CN110931871A - High-temperature-resistant electrolyte adaptive to silicon-carbon negative electrode material for lithium ion battery - Google Patents

High-temperature-resistant electrolyte adaptive to silicon-carbon negative electrode material for lithium ion battery Download PDF

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CN110931871A
CN110931871A CN201911241829.XA CN201911241829A CN110931871A CN 110931871 A CN110931871 A CN 110931871A CN 201911241829 A CN201911241829 A CN 201911241829A CN 110931871 A CN110931871 A CN 110931871A
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electrolyte
temperature
negative electrode
lithium ion
silicon
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杨书廷
李娟�
岳红云
王伟民
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Henan Battery Research Institute Co Ltd
Henan Normal University
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Henan Battery Research Institute Co Ltd
Henan Normal University
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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
    • H01M10/056—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
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention discloses a high-temperature-resistant electrolyte of a lithium ion battery adaptive to a silicon-carbon negative electrode material, which comprises lithium hexafluorophosphate, a non-aqueous organic solvent, a high-temperature-resistant additive and a negative electrode film-forming additive, wherein the high-temperature-resistant additive is pentafluorophenyl diphenyl phosphine; the negative film-forming additive is pentafluorophenyl isocyanate or fluoroethylene carbonate. The lithium ion battery high-temperature-resistant electrolyte adaptive to the silicon-carbon negative electrode material forms a compact Solid Electrolyte Interface (SEI) layer with good lithium conductivity, high melting point and high elasticity on the surface of a silicon-carbon negative electrode of a lithium ion battery and forms a thin and compact carbon (C) layer on the surface of a positive electrode through the synergistic effect of pentafluorophenyl diphenylphosphine and a negative film-forming additive pentafluorophenyl isocyanate or fluoroethylene carbonateEI film while suppressing the emission of PF5The generated side decomposition reaction of the electrolyte increases the stability of the electrolyte. The high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material obviously improves the high-temperature-resistant performance and the cycle performance of the battery.

Description

High-temperature-resistant electrolyte adaptive to silicon-carbon negative electrode material for lithium ion battery
Technical Field
The invention relates to an electrolyte, in particular to a high-temperature-resistant electrolyte of a lithium ion battery matched with a silicon-carbon negative electrode material.
Background
Over the past few decades, rechargeable lithium ion batteries have rapidly developed for reasons of high energy density, no memory effect, low self-discharge, etc. The electronic equipment market is dominated by the portable electronic equipment market at present, the portable electronic equipment market is also used for electric automobiles and unmanned planes, the daily life of people is deeply influenced, and the portable electronic equipment market plays a vital role in modern technology development. At present, the commonly used negative electrode material in commercial lithium ion batteries is mainly graphite, but the cycle life and the theoretical capacity of the lithium ion batteries cannot meet the requirements of large-scale energy storage, aerospace application, robots and electric automobiles on energy density. Therefore, finding a high capacity to replace traditional carbon-based materials is one of the hot spots in lithium ion battery research.
The silicon-based negative electrode material for the lithium ion battery has the advantages of rich reserves, low working voltage (0.2V) and high theoretical capacity (4200mAh g)-1)Far higher than that of the traditional graphite (372mAh g)-1). However, the application of silicon-based anode materials also faces a number of obstacles. The greatest challenge is the volume expansion in repeated lithiations: (>300%), which results in the pulverization of silicon-based active particles in the material on the copper foil, the continuous breakage and recombination of a Solid Electrolyte Interphase (SEI) film, thereby deteriorating the interfacial characteristics and cycle life of the lithium ion battery. The introduction of film forming additive into electrolyte is a simple method for improving the surface stability of the electrode, so that the formed SEI film can adapt to the rapid deterioration of the electrode and is not easy to break in the charging and discharging process, thereby improving the cycle performance of the battery. The electrolyte additive has the characteristics of small dosage and obvious influence on the performance of the lithium ion battery, and can obviously improve the performance of the material on the premise of not increasing the economic cost and changing the production process of the battery. The high-temperature environment is also commonly encountered in the use process of the battery, and the battery is easy to generate thermal runaway under the high-temperature condition, so that the service life of the battery is reduced, and even the service life of the battery is reducedExplosion may occur, and it is important to select a high temperature resistant additive that can inhibit the decomposition of the positive electrode material and has a good film forming effect on the negative electrode.
Disclosure of Invention
The invention aims to provide a high-temperature-resistant electrolyte of a lithium ion battery adaptive to a silicon-carbon negative electrode material, which has good high-temperature resistance and cycle performance.
The technical scheme of the invention is as follows:
the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material comprises lithium hexafluorophosphate, a non-aqueous organic solvent, a high-temperature-resistant additive and a negative electrode film forming additive, wherein the high-temperature-resistant additive is pentafluorophenyl diphenyl phosphine; the negative film forming additive is pentafluorophenyl isocyanate or fluoroethylene carbonate. The high temperature resistant additive pentafluorophenyl diphenylphosphine has the structure of formula (1):
Figure BDA0002306468990000021
in the process of charging and discharging of the battery, on one hand, a thin and compact interfacial film (CEI film for short) is formed on the surface of a positive electrode by using the high-temperature resistant additive pentafluorophenyl diphenyl phosphine; on the other hand, the high-temperature resistant additive pentafluorophenyl diphenyl phosphine can be taken as Lewis base in the electrolyte to react with PF5Good complexation and thus active PF5Complexing with pentafluorophenyl diphenyl phosphine to remove LiPF from electrolyte6PF produced by micro decomposition of5In time inhibit PF5The catalytic destruction effect on the electrolyte is realized, and the LiPF is effectively reduced6The related side reaction occurs, thereby preventing the decomposition of the electrolyte and improving the LiPF content6The stability of the electrolyte reduces the occurrence of side reactions at SEI and CEI films, and improves the cycle life and the thermal stability of the battery.
The negative electrode film forming additive, namely the pentafluorophenyl isocyanate and the fluoroethylene carbonate, both have reductive polymerization reaction capability, can form a compact SEI layer with good lithium conductivity, high melting point and high elasticity on the surface of a silicon-carbon negative electrode, can inhibit the decomposition of a carbonate solvent, bear the volume expansion generated by silicon oxide in the repeated charge and discharge process of a battery, reduce the gas generation of the battery, ensure that the battery has better cycle stability, and have good capacity recovery rate and retention rate at high temperature.
In the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material, a high-temperature-resistant additive pentafluorophenyl diphenyl phosphine and a negative film forming additive pentafluorophenyl isocyanate or fluoroethylene carbonate are simultaneously added, and due to the fact that the pentafluorophenyl diphenyl phosphine generates a trace amount of PF in a side reaction5Complexing in time to prevent further side reactions; meanwhile, a thin and compact CEI film is formed on the surface of the positive electrode by the pentafluorophenyl diphenyl phosphine, and an SEI layer which is compact, good in lithium conductivity, high in melting point and high in elasticity is formed on the silicon-carbon negative electrode by the pentafluorophenyl isocyanate or the fluoroethylene carbonate, so that the high temperature resistance and the cycle performance of the battery are remarkably improved under the synergistic effect of the pentafluorophenyl isocyanate or the fluoroethylene carbonate.
Preferably, the high temperature resistant additive further comprises 1, 3-propanedisulfonic anhydride. 1, 3-propanedisulfonic anhydride has the structure of formula (2).
Figure BDA0002306468990000022
The high-temperature resistant additive 1, 3-propane disulfonic anhydride can form an SEI film on the surface of the silicon-carbon cathode in advance of a solvent, so that co-intercalation of solvent molecules can be effectively prevented, and the inhibition of side reactions on the surface of an electrode of a lithium ion battery during long-term charge-discharge cycles is facilitated, so that the cycle performance and the service life of the electrode are greatly improved; the 1, 3-propanedisulfonic anhydride also forms a thin and compact CEI film on the surface of the positive electrode, so that the oxidation of electrolyte is effectively inhibited, the interface impedance of the electrode is stabilized, the cycling stability of the battery is improved, and the high-temperature storage performance of the battery is improved.
Preferably, the pentafluorophenyl diphenyl phosphine accounts for 0.05-1% of the total mass of the electrolyte.
Preferably, the mass of the 1, 3-propanedisulfonic anhydride accounts for 0.5-3% of the total mass of the electrolyte.
Preferably, the mass of the negative electrode film forming additive accounts for 1-5% of the total mass of the electrolyte.
The lithium hexafluorophosphate as the lithium salt may be prepared in a desired concentration as long as it satisfies the use requirement of the battery, and in the present invention, it is preferable that the mass of lithium hexafluorophosphate is 14% of the total mass of the electrolyte.
The non-aqueous organic solvent can be selected according to requirements, and preferably is one or more of ethylene carbonate, ethyl methyl carbonate or diethyl carbonate. The high-temperature-resistant electrolyte of the lithium ion battery with the silicon-carbon negative electrode material uses the substances as the non-aqueous organic solvent, so that the high-temperature resistance and the cycle performance of the lithium ion battery are improved more obviously, and the proportion of the substances in the non-aqueous organic solvent can be selected according to the requirements, for example, the substances can be the mixture of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate in the mass ratio of 1:1: 1; more preferably, the non-aqueous organic solvent is ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in a mass ratio of 3: 3: 4, and (4) mixing.
The invention has the beneficial effects that:
the lithium ion battery high-temperature resistant electrolyte adaptive to the silicon-carbon negative electrode material forms a compact SEI (solid electrolyte interphase) layer with good lithium conductivity, high melting point and high elasticity on the surface of a silicon-carbon negative electrode of a lithium ion battery and a thin and compact CEI (ceramic electrolyte interface) film on the surface of a positive electrode by the synergistic effect of a high-temperature resistant additive pentafluorophenyl diphenylphosphine and a negative film forming additive pentafluorophenyl isocyanate or fluoroethylene carbonate, and simultaneously inhibits PF (positive electrode active substance)5The generated side decomposition reaction of the electrolyte increases the stability of the electrolyte. Therefore, the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material obviously improves the high-temperature-resistant performance and the cycle performance of the battery.
Detailed Description
The present invention will be described in detail with reference to examples. In the following description, pentafluorophenyl diphenylphosphine is abbreviated as PFPDPP, 1, 3-propanedisulfonic anhydride is abbreviated as ODTO, pentafluorophenyl isocyanate is abbreviated as PFPI, fluoroethylene carbonate is abbreviated as FEC, diethyl carbonate is abbreviated as DEC, methylethyl carbonate is abbreviated as EMC, and ethylene carbonate is abbreviated as EC.
Example 1
DEC, EMC and EC were mixed uniformly in a 4:3:3 mass ratio in an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), 3.0% of FEC and 0.3% of PFPDPP were added to the mixed solution, and 14% of LiPF based on the total mass of electrolyte was slowly added to the mixed solution6And stirring until the solution is completely dissolved to obtain the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material.
Example 2
DEC, EMC and EC were mixed uniformly in a 4:3:3 mass ratio in an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), 3.0% of FEC, 0.3% of PFPDPP and 0.5% of ODTO were added to the mixed solution, and 14% of LiPF based on the total mass of electrolyte was slowly added to the mixed solution6And stirring until the solution is completely dissolved to obtain the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material.
Example 3
DEC, EMC and EC were mixed uniformly in a 4:3:3 mass ratio in an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), 3.0% of FEC, 0.3% of PFPDPP and 3.0% of ODTO were added to the mixed solution, and 14% of LiPF based on the total mass of electrolyte was slowly added to the mixed solution6And stirring until the solution is completely dissolved to obtain the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material.
Example 4
DEC, EMC and EC were mixed uniformly in a 4:3:3 mass ratio in an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), 3.0% of FEC, 0.3% of PFPDPP and 1.0% of ODTO were added to the mixed solution, and 14% of LiPF based on the total mass of electrolyte was slowly added to the mixed solution6And stirring until the solution is completely dissolved to obtain the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material.
Example 5
In an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), DEC, EMC, EC were mixed at 4:3:3The amount ratio is evenly mixed, FEC accounting for 3.0 percent of the total mass of the electrolyte, PFPDPP accounting for 0.05 percent of the total mass of the electrolyte and ODTO accounting for 1.0 percent of the total mass of the electrolyte are added into the mixed solution, and LiPF accounting for 14 percent of the total mass of the electrolyte is slowly added into the mixed solution6And stirring until the solution is completely dissolved to obtain the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material.
Example 6
DEC, EMC and EC were mixed uniformly in a 4:3:3 mass ratio in an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), 3.0% of FEC, 1.0% of PFPDPP and 1.0% of ODTO were added to the mixed solution, and 14% of LiPF based on the total mass of electrolyte was slowly added to the mixed solution6And stirring until the solution is completely dissolved to obtain the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material.
Example 7
DEC, EMC and EC were mixed uniformly in a 4:3:3 mass ratio in an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), 1.0% of FEC and 0.05% of PFPDPP were added to the mixed solution, and 14% of LiPF based on the total mass of electrolyte was slowly added to the mixed solution6And stirring until the solution is completely dissolved to obtain the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material.
Example 8
DEC, EMC and EC were mixed uniformly in a 4:3:3 mass ratio in an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), 1.0% of FEC, 0.3% of PFPDPP and 1.0% of ODTO were added to the mixed solution, and 14% of LiPF based on the total mass of electrolyte was slowly added to the mixed solution6And stirring until the solution is completely dissolved to obtain the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material.
Example 9
DEC, EMC and EC were mixed uniformly in a 4:3:3 mass ratio in an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), 5.0% of FEC, 0.3% of PFPDPP and 1.0% of ODTO were added to the mixed solution based on the total mass of the electrolyte, and then electricity-based solution was slowly added to the mixed solutionLiPF accounting for 14% of total mass of electrolyte6And stirring until the solution is completely dissolved to obtain the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material.
Example 10
In an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), DEC, EMC, and EC were mixed uniformly at a mass ratio of 4:3:3, PFPI 1.0%, PFPDPP 0.3%, and ODTO 1.0% based on the total mass of the electrolyte were added to the mixed solution, and LiPF 14% based on the total mass of the electrolyte was slowly added to the mixed solution6And stirring until the solution is completely dissolved to obtain the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material.
Example 11
DEC, EMC and EC were mixed uniformly in a 4:3:3 mass ratio in an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), PFPI 2.0%, PFPDPP 0.3%, ODTO 1.0% based on the total mass of the electrolyte were added to the mixed solution, and LiPF 14% based on the total mass of the electrolyte was slowly added to the mixed solution6And stirring until the solution is completely dissolved to obtain the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material.
Example 12
DEC, EMC and EC were mixed uniformly in a 4:3:3 mass ratio in an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), PFPI 5.0%, PFPDPP 0.3%, ODTO 1.0% based on the total mass of the electrolyte were added to the mixed solution, and LiPF 14% based on the total mass of the electrolyte was slowly added to the mixed solution6And stirring until the solution is completely dissolved to obtain the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material.
Example 13
In an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), DEC, EMC and EC were mixed uniformly at a mass ratio of 4:3:3, PFPI (1.0% based on the total mass of the electrolyte) and PFPDPP (0.05%) were added to the mixed solution, and LiPF (14% based on the total mass of the electrolyte) was slowly added to the mixed solution6And stirring until the solution is completely dissolved to obtain the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material.
Example 14
DEC, EMC and EC were mixed uniformly in a 4:3:3 mass ratio in an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), 5.0% of FEC, 1.0% of PFPDPP and 0.5% of ODTO were added to the mixed solution, and 14% of LiPF based on the total mass of electrolyte was slowly added to the mixed solution6And stirring until the solution is completely dissolved to obtain the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material.
Example 15
DEC, EMC and EC were mixed uniformly in a 4:3:3 mass ratio in an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), PFPI 5.0%, PFPDPP 1.0%, ODTO 3.0% based on the total mass of the electrolyte were added to the mixed solution, and LiPF 14% based on the total mass of the electrolyte was slowly added to the mixed solution6And stirring until the solution is completely dissolved to obtain the high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material.
Comparative example 1
DEC, EMC and EC were mixed uniformly in a 4:3:3 mass ratio in an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), and then 14% of LiPF based on the total mass of the electrolyte was slowly added to the mixed solvent6And stirring until the electrolyte is completely dissolved to obtain the lithium ion battery electrolyte.
Comparative example 2
Mixing DEC, EMC and EC at a mass ratio of 4:3:3 in an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), adding PFPDPP in an amount of 0.3% based on the total mass of the electrolyte to the mixed solution, and slowly adding LiPF in an amount of 14% based on the total mass of the electrolyte to the mixed solution6And stirring until the electrolyte is completely dissolved to obtain the lithium ion battery electrolyte.
Comparative example 3
DEC, EMC and EC were mixed uniformly in a 4:3:3 mass ratio in an argon-filled glove box (moisture < 1ppm, oxygen < 1ppm), PFPDPP 0.3% based on the total mass of the electrolyte and ODTO 1.0% based on the total mass of the electrolyte were added to the mixed solution, and LiPF 14% based on the total mass of the electrolyte was slowly added to the mixed solution6And stirring until the electrolyte is completely dissolved to obtain the lithium ion battery electrolyte.
In order to more clearly illustrate the examples and the comparative examples, the formulations of the refractory electrolytes of lithium ion batteries prepared by the above examples and adapted to silicon-carbon negative electrode materials and the formulations of the electrolytes prepared by various proportions are shown in table 1.
And (3) performance testing:
and (3) manufacturing a positive electrode: LiNi serving as a positive electrode active material0.5Co0.2Mn0.3O2Acetylene black and polyvinylidene fluoride according to a mass ratio of 95: 2: 3, uniformly mixing, and then dispersing in N-methyl-2-pyrrolidone to obtain anode slurry; and uniformly coating the anode slurry on two sides of the aluminum foil, rolling, slitting and die-cutting to obtain an anode plate, and finally baking and vacuum drying for later use.
And (3) manufacturing a negative electrode: silicon carbon cathode material SiOx-C, acetylene black, styrene butadiene rubber and carboxymethyl cellulose in a mass ratio of 95: 1: 2: 2, uniformly mixing, and then dispersing in deionized water to obtain negative electrode slurry; and uniformly coating the negative electrode slurry on two surfaces of the copper foil, rolling, slitting and die cutting to obtain a negative electrode sheet, and finally baking and vacuum drying for later use.
And laminating, spot welding, encasing and baking the manufactured positive pole piece and negative pole piece to obtain the battery core of the soft package battery. And respectively injecting the lithium ion battery electrolytes prepared in examples 1-15 and comparative examples 1-3 into different soft package battery cells of the same batch prepared above, and performing processes of packaging, laying aside, formation, aging, air extraction packaging, capacity grading and the like after liquid injection to obtain the silicon-carbon negative electrode lithium ion battery.
The lithium ion batteries prepared above were subjected to the following performance tests, respectively, and the test results are shown in table 2.
(1) And (3) testing the normal-temperature cycle performance: the batteries after capacity grading were charged to 4.2V with a constant current of 0.5C at a constant voltage and a cutoff current of 0.05C at 25C, and then discharged to 3.0V with a constant current of 0.5C. And calculating the capacity retention rate of the 800 th cycle after 800 cycles of charging and discharging. The calculation formula is as follows:
the 800 th cycle capacity retention (%) was (800 th cycle discharge capacity/1 st cycle discharge capacity) × 100%;
(2) high-temperature storage performance: charging the batteries after capacity grading to 4.2V at a constant current and a constant voltage of 0.5C at 25 ℃, stopping the current to 0.05C, then discharging to 3.0V at a constant current of 0.5C, recording the discharge capacity, and taking the discharge capacity as the initial capacity of the batteries before storage; then charging the battery to 4.2V at constant current and constant voltage, wherein the cut-off current is 0.05C, namely the battery is in a full state, and measuring the thickness of the battery as the initial thickness; then, the battery is placed in a 60 ℃ oven for storage for 7 days, and after the storage is finished, the battery is taken out and cooled to 25 ℃ and the thickness of the battery is measured to be used as the final thickness; then, the discharge capacity of the battery is measured as the retention capacity of the battery by discharging from 0.5C to 3.0V, and the discharge capacity is recorded as the recovery capacity by charging and discharging for 1 time (4.2-3.0V) at the temperature of 25 ℃ in a 0.5C cycle. The calculation formula is as follows:
battery thickness expansion (%) (final thickness-initial thickness)/initial thickness × 100%;
battery capacity retention (%) — retention capacity/initial capacity × 100%;
the battery capacity recovery ratio (%) — recovery capacity/initial capacity × 100%.
(3) And (3) testing high-temperature cycle performance: at 60 ℃, the battery after capacity grading is charged to 4.2V with a constant current and a constant voltage of 0.5C and the cut-off current is 0.05C, and then discharged to 3.0V with a constant current of 0.5C. The retention rate of the capacity at the 300 th cycle was calculated after 300 cycles according to the above charge-discharge system. The calculation formula is as follows:
the 300 th cycle capacity retention ratio (%) (300 th cycle discharge capacity/1 st cycle discharge capacity) × 100%.
The results of the above performance tests for the examples are shown in table 2.
TABLE 1
Electrolyte composition and mass percentage of each embodiment and each proportion
Figure BDA0002306468990000081
TABLE 2
Performance test results of lithium ion batteries corresponding to each embodiment and each comparative example
Figure BDA0002306468990000091
From the above results, it can be seen that the PFPDPP additive improves the high temperature performance of the battery. On one hand, fluorine and phosphorus free radicals in PFPDPP can better capture hydrogen free radicals of electrolyte, reduce heat released during thermal polymerization of electrolyte and further improve thermal stability of the battery; on the other hand, a thin and stable passivation film is formed on the surface of the positive electrode, so that the thermal stability of the battery is improved; at the same time, PFPDPP improves LiPF through complexation6Stability of (2), reduction of LiPF6The HF generated by decomposition protects the anode material and the aluminum foil current collector from being corroded by the HF in the circulation process, and effectively avoids the volume expansion and internal resistance increase of the battery caused by the reaction of the HF and the silicon-carbon cathode to generate gas.
The addition of the ODTO additive further improves the normal-temperature and high-temperature cycle performance of the battery. This may be due to the fact that ODTO may be around 1.4V vs. Li/Li+An SEI film is formed on the surface of graphite under the potential, and a CEI film is formed on the positive electrode, so that the side reaction between the electrolyte and the electrode is inhibited, the loss of active lithium is weakened, the interface impedance of the electrode/electrolyte is stabilized, and the cycle life of the battery is prolonged.
The addition of the FEC or PFPI additive improves the cycle stability and the high-temperature storage performance of the battery, the FEC or PFPI can form a stable, compact and LiF-rich SEI film on the surface of the silicon-carbon cathode, LiF can effectively relieve the volume change of silicon oxide particles in the cycle process, and reduce the cracking and crushing of the silicon oxide particles; the formed SEI film can prevent small molecular compounds from diffusing and migrating to the inner layer, so that the hydrolysis and electrochemical reduction side reactions of electrolyte components are reduced.
It can be seen from the components used in the electrolytes in comparative examples 1 and 2 and the electrical performance test results of the prepared lithium ion batteries that the thickness expansion rate, the capacity retention rate, the capacity recovery rate and the capacity retention rate of the lithium ion battery prepared by the electrolyte in which the high temperature resistant additive PFPDPP is only added are much better than those of the lithium ion battery prepared by the electrolyte without the high temperature resistant additive and the negative film forming additive of the invention after being cycled for 300 times at 60 ℃; it can be seen from the components used in the electrolytes of examples 7 and 13 and comparative examples 2 and 3 and the electrical property test results of the prepared lithium ion batteries that the high temperature resistant additive and the negative film forming additive are added into the electrolyte of the invention, the electrical property of the prepared lithium ion batteries is obviously improved, which is much better than that of the lithium ion batteries added with the high temperature resistant additive alone, which indicates that the high temperature resistant additive PFPDPP and the negative film forming additive FEC or PFPI in the invention have synergistic effect. According to the invention, through the synergistic effect of the high-temperature-resistant additive and the negative film-forming additive, the electrolyte can form a good interface film on the surface of the electrode, the damage of HF to the silicon-carbon negative electrode is delayed, the normal-temperature and high-temperature cycle stability of the silicon-carbon negative electrode lithium ion battery is enhanced, the gas generation of the battery during high-temperature storage is effectively inhibited, the high-temperature storage performance of the battery is obviously improved, and the thickness expansion rate of the battery is reduced, and the capacity retention rate and the recovery rate are improved.
It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. The technical features of the embodiments of the present invention described above may be combined with each other as long as they do not conflict with each other, and it is obvious to those skilled in the art that variations or modifications in other different forms may be made on the basis of the above description. Not all embodiments are exhaustive. All obvious changes and modifications which are obvious to the technical scheme of the invention are covered by the protection scope of the invention.

Claims (8)

1. The high-temperature-resistant electrolyte of the lithium ion battery, which is matched with a silicon-carbon negative electrode material, is characterized by comprising lithium hexafluorophosphate, a non-aqueous organic solvent, a high-temperature-resistant additive and a negative electrode film forming additive, wherein the high-temperature-resistant additive is pentafluorophenyl diphenyl phosphine; the negative film forming additive is pentafluorophenyl isocyanate or fluoroethylene carbonate.
2. The high temperature resistant electrolyte for lithium ion batteries adapted to silicon carbon negative electrode materials according to claim 1, wherein the high temperature resistant additive further comprises 1, 3-propanedisulfonic anhydride.
3. The high-temperature-resistant lithium ion battery electrolyte adaptive to the silicon-carbon negative electrode material as claimed in claim 2, wherein the pentafluorophenyl diphenyl phosphine accounts for 0.05-1% of the total mass of the electrolyte.
4. The high-temperature-resistant electrolyte for the lithium ion battery with the silicon-carbon negative electrode material adapted to the claim 3, wherein the mass of the 1, 3-propanedisulfonic anhydride accounts for 0.5-3% of the total mass of the electrolyte.
5. The high-temperature-resistant electrolyte for the lithium ion battery with the silicon-carbon negative electrode material adapted to the claim 4, wherein the mass of the negative electrode film-forming additive accounts for 1-5% of the total mass of the electrolyte.
6. The high-temperature-resistant electrolyte for the lithium ion battery adapting to the silicon-carbon negative electrode material, which is prepared by the method according to one of claims 1 to 5, wherein the mass of the lithium hexafluorophosphate accounts for 14% of the total mass of the electrolyte.
7. The high-temperature-resistant electrolyte of the lithium ion battery matched with the silicon-carbon negative electrode material as claimed in one of claims 1 to 5, wherein the non-aqueous organic solvent is one or more of ethylene carbonate, ethyl methyl carbonate or diethyl carbonate.
8. The high-temperature-resistant electrolyte of the lithium ion battery adaptive to the silicon-carbon negative electrode material, according to claim 7, wherein the non-aqueous organic solvent is ethylene carbonate, ethyl methyl carbonate and diethyl carbonate, and the mass ratio of the non-aqueous organic solvent to the diethyl carbonate is 3: 3: 4, and (4) mixing.
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