high-temperature storage characteristics of battery and lithium ion battery |
| CN113948770B (en) * | 2021-10-12 | 2024-01-30 | 远景动力技术(江苏)有限公司 | Electrolyte for improving high-temperature storage characteristics of battery and lithium ion battery |
| CN115588779A (en) * | 2022-11-11 | 2023-01-10 | 广州天赐高新材料股份有限公司 | High-temperature nonaqueous electrolyte solution and secondary battery |
| CN115588779B (en) * | 2022-11-11 | 2023-11-28 | 广州天赐高新材料股份有限公司 | High-temperature non-aqueous electrolyte and secondary battery |
| CN117712488A (en) * | 2024-02-04 | 2024-03-15 | 深圳海辰储能科技有限公司 | Electrolyte, secondary battery containing same, battery pack and electric equipment |
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