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CN115172879B - Lithium ion battery electrolyte and lithium ion battery containing the electrolyte - Google Patents

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

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Publication number
CN115172879B
CN115172879B CN202210903898.8A CN202210903898A CN115172879B CN 115172879 B CN115172879 B CN 115172879B CN 202210903898 A CN202210903898 A CN 202210903898A CN 115172879 B CN115172879 B CN 115172879B
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lithium
ion battery
electrolyte
lithium ion
carbonate
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CN115172879A (en
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刘春彦
孙操
惠银银
钱雨涛
甘朝伦
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Zhangjiagang Guotai Huarong New Chemical Materials 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
    • H01M10/056—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
    • 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

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  • Condensed Matter Physics & Semiconductors (AREA)
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  • Inorganic Chemistry (AREA)
  • Secondary Cells (AREA)

Abstract

本发明涉及一种锂离子电池电解液及含有该电解液的锂离子电池。为了解决现有锂离子电池电解液无法同时兼顾高电压条件下的循环性能和高温性能的问题，本发明提供一种锂离子电池电解液，包括非水有机溶剂、锂盐和添加剂，添加剂包括硅氮类化合物以及选择性地包括氮杂环‑三氟化硼配位化合物，本发明中使用的硅氮类化合物可以改善电解液在存储过程中HF的产生，可以提高电解液在高电压条件下的耐氧化性，而氮杂环‑三氟化硼配位化合物可以提高正极固体表面膜中LiF的溶解度，降低固体界面膜的阻抗，两者协同作用可以提升电池在高电压条件下的循环性能、高温性能。The present invention relates to a lithium ion battery electrolyte and a lithium ion battery containing the electrolyte. In order to solve the problem that the existing lithium ion battery electrolyte cannot take into account both the cycle performance and high temperature performance under high voltage conditions, the present invention provides a lithium ion battery electrolyte, including a non-aqueous organic solvent, a lithium salt and an additive, the additive including a silicon nitrogen compound and selectively including a nitrogen heterocycle-boron trifluoride coordination compound, the silicon nitrogen compound used in the present invention can improve the generation of HF in the electrolyte during storage, and can improve the oxidation resistance of the electrolyte under high voltage conditions, while the nitrogen heterocycle-boron trifluoride coordination compound can increase the solubility of LiF in the positive electrode solid surface film and reduce the impedance of the solid interface film, and the synergistic effect of the two can improve the cycle performance and high temperature performance of the battery under high voltage conditions.

Description

Lithium ion battery electrolyte and lithium ion battery containing same
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to lithium ion battery electrolyte and a lithium ion battery containing the same.
Background
The lithium ion battery has the advantages of high capacity, high energy density, environmental friendliness and the like, and is rapidly developed in the fields of mobile equipment, electric automobiles and energy storage. The lithium ion battery can be divided into a liquid lithium ion battery, a solid lithium ion battery and a solid-liquid mixture, namely a so-called semi-solid lithium ion battery according to the state of electrolyte, the technology of the solid lithium ion battery is not perfected so far, the problems of low circulation efficiency, serious capacity attenuation and the like of the solid lithium ion battery are caused by the low ionic conductivity and interface contact problem of a solid film, and the problem can be relieved by adding a small amount of electrolyte into the solid film, but the requirement of current life can not be met, so that the liquid lithium ion battery still takes the dominant role in a short term.
The liquid electrolyte consists of a nonaqueous organic solvent, lithium salt and additives, wherein the common lithium salt is lithium hexafluorophosphate, is unstable in the electrolyte and can react with a small amount of water to generate hydrofluoric acid, so that on one hand, effective lithium ions in the electrolyte are consumed, on the other hand, the HF can dissolve transition metal oxide materials in the positive electrode into the electrolyte to damage the structure of the positive electrode material, thereby reducing the battery capacity, and the phenomenon is more obvious in a high-temperature state. The method is characterized in that the electrolyte is prepared from a solution of a carbonic acid ester, a material and an additive, wherein the solution is prepared from a solution of a carbonic acid ester, a material and an additive, the solution is prepared from a solution of a carbonic acid ester, a material and the additive, and the solution is prepared from a solution of a carbonic acid ester, a material and the additive. However, in order to solve the problems of the battery, a synergistic effect between various additives is generally required, which not only brings about higher cost, but also the internal resistance of the battery is not easy to control, so that it is highly desirable to find a multi-compatible additive to solve the problems of the battery.
Disclosure of Invention
The invention aims to provide a lithium ion battery electrolyte which can simultaneously achieve cycle performance and high-temperature performance under a high-voltage condition.
Another object of the present invention is to provide a lithium ion battery excellent in high temperature performance.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
A lithium ion battery electrolyte comprises a nonaqueous organic solvent, lithium salt and an additive, wherein the additive comprises a silazane compound shown as a formula I and optionally comprises a nitrogen heterocycle-boron trifluoride coordination compound
Wherein Z in the formula I is sulfonyl or carbonyl, R1, R2 and R3 are respectively and independently selected from any one of halogen atoms, halogen substituted or unsubstituted aryl groups, halogen substituted or unsubstituted alkyl or alkenyl groups containing 1-4 carbon atoms, and R4, R5, R6 and R7 are respectively and independently selected from any one of hydrogen, halogen atoms, nitro, amino and halogen substituted or unsubstituted alkyl or alkenyl groups containing 1-4 carbon atoms.
The silicon-nitrogen compound with a specific structure used in the invention has 1) higher HUMO electron orbits, so that the capability of obtaining electrons is poor, oxidation is not easy, the potential window of electrolyte is widened, sufficient conditions are provided for the electrolyte to work under high voltage conditions, 2) the introduction of silane groups in the silicon-nitrogen compound can consume moisture existing in the electrolyte, the reaction link of the moisture and lithium hexafluorophosphate for generating HF is blocked, the corrosion of the HF on a positive electrode material and the dissolution of transition metal ions therein are avoided, thereby prolonging the service life of a battery, 3) the silicon-nitrogen compound can generate an SEI film through reduction reaction on the surface of a negative electrode, and because of the existence of lone pair electrons in hetero atoms such as S, N, the transmission rate of electrons in an interface can be improved after two elements participate in the formation of a solid interface film, the interface resistance of the battery can be reduced, and the cycle efficiency of the battery is improved. Further, the silicon nitrogen compound with a specific structure and the nitrogen heterocycle-boron trifluoride complex compound are combined in a compounding way, so that the high-temperature resting performance and the high-temperature cycle performance of the battery are further improved, besides the N atom in the nitrogen heterocycle-boron trifluoride complex compound can realize the function in 3), a thin and compact solid interface film can be formed on the surface of the positive electrode, the B atom can be complexed with transition metal ions in the positive electrode material, the dissolution of the transition metal ions from the material is reduced, and the problem that the cycle capacity of the battery is influenced due to structural collapse of the positive electrode material is avoided.
Preferably, R1, R2 and R3 are each independently halogen substituted or unsubstituted alkyl or alkenyl containing 1-4 carbon atoms, and R4, R5, R6 and R7 are each independently selected from any one of hydrogen, halogen atoms and halogen substituted or unsubstituted alkyl or alkenyl containing 1-4 carbon atoms.
Further preferably, R1, R2, R3 are each independently halogen substituted or unsubstituted methyl, R4, R5, R6, R7 are each independently any one of hydrogen, unsubstituted alkyl or alkenyl groups having 1 to 4 carbon atoms.
Still more preferably, R1, R2 and R3 in the formula I are the same and are selected from one of fluorine atoms, methyl groups and trifluoromethyl groups, and at least two of R4, R5, R6 and R7 are hydrogen atoms.
According to some preferred embodiments, the silazane compound is
One or more of the following.
Specifically, the preparation method of the compound 3 comprises the steps of reacting o-benzoyl sulfimide with tris (trifluoromethyl) chlorosilane in the presence of n-butyl lithium and tetrahydrofuran at a temperature of-80 ℃ to-65 ℃ in a nitrogen atmosphere to obtain the compound 3.
Further, the phthaloyl sulfimide is dissolved in dry tetrahydrofuran, the solution is cooled to-80 ℃ to-65 ℃, then n-butyllithium with the concentration of 2-3 mol/L is added into the cooling liquid under the nitrogen atmosphere, the heat preservation reaction is carried out for 80-100 min, and then tris (trifluoromethyl) chlorosilane is added for continuous heat preservation reaction for 1.5-2.5 h, so that the product 3 is obtained.
Specifically, the preparation method of the compound 4 comprises the steps of reacting phthalimide with tris (trifluoromethyl) chlorosilane in the presence of n-butyllithium and tetrahydrofuran at-80 ℃ to-65 ℃ in nitrogen atmosphere to obtain the compound 3.
Further, the phthalimide is dissolved in dry tetrahydrofuran, the solution is cooled to-80 ℃ to-65 ℃, then n-butyllithium with the concentration of 2-3 mol/L is added into the cooling liquid under the nitrogen atmosphere, the heat preservation reaction is carried out for 80-100 min, and then tri (trifluoromethyl) chlorosilane is added for continuous heat preservation for 1.5-2.5 h, so that the product 4 can be obtained.
Preferably, the nitrogen heterocycle in the nitrogen heterocycle-boron trifluoride compound is one or more of a pyridine group-containing heterocycle, a pyridazinyl group-containing heterocycle, a pyrimidine group-containing heterocycle, a pyrazinyl group-containing heterocycle, a pyrrole group-containing heterocycle, a pyrazole group-containing heterocycle and an imidazole group-containing heterocycle.
According to some preferred embodiments, the nitrogen heterocycle-boron trifluoride complex is pyridine-boron trifluoride.
Preferably, the nitrogen heterocycle-boron trifluoride complex accounts for 0.05% -2% of the total mass of the lithium ion battery electrolyte, for example 0.05％,0.1％,0.2％,0.3％,0.4％,0.5％,0.6％,0.7％,0.8％,0.9％,1％,1.1％,1.2％,1.3％,1.4％,1.5％,1.6％,1.7％,1.8％,1.9％,2％.
Preferably, the silicon-nitrogen compound accounts for 0.05% -5% of the total mass of the lithium ion battery electrolyte, for example, 0.05%,0.1%,0.5%,1%,1.5%,2%,2.5%,3%,3.5%,4%,4.5%,5%.
Preferably, the additive further comprises 0.05% -5% of other additives, such as 0.05%,0.1%,0.5%,1%,1.5%,2%,2.5%,3%,3.5%,4%,4.5%,5% of the total mass of the lithium ion battery electrolyte.
Preferably, the other additive is one or more of succinonitrile, adiponitrile, fluoroethylene carbonate, 1, 3-propane sultone, vinyl sulfate, methylene methylsulfonate, propylene sulfate, tris (trimethylsilyl) borate, tris (trimethylsilyl) phosphite, tris (trimethylsilyl) phosphate, ethylene carbonate, maleic anhydride, glutaric anhydride.
Further preferably, the other additives are fluoroethylene carbonate and adiponitrile.
Preferably, the lithium salt is selected from one or more of lithium perchlorate, lithium tetrafluoroborate, lithium difluorooxalato borate, lithium hexafluorophosphate, lithium carbonate, lithium sulfate, lithium sulfite, lithium nitrate, lithium bis (trifluoromethylsulfonyl) imide, lithium difluorophosphate, and lithium difluorobis oxalato phosphate.
Preferably, the concentration of the lithium salt is 0.5-5 mol/L, for example 0.5mol/L,1mol/L,1.5mol/L,2mol/L,2.5mol/L,3mol/L,3.5mol/L,4mol/L,4.5mol/L,5mol/L.
Preferably, the nonaqueous organic solvent is one or more of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethylene carbonate, methyl formate, ethyl acetate, methyl butyrate, methyl acrylate, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, acetonitrile, N-dimethylformamide, sulfolane, dimethyl sulfoxide, methyl sulfide, gamma-butyrolactone and tetrahydrofuran.
Further preferably, the nonaqueous organic solvent is a mixture of diethyl carbonate, ethylene carbonate and ethylmethyl carbonate.
The invention also provides a lithium ion battery, which comprises a positive plate, a negative plate, a separation film arranged between the positive plate and the negative plate and electrolyte, wherein the electrolyte is the lithium ion battery electrolyte.
Preferably, the positive electrode material is a lithium transition metal composite oxide, and the lithium transition metal composite oxide contains one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, or a compound obtained by adding other transition metals or non-transition metals to the lithium transition metal composite oxide.
Preferably, the negative electrode material is selected from one or more of soft carbon, hard carbon, artificial graphite, natural graphite, silicon oxygen compound, silicon carbon compound, lithium titanate and metal capable of forming alloy with lithium.
Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages:
The silicon-nitrogen compound additive in the lithium ion battery electrolyte can greatly reduce the generation of HF in the electrolyte, avoid the structural collapse of the anode material in the shelving process, and lead the heteroatom N introduced by the silicon-nitrogen compound additive to contain lone pair electrons, so that the resistance of electrons passing through the anode interface film can be reduced, thereby reducing the internal resistance of the battery, and further leading the lithium ion battery electrolyte to be capable of simultaneously taking into account the high-temperature shelving performance and the high-temperature cycle performance. Further, the pyridine-boron trifluoride can form an anode interfacial film on the surface of the anode material, and the silicon-nitrogen compound additive and the nitrogen heterocycle-boron trifluoride coordination compound additive are combined, so that the oxidation of the anode to the electrolyte under the conditions of high voltage and high temperature can be further reduced, the gas production of the battery in the high-temperature shelving process is reduced, and the electrolyte further shows more excellent high-temperature performance.
Detailed Description
The technical scheme, the implementation process and the principle thereof are further explained below. It should be understood that the examples described in this specification are for the purpose of illustrating the invention only and are not intended to limit the invention. The implementation conditions adopted in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions which are not noted are conventional conditions in the industry. The technical features of the various embodiments of the present invention may be combined with each other as long as they do not collide with each other.
In the following examples and comparative examples, all the raw materials used were commercially available unless otherwise specified.
In the following examples and comparative examples, compound 3 and Compound 4 were self-made by the preparation method described in patent US4181660A, compound 3 was prepared by reacting 0.36mol of O-benzoylsulfonylimideDissolving in 600ml of dry tetrahydrofuran, cooling the solution to-73 ℃, adding 130ml of n-butyllithium with the concentration of 2.4mol/L into the cooling liquid under nitrogen atmosphere, carrying out heat preservation reaction for 90min, adding 0.3mol of tris (trifluoromethyl) chlorosilane, and carrying out heat preservation reaction for 2h to obtain the product 3.
The preparation method of the compound 4 comprises the steps of mixing 0.36mol of phthalimideDissolving in dry 600ml tetrahydrofuran, cooling the solution to-73 ℃, adding 130ml of n-butyllithium with the concentration of 2.4mol/L into the cooling liquid under nitrogen atmosphere, carrying out heat preservation reaction for 90min, adding 0.3mol of tris (trifluoromethyl) chlorosilane, and carrying out heat preservation for 2h to obtain the product 4.
Example 1
The electrolyte is prepared by mixing diethyl carbonate (DEC), ethylene Carbonate (EC) and ethylmethyl carbonate (EMC) in a weight ratio of 20:30:50, fully dissolving 1M lithium salt LiPF 6, adding fluoroethylene carbonate accounting for 2 percent of the total weight of the electrolyte, adiponitrile accounting for 0.3 percent of the total weight of the electrolyte and compound 1 accounting for 0.5 percent of the total weight of the electrolyte.
And (3) preparing a positive plate, namely fully stirring and uniformly mixing the ternary NCM622 of the positive active material, acetylene black serving as a conductive agent and polyvinylidene fluoride (PVDF) serving as a binder in an N-methylpyrrolidone solvent system according to a mass ratio of 95:3:2, coating the mixture on an Al foil of a positive current collector, and drying and cold pressing the mixture to obtain the positive plate.
The preparation of the negative plate comprises the steps of fully and uniformly stirring and mixing negative active substances graphite, a conductive agent acetylene black, a binder Styrene Butadiene Rubber (SBR) and a thickener sodium carboxymethylcellulose (CMC) in a deionized water solvent system according to a mass ratio of 95:2:2:1, coating the mixture on a negative current collector Cu foil, and drying and cold pressing the mixture to obtain the negative plate.
And (3) preparing a separation membrane, namely taking the PE porous polymer film as the separation membrane.
The preparation of the lithium ion battery comprises the steps of sequentially stacking the prepared positive plate, the isolation film and the prepared negative plate, enabling the isolation film to be positioned between the positive plate and the negative plate to play a role in isolation, winding to obtain a bare cell, placing the bare cell in an outer package, injecting the prepared electrolyte, and packaging to obtain the lithium ion battery, wherein the design capacity of the lithium ion battery is 1800mAh.
Example 2
The electrolyte was prepared substantially as in example 1 except that diethyl carbonate (DEC), ethylene Carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a weight ratio of 20:30:50, 1M lithium salt LiPF 6 was sufficiently dissolved, fluoroethylene carbonate was added in an amount of 2% by weight based on the total weight of the electrolyte, adiponitrile was added in an amount of 0.3% by weight based on the total weight of the electrolyte, and compound 1 was added in an amount of 1% by weight based on the total weight of the electrolyte.
Example 3
The electrolyte was prepared substantially as in example 1 except that diethyl carbonate (DEC), ethylene Carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a weight ratio of 20:30:50, 1M lithium salt LiPF 6 was sufficiently dissolved, and fluoroethylene carbonate, which was 2% of the total weight of the electrolyte, 0.3% of adiponitrile, 1% of the total weight of the electrolyte, and 0.5% of pyridine-boron trifluoride, which was the total weight of the electrolyte, were added.
Example 4
The electrolyte was prepared substantially as in example 1 except that diethyl carbonate (DEC), ethylene Carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a weight ratio of 20:30:50, 1M lithium salt LiPF 6 was sufficiently dissolved, fluoroethylene carbonate was added in an amount of 2% by weight based on the total weight of the electrolyte, adiponitrile was added in an amount of 0.3% by weight based on the total weight of the electrolyte, and compound 1 was added in an amount of 2% by weight based on the total weight of the electrolyte.
Example 5
The electrolyte was prepared substantially as in example 1 except that diethyl carbonate (DEC), ethylene Carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a weight ratio of 20:30:50, 1M lithium salt LiPF 6 was sufficiently dissolved, fluoroethylene carbonate was added in an amount of 2% by weight based on the total weight of the electrolyte, adiponitrile was added in an amount of 0.3% by weight based on the total weight of the electrolyte, and compound 1 was added in an amount of 5% by weight based on the total weight of the electrolyte.
Example 6
The electrolyte was prepared substantially as in example 1 except that diethyl carbonate (DEC), ethylene Carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a weight ratio of 20:30:50, 1M lithium salt LiPF 6 was sufficiently dissolved, and fluoroethylene carbonate was added in an amount of 2% by weight based on the total weight of the electrolyte, adiponitrile in an amount of 0.3% by weight based on the total weight of the electrolyte, compound 2 in an amount of 1% by weight based on the total weight of the electrolyte, and pyridine-boron trifluoride in an amount of 0.5% by weight based on the total weight of the electrolyte.
Example 7
The electrolyte was prepared substantially as in example 1 except that diethyl carbonate (DEC), ethylene Carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a weight ratio of 20:30:50, 1M lithium salt LiPF 6 was sufficiently dissolved, and fluoroethylene carbonate was added in an amount of 2% by weight based on the total weight of the electrolyte, adiponitrile in an amount of 0.3% by weight based on the total weight of the electrolyte, compound 3 in an amount of 1% by weight based on the total weight of the electrolyte, and pyridine-boron trifluoride in an amount of 0.5% by weight based on the total weight of the electrolyte.
Example 8
The electrolyte was prepared substantially as in example 1 except that diethyl carbonate (DEC), ethylene Carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a weight ratio of 20:30:50, 1M lithium salt LiPF 6 was sufficiently dissolved, and fluoroethylene carbonate was added in an amount of 2% by weight based on the total weight of the electrolyte, adiponitrile in an amount of 0.3% by weight based on the total weight of the electrolyte, compound 4 in an amount of 1% by weight based on the total weight of the electrolyte, and pyridine-boron trifluoride in an amount of 0.5% by weight based on the total weight of the electrolyte.
Comparative example 1
The electrolyte was prepared substantially as in example 1 except that diethyl carbonate (DEC), ethylene Carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a weight ratio of 20:30:50, 1M lithium salt LiPF 6 was sufficiently dissolved, and fluoroethylene carbonate was added in an amount of 2% by weight based on the total weight of the electrolyte, and adiponitrile was added in an amount of 0.3% by weight based on the total weight of the electrolyte.
Comparative example 2
The electrolyte was prepared substantially as in example 1 except that diethyl carbonate (DEC), ethylene Carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a weight ratio of 20:30:50, 1M lithium salt LiPF 6 was sufficiently dissolved, and fluoroethylene carbonate was added in an amount of 2% by weight based on the total weight of the electrolyte, adiponitrile was 0.3% by weight based on the total weight of the electrolyte, and 2-sulfobenzoic anhydride was 1% by weight based on the total weight of the electrolyte.
Comparative example 3
The electrolyte was prepared substantially as in example 1 except that diethyl carbonate (DEC), ethylene Carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a weight ratio of 20:30:50, 1M lithium salt LiPF 6 was sufficiently dissolved, fluoroethylene carbonate was added in an amount of 2% by weight based on the total weight of the electrolyte, adiponitrile was added in an amount of 0.3% by weight based on the total weight of the electrolyte, and phthalic anhydride was added in an amount of 0.8% by weight based on the total weight of the electrolyte.
Comparative example 4
The electrolyte was prepared substantially as in example 1 except that diethyl carbonate (DEC), ethylene Carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a weight ratio of 20:30:50, 1M lithium salt LiPF 6 was sufficiently dissolved, and fluoroethylene carbonate was added in an amount of 2% by weight based on the total weight of the electrolyte, adiponitrile was added in an amount of 0.3% by weight based on the total weight of the electrolyte, and lithium bis (trifluoromethylsulfonyl) imide was added in an amount of 1.5% by weight based on the total weight of the electrolyte.
In the above examples, compound 1: Compound 2: Compound 3: Compound 4:
electrolyte storage test
The fresh electrolytes prepared in examples 1 to 8 and comparative examples 1 to 4 above were transferred into an aluminum plastic bottle, sealed, left at 45 ℃ for 48 hours, and after the completion of the leaving, the HF content in the electrolytes was measured.
The results of the HF content in the electrolyte after resting are shown in table 1.
TABLE 1
Electrolyte solution HF
Example 1 115
Example 2 91
Example 3 83
Example 4 65
Example 5 26
Example 6 78
Example 7 56
Example 8 62
Comparative example 1 141
Comparative example 2 228
Comparative example 3 303
Comparative example 4 126
Table 1 shows that the HF content in the electrolyte after leaving at 45℃is significantly increased after adding the additives 2-sulfobenzoic anhydride and phthalic anhydride, respectively, in comparative examples 2 and 3, compared to comparative example 1, whereas examples 1-8 show that the HF content in the electrolyte after leaving at 45℃is reduced to a different extent after adding compounds 1-4, compared to comparative example 1, because the silicon-based groups in the compounds can consume the residual moisture in the electrolyte, preventing decomposition of LiPF 6, improving the stability of the electrolyte. In addition, comparative example 4 shows that the addition of lithium bis (trifluoromethylsulfonyl) imide also reduces the HF content in the electrolyte after resting at 45 ℃ to some extent, as compared to comparative example 1.
High temperature cycle test
And (3) under the condition of 45 ℃, carrying out 300-week charge-discharge cycle test on the battery at a 1/1C charge-discharge rate, wherein the charge-discharge voltage interval is 3.0-4.35V, and recording the first-week and 300-week discharge capacities respectively. Week 300 capacity retention (%) =week 300 discharge capacity/first week discharge capacity ×100%.
High temperature storage test
Firstly, charging and discharging the formed battery for 3 times at the normal temperature with the temperature of 1C, wherein the charging and discharging voltage interval is 3.0-4.35V, recording the third discharging capacity as Q1, then charging the battery to 4.35V at constant current and constant voltage with the temperature of 1C, keeping the cut-off current as 0.05C, then keeping the temperature for 7 days at 60 ℃, measuring the thickness of the battery before keeping as t1, measuring the thickness of the battery again as t2 after the battery is completely cooled after the battery is stored at high temperature, then performing discharging test on the taken battery with the temperature of 1C, and recording the discharging capacity of the battery as Q2.
The thickness change rate= (t 2-t 1)/t1×100%, and the storage capacity retention rate=q2/q1×100%.
The results of the high temperature cycling and high temperature rest performance of the cells are shown in table 2.
TABLE 2
Table 2 shows that the high temperature cycle performance and the high temperature shelf performance of examples 1 and 2 are both superior to those of comparative examples 1 to 4, and that although lithium bis (trifluoromethylsulfonyl) imide of comparative example 4 can also reduce the HF content in the electrolyte after being placed at 45 ℃ to some extent, the improvement effect on the high temperature performance of the electrolyte is inferior to that of examples 1 to 8, and it is speculated that the silicon-nitrogen compound used in the invention contains a silicon group, so that the generation of HF in the electrolyte is greatly reduced, and structural collapse of the cathode material in the placing process is avoided, and on the other hand, as heteroatom N introduced in the system contains lone pair electrons, the resistance of electrons passing through the cathode interface film can be reduced, thereby reducing the internal resistance of the battery.
Comparative examples 1 to 8 show that the silicon nitrogen compound of the present invention exhibits more excellent high temperature performance when used in combination with pyridine-boron trifluoride, presumably because pyridine-boron trifluoride can form a positive electrode interfacial film on the surface of a positive electrode material, reduce oxidation of the electrolyte by the positive electrode under high voltage and high temperature conditions, and reduce gas generation of the battery during the high temperature rest.
The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the present invention and to implement the same, but are not intended to limit the scope of the present invention, and all equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of the present invention.

Claims (11)

1. A lithium ion battery electrolyte comprises a nonaqueous organic solvent, lithium salt and an additive, and is characterized in that the additive comprises a silicon-nitrogen compound shown in a formula I,
Wherein Z in the formula I is sulfonyl or carbonyl, R 1、R2、R3 is selected from any one of halogen atom, halogen substituted or unsubstituted aryl, halogen substituted or unsubstituted alkyl containing 1-4 carbon atoms and halogen substituted or unsubstituted alkenyl containing 1-4 carbon atoms, R 4、R5、R6、R7 is selected from any one of hydrogen, halogen atom, nitro, amino, halogen substituted or unsubstituted alkyl containing 1-4 carbon atoms and halogen substituted or unsubstituted alkenyl containing 1-4 carbon atoms.
2. The lithium ion battery electrolyte according to claim 1, wherein R 1、R2、R3 in the formula I is the same and is selected from one of fluorine atom, methyl group or trifluoromethyl group, and at least two of R 4、R5、R6、R7 are hydrogen atoms.
3. The lithium ion battery electrolyte according to claim 2, wherein the silicon-nitrogen compound is
、、、One or more of the following.
4. The lithium ion battery electrolyte according to claim 1, wherein the additive further comprises an aza-boron trifluoride complex.
5. The lithium ion battery electrolyte according to claim 4, wherein the nitrogen heterocycle in the nitrogen heterocycle-boron trifluoride complex is one or more of a pyridyl group-containing heterocycle, a pyridazinyl group-containing heterocycle, a pyrimidinyl group-containing heterocycle, a pyrazinyl group-containing heterocycle, a pyrrolyl group-containing heterocycle, a pyrazolyl group-containing heterocycle and an imidazolyl group-containing heterocycle.
6. The lithium ion battery electrolyte according to claim 5, wherein the nitrogen heterocycle-boron trifluoride complex compound is pyridine-boron trifluoride.
7. The lithium ion battery electrolyte according to claim 4, wherein the nitrogen heterocycle-boron trifluoride complex is 0.05-2% of the total mass of the lithium ion battery electrolyte, and the silicon nitrogen compound is 0.05-5% of the total mass of the lithium ion battery electrolyte.
8. The electrolyte of lithium ion battery according to claim 1, wherein the additive further comprises 0.05% -5% of other additives based on the total mass of the electrolyte of lithium ion battery, and the other additives are one or more of succinonitrile, adiponitrile, fluoroethylene carbonate, 1, 3-propane sultone, ethylene sulfate, methylene methylsulfonate, propylene sulfate, tris (trimethylsilyl) borate, tris (trimethylsilyl) phosphite, tris (trimethylsilyl) phosphate, ethylene carbonate, maleic anhydride, glutaric anhydride.
9. The lithium ion battery electrolyte according to claim 1, wherein the lithium salt is one or more selected from the group consisting of lithium perchlorate, lithium tetrafluoroborate, lithium difluorooxalato borate, lithium hexafluorophosphate, lithium carbonate, lithium sulfate, lithium sulfite, lithium nitrate, lithium difluorosulfonimide, lithium bis (trifluoromethylsulfonyl) imide, lithium difluorophosphate, and lithium difluorobisoxalato phosphate;
And/or the nonaqueous organic solvent is one or more of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethylene carbonate, methyl formate, ethyl acetate, methyl butyrate, methyl acrylate, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, acetonitrile, N-dimethylformamide, sulfolane, dimethyl sulfoxide, methyl sulfide, gamma-butyrolactone and tetrahydrofuran.
10. A lithium ion battery comprises a positive plate, a negative plate, a separation film arranged between the positive plate and the negative plate and electrolyte, and is characterized in that the electrolyte is the lithium ion battery electrolyte according to any one of claims 1 to 9.
11. The lithium ion battery according to claim 10, wherein the positive electrode active material is a lithium transition metal composite oxide, and the lithium transition metal composite oxide contains one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, and a compound obtained by adding other transition metal or non-transition metal to the lithium transition metal composite oxide;
And/or the negative active material is selected from one or more of soft carbon, hard carbon, artificial graphite, natural graphite, silicon oxygen compound, silicon carbon compound, lithium titanate and metal capable of forming alloy with lithium.
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