阅读说明：本技术 一种高压功能电解液及其制备方法与应用 (High-voltage functional electrolyte and preparation method and application thereof ) 是由 邵俊华 李海杰 张利娟 孔东波 王郝为 郭飞 闫国锋 宋东亮 王亚洲 侯红歧 谢 于 2021-08-18 设计创作，主要内容包括：本发明公开了一种高压功能电解液及其制备方法与应用,一种高压功能电解液,包括二氟草酸硼酸锂、锂盐和添加剂；上述添加剂为乙烯基磷酸酯和乙烯基磺酰氟中的至少一种,上述添加剂和二氟草酸硼酸锂在电极表面形成一层致密的界面膜,避免了电解液主体溶剂在电极表面发生连续的电化学反应,进而提高电池的安全性能和循环性能。(The invention discloses a high-voltage functional electrolyte and a preparation method and application thereof, wherein the high-voltage functional electrolyte comprises lithium difluoro oxalate borate, lithium salt and an additive; the additive is at least one of vinyl phosphate and vinyl sulfonyl fluoride, and the additive and the lithium difluoro-oxalato-borate form a layer of compact interfacial film on the surface of the electrode, so that continuous electrochemical reaction of a main solvent of the electrolyte on the surface of the electrode is avoided, and the safety performance and the cycle performance of the battery are improved.)

1. A high-voltage functional electrolyte is characterized in that:

comprises lithium difluoro-oxalato-borate, lithium salt and additive;

the additive is at least one of vinyl phosphate and vinyl sulfonyl fluoride.

2. The functional electrolyte of claim 1, wherein:

the lithium salt comprises at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate phosphate and lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bistrifluoromethylsulfonyl imide, lithium bistrifluoromethylimide, lithium bistrifluorosulfonimide and lithium perchlorate.

3. The functional electrolyte of claim 1, wherein:

the lithium difluoro oxalate borate, the lithium salt and the additive are prepared from the following components in parts by mass: 1-3:5-16:4-9.

4. The functional electrolyte of claim 1, wherein:

the mass ratio of the vinyl phosphate to the vinyl sulfonyl fluoride in the additive is 1-2: 0.5-1.

5. The functional electrolyte of claim 1, wherein:

the molar concentration of the lithium salt in the electrolyte is 0.8-2.0 mol/L.

6. The functional electrolyte of claim 1, wherein:

the solvent is at least one of dimethyl carbonate, diethyl carbonate, methyl formate, methyl acetate and methyl propionate.

7. The functional electrolyte of claim 1, wherein:

the additive also includes fluoroethylene carbonate.

8. A method of preparing a high voltage functional electrolyte as claimed in any one of claims 1 to 7, characterized in that: the method comprises the following steps:

the weight portion ratio is as follows: 1-3:5-16:4-9, and mixing the lithium difluoro-oxalato-borate, the lithium salt and the additive in sequence.

9. Use of a high voltage functional electrolyte as claimed in any one of claims 1 to 7 in a battery.

Technical Field

The invention belongs to the technical field of electrolyte, and particularly relates to high-voltage functional electrolyte and a preparation method and application thereof.

Background

The lithium ion battery has the advantages of high specific energy, long cycle life, no memory effect and the like, and is widely applied to the fields of mobile phones, computers, cameras, electric vehicles and the like. However, with the continuous development of scientific technology, various application fields have put higher requirements on the performance of lithium ion batteries.

At present, the anode materials of commercial lithium ion batteries mainly comprise lithium manganate, lithium cobaltate, ternary materials and lithium iron phosphate, and the charge cut-off voltage of the lithium ion batteries is generally not more than 4.2V. With the progress of science and technology and the continuous development of the market, it is increasingly important and urgent to improve the energy density of lithium batteries. Therefore, it is a focus of current research to increase the voltage of lithium ion batteries and thus increase the energy density of the batteries.

Disclosure of Invention

The first technical problem to be solved by the invention is as follows:

a high-voltage functional electrolyte is provided.

The second technical problem to be solved by the invention is:

provides a preparation method of the high-voltage functional electrolyte.

The third technical problem to be solved by the invention is:

the application of the high-voltage functional electrolyte is provided.

In order to solve the first technical problem, the invention adopts the technical scheme that:

a high-voltage functional electrolyte is provided,

comprises lithium difluoro-oxalato-borate, lithium salt and additive;

the additive is at least one of vinyl phosphate and vinyl sulfonyl fluoride.

When the high-voltage functional electrolyte is electrified to work, due to the fact that the reduction potential of the vinyl phosphate and the vinyl sulfonyl fluoride is low, the vinyl phosphate and the vinyl sulfonyl fluoride can generate electrochemical reaction in one step, a layer of compact interface film is formed on the surface of an electrode, continuous electrochemical reaction of a main solvent of the electrolyte on the surface of the electrode is avoided, and the safety performance and the cycle performance of a battery are improved.

When the electrolyte is in a high-pressure environment and the temperature of the electrolyte is linearly increased, the vinylphosphate molecules generate phosphorus-containing free radicals, and oxygen radicals and hydroxyl radicals generated by an organic solvent in the electrolyte are captured to form a thermal hysteresis layer, so that the combustion of the electrolyte is prevented.

The lithium difluorooxalato borate is opposite to the vinyl phosphate, the reduction potential of the vinyl phosphate is low, so that the vinyl phosphate can generate electrochemical reaction in one step, and the reduction potential of the lithium difluorooxalato borate is high, so that the lithium difluorooxalato borate can generate electrochemical reaction in the next step, and a compact and stable film is formed on a positive electrode and a negative electrode of the battery, so that the further contact between the electrolyte and an electrode active material is inhibited.

The combination of the vinyl phosphate, the vinyl sulfonyl fluoride and the lithium difluoro-oxalato-borate enables the electrolyte to be more stable and safer under the conditions of low pressure and high pressure, and particularly under the condition of high pressure, the flame retardance of the electrolyte can be improved to a greater extent through the matching of the vinyl phosphate, the vinyl sulfonyl fluoride and the lithium difluoro-oxalato-borate.

According to an embodiment of the present invention, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalato phosphate and lithium tetrafluoroborate, lithium difluorooxalato borate, lithium bistrifluoromethylsulfonyl imide, lithium bistrifluoromethylimide, lithium bistrifluorosulfonylimide, lithium perchlorate.

According to one embodiment of the present invention, the lithium difluoroborate, the lithium salt and the additive are in a mass ratio of: 1-3:5-16:4-9.

According to one embodiment of the present invention, the mass ratio of the vinyl phosphate ester to the vinyl sulfonyl fluoride in the additive is 1-2: 0.5-1.

According to one embodiment of the present invention, the molar concentration of the lithium salt in the electrolyte is 0.8 to 2.0 mol/L.

According to an embodiment of the present invention, the method further comprises a step of adding a solvent, wherein the solvent is at least one of dimethyl carbonate, diethyl carbonate, methyl formate, methyl acetate and methyl propionate.

According to an embodiment of the present invention, the additive further comprises fluoroethylene carbonate.

In order to solve the second technical problem, the invention adopts the technical scheme that:

the method for preparing the high-voltage functional electrolyte comprises the following steps:

the weight portion ratio is as follows: 1-3:5-16:4-9, and mixing the lithium difluoro-oxalato-borate, the lithium salt and the additive in sequence.

In another aspect, the invention also relates to application of the high-voltage functional electrolyte in a battery.

One of the above technical solutions has at least one of the following advantages or beneficial effects:

when the potential in the electrolyte is low, the vinyl phosphate and the vinyl sulfonyl fluoride are subjected to electrochemical reaction in one step to form a layer of compact interface film on the surface of the electrode, so that continuous electrochemical reaction of a main solvent of the electrolyte on the surface of the electrode is avoided, and the safety performance and the cycle performance of the battery are improved;

when the potential in the electrolyte is high, lithium difluoro oxalate borate can generate electrochemical reaction in the next step, and a layer of compact and stable film is formed on the positive electrode and the negative electrode of the battery, so that the further contact between the electrolyte and an electrode active substance is inhibited, and the vinyl phosphate molecules can generate phosphorus-containing free radicals at the moment, and oxygen radicals and hydroxyl radicals generated by an organic solvent in the electrolyte are captured to form a thermal retardation layer, so that the combustion of the electrolyte is prevented.

Detailed Description

In order to explain the technical content, the objects and the effects of the present invention in detail, the following description will be given with reference to the embodiments.

Example 1

1g of lithium difluorooxalato borate, 5g of lithium hexafluorophosphate, 2g of diethyl vinylphosphate and 2g of vinylsulfonyl fluoride were mixed in this order and dissolved in 100g of diethyl carbonate to obtain the above-mentioned high-pressure functional electrolyte.

Example 2

3g of lithium difluorooxalato borate, 16g of lithium hexafluorophosphate, 4.5g of diethyl vinylphosphonate and 4.5g of vinylsulfonylfluoride were mixed in this order and dissolved in 100g of diethyl carbonate to obtain the above-mentioned high-pressure functional electrolyte.

Example 3

1.5g of lithium difluorooxalato borate, 10g of lithium hexafluorophosphate, 3g of diethyl vinylphosphate and 3g of vinylsulfonyl fluoride were mixed in this order and dissolved in 100g of diethyl carbonate to obtain the above-mentioned high-pressure functional electrolyte.

Comparative example 1

Lithium hexafluorophosphate (10 g), diethyl vinylphosphate (3 g) and vinylsulfonyl fluoride (3 g) were mixed in this order and dissolved in diethyl carbonate (100 g) to obtain an electrolytic solution.

Comparative example 2

1.5g of lithium difluorooxalato borate and 10g of lithium hexafluorophosphate were mixed in this order and dissolved in 100g of diethyl carbonate to obtain an electrolytic solution.

And (3) performance testing:

li₂MnSiO₄The battery comprises a positive electrode, a negative electrode, a PE diaphragm and the electrolyte prepared according to the invention.

The experimental examples 1 to 3 and the comparative examples 1 to 2 were respectively tested for charge and discharge efficiency and capacity retention rate, and the test results are as follows.

TABLE 1

As can be seen from table 1, the addition of lithium difluorooxalato borate, diethyl vinylphosphonate, and vinylsulfonyl fluoride has little effect on the first charge-discharge efficiency of the lithium ion battery. However, after 300 times of circulation, the capacity retention rate of the battery is obviously different, and the capacity retention rate of the lithium ion battery added with the lithium difluoro oxalato borate, the vinyl diethyl phosphate and the vinyl sulfonyl fluoride can reach at least 87.3% after 300 times of circulation, but the capacity retention rate of the lithium ion battery not completely added with the lithium difluoro oxalato borate, the vinyl diethyl phosphate and the vinyl sulfonyl fluoride can only reach 62.5% -70.4% after 300 times of circulation.

The above description is only an example of the present invention and is not intended to limit the scope of the present invention, and all equivalent modifications made by the present invention as described in the specification of the present invention or directly or indirectly applied to the related technical fields are included in the scope of the present invention.