CN112510256B - Lithium ion battery electrolyte and lithium ion battery containing same - Google Patents

Lithium ion battery electrolyte and lithium ion battery containing same Download PDF

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CN112510256B
CN112510256B CN201910869640.9A CN201910869640A CN112510256B CN 112510256 B CN112510256 B CN 112510256B CN 201910869640 A CN201910869640 A CN 201910869640A CN 112510256 B CN112510256 B CN 112510256B
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lithium
ion battery
additive
lithium ion
electrolyte
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CN112510256A (en
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蒋志敏
张正华
马国强
盛楠
李中凯
沈旻
徐冲
丁祥欢
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Zhejiang Zhonglan New Energy Materials Co ltd
Zhejiang Chemical Industry Research Institute Co Ltd
Sinochem Lantian Co Ltd
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Zhejiang Zhonglan New Energy Materials Co ltd
Zhejiang Chemical Industry Research Institute Co Ltd
Sinochem Lantian Co Ltd
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Priority to PCT/CN2019/129128 priority patent/WO2020135694A1/en
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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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Abstract

The application discloses a lithium ion battery electrolyte and a lithium ion battery containing the same, wherein the electrolyte comprises lithium salt, a nonaqueous solvent and an additive, the additive comprises vinyl sulfate, a first additive and a second additive, the first additive is selected from isocyanate compounds, the isocyanate compounds contain 1-3-N=C=O groups, and the second additive is selected from fluoroalcohol lithium compounds. The lithium ion battery electrolyte has the advantages of inhibiting the acidity rise of the electrolyte, preventing the electrolyte from changing color, improving the capacity retention rate of the electrolyte, and the like.

Description

Lithium ion battery electrolyte and lithium ion battery containing same
Technical Field
The application relates to lithium ion battery electrolyte, in particular to lithium ion battery electrolyte containing vinyl sulfate and a lithium ion battery containing the same.
Background
The electrolyte is the 'blood' of the lithium ion battery, bears the heavy duty of transporting lithium ions, and can directly influence the performance of the lithium ion battery. Currently commercial electrolyte lithium salts are mainly LiPF 6 It is extremely susceptible to thermal decomposition and hydrolysis reactions to form PF5 and HF. PF5 and HF catalyze Ethylene Carbonate (EC), methyl ethyl carbonate (EMC) and other solvent molecules to generate polymerization reaction, and a polymer containing conjugated double bonds is generated, so that the electrolyte is discolored.
The ethylene sulfate (DTD for short) has the advantage of obviously reducing the internal resistance of the battery, is widely used as an electrolyte additive at present, particularly in a high-nickel NCM battery, can effectively inhibit capacity attenuation in the battery cycle process and reduce the expansion of the battery after high-temperature placement. However, the stability of the DTD is poor, and after the DTD is configured into an electrolyte, the acidity and chromaticity of the electrolyte are easily out of standard, so that the performance of the battery is greatly affected. Therefore, the electrolyte containing the DTD is unfavorable for transportation and storage, and greatly limits the application prospect in the electrolyte.
At present, no report is made on additives which can inhibit acidity and chromaticity of the electrolyte containing DTD. The application adopts common electrolyte stabilizer types for the electrolyte containing DTD, and researches find that the following defects exist:
(1) Silazane compounds, such as hexamethylsilazane disclosed in patent CN105470563a, can react with HF, effectively reducing the HF content in the electrolyte. However, when a silazane compound is used in a DTD-containing electrolyte, white insoluble precipitate is extremely likely to be generated.
(2) Phosphite ester compounds, such as triphenyl phosphite disclosed in patent CN105895954A, have an antioxidation effect and can relieve the chromaticity rise of the electrolyte in the normal-temperature storage process. However, phosphite compounds have very small acidity inhibition effect on DTD-containing electrolyte, have large pungent odor, are harmful to body health, and are not suitable for industrial production.
(3) The carbodiimide compound, such as the cyclohexylcarbodiimide disclosed in patent US6077628A, can undergo a slow hydrolysis reaction in the electrolyte, and the alkaline hydrolysis product thereof can slowly capture a trace amount of HF in the electrolyte, but when used in a DTD-containing electrolyte, white precipitates are also easily produced.
(4) Isocyanate compounds, which are less useful as stabilizers, are often used for other applications. Hexamethylene diisocyanate as disclosed in patent CN106025339a for improving the storage properties of lithium ion batteries at high temperatures; as another example, an isocyanate compound disclosed in patent CN103380530a is used to suppress capacity deterioration and gas generation of a nonaqueous electrolyte battery upon high-temperature storage. Even if the isocyanate compound is used as a stabilizer in the prior art, only the parallel generalization with other stabilizers is involved, and no test data indicate that the isocyanate compound can inhibit the discoloration of the electrolyte when used as the stabilizer.
Disclosure of Invention
In order to solve the technical problems, the application provides the lithium ion battery electrolyte which can inhibit the acidity rise of the electrolyte containing the DTD, prevent the electrolyte from changing color, improve the electrochemical performance of the battery and especially improve the capacity retention rate of the battery.
The application aims at realizing the following technical scheme:
a lithium ion battery electrolyte comprising a lithium salt, a nonaqueous solvent and an additive, wherein the additive comprises vinyl sulfate and a first additive, the first additive is selected from isocyanate compounds, and the isocyanate compounds contain 1-3-n=c=o groups; preferably, the isocyanate-based compound comprises 2-n=c=o groups.
According to the above lithium ion battery electrolyte, preferably, the first additive is selected from isocyanate compounds represented by the following general formula (I):
wherein R is 1 Selected from C 1 -C 20 Alkyl, C 1 -C 20 Substituted alkyl, substituted phenyl, substituted biphenyl, said alkyl being an alkanyl or cycloalkyl group, said substituents being hydrogen, halogen, C 1 -C 20 Alkyl, phosphate, sulfonyl, thio; the halogen is selected from fluorine, chlorine, bromine and iodine;
0≤x≤1，0≤y≤1，0≤z≤1。
preferably, R 1 Selected from C 1 -C 10 Alkyl, C 1 -C 10 Substituted alkyl, said substituents being hydrogen, halogen, C 1 -C 10 An alkyl group.
In order to further suppress the acidity of the lithium ion battery electrolyte, preferably, the additive further comprises a second type of additive selected from the group consisting of lithium fluoroalkoxides represented by the following general formula (II):
wherein R2, R3, R4 are independently selected from hydrogen, halogen, C 1 -C 20 Alkyl, C 1 -C 20 Haloalkyl, said halogen being selected from fluorine, chlorine, bromine and iodine. Preferably, R 2 、R 3 、R 4 Independently selected from hydrogen, fluorine, C 1 -C 10 Alkyl, C 1 -C 10 A fluoroalkyl group.
According to the lithium ion battery electrolyte, optionally, the isocyanate compound is at least one of the following compounds 1-12:
according to the above lithium ion battery electrolyte, optionally, the lithium fluoroalcohol compound is selected from at least one of lithium trifluoroethoxide, lithium tetrafluoroethoxide, lithium hexafluoroisopropanol, lithium heptafluorobutanol, lithium octafluoropentanol and lithium dodecafluoroheptanol. Preferably, the lithium fluoroalcohol compound is at least one selected from the group consisting of lithium trifluoroethoxide, lithium tetrafluoroethoxide and lithium hexafluoroisopropoxide.
According to the lithium ion battery electrolyte, optionally, the content of the vinyl sulfate accounts for 0.01% -5% of the total mass of the lithium ion battery electrolyte. Preferably, the content of the vinyl sulfate accounts for 0.5 to 3 percent of the total mass of the lithium ion battery electrolyte
According to the lithium ion battery electrolyte, optionally, the content of the isocyanate compound accounts for 0.005% -5% of the total mass of the lithium ion battery electrolyte. Preferably, the content of the isocyanate compound accounts for 0.02% -1% of the total mass of the lithium ion battery electrolyte.
According to the lithium ion battery electrolyte, optionally, the content of the lithium fluoroalcohol compound is 0.005% -5% of the total mass of the lithium ion battery electrolyte. Preferably, the content of the lithium fluoroalkoxide compound accounts for 0.02% -1% of the total mass of the lithium ion battery electrolyte.
According to the lithium ion battery electrolyte, optionally, the nonaqueous solvent is at least two selected from dimethyl carbonate, diethyl carbonate, methylethyl carbonate, propylene carbonate, ethylene carbonate, methylpropyl carbonate, ethyl propionate, ethyl acetate, ethyl formate, propyl butyrate, tetrahydrofuran, dioxane, diethanol diethyl ether and gamma-butyrolactone, and the content of the nonaqueous solvent accounts for 75.0% -88.0% of the total mass of the lithium ion battery electrolyte.
According to the lithium ion battery electrolyte, optionally, the lithium salt is at least one selected from lithium hexafluorophosphate, lithium bisoxalato borate, lithium difluorooxalato borate and lithium bisfluorosulfonyl imide, and the content of the lithium salt accounts for 10.0% -18.0% of the total mass of the lithium ion battery electrolyte.
According to the lithium ion battery electrolyte described above, optionally, the additive further comprises a third type of additive selected from at least one of vinylene carbonate, 1, 3-propane sulfonate, tris (trimethylsilane) borate, tris (trimethylsilane) phosphate, fluoroethylene carbonate, and ethylene carbonate.
According to the lithium ion battery electrolyte, optionally, the content of the third additive accounts for 0.1% -5.0% of the total mass of the lithium ion battery electrolyte.
The application also provides a lithium ion battery, which comprises a positive electrode, a negative electrode and any one of the lithium ion battery electrolyte.
Compared with the prior art, the application has the following beneficial effects:
1. the application adopts isocyanate compound as the first additive, and the-N=C=O functional group contained in the isocyanate compound can react with trace water in the electrolyte to inhibit LiPF from the source 6 Is prevented from producing PF by hydrolysis reaction 5 And HF, thereby preventing discoloration of the electrolyte.
2. The application adopts the lithium fluoroalcohol compound as the second type additive, and the acidity of the electrolyte can be reduced by adding a small amount of the second type additive; the electrolyte is used in DTD-containing electrolyte together with isocyanate compound, so that the consumption of the isocyanate compound can be greatly reduced, and the electrolyte can be better prevented from changing color and the acidity of the electrolyte is inhibited by using a small amount of isocyanate compound and lithium fluoroalkoxide compound.
3. According to the application, the isocyanate compound and the lithium fluoroalkoxide compound are simultaneously added into the electrolyte containing the DTD, and the two products are both dissolved in most organic solvents, so that insoluble precipitate can not be generated.
4. When the electrolyte is used in a lithium ion battery, the isocyanate compound can inhibit the electrolyte from changing color, can be decomposed on the surface of a negative electrode preferentially, forms a stable solid electrolyte interface film and improves the cycle performance of the battery; the lithium fluoroalkoxide compound can greatly improve the infiltration capacity of electrolyte and reduce the impedance of a battery; the two compounds are combined in the electrolyte containing the DTD, so that the electrochemical performance of the lithium ion battery can be improved, and the capacity retention rate of the battery can be improved.
Drawings
Fig. 1 is a discharge capacity-cycle number comparison chart of comparative example 1, example 2, comparative example 6 and example 15 of the present application;
FIG. 2 is a graph of the cycle 100 cycle impedance contrast for comparative example 1, example 2, comparative example 6 and example 15 of the present application.
Detailed Description
The application will be further illustrated with reference to the following specific examples, without limiting the application to these specific embodiments. It will be appreciated by those skilled in the art that the application encompasses all alternatives, modifications and equivalents as may be included within the scope of the claims.
Example 1:
in a glove box filled with argon (moisture is less than 1ppm, oxygen is less than 1 ppm), uniformly mixing dimethyl carbonate, methyl ethyl carbonate and ethylene carbonate in a mass ratio of 1:1:1, slowly adding LiPF6 with a mass fraction of 12.0% (total electrolyte mass ratio) into the mixed solution, stirring until the LiPF6 is completely dissolved, adding ethylene sulfate with a mass fraction of 2.0% (total electrolyte mass ratio) into the mixed solution, and finally adding isocyanate compound into the mixed solution to obtain the lithium ion battery electrolyte, wherein the isocyanate compound is hexamethylene diisocyanate with a mass fraction of 0.05% (total electrolyte mass ratio).
Example 2:
the operation is the same as in example 1, except that: finally, the isocyanate compound added into the mixed solution is hexamethylene diisocyanate with the mass percent of 0.1 percent.
Example 3:
the operation is the same as in example 1, except that: finally, the isocyanate compound added into the mixed solution is hexamethylene diisocyanate with the mass fraction of 0.5 percent.
Example 4:
the operation is the same as in example 1, except that: finally, the isocyanate compound added into the mixed solution is isophorone diisocyanate with the mass percent of 0.05 percent.
Example 5:
the operation is the same as in example 1, except that: finally, the isocyanate compound added into the mixed solution is isophorone diisocyanate with the mass percent of 0.1 percent.
Example 6:
the operation is the same as in example 1, except that: finally, the isocyanate compound added into the mixed solution is isophorone diisocyanate with the mass fraction of 0.5 percent.
Example 7:
the operation is the same as in example 1, except that: finally, the isocyanate compound added into the mixed solution is phenyl isocyanate with the mass percent of 0.1 percent.
Example 8:
in a glove box filled with argon (moisture is less than 1ppm, oxygen is less than 1 ppm), uniformly mixing dimethyl carbonate, methyl ethyl carbonate and ethylene carbonate in a mass ratio of 1:1:1, slowly adding LiPF6 with a mass fraction of 12.0% (total electrolyte mass ratio) into the mixed solution, stirring until the LiPF6 is completely dissolved, adding ethylene sulfate with a mass fraction of 2.0% (total electrolyte mass ratio) into the mixed solution, and finally adding an isocyanate compound and a lithium fluoroalcohol compound into the mixed solution to obtain the lithium ion battery electrolyte, wherein the isocyanate compound is hexamethylene diisocyanate with a mass fraction of 0.05% (total electrolyte mass ratio), and the lithium fluoroalcohol compound is lithium trifluoroethanol with a mass fraction of 0.01% (total electrolyte mass ratio).
Example 9:
the operation is the same as in example 7, except that: finally, the isocyanate compound added into the mixed solution is hexamethylene diisocyanate with the mass fraction of 0.05 percent, and the added lithium fluoroalkoxide compound is lithium trifluoroethoxide with the mass fraction of 0.05 percent.
Example 10:
the operation is the same as in example 7, except that: finally, the isocyanate compound added into the mixed solution is hexamethylene diisocyanate with the mass fraction of 0.05 percent, and the added lithium fluoroalkoxide compound is lithium trifluoroethoxide with the mass fraction of 0.1 percent.
Example 11:
the operation is the same as in example 7, except that: finally, the isocyanate compound added into the mixed solution is hexamethylene diisocyanate with the mass fraction of 0.05 percent, and the added lithium fluoroalkoxide compound is lithium hexafluoroisopropanol with the mass fraction of 0.01 percent.
Example 12:
the operation is the same as in example 7, except that: finally, the isocyanate compound added into the mixed solution is hexamethylene diisocyanate with the mass fraction of 0.05 percent, and the added lithium fluoroalkoxide compound is lithium hexafluoroisopropanol with the mass fraction of 0.05 percent.
Example 13:
the operation is the same as in example 7, except that: finally, the isocyanate compound added into the mixed solution is hexamethylene diisocyanate with the mass fraction of 0.05 percent, and the added lithium fluoroalkoxide compound is lithium hexafluoroisopropoxide with the mass fraction of 0.1 percent.
Example 14:
the operation is the same as in example 7, except that: finally, the isocyanate compound added into the mixed solution is isophorone diisocyanate with the mass fraction of 0.05 percent, and the added fluorolithium alkoxide compound is lithium trifluoroethanol with the mass fraction of 0.05 percent.
Example 15:
the operation is the same as in example 7, except that: finally, the isocyanate compound added into the mixed solution is isophorone diisocyanate with the mass fraction of 0.05 percent, and the added lithium fluoroalkoxide compound is lithium hexafluoroisopropanol with the mass fraction of 0.05 percent.
Comparative example 1:
in a glove box filled with argon (moisture is less than 1ppm, oxygen is less than 1 ppm), uniformly mixing dimethyl carbonate, methyl ethyl carbonate and ethylene carbonate in a mass ratio of 1:1:1, slowly adding LiPF6 with a mass fraction of 12.0% (total electrolyte mass ratio) into the mixed solution, stirring until the LiPF6 is completely dissolved, and adding ethylene sulfate with a mass fraction of 2.0% (total electrolyte mass ratio) into the mixed solution to obtain the lithium ion battery electrolyte.
Comparative example 2:
the procedure is as in comparative example 1, with the difference that: hexamethyldisilazane was added as an additive in an amount of 0.05% by mass (total mass of electrolyte) based on comparative example 1.
Comparative example 3:
the procedure is as in comparative example 1, with the difference that: triphenyl phosphite with a mass fraction of 0.05% (total electrolyte mass ratio) was added as an additive on the basis of comparative example 1.
Comparative example 4:
the procedure is as in comparative example 1, with the difference that: a cyclohexylcarbodiimide was added as an additive in a mass fraction of 0.05% (total electrolyte mass ratio) based on comparative example 1.
Comparative example 5:
the procedure is as in comparative example 1, with the difference that: lithium trifluoroethoxide was added as an additive in an amount of 0.05% by mass (total mass of electrolyte) based on comparative example 1.
Comparative example 6:
the procedure is as in comparative example 1, with the difference that: lithium hexafluoroisopropoxide was added as an additive in an amount of 0.05% by mass (total mass of electrolyte) based on comparative example 1.
Comparative example 7:
the procedure is as in comparative example 1, with the difference that: lithium trifluoroethoxide was added as an additive in an amount of 0.1% by mass (total mass of electrolyte) based on comparative example 1.
Comparative example 8:
the procedure is as in comparative example 1, with the difference that: lithium hexafluoroisopropoxide was added as an additive in an amount of 0.1% by mass (total mass of electrolyte) based on comparative example 1.
Comparative example 9:
the procedure is as in comparative example 1, with the difference that: triphenyl phosphite with a mass fraction of 0.05% (total mass of electrolyte) and lithium trifluoroethoxide with a mass fraction of 0.05% (total mass of electrolyte) were added as additives on the basis of comparative example 1.
Comparative example 10:
the procedure is as in comparative example 1, with the difference that: triphenyl phosphite with a mass fraction of 0.05% (total mass of electrolyte) and lithium hexafluoroisopropoxide with a mass fraction of 0.05% (total mass of electrolyte) were added as additives on the basis of comparative example 1.
1. Electrolyte storage acidity and chromaticity test
Transferring a part of the prepared electrolyte solutions of examples 1-15 and comparative examples 1-10 into a sealed aluminum bottle, placing the sealed aluminum bottle in a constant temperature oven at 50 ℃ for storage, sampling and detecting the acidity value and the chromaticity value of the electrolyte solution in a glove box before storage, 7 days of storage and 28 days of storage respectively, wherein the acidity test method adopts a triethylamine titration method, the acidity unit is ppm, the chromaticity test method adopts a platinum-cobalt colorimetric method and the chromaticity unit is Hazen. The test results are shown in table 1 below:
TABLE 1 results of acidity and chromaticity tests for electrolytes
As shown in Table 1, the use of a single isocyanate compound additive or a mixed additive of isocyanate compound and lithium fluoroalkoxide compound has a remarkable effect of reducing the acidity and chromaticity of the electrolyte, and a very remarkable inhibition effect can be achieved by using a lower additive amount, thereby being beneficial to the storage and transportation of the electrolyte containing DTD.
As is clear from a comparison of comparative examples 1 to 4 in Table 1, the use of conventional additives has a certain effect of reducing both acidity and chromaticity of the electrolyte stored at a high temperature of 50℃as compared with the use of no additives, but comparative example 2 shows white precipitation, comparative example 3 shows a pungent smell, and comparative example 4 shows a small amount of white precipitation.
As is clear from a comparison between comparative example 1 and examples 1 to 7 in Table 1, the use of a single isocyanate compound additive does not cause adverse reaction or irritating odor, and has a more remarkable effect of reducing the acidity and chromaticity of the electrolyte, as compared with the use of no additive. With the increase of the addition amount, the inhibition of the acidity and chromaticity of the electrolyte is more obvious.
As is clear from comparison of comparative examples 1 and comparative examples 5 to 8 in Table 1, the use of a single lithium fluoroalkoxide additive has a certain effect on the suppression of acidity and chromaticity of the electrolyte as compared with the use of no additive, but is slightly inferior to the use of a single isocyanate compound additive.
Comparing examples 7, 2 and 5 in table 1, it is known that the same additive amount used has a more remarkable inhibitory effect on the acidity and chromaticity of the electrolyte as compared with the use of the monoisocyanate compound additive.
As can be seen from a comparison of examples 1 to 7, comparative examples 5 to 8 and examples 8 to 15 in Table 1, the use of the mixed additive of isocyanate compound and lithium fluoroalkoxide has a very significant inhibitory effect on the acidity and chromaticity of the electrolyte, as compared with the use of the single isocyanate compound additive or the single lithium fluoroalkoxide additive. When the same inhibition effect as that of using a single isocyanate compound additive or a single lithium fluoroalkoxide compound additive is achieved, the addition amount of the additive can be greatly reduced.
Examples 8 to 15 and comparative examples 9 to 10 in Table 1 were compared, and the conventional additive and the lithium fluoroalkoxide compound mixed additive were used, but the effect of inhibition was inferior to that of the isocyanate compound and the lithium fluoroalkoxide compound mixed additive, although the effect of inhibition was large on the acidity and chromaticity of the electrolyte.
2. Electrochemical performance test of electrolyte
The lithium ion battery electrolytes of the above prepared examples 1 to 15 and comparative examples 1 to 10 were injected into a 1Ah LiNi0.6Co0.2Mn0.2O2/graphite pouch battery which had been sufficiently dried, the injection amount was 4g, and after 12 hours of standing, thermocompression forming, secondary sealing and conventional capacity division, 1C cycle performance test was performed: at 25 ℃, charging the separated battery to 4.35V at a constant current and a constant voltage of 1C, cutting off the current by 0.05C, discharging to 3.0V at a constant current of 1C, and calculating the cyclic capacity retention rate according to the following calculation formula:
500 th cycle capacity retention (%) = (500 th cycle discharge capacity/first cycle discharge capacity) ×100%;
the test results are shown in table 2 below: .
Table 2 capacity retention test results table
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As is clear from table 2 above, when a single isocyanate compound was used as an additive, the battery capacity retention rate gradually decreased with increasing addition amount, and was substantially maintained or lower than the case where no additive was contained. When a single lithium fluoroalkoxide compound is used as the additive, the battery capacity retention rate does not show a significant change rule with increasing addition amount, but the battery capacity is substantially maintained or slightly higher than that in the case where the additive is not contained.
When the isocyanate compound and the lithium fluoroalkoxide compound were used as the mixed additive, the battery capacity retention rate was higher than that in the case where the additive was not contained (comparative example 1), higher than that in the case where the conventional additive was used (comparative examples 2 to 4), higher than that in the case where the single isocyanate compound was used or that in the case where the lithium fluoroalkoxide compound was used alone (comparative examples 5 to 8), and also higher than that in the case where the additive was combined with the lithium fluoroalkoxide compound (comparative examples 9 to 10).
The electrolytes of comparative examples 1, 2, 6 and 15 were used in lithium batteries to perform battery cycle performance comparison. Fig. 1 is a graph of discharge capacity versus cycle number, and fig. 2 is a graph of cycle 100-week impedance versus cycle number.
As shown in fig. 1, the battery cycle performance was more excellent when the isocyanate compound and lithium fluoroalkoxide compound mixed additive of example 15 of the present application were used, as compared with when the additive was not used (comparative example 1), or a single isocyanate compound additive (example 2), or a single lithium fluoroalkoxide compound additive (comparative example 6). The isocyanate compound is used as a first additive, the lithium fluoroalcohol compound is used as a second additive, and the two additives have good synergistic effect on improving the cycle performance of the battery.
As shown in fig. 2, the impedance value during battery cycling was smaller when the isocyanate compound and lithium fluoroalkoxide compound mixed additive of example 15 of the present application was used, as compared with when the additive was not used (comparative example 1), or a single isocyanate compound additive (example 2), or a single lithium fluoroalkoxide compound additive (comparative example 6). This indicates that the improvement in battery cycle performance benefits from a smaller internal battery resistance.

Claims (7)

1. The lithium ion battery electrolyte comprises lithium salt, a nonaqueous solvent and an additive, and is characterized in that: the additives include vinyl sulfate, a first type of additive and a second type of additive;
the content of the vinyl sulfate accounts for 0.5-3% of the total mass of the lithium ion battery electrolyte;
the first additive is at least one of the following isocyanate compounds shown in 1-8, and the content of the first additive accounts for 0.02% -0.1% of the total mass of the lithium ion battery electrolyte:
the second type of additive is at least one of lithium trifluoroethanol, lithium tetrafluoroethanol, lithium hexafluoroisopropanol, lithium heptafluorobutanol, lithium octafluoropentanol and lithium dodecafluoroheptanol, and the content of the second type of additive is 0.01-0.1% of the total mass of the lithium ion battery electrolyte.
2. The lithium ion battery electrolyte according to claim 1, wherein: the second type of additive is at least one selected from lithium trifluoroethanol, lithium tetrafluoroethanol and lithium hexafluoroisopropanol.
3. The lithium ion battery electrolyte according to claim 1, wherein: the nonaqueous solvent is at least two selected from dimethyl carbonate, diethyl carbonate, methylethyl carbonate, propylene carbonate, ethylene carbonate, methylpropyl carbonate, ethyl propionate, ethyl acetate, ethyl formate, propyl butyrate, tetrahydrofuran, dioxane, diethanol diethyl ether and gamma-butyrolactone, and the content of the nonaqueous solvent accounts for 75.0-88.0% of the total mass of the lithium ion battery electrolyte.
4. The lithium ion battery electrolyte according to claim 1, wherein: the lithium salt is at least one selected from lithium hexafluorophosphate, lithium bisoxalato borate, lithium difluorooxalato borate and lithium bisfluorosulfonyl imide, and the content of the lithium salt accounts for 10.0-18.0% of the total mass of the lithium ion battery electrolyte.
5. The lithium ion battery electrolyte according to claim 1, wherein: the additive further comprises a third type of additive selected from at least one of vinylene carbonate, 1, 3-propane sultone, tris (trimethylsilane) borate, tris (trimethylsilane) phosphate, fluoroethylene carbonate and ethylene carbonate.
6. The lithium ion battery electrolyte according to claim 5, wherein: the content of the third additive accounts for 0.1-5.0% of the total mass of the lithium ion battery electrolyte.
7. A lithium ion battery, characterized in that the lithium ion battery comprises the lithium ion battery electrolyte according to any one of claims 1-6.
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