CN110061292B - Low-temperature electrolyte and lithium battery using same - Google Patents

Low-temperature electrolyte and lithium battery using same Download PDF

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CN110061292B
CN110061292B CN201910245677.4A CN201910245677A CN110061292B CN 110061292 B CN110061292 B CN 110061292B CN 201910245677 A CN201910245677 A CN 201910245677A CN 110061292 B CN110061292 B CN 110061292B
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electrolyte
lithium
carbonate
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CN110061292A (en
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张健
高田慧
梁大宇
崔伟
丁楚雄
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Hefei Gotion High Tech Power Energy Co Ltd
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Hefei Guoxuan High Tech Power Energy Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0568—Liquid materials characterised by the solutes
    • 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
    • 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 invention discloses a low-temperature electrolyte and a lithium battery using the same, and relates to the technical field of lithium ion batteries, wherein the low-temperature electrolyte comprises a lithium salt, an organic solvent and an additive, wherein the lithium salt is alkyl sulfur-containing oxygen-containing fluoro lithium phosphate; compared with the traditional lithium salt, the lithium alkyl sulfur-oxygen-containing fluorophosphates used in the electrolyte still have higher ionic conductivity under the ultralow temperature condition of minus 50 ℃, and the lithium alkyl sulfur-oxygen-containing fluorophosphates can form a stable SEI film with low impedance on the surface of a negative electrode, so that the lithium ion can be rapidly inserted and removed under the low temperature condition, the problem of lithium precipitation of the negative electrode caused by the ultralow temperature is effectively solved, and the lithium alkyl sulfur-oxygen-containing fluorophosphates can show more excellent low-temperature discharge and cycle performance in the ultralow temperature environment.

Description

Low-temperature electrolyte and lithium battery using same
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a low-temperature electrolyte and a lithium battery using the same.
Background
The lithium ion battery has high working voltage, large specific energy density, long cycle life and environmental friendliness, and becomes one of the indispensable important chemical energy sources in the fields of electronic digital, electric automobiles, energy storage application, aerospace and the like. The electrolyte is an important component of the lithium ion battery, is called as 'blood' of the lithium ion battery, generally consists of lithium salt, solvent and additive, and has important influence on the cycle performance, rate capability and safety performance of the lithium ion battery. Because the electrolyte simultaneously meets the requirements of compatibility with positive and negative electrode materials, physical and chemical stability, higher conductivity, lower viscosity and the like in the working process, a combined solvent is generally formed by selecting cyclic carbonate, chain carbonate and a low-viscosity carboxylate compound, the problem of the viscosity of the solvent at a low temperature can be solved, but the solvent containing linear carbonate and carboxylate has a lower dielectric constant at a low temperature, so that the conventional lithium salt is difficult to completely dissolve at a low temperature, the ionic conductivity is lower, the fast lithium ion migration rate is difficult to maintain, and the low-temperature performance of the lithium ion battery is poorer.
At present, the method for improving the low-temperature performance of the lithium ion battery electrolyte mainly comprises two aspects of solvent system optimization and low-impedance additives, for example, the patent with the publication number of CN 105811003 discloses a low-temperature electrolyte which is composed of cyclic carbonate and chain carboxylate, and the lithium salt is conventional LiPF6And LiBF4The low-temperature conductivity is improved through an organic solvent system and dosage improvement, and the improvement of the low-temperature cycle performance at the temperature of minus 20 ℃ is realized; in the publication No. CN 108270033, functional additives of fluoroethylene carbonate and propenyl-1, 3-propane sultone are added into a LiBOB and LiODFB lithium salt system, so that the interface impedance of the electrolyte is reduced, and the low-temperature performance of the lithium ion battery is improved. Although the battery performance is improved under the general low-temperature environment condition, the problem of low lithium salt conductivity cannot be solved under the ultralow temperature condition of-50 ℃, so that the development of a novel ultralow-temperature lithium salt electrolyte has important significance for widening the application range of the lithium ion battery and improving the application value under the extreme condition.
Disclosure of Invention
The invention aims to provide a low-temperature electrolyte and a lithium battery using the same, which are beneficial to the rapid insertion and extraction of lithium ions under a low-temperature condition, solve the problem of lithium precipitation of a negative electrode caused by low temperature, and enable the lithium battery to show more excellent low-temperature discharge and cycle performance in an ultralow-temperature environment.
In order to achieve the purpose, the invention adopts the following technical scheme:
the low-temperature electrolyte comprises lithium salt, an organic solvent and an additive, wherein the lithium salt is alkyl sulfur-containing oxygen-containing fluoro lithium phosphate, and the structure of the lithium salt is shown in a general formula (I) or a general formula (II)
Figure BDA0002010986890000021
Wherein R is1、R2、R3And R4Each independently selected from F or C1-5And R is alkyl of1、R2、R3And R4In which at least one F and one C1-5Alkyl group of (1).
Preferably, the organic solvent is organic carbonate C1-20At least one of alkyl ether, phenyl sulfide, carboxylic ester, sulfone, nitrile, dinitrile and phosphazene.
Preferably, the organic solvent is at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, 1, 4-butyrolactone, methyl ethyl carbonate, dimethyl ether, diphenyl sulfide, acetonitrile, glutaronitrile, sulfolane, pentafluoroethoxycyclotriphosphazene, methyl propionate, ethyl propionate, butyl propionate and ethyl butyrate.
Preferably, the additive is at least one of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, vinyl sulfate, tris (trimethylsilyl) borate, trimethyl phosphate, dimethyl methylphosphonate, and hexamethyldisilazane.
Preferably, the additives are vinylene carbonate and fluoroethylene carbonate.
Preferably, the electrolyte comprises the following components in percentage by mass based on the total mass of the electrolyte: 81-90% of organic solvent, 8-15% of lithium salt and 0.5-10% of additive.
Preferably, the organic solvent is 85-90%, the lithium salt is 9-14%, and the additive is 0.5-1%.
The invention also provides a lithium battery using the low-temperature electrolyte.
Preferably, the positive electrode material of the lithium battery is at least one of a transition metal lithium intercalation oxide, a metal oxide and a metal sulfide.
Preferably, the negative electrode material of the lithium battery is at least one of a carbon-containing material, silicon carbon, silicon oxygen, ferrite, nitride and an alloy material.
The invention has the following beneficial effects:
1. compared with the traditional lithium salt, the lithium alkyl fluoride phosphate containing sulfur and oxygen is easier to dissolve in a solvent system at low temperature, has better compatibility with the solvent system, cannot cause lithium salt precipitation due to over low temperature, and can ensure higher ionic conductivity at the ultralow temperature of 50 ℃ below zero.
2. The alkyl sulfur-containing oxygen-containing fluoro lithium phosphate used in the invention can form a stable SEI film with low impedance on the surface of the negative electrode, is beneficial to the rapid insertion and extraction of lithium ions under the low temperature condition, effectively solves the problem of lithium precipitation of the negative electrode caused by over-low temperature, and can show more excellent low-temperature discharge and cycle performance in the ultralow temperature environment.
Detailed Description
The technical solution of the present invention will be described in detail by specific examples.
Example 1
Preparing an electrolyte: taking an organic mixed solution of dimethyl carbonate, ethylene carbonate, methyl ethyl carbonate and ethyl propionate accounting for 85% of the total mass of the electrolyte in a glove box (the water content is less than 0.1ppm and the oxygen content is less than 0.1ppm) filled with argon, wherein the mass ratio of the dimethyl carbonate to the ethylene carbonate to the methyl ethyl carbonate to the ethyl propionate is 1:3:3: 3; then, the additive vinylene carbonate and fluoroethylene carbonate which account for 1% of the total mass of the electrolyte are added into the mixed solution, the mass ratio of the vinylene carbonate to the fluoroethylene carbonate is 1:1, finally, the alkyl sulfur-containing oxygen-containing lithium fluorophosphate (a) which accounts for 14% of the total mass of the electrolyte is slowly added into the mixed solution, and the lithium ion battery electrolyte of the embodiment 1 of the invention is obtained after uniform stirring.
Figure BDA0002010986890000041
A lithium ion battery was prepared using the electrolyte of this example:
preparing a positive electrode material: NCM111, CNT (carbon nanotube) and PVDF (binder) were mixed in an amount of 95 wt%, 3 wt% and 2 wt%, and N-methylpyrrolidone was added to prepare a slurry, which was coated on an aluminum foil, dried and then rolled to obtain a positive electrode material.
Preparing a negative electrode material: mixing 80 wt% of artificial graphite, 15 wt% of natural graphite and 5 wt% of SBR (binding agent), adding deionized water, coating the slurry on a copper foil, drying and rolling to obtain the negative electrode material.
The anode and cathode materials are prepared into 2580160 square batteries (the length, width and height are respectively 160mm, 80mm and 25mm), wherein the compacted density of the anode material is 3.3g/cm3Areal density of 175g/cm2(one side), compacted density of negative electrode Material 1.5g/cm3Areal density of 105g/cm2(one side).
Example 2
Preparing an electrolyte: taking an organic mixed solution of dimethyl carbonate, ethylene carbonate, methyl ethyl carbonate and ethyl propionate accounting for 85% of the total mass of the electrolyte in a glove box (the water content is less than 0.1ppm and the oxygen content is less than 0.1ppm) filled with argon, wherein the mass ratio of the dimethyl carbonate to the ethylene carbonate to the methyl ethyl carbonate to the ethyl propionate is 1:3:3: 3; then, the additive vinylene carbonate and fluoroethylene carbonate which account for 1% of the total mass of the electrolyte are added into the mixed solution, the mass ratio of the vinylene carbonate to the fluoroethylene carbonate is 1:1, finally, the alkyl sulfur-containing oxygen-containing lithium fluorophosphate (b) which accounts for 14% of the total mass of the electrolyte is slowly added into the mixed solution, and the lithium ion battery electrolyte of the embodiment 2 of the invention is obtained after uniform stirring.
Figure BDA0002010986890000051
The preparation method of the lithium ion battery prepared by using the electrolyte of the embodiment is the same as the embodiment I.
Example 3
Preparing an electrolyte: taking an organic mixed solution of dimethyl carbonate, ethylene carbonate, methyl ethyl carbonate and ethyl propionate accounting for 85% of the total mass of the electrolyte in a glove box (the water content is less than 0.1ppm and the oxygen content is less than 0.1ppm) filled with argon, wherein the mass ratio of the dimethyl carbonate to the ethylene carbonate to the methyl ethyl carbonate to the ethyl propionate is 1:3:3: 3; then, the additive vinylene carbonate and fluoroethylene carbonate which account for 1% of the total mass of the electrolyte are added into the mixed solution, the mass ratio of the vinylene carbonate to the fluoroethylene carbonate is 1:1, finally, the alkyl sulfur-containing oxygen-containing lithium fluorophosphate (c) which accounts for 14% of the total mass of the electrolyte is slowly added into the mixed solution, and the lithium ion battery electrolyte of the embodiment 3 of the invention is obtained after uniform stirring.
Figure BDA0002010986890000061
The preparation method of the lithium ion battery prepared by using the electrolyte of the embodiment is the same as the embodiment I.
Example 4
Preparing an electrolyte: taking an organic mixed solution of dimethyl carbonate, ethylene carbonate, methyl ethyl carbonate and ethyl propionate accounting for 85% of the total mass of the electrolyte in a glove box (the water content is less than 0.1ppm and the oxygen content is less than 0.1ppm) filled with argon, wherein the mass ratio of the dimethyl carbonate to the ethylene carbonate to the methyl ethyl carbonate to the ethyl propionate is 1:3:3: 3; then, the additive vinylene carbonate and fluoroethylene carbonate which account for 1% of the total mass of the electrolyte are added into the mixed solution, the mass ratio of the vinylene carbonate to the fluoroethylene carbonate is 1:1, finally, the alkyl sulfur-containing oxygen-containing lithium fluorophosphate (d) which accounts for 14% of the total mass of the electrolyte is slowly added into the mixed solution, and the lithium ion battery electrolyte of the embodiment 4 of the invention is obtained after uniform stirring.
Figure BDA0002010986890000071
The preparation method of the lithium ion battery prepared by using the electrolyte of the embodiment is the same as the embodiment I.
Example 5
Preparing an electrolyte: taking an organic mixed solution of propylene carbonate, butylene carbonate, dimethyl ether and sulfolane accounting for 81 percent of the total mass of the electrolyte in a glove box (the water content is less than 0.1ppm and the oxygen content is less than 0.1ppm) filled with argon, wherein the mass ratio of the propylene carbonate to the butylene carbonate to the dimethyl ether to the sulfolane is 1:3:3: 3; then, the additive of vinyl ethylene carbonate and tris (trimethylsilyl) borate, which account for 4% of the total mass of the electrolyte, is added to the mixed solution, the mass ratio of the vinyl ethylene carbonate to the tris (trimethylsilyl) borate is 1:1, finally, the alkyl sulfur-containing oxygen-containing lithium fluorophosphate (b), which accounts for 15% of the total mass of the electrolyte, is slowly added to the mixed solution, and the lithium ion battery electrolyte of embodiment 5 of the invention is obtained after uniform stirring.
Figure BDA0002010986890000072
The preparation method of the lithium ion battery prepared by using the electrolyte of the embodiment is the same as the embodiment I.
Example 6
Preparing an electrolyte: taking an organic mixed solution of 1, 4-butyrolactone, diphenyl sulfide, acetonitrile and butyl propionate accounting for 81 percent of the total mass of the electrolyte in a glove box (the water content is less than 0.1ppm and the oxygen content is less than 0.1ppm) filled with argon, wherein the mass ratio of the 1, 4-butyrolactone, the diphenyl sulfide, the acetonitrile and the butyl propionate is 1:3: 3; and adding additives of trimethyl phosphate and hexamethyldisilazane which account for 10% of the total mass of the electrolyte into the mixed solution, wherein the mass ratio of trimethyl phosphate to hexamethyldisilazane is 1:1, finally slowly adding alkyl sulfur-containing oxygen-containing fluoro lithium phosphate (b) which accounts for 9% of the total mass of the electrolyte into the mixed solution, and uniformly stirring to obtain the lithium ion battery electrolyte of the embodiment 6 of the invention.
Figure BDA0002010986890000081
The preparation method of the lithium ion battery prepared by using the electrolyte of the embodiment is the same as the embodiment I.
Example 7
Preparing an electrolyte: taking an organic mixed solution of glutaronitrile, pentafluoroethoxycyclotriphosphazene, methyl propionate and ethyl butyrate accounting for 88.5 percent of the total mass of the electrolyte in a glove box (the water content is less than 0.1ppm and the oxygen content is less than 0.1ppm) filled with argon, wherein the mass ratio of the glutaronitrile, the pentafluoroethoxycyclotriphosphazene, the methyl propionate and the ethyl butyrate is 1:3:3: 3; and then adding an additive, namely vinyl sulfate and dimethyl methylphosphonate, which account for 0.5 percent of the total mass of the electrolyte into the mixed solution, wherein the mass ratio of the vinyl sulfate to the dimethyl methylphosphonate is 1:1, finally slowly adding alkyl sulfur-containing oxygen-containing lithium fluorophosphate (e) which accounts for 11 percent of the total mass of the electrolyte into the mixed solution, and uniformly stirring to obtain the lithium ion battery electrolyte of the embodiment 7 of the invention.
Figure BDA0002010986890000091
The preparation method of the lithium ion battery prepared by using the electrolyte of the embodiment is the same as the embodiment I.
Example 8
Preparing an electrolyte: taking an organic mixed solution of glutaronitrile, pentafluoroethoxycyclotriphosphazene, methyl propionate and ethyl butyrate accounting for 90% of the total mass of the electrolyte in a glove box (the water content is less than 0.1ppm and the oxygen content is less than 0.1ppm) filled with argon, wherein the mass ratio of the glutaronitrile, the pentafluoroethoxycyclotriphosphazene, the methyl propionate and the ethyl butyrate is 1:3:3: 3; and then adding an additive of vinyl sulfate and dimethyl methylphosphonate which account for 2% of the total mass of the electrolyte into the mixed solution, wherein the mass ratio of the vinyl sulfate to the dimethyl methylphosphonate is 1:1, finally slowly adding alkyl sulfur-containing oxygen-containing lithium fluorophosphate (f) which accounts for 8% of the total mass of the electrolyte into the mixed solution, and uniformly stirring to obtain the lithium ion battery electrolyte of the embodiment 8 of the invention.
Figure BDA0002010986890000101
Comparative example 1
Preparing an electrolyte: taking an organic mixed solution of dimethyl carbonate, ethylene carbonate, methyl ethyl carbonate and ethyl propionate accounting for 85% of the total mass of the electrolyte in a glove box (the water content is less than 0.1ppm and the oxygen content is less than 0.1ppm) filled with argon, wherein the mass ratio of the dimethyl carbonate to the ethylene carbonate to the methyl ethyl carbonate to the ethyl propionate is 1:3:3: 3; then, the additive vinylene carbonate and fluoroethylene carbonate accounting for 1 percent of the total mass of the electrolyte are added into the mixed solution, the mass ratio of the vinylene carbonate to the fluoroethylene carbonate is 1:1, and finally, lithium hexafluorophosphate accounting for 14 percent of the total mass of the electrolyte is slowly added into the mixed solution and is uniformly stirred to obtain the lithium ion battery electrolyte of the comparative example 1.
The preparation method of the lithium ion battery prepared by using the electrolyte of the comparative example is the same as that of the first example.
Comparative example 2
Preparing an electrolyte: taking an organic mixed solution of dimethyl carbonate, ethylene carbonate, methyl ethyl carbonate and ethyl propionate accounting for 85% of the total mass of the electrolyte in a glove box (the water content is less than 0.1ppm and the oxygen content is less than 0.1ppm) filled with argon, wherein the mass ratio of the dimethyl carbonate to the ethylene carbonate to the methyl ethyl carbonate to the ethyl propionate is 1:3:3: 3; and then adding an additive of vinylene carbonate and fluoroethylene carbonate which account for 1% of the total mass of the electrolyte into the mixed solution, wherein the mass ratio of the vinylene carbonate to the fluoroethylene carbonate is 1:1, finally slowly adding lithium tetrafluoroborate which accounts for 14% of the total mass of the electrolyte into the mixed solution, and uniformly stirring to obtain the lithium ion battery electrolyte of the comparative example 2.
The preparation method of the lithium ion battery prepared by using the electrolyte of the comparative example is the same as that of the first example.
Comparative example 3
Preparing an electrolyte: taking an organic mixed solution of dimethyl carbonate, ethylene carbonate, methyl ethyl carbonate and ethyl propionate accounting for 85% of the total mass of the electrolyte in a glove box (the water content is less than 0.1ppm and the oxygen content is less than 0.1ppm) filled with argon, wherein the mass ratio of the dimethyl carbonate to the ethylene carbonate to the methyl ethyl carbonate to the ethyl propionate is 1:3:3: 3; and then adding an additive of vinylene carbonate and fluoroethylene carbonate which account for 1% of the total mass of the electrolyte into the mixed solution, wherein the mass ratio of the vinylene carbonate to the fluoroethylene carbonate is 1:1, finally slowly adding lithium bis (oxalato) borate which accounts for 14% of the total mass of the electrolyte into the mixed solution, and uniformly stirring to obtain the lithium ion battery electrolyte of the comparative example 3.
The preparation method of the lithium ion battery prepared by using the electrolyte of the comparative example is the same as that of the first example.
The electrolyte and the lithium battery prepared in the above examples 1 to 8 and comparative examples 1 to 3 were respectively tested for viscosity of the electrolyte, conductivity of the lithium battery and cycle performance:
1. viscosity and conductivity test of the electrolyte at-50 ℃: the viscosities of the electrolyte samples obtained in examples 1 to 8 and comparative examples 1 to 3 were measured by using a rotational viscometer at a measurement temperature of-50 ℃, a rotor measurement range of 0.01 to 25mPa/s, and a measurement rotation speed of 60 rpm; the conductivity of the electrolyte samples obtained in examples 1 to 8 and comparative examples 1 to 3 was measured using a bench conductivity tester at a test temperature of-50 c, and the test results of each sample were averaged over three measurements, and the relevant comparative parameters are shown in table 1.
2. Charge-discharge cycling test at-50 ℃ for experimental cells: placing the lithium batteries of the examples 1-8 and the comparative examples 1-3 after capacity grading in an ultralow temperature incubator at-50 ℃ and connecting the lithium batteries with a charge and discharge tester, firstly charging the lithium batteries to 4.2V at a constant current and a constant voltage of 1C, and setting the cut-off current to 0.01C; after standing for 10min, discharging to 3.0V at a constant current of 1C, so as to perform a cyclic charge-discharge test, recording each discharge capacity, and calculating the cell capacity retention rates at 100 weeks, 150 weeks and 300 weeks, respectively, wherein the nth cycle capacity retention rate (%) of the lithium ion cell is nth cycle discharge capacity/first cycle discharge capacity 100%, and the related comparative data are shown in table 1.
Table 1:
Figure BDA0002010986890000121
as can be seen from the results of the conductivity and viscosity tests in Table 1, the electrolytes of examples 1-8 of the present invention have a higher conductivity and a lower viscosity value even at-50 ℃ due to the use of the lithium alkyl thio-oxy fluorophosphates of the present invention, and the retention rate of discharge capacity at-50 ℃ is significantly improved.
It can be seen from the cycle capacity retention rate that the lithium battery of the comparative example is almost unable to be cycled due to the rapid attenuation of the electrolyte using the normal temperature lithium salt at-50 ℃, the capacity retention rate of the conventional lithium salt lithium bis (oxalato) borate used in the comparative example 3 is only 36.45% after cycling for 100 weeks, while the capacity retention rates of the lithium batteries of the embodiments 1 to 8 of the invention are all over 80% due to the use of the alkyl sulfur-containing fluoro lithium phosphate, and the low-temperature cycle performance is greatly improved.
The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solution of the present invention by those skilled in the art should fall within the protection scope defined by the claims of the present invention without departing from the spirit of the present invention.

Claims (10)

1. A low-temperature electrolyte comprises a lithium salt, an organic solvent and an additive, and is characterized in that: the lithium salt is alkyl sulfur-containing oxygen-containing fluoro lithium phosphate, and the structure of the lithium salt is shown in a general formula (I) or a general formula (II)
Figure FDA0002828029570000011
Wherein R is1、R2、R3And R4Each independently selected from F or C1-5And R is alkyl of1、R2、R3And R4In which at least one F and one C1-5Alkyl group of (1).
2. A cryogenic electrolyte as claimed in claim 1 wherein: the organic solvent is organic carbonate C1-20At least one of alkyl ether, phenyl sulfide, carboxylic ester, sulfone, nitrile, dinitrile and phosphazene.
3. A cryogenic electrolyte as claimed in claim 2 wherein: the organic solvent is at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, 1, 4-butyrolactone, methyl ethyl carbonate, dimethyl ether, diphenyl sulfide, acetonitrile, glutaronitrile, sulfolane, pentafluoroethoxycyclotriphosphazene, methyl propionate, ethyl propionate, butyl propionate and ethyl butyrate.
4. A cryogenic electrolyte as claimed in claim 1 wherein: the additive is at least one of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, vinyl sulfate, tri (trimethylsilyl) borate, trimethyl phosphate, dimethyl methylphosphonate and hexamethyldisilazane.
5. A cryogenic electrolyte as claimed in claim 4 wherein: the additive is vinylene carbonate and fluoroethylene carbonate.
6. A cryogenic electrolyte as claimed in claim 1 wherein: based on the total mass of the electrolyte, the electrolyte comprises the following components in percentage by mass: 81-90% of organic solvent, 8-15% of lithium salt and 0.5-10% of additive.
7. A cryogenic electrolyte according to claim 6, wherein: 85-90% of organic solvent, 9-14% of lithium salt and 0.5-1% of additive.
8. A lithium battery, characterized in that: use of a low temperature electrolyte as claimed in any one of claims 1 to 7.
9. A lithium battery as claimed in claim 8, characterized in that: the positive electrode material of the lithium battery is at least one of transition metal lithium intercalation oxide, metal oxide and metal sulfide.
10. A lithium battery as claimed in claim 8, characterized in that: the negative electrode material of the lithium battery is at least one of a carbon-containing material, silicon carbon, silicon oxygen, ferrite, nitride and an alloy material.
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