An additive for high-voltage lithium cobalt oxide battery electrolytes

Abstract

This invention discloses an additive for high-voltage lithium cobalt oxide battery electrolytes. The additive comprises vinylene carbonate, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane. The ratio of vinylene carbonate, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane, by mass, is (0.05-0.3 parts):(0.5-5 parts):(0.1-2 parts):(0.1-2 parts). This invention achieves excellent electrical performance of the electrolyte at high voltage through the interaction of these four substances in the additive.

Description

[0001] This application is a divisional application of application number "2021116740237" entitled "An electrolyte for a high-voltage lithium cobalt oxide battery and a lithium cobalt oxide battery". Technical Field

[0002] This invention relates to the field of materials technology, and in particular to an additive for high-voltage lithium cobalt oxide battery electrolytes. Background Technology

[0003] With technological advancements, people's demands for consumer electronics and electric vehicles are constantly increasing. Lithium-ion batteries based on the lithium cobalt oxide system still hold a significant share of the consumer electronics market due to their excellent cycle stability, high volumetric energy density, and long cycle life. Today's smart consumer electronics require high-energy-density lithium batteries to extend their operating time and lifespan. To meet public demand, it is essential to develop lithium-ion batteries with higher energy and power densities to achieve longer battery life and energy storage. Currently, most commercially available lithium cobalt oxide batteries have a charging cutoff voltage of 4.4V and a specific capacity of 160mAh / g, which is still some distance from their theoretical specific capacity of 275mAh / g. Therefore, lithium cobalt oxide batteries have significant development potential, and improving their performance has practical economic implications.

[0004] Developing high-energy-density lithium batteries can improve the specific capacity of positive and negative electrode materials by increasing the battery's operating voltage, thereby increasing the mass energy density and volumetric energy density of lithium-ion batteries. At the same time, it can also reduce the cost of lithium batteries, making it a hot research topic in recent years.

[0005] However, in the process of researching high-voltage lithium batteries, it has been found that as the working voltage of lithium-ion batteries increases, traditional lithium battery electrolytes not only oxidize and decompose themselves, but also undergo irreversible chemical reactions with the cathode material, continuously consuming active lithium, resulting in increased battery impedance, low capacity retention, performance degradation, and severely shortened battery life. Therefore, the development of electrolyte technology that matches high-voltage lithium batteries has become crucial. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing an electrolyte for high-voltage lithium cobalt oxide batteries and a lithium cobalt oxide battery. The application of this electrolyte can ensure the stability of the high-voltage lithium cobalt oxide battery system and achieve its excellent electrical performance.

[0007] In a first aspect, embodiments of the present invention provide an electrolyte for a high-voltage lithium cobalt oxide battery, the electrolyte comprising: a lithium salt electrolyte, an organic solvent, and additives;

[0008] The additives include: vinylene carbonate, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane.

[0009] Preferably, the lithium salt electrolyte comprises one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium difluorooxalate borate, or lithium bis(trifluoromethanesulfonylimide).

[0010] The lithium salt electrolyte accounts for 10%-20% of the total mass of the electrolyte.

[0011] Preferably, the organic solvent includes any one or a mixture of several of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, 1,4-butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, ethyl butyrate, and their halogenated derivatives.

[0012] The organic solvent accounts for 70%-85% of the total mass of the electrolyte.

[0013] More preferably, the organic solvent is a mixture of the ethylene carbonate, the propylene carbonate, the halogenated derivative of the ethylene carbonate, fluoroethylene carbonate, and the methyl ethyl carbonate;

[0014] The ethylene carbonate accounts for 5%-15% of the total mass of the organic solvent, the propylene carbonate accounts for 5%-15% of the total mass of the organic solvent, the fluoroethylene carbonate accounts for 3%-10% of the total mass of the organic solvent, and the methyl ethyl carbonate accounts for 60%-80% of the total mass of the organic solvent.

[0015] Preferably, the additive accounts for 0.75%-10% of the total mass of the electrolyte; wherein the vinylene carbonate accounts for 0.05%-0.3% of the total mass of the electrolyte, the difluoromethyl oxalate phosphate accounts for 0.5%-5% of the total mass of the electrolyte, the heptafluorobutyric anhydride accounts for 0.1%-2% of the total mass of the electrolyte, and the divinyltetra(trimethylsiloxy)disiloxane accounts for 0.1%-2% of the total mass of the electrolyte.

[0016] Preferably, the additive further includes: vinyl sulfate and / or adiponitrile;

[0017] The ethylene sulfate accounts for 0.1%-1% of the total mass of the electrolyte; the adiponitrile accounts for 0.1%-1% of the total mass of the electrolyte.

[0018] Preferably, the high-voltage lithium cobalt oxide battery is a lithium cobalt oxide battery with an operating voltage of 4.4V or higher.

[0019] In a second aspect, embodiments of the present invention provide an additive used in the electrolyte of the first aspect described above; the additive comprises: vinylene carbonate, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane; wherein the structural formula of the difluoromethyl oxalate phosphate is:

[0020]

[0021] The difluoromethyl oxalate phosphate was obtained by sequentially adding dichloromethane, difluoromethyl phosphate, and pyridine to a dry three-necked round-bottom flask, stirring thoroughly under ice bath conditions, adding oxaloyl chloride dropwise, allowing the reaction to proceed fully, filtering, extracting with water, and finally distilling the solvent under reduced pressure to collect the distillate.

[0022] Thirdly, embodiments of the present invention provide a high-voltage lithium cobalt oxide battery, the high-voltage lithium cobalt oxide battery comprising the electrolyte for high-voltage lithium cobalt oxide batteries described in the first aspect.

[0023] Preferably, the charging cutoff voltage of the high-voltage lithium cobalt oxide battery is 4.4V or higher.

[0024] The electrolyte for high-voltage lithium cobalt oxide batteries provided in this invention uses vinylene carbonate as an additive. During the initial formation, vinylene carbonate only participates in the formation of the solid electrolyte interphase (SEI) film at the negative electrode, forming a stable SEI. After the SEI film is formed, vinylene carbonate is completely consumed, preventing negative impacts on the positive electrode caused by high-voltage instability. Under high voltage, difluoromethyl oxalate phosphate and heptafluorobutyric anhydride are oxidized and decomposed, forming a positive electrode-electrolyte interphase (CEI) film containing LiF and inorganic phosphates on the surface of the positive electrode material. This CEI film is uniform, dense, and completely covers the electrolyte. Lithium cobalt oxide particles are used to prevent direct contact between the cathode material surface and the electrolyte, inhibiting the dissolution of highly oxidizing transition metal ions in the cathode material, reducing continuous oxidative decomposition of the electrolyte, and ensuring the stability of the battery system. Divinyltetra(trimethylsiloxy)disiloxane, due to the change in bond energy of the silicon-oxygen bond under the influence of polymethyl groups, facilitates its reaction with HF in the electrolyte, thereby reducing the HF content in the electrolyte and preventing HF from attacking the electrode material surface and the solid electrolyte membrane, thus protecting the stability of the electrode surface and electrolyte components. This application achieves excellent electrical performance of the electrolyte under high voltage through the interaction of these four substances in the additives. Detailed Implementation

[0025] The present invention will be further described below through specific embodiments. However, it should be understood that these embodiments are only for more detailed description and should not be construed as limiting the present invention in any way, that is, not intended to limit the scope of protection of the present invention.

[0026] This invention provides an electrolyte for high-voltage lithium cobalt oxide batteries, comprising: lithium salt electrolyte, organic solvent, and additives.

[0027] The lithium salt electrolyte includes one or more of the following: lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium difluorooxalate borate, or lithium bis(trifluoromethanesulfonylimide); the lithium salt electrolyte accounts for 10%-20% of the total mass of the electrolyte.

[0028] The organic solvent includes any one or a mixture of several of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, 1,4-butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, ethyl butyrate, and their halogenated derivatives; the organic solvent accounts for 70%-85% of the total mass of the electrolyte.

[0029] The organic solvent is preferably a mixture of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and methyl ethyl carbonate; wherein the mass of ethylene carbonate accounts for 5%-15% of the total mass of the organic solvent, the mass of propylene carbonate accounts for 5%-15% of the total mass of the organic solvent, the mass of fluoroethylene carbonate accounts for 3%-10% of the total mass of the organic solvent, and the mass of methyl ethyl carbonate accounts for 60%-80% of the total mass of the organic solvent.

[0030] The additives include: vinylene carbonate (VC), difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane; the additives account for 0.75%-10% of the total mass of the electrolyte; wherein, vinylene carbonate accounts for 0.05%-0.3% of the total mass of the electrolyte, difluoromethyl oxalate phosphate accounts for 0.5%-5% of the total mass of the electrolyte, heptafluorobutyric anhydride accounts for 0.1%-2% of the total mass of the electrolyte, and divinyltetra(trimethylsiloxy)disiloxane accounts for 0.1%-2% of the total mass of the electrolyte. This application achieves excellent electrical performance of the electrolyte under high voltage through the interaction of these four additives.

[0031] Difluoromethyl oxalate phosphate is synthesized from difluoromethyl phosphoric acid (F2PO(OH)2, CAS code 74963-39-6) and oxalyl chloride ((COCl)2).

[0032] The structural formula of difluoromethylphosphoric acid (F₂PO(OH)₂) is:

[0033]

[0034] The structural formula of oxalyl chloride ((COCl)2) is:

[0035]

[0036] The synthesis process is as follows: In a dry 250ml three-necked round-bottom flask equipped with a thermometer, dropping funnel, reflux condenser (with a drying tube containing anhydrous CaCl2 inserted into the tube opening), and water separator, a measured amount of dichloromethane, difluoromethylphosphoric acid, and pyridine are added sequentially. Oxaloyl chloride is slowly added dropwise under ice bath conditions with thorough stirring. After the reaction is complete, the mixture is filtered, extracted with water, and finally the solvent is distilled under reduced pressure. The distillate is collected to obtain difluoromethylphosphoric acid oxalate.

[0037] The chemical reaction equation is: F2PO(OH)2+(COCl)2→F2PO(OCO)2+2HCl↑.

[0038] The structural formula of difluoromethyl oxalate phosphate is:

[0039]

[0040] The structural formula of divinyltetra(trimethylsiloxy)disiloxane is:

[0041]

[0042] In the initial formation, the additive vinylene carbonate only participates in the formation of the solid electrolyte interphase (SEI) film at the negative electrode, forming a stable SEI. It is completely consumed after SEI film formation, preventing negative impacts caused by high-voltage instability at the positive electrode. Under high voltage, difluoromethyl oxalate phosphate and heptafluorobutyric anhydride undergo oxidative decomposition, forming a composite CEI film containing LiF and inorganic phosphates on the surface of the positive electrode material. This CEI film is uniform and dense, completely coating the lithium cobalt oxide particles, preventing direct contact between the positive electrode material surface and the electrolyte, inhibiting the dissolution of highly oxidizing transition metal ions in the positive electrode material, reducing the continuous oxidative decomposition of the electrolyte, and ensuring the stability of the battery system. Divinyltetra(trimethylsiloxy)disiloxane, due to the change in bond energy of the silicon-oxygen bond under the influence of polymethyl groups, easily reacts with HF in the electrolyte, thereby reducing the HF content in the electrolyte and preventing HF from attacking the electrode material surface and the solid electrolyte film, thus protecting the stability of the electrode surface and electrolyte components. The excellent electrical properties of the electrolyte under high voltage are achieved through the interaction of these four substances in the additive.

[0043] In a preferred embodiment, the additives further include: vinyl sulfate (DTD) and adiponitrile (ADN); wherein the mass of vinyl sulfate accounts for 0.1%-1% of the total mass of the electrolyte; and the mass of adiponitrile accounts for 0.1%-1% of the total mass of the electrolyte. These additives, acting as auxiliary additives in the system, can form films on the positive and negative electrode surfaces, protecting the positive and negative electrodes.

[0044] The electrolyte for high-voltage lithium cobalt oxide batteries provided in this invention can be used in high-voltage lithium cobalt oxide batteries, with lithium cobalt oxide as the positive electrode material and artificial graphite or silicon-carbon composite negative electrode as the negative electrode. The charging cut-off voltage of lithium cobalt oxide batteries using the electrolyte of this invention can reach 4.4V or higher.

[0045] Because lithium cobalt oxide exhibits higher specific capacity under high voltage, the electrolyte proposed in this invention for high-voltage lithium cobalt oxide batteries effectively improves the operating voltage and energy density of lithium cobalt oxide batteries. Moreover, under the same energy density conditions, the amount of lithium cobalt oxide material used can be reduced, thereby lowering the cost of the battery.

[0046] To better understand the technical solution provided by this invention, the following uses several specific examples to illustrate the specific implementation of the electrolyte of this invention, as well as the method and battery characteristics applied to high-voltage lithium cobalt oxide batteries.

[0047] Example 1

[0048] This embodiment provides an electrolyte for high-voltage lithium cobalt oxide batteries, and the specific preparation process is as follows:

[0049] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Lithium hexafluorophosphate was then added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Additives ethylene carbonate (VC), vinyl sulfate (DTD), adiponitrile (ADN), difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane were then added to the electrolyte base at mass fractions of 0.2%, 0.3%, 0.3%, 1%, 1%, and 1%, respectively, to obtain the final electrolyte.

[0050] The electrolyte prepared in this embodiment is numbered 1#.

[0051] Example 2

[0052] This embodiment provides an electrolyte for high-voltage lithium cobalt oxide batteries, and the specific preparation process is as follows:

[0053] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 10 / 15 / 5 / 70. Lithium hexafluorophosphate was then added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Additives VC, DTD, ADN, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane were then added to the electrolyte base at mass fractions of 0.2%, 0.3%, 0.3%, 1%, 1%, and 1%, respectively, to obtain the final electrolyte.

[0054] The electrolyte prepared in this embodiment is numbered 2#.

[0055] Example 3

[0056] This embodiment provides an electrolyte for high-voltage lithium cobalt oxide batteries, and the specific preparation process is as follows:

[0057] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Lithium hexafluorophosphate was then added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Additives VC, DTD, ADN, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane were then added to the electrolyte base at mass fractions of 0.2%, 0.3%, 0.3%, 2%, 1%, and 1%, respectively, to obtain the final electrolyte.

[0058] The electrolyte prepared in this embodiment is numbered 3#.

[0059] Example 4

[0060] This embodiment provides an electrolyte for high-voltage lithium cobalt oxide batteries, and the specific preparation process is as follows:

[0061] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Lithium hexafluorophosphate was then added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Additives VC, DTD, ADN, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane were then added to the electrolyte base at mass fractions of 0.2%, 0.3%, 0.3%, 3%, 1%, and 1%, respectively, to obtain the final electrolyte.

[0062] The electrolyte prepared in this embodiment is numbered 4#.

[0063] Example 5

[0064] This embodiment provides an electrolyte for high-voltage lithium cobalt oxide batteries, and the specific preparation process is as follows:

[0065] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Lithium hexafluorophosphate was then added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Additives VC, DTD, ADN, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane were then added to the electrolyte base at mass fractions of 0.2%, 0.3%, 0.3%, 1%, 2%, and 1%, respectively, to obtain the final electrolyte.

[0066] The electrolyte prepared in this embodiment is numbered 5#.

[0067] Example 6

[0068] This embodiment provides an electrolyte for high-voltage lithium cobalt oxide batteries, and the specific preparation process is as follows:

[0069] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Lithium hexafluorophosphate was then added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Additives VC, DTD, ADN, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane were then added to the electrolyte base at mass fractions of 0.2%, 0.3%, 0.3%, 1%, 1%, and 1.5%, respectively, to obtain the final electrolyte.

[0070] The electrolyte prepared in this embodiment is numbered 6#.

[0071] Example 7

[0072] This embodiment provides an electrolyte for high-voltage lithium cobalt oxide batteries, and the specific preparation process is as follows:

[0073] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Lithium hexafluorophosphate was then added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Additives VC, DTD, ADN, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane were then added to the electrolyte base at mass fractions of 0.2%, 0.3%, 0.3%, 2%, 0.5%, and 1%, respectively, to obtain the final electrolyte.

[0074] The electrolyte prepared in this embodiment is numbered 7#.

[0075] Example 8

[0076] This embodiment provides an electrolyte for high-voltage lithium cobalt oxide batteries, and the specific preparation process is as follows:

[0077] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Lithium hexafluorophosphate was then added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Additives VC, DTD, ADN, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane were then added to the electrolyte base at mass fractions of 0.2%, 0.3%, 0.3%, 2%, 0.5%, and 2%, respectively, to obtain the final electrolyte.

[0078] The electrolyte prepared in this embodiment is numbered 8#.

[0079] To better illustrate the effects of the embodiments of the present invention, comparative examples 1, 2 and 3 are compared with the above embodiments.

[0080] Comparative Example 1

[0081] This comparative example provides an electrolyte, the specific preparation process of which is as follows:

[0082] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Then, lithium hexafluorophosphate was added to dissolve the mixture to prepare an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Then, additives DTD and ADN were added to the electrolyte base at mass fractions of 0.3% and 0.3%, respectively, to obtain the electrolyte.

[0083] The electrolyte prepared in this comparative example is numbered 9#.

[0084] Comparative Example 2

[0085] This comparative example provides an electrolyte, the specific preparation process of which is as follows:

[0086] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Lithium hexafluorophosphate was then added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Additives VC, DTD, ADN, and difluoromethyl oxalate phosphate were then added to the electrolyte base at mass fractions of 0.2%, 0.3%, 0.3%, and 1%, respectively, to obtain the final electrolyte.

[0087] The electrolyte prepared in this comparative example is numbered 10#.

[0088] Comparative Example 3

[0089] This comparative example provides an electrolyte, the specific preparation process of which is as follows:

[0090] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Lithium hexafluorophosphate was then added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Additives VC, DTD, ADN, and divinyltetra(trimethylsiloxy)disiloxane were then added to the electrolyte base at mass fractions of 0.2%, 0.3%, 0.3%, and 1%, respectively, to obtain the final electrolyte.

[0091] The electrolyte prepared in this comparative example is numbered 11#.

[0092] The electrolytes obtained in the above embodiments and comparative examples were used to assemble and test the batteries in the following manner.

[0093] Preparation of lithium cobalt oxide batteries:

[0094] Lithium cobalt oxide, suitable for high voltage, was selected as the cathode material. LiCoO2, carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) were mixed uniformly in a ratio of 98:1:1, coated onto an aluminum foil current collector, dried in an oven, and then rolled on a roller press to a compaction density of 4.0 g / cm³. 3 The desired positive electrode sheet is obtained.

[0095] Artificial graphite was selected as the negative electrode material. The artificial negative electrode, carboxymethyl cellulose (CMC), conductive agent Super P, and binder styrene-butadiene rubber (SBR) were mixed uniformly in a ratio of 95:1.2:1.8:2 to obtain the negative electrode sheet. The compacted density of the electrode sheet was 1.65 g / cm³. 3 .

[0096] A 9μm PE film was selected as the base film, and a 3μm ceramic material was coated to obtain a (9+3) coated separator. The electrode sheets were then stacked to form a 2Ah small soft-pack battery. The electrolyte used was the same as that in the above examples and comparative examples.

[0097] Lithium battery performance testing:

[0098] The charge / discharge voltage window for the lithium battery is set to 3.0-4.5V, the cycle charge / discharge current is set to 1A (0.5C), and the cycle test temperature is 25℃.

[0099] Test results and discussion:

[0100] Table 1 shows the electrical performance test results of the small pouch batteries using the electrolytes of Examples 1-8 and Comparative Examples 1-3.

[0101]

[0102]

[0103] Table 1

[0104] As can be seen from the data in Table 1, compared with the battery prepared using electrolyte 9# of Comparative Example 1 which uses DTD and ADN additives, the battery prepared using the electrolyte of Examples 1-8 of this invention has a very significant improvement in capacity retention after 200 cycles.

[0105] Compared to the battery prepared with electrolyte #10 in Comparative Example 2, which does not contain difluoromethyl oxalate phosphate or heptafluorobutyric anhydride, the batteries prepared with electrolytes from Examples 1-8 of this invention exhibit superior capacity retention after 200 cycles. This is because, under high voltage, the oxidative decomposition of difluoromethyl oxalate phosphate and heptafluorobutyric anhydride forms a composite CEI film containing LiF and inorganic phosphates on the surface of the cathode material. This CEI film is uniform and dense, completely coating the lithium cobalt oxide particles, preventing direct contact between the cathode material surface and the electrolyte, inhibiting the dissolution of highly oxidizing transition metal ions in the cathode material, reducing the continuous oxidative decomposition of the electrolyte, and ensuring the stability of the battery system.

[0106] Compared to the battery prepared with electrolyte 11# in Comparative Example 3, which does not contain divinyltetra(trimethylsiloxy)disiloxane, the batteries prepared with electrolytes from Examples 1-8 of this invention exhibit superior capacity retention after 200 cycles. This is because the bond energy of the silicon-oxygen bond in divinyltetra(trimethylsiloxy)disiloxane changes under the influence of polymethyl groups, making it more readily react with HF in the electrolyte. This reduces the HF content in the electrolyte, preventing HF from attacking the electrode material surface and the solid electrolyte membrane, thereby protecting the stability of the electrode surface and electrolyte components.

[0107] Compared to Comparative Examples 1-3, the use of the high-voltage electrolyte of this invention resulted in a certain improvement in the cycle life of lithium cobalt oxide batteries under a high voltage of 4.5V. This indicates that the high-voltage electrolyte of this invention performs well under 4.5V lithium cobalt oxide battery conditions, and is more advantageous compared to existing lithium cobalt oxide batteries, most of which have a charging cutoff voltage of 4.4V.

[0108] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An additive for use in high-voltage lithium cobalt oxide battery electrolytes, characterized in that, The additives include vinylene carbonate, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane, wherein the ratio of vinylene carbonate, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane by mass is (0.05-0.3 parts):(0.5-5 parts):(0.1-2 parts):(0.1-2 parts); the high-voltage lithium cobalt oxide battery is a lithium cobalt oxide battery with an operating voltage of 4.4V or higher.

2. The additive for high-voltage lithium cobalt oxide battery electrolyte according to claim 1, characterized in that, The additives include vinylene carbonate, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane, wherein the ratio of vinylene carbonate, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane by mass is 0.2 parts:(1-3 parts):(0.5-2 parts):(1-2 parts).

3. The additive for high-voltage lithium cobalt oxide battery electrolyte according to claim 1, characterized in that, The additives also include vinyl sulfate and adiponitrile; by mass, the ratio of vinyl sulfate, adiponitrile, vinylene carbonate, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane is (0.1-1 parts):(0.1-1 parts):(0.05-0.3 parts):(0.5-5 parts):(0.1-2 parts):(0.1-2 parts).

4. The additive for high-voltage lithium cobalt oxide battery electrolyte according to claim 3, characterized in that, The additives include vinylene carbonate, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, divinyltetra(trimethylsiloxy)disiloxane, vinyl sulfate, and adiponitrile; by mass, the ratio of vinyl sulfate, adiponitrile, vinylene carbonate, difluoromethyl oxalate phosphate, heptafluorobutyric anhydride, and divinyltetra(trimethylsiloxy)disiloxane is 0.3 parts: 0.3 parts: 0.2 parts: (1-3 parts): (0.5-2 parts): (1-2 parts).

5. The application of the additive according to any one of claims 1-4 in the electrolyte of a high-voltage lithium cobalt oxide battery.

6. The application according to claim 5, characterized in that, The additives in the electrolyte account for 0.75%-10% of the total mass of the electrolyte.

7. The application according to claim 5, characterized in that, The electrolyte also includes lithium salt electrolyte and organic solvent.

8. The application according to claim 7, characterized in that, The lithium salt electrolyte includes one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium difluorooxalate borate, or lithium bis(trifluoromethanesulfonylimide). The lithium salt electrolyte accounts for 10%-20% of the total mass of the electrolyte.

9. The application according to claim 7, characterized in that, The organic solvent includes any one or a mixture of several of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, 1,4-butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, ethyl butyrate, and halogenated derivatives of these organic compounds. The organic solvent accounts for 70%-85% of the total mass of the electrolyte.

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