WO2017128580A1 - Method and technique for preparing electrolyte solution for high-safety lithium ion battery - Google Patents

Abstract

An electrolyte solution for a high-safety lithium ion battery, falling within the field of lithium ion batteries. The main ingredients of the electrolyte solution comprise organic solvents, an electrolyte and additives, wherein the organic solvents comprise at least one high flash point solvent, and the additives comprise a film additive and a flame retardant additive. The molar concentration of the electrolyte in the organic solvents is 0.8-1.5 mol/L, and the weight percentages of the additives in the electrolyte solution are 2%-8% and 1%-2% respectively. With regard to the electrolyte solution for the high-safety lithium ion battery, by using a method of using a high flash point solvent in combination with a small amount of a flame retardant additive, the electrolyte solution has a good flame retardant effect, and is difficult to ignite and has a relatively short self-extinguishing time. When the electrolyte solution is used in a lithium ion battery, the safety performance of the battery can be improved.

Description

Preparation method and technology of high safety lithium ion battery electrolyte Technical field

The invention relates to the field of lithium ion batteries, in particular to a method and a technology for preparing a high-safety lithium ion battery electrolyte.

Background technique

In recent years, with the development of science and technology, people's demand for high energy density lithium ion batteries is more urgent. At present, increasing the working voltage of lithium ion batteries is considered to be an effective way to increase their energy density. However, conventional carbonate electrolytes are prone to side reactions with the surface of the positive electrode material at high voltage. When the heat released by these chemical reactions cannot be evacuated in time, a series of chemical reactions are triggered and the temperature of the battery rises sharply, eventually leading to The battery burns and explodes in severe cases. On the other hand, lithium ion secondary batteries emit a large amount of heat in the case of excessive charge and discharge, short circuit and large current operation for a long time, and these heats become safety hazards of flammable electrolytes, which may cause catastrophic thermal breakdown or even battery explosion. Therefore, the safety issue has become an important prerequisite for the innovation of the lithium-ion battery market. In particular, applications in the field of electric vehicles have put forward higher and newer requirements for battery safety.

In order to improve the safety of lithium-ion batteries, researchers have made many efforts from the external management of batteries, internal materials of batteries and electrolytes, such as the use of positive temperature coefficient heat sensitive material (PTC) protection board, material modification, solid electrolyte, resistance Burning electrolytes, etc. The development of a non-flammable electrolyte system is an effective way to solve the safety problems of lithium-ion batteries.

The lithium ion electrolyte disclosed in US Pat. No. 6,589,697 uses a phosphate ester such as trimethyl phosphate (TMP) as an electrolyte additive to reduce the flammability of the electrolyte. However, most of these additives have high viscosity, high freezing point, and when used as a flame retardant additive, more than 10% are added to have a flame retardant effect, and excessive addition of the flame retardant additive may have a large negative impact on the performance of the battery. Therefore, there is an urgent need to develop an electrolyte that can achieve flame retardant performance without affecting the basic performance of a lithium ion battery.

When the solvent with high boiling point and high flash point is the main solvent of the electrolyte, the flash point of the electrolyte is correspondingly increased, and the electrolyte is difficult to ignite. A. Abouimrane et al. reported that Li4Ti5O12/ prepared by using a sulfone solvent as an electrolyte. The LiMn2O4 battery has good cycle performance and is difficult to ignite (. Electrochem Commun, 2009, 11(5): 1073-1076.). Patent US0204857 reports a flame retardant electrolyte using LiBF4 as a lithium salt, 10% to 30% high flash point, high boiling point γ-BL + 70% to 90% EC as a solvent. The addition of a high boiling point, high flash point solvent increases the flash point of the electrolyte, making the electrolyte difficult to ignite, but does not reduce the self-extinguishing time of the electrolyte.

Summary of the invention

The object of the present invention is to provide a high-safety lithium ion battery electrolyte, which makes the electrolyte difficult to ignite and self The extinguishing time is short, and at the same time, the performance of the battery performance is less affected.

The technical solution of the present invention is: a high-safety lithium ion battery electrolyte, characterized in that: the main component of the electrolyte includes an organic solvent, an electrolyte and an additive, and the organic solvent contains at least one high flash point solvent, The additive includes a film additive and a flame retardant additive; the electrolyte is prepared by adding a high-purity organic solvent to the mixing ratio in an argon-protected glove box, then slowly adding the electrolyte lithium salt, stirring and mixing uniformly, and finally adding the additive separately. The high-safety lithium ion battery electrolyte of the present invention can be obtained by adding the above mixed solution, stirring and mixing uniformly, and standing for a while.

The molar concentration of the electrolyte in the organic solvent is from 0.8 to 1.5 mol/L.

A preferred electrolyte has a molar concentration in the organic solvent of from 1 to 1.2 mol/L.

The high flash point solvent of the present invention is one or more of the following solvents: a fluorinated solvent, a sulfone solvent, and a cyclic carboxylic acid ester.

The fluorinated solvent is preferably fluoroethylene carbonate (FEC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether or the like, and the sulfone solvent is preferably sulfolane. (TMS), dimethyl sulfite (DMS), etc., and the cyclic carboxylic acid ester is preferably γ-butyrolactone (BL).

The film-forming additive in the additive of the present invention is one of vinylene carbonate, vinyl ethylene carbonate, and fluoroethylene carbonate.

The flame retardant additive is one of trimethyl phosphate, triphenyl phosphate, hexamethylphosphazene and the like.

The weight percentage of the film-forming additive in the electrolyte is 1-2%, and the weight percentage of the flame-retardant additive in the electrolyte is 5 to 8%.

Among them, the argon-protected glove box has a water content of <10 ppm and an oxygen content of <10 ppm.

The electrolyte burning performance test of the present invention can be carried out by cutting a 5 mm thick ceramic fiber paper into a strip of 15×20 mm size and drying it in a constant temperature drying oven at 85 ° C for 8 hours. The copper wire was cut into 10 cm length, hooked about 5 mm above the center of the ceramic fiber paper, and the total mass m1 of the ceramic fiber paper and the copper wire was weighed to the nearest 0.01 g. The ceramic fiber paper was placed in a 100 ml beaker, poured into an electrolyte for 5 minutes, the ceramic fiber paper was taken out, and the total mass m2 after soaking the electrolyte was weighed by a weight loss method to the nearest 0.01 g. The ceramic fiber paper impregnating the electrolyte is hung on the iron stand, ignited, and the time from the exit of the fire source to the time when the ceramic fiber paper is extinguished is recorded, and the self-extinguishing time is calculated:

The beneficial effects of the invention are: adding a high flash point solvent and a small amount of flame retardant additive to the electrolyte of the lithium ion battery at the same time, not only can the electrolyte be difficult to ignite, but also the self-extinguishing electrolyte contains a small amount of flame retardant additive. The time is short. Therefore, the impact on battery performance is small.

detailed description

The invention is further illustrated by the following examples; however, it is not intended to limit the scope of the invention, and any changes or modifications of the invention may be made without departing from the spirit and scope of the invention.

Example 1

A high-safety lithium-ion battery electrolyte in an organic solvent (EC), 1 in a weight ratio of 1:4 in a glove phase filled with argon (H ₂ O < 10 ppm, O ₂ < 10 ppm) 1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is uniformly mixed; then, the conductive lithium salt LiPF _{6 is} added to have a concentration of 1.0 mol/L in an organic solvent. Finally, trimethyl phosphate (TMP) was added in an amount of 5 wt.%; vinylene carbonate (VC) was used in an amount of 2 wt%, uniformly mixed, and allowed to stand to obtain the high-safety lithium ion battery electrolyte.

Example 2

A highly safe lithium ion battery electrolyte in which ethylene carbonate (EC), fluoroethylene carbonate (FEC) is used in a glove phase filled with argon (H ₂ O < 10 ppm, O ₂ < 10 ppm). The mixture was uniform; the weight ratio of EC to FEC was EC:FEC=1:1, and then the conductive lithium salt LiPF _{6 was} added to a concentration of 1.2 mol/L in an organic solvent, and finally trimethyl phosphate (TPP) was added. The amount is 5wt.%; the vinylene carbonate (VC) is used in an amount of 1% by weight, uniformly mixed, and left to stand, thereby obtaining the high-safety lithium ion battery electrolyte.

Example 3

A high-safety lithium-ion battery electrolyte in which ethylene carbonate (EC) and dimethyl sulfite (DMS) are used in a glove phase filled with argon (H ₂ O < 10 ppm, O ₂ < 10 ppm). The mixture was uniformly mixed; the weight ratio of EC and DMS was EC:DMS=3:7, and then the conductive lithium salt LiPF _{6 was} added to a concentration of 1.5 mol/L in an organic solvent, and finally trimethyl phosphate (TMP) was separately added. The amount is 5wt.%; the vinylene carbonate (VC) is used in an amount of 1% by weight, uniformly mixed, and left to stand, thereby obtaining the high-safety lithium ion battery electrolyte.

Example 4

A high-safety lithium-ion battery electrolyte. In a glove phase filled with argon (H ₂ O<10ppm, O ₂ <10ppm), the organic solvent ethylene carbonate (EC), sulfolane (TMS), and ethylene carbonate The ester (EMC) is uniformly mixed; the weight ratio is EC:TMS: GBL=3:2:5, and then the conductive lithium salt LiPF _{6 is} added to a concentration of 1 mol/L in an organic solvent, and finally triphenyl phosphate is added separately. (TPP), the amount is 5 wt.%; the vinylene carbonate (VC), the amount is 1.5 wt%, the mixture is uniformly mixed, and the high-safety lithium ion battery electrolyte is obtained.

Example 5

A high-safety lithium-ion battery electrolyte. In a glove phase filled with argon (H ₂ O<10ppm, O ₂ <10ppm), the organic solvent ethylene carbonate (EC), propylene carbonate (PC), γ - Butyrolactone (BL) is uniformly mixed; the weight ratio is EC:PC:BL=2:1:7, after which the conductive lithium salt LiPF _{6 is} added to a concentration of 1 mol/L in an organic solvent, and finally phosphoric acid is added respectively. The trimethyl ester (TMP) is used in an amount of 5 wt.%; the vinylene carbonate (VC) is used in an amount of 1% by weight, uniformly mixed, and allowed to stand to obtain the high-safety lithium ion battery electrolyte.

Example 6

A high-safety lithium-ion battery electrolyte. In a glove phase filled with argon (H ₂ O<10ppm, O ₂ <10ppm), the organic solvent ethylene carbonate (EC), propylene carbonate (PC), γ - Butyrolactone (BL) was uniformly mixed; the weight ratio was EC:PC:BL=2:1:7, and then the conductive lithium salt LiPF _{6 was} added to a concentration of 0.8 mol/L in an organic solvent, and finally added separately. Trimethyl phosphate (TMP) is used in an amount of 8 wt.%; vinylene carbonate (VC) is used in an amount of 1 wt%, uniformly mixed, and allowed to stand to obtain the high-safety lithium ion battery electrolyte.

Example 7

A high-safety lithium-ion battery electrolyte. In a glove phase filled with argon (H ₂ O<10ppm, O ₂ <10ppm), the organic solvent ethylene carbonate (EC), propylene carbonate (PC), γ - Butyrolactone (BL) is uniformly mixed; the weight ratio is EC:PC:BL=2:1:7, after which the conductive lithium salt LiPF _{6 is} added to a concentration of 1 mol/L in an organic solvent, and finally phosphoric acid is added respectively. The trimethyl ester (TMP) is used in an amount of 2 wt.%; the vinylene carbonate (VC) is used in an amount of 1% by weight, uniformly mixed, and allowed to stand to obtain the high-safety lithium ion battery electrolyte.

Example 8

A high-safety lithium-ion battery electrolyte in which ethylene carbonate (EC) and dimethyl sulfite (DMS) are used in a glove phase filled with argon (H ₂ O < 10 ppm, O ₂ < 10 ppm). Mixing uniformly; EC and DMS weight ratio is EC: DMS = 3:7, then adding conductive lithium salt LiPF ₆ to a concentration of 1 mol / L in an organic solvent, and finally adding hexamethylphosphazene (HMPN) The dosage is 5wt.%; the 1,3-propane sultone (1,3-PS) is used in an amount of 1.5%, uniformly mixed, and left to stand, thereby obtaining the high-safety lithium ion battery electrolyte.

Example 9

A high-safety lithium-ion battery electrolyte in which an organic solvent, ethylene carbonate (EC), γ-butyrolactone (BL), is used in a glove phase filled with argon (H ₂ O < 10 ppm, O ₂ < 10 ppm). The mixture was uniform; the weight ratio of EC to BL was EC:BL=1:1, and then the conductive lithium salt LiPF _{6 was} added to a concentration of 1 mol/L in an organic solvent, and finally trimethyl phosphate (TMP) was added. The amount is 5 wt.%; the vinylene carbonate (VC) is used in an amount of 1 wt%, uniformly mixed, and allowed to stand to obtain the high-safety lithium ion battery electrolyte.

Comparative example 1

In the glove phase filled with argon (H ₂ O<10ppm, O ₂ <10ppm), the organic solvent ethylene carbonate (EC) and dimethyl carbonate (DMC) are uniformly mixed; the weight ratio of EC to DMC is EC: DMC = 3:7, and then the conductive lithium salt LiPF _{6 was} added to a concentration of 1 mol/L in an organic solvent, and the mixture was uniformly mixed.

Comparative example 2

In the glove phase filled with argon (H ₂ O<10ppm, O ₂ <10ppm), the organic solvent ethylene carbonate (EC), γ-butyrolactone (BL) is uniformly mixed; the weight ratio of EC to BL is EC :BL=3:7, and then the conductive lithium salt LiPF _{6 was} added to a concentration of 1 mol/L in an organic solvent, uniformly mixed, and allowed to stand.

Comparative example 3

In the glove phase filled with argon (H ₂ O<10ppm, O ₂ <10ppm), the organic solvent ethylene carbonate (EC) and dimethyl carbonate (DMC) are uniformly mixed; the weight ratio of EC to DMC is EC: DMC=3:7, after which the conductive lithium salt LiPF _{6 was} added to a concentration of 0.8 mol/L in an organic solvent, and finally trimethyl phosphate (TMP) was added in an amount of 5 wt.%; vinylene carbonate ( VC), the amount is 1wt.%, mixed evenly, and allowed to stand.

The above examples and comparative examples were subjected to a burning test, and the burning test was as follows: 5 mm thick ceramic fiber paper was cut into strips of 15×20 mm size and placed in a constant temperature drying oven at 85 ° C for 8 hours. The copper wire was cut into 10 cm long, hooked about 5 mm above the center of the ceramic fiber paper, and the total mass m _{1 of the} ceramic fiber paper and the copper wire was weighed to the nearest 0.01 g. The ceramic fiber paper was placed in a 100 ml beaker, poured into an electrolyte for 5 minutes, the ceramic fiber paper was taken out, and the total mass m ₂ after soaking the electrolyte was weighed by a weight loss method to the nearest 0.01 g. The ceramic fiber paper impregnating the electrolyte is hung on the iron stand, ignited, and the time from the exit of the fire source to the time when the ceramic fiber paper is extinguished is recorded, and the self-extinguishing time is calculated:

The test results are shown in Table 1.

It can be seen from Table 1 that when the electrolyte solution of the embodiment contains a high content of a high flash point solvent, the electrolyte is difficult to ignite, but the self-extinguishing time is long, and the electrolyte contains a high flash point solvent and a flame retardant additive. Liquid is difficult to ignite while Self-extinguishing time is shorter. The electrolytic solution of the present invention has characteristics of being difficult to ignite and having a short self-extinguishing time.

Claims (9)

1. A high-safety lithium ion battery electrolyte characterized in that: the main component of the electrolyte includes an organic solvent, an electrolyte and an additive, and the organic solvent contains at least one high flash point solvent, and the additive includes a film additive and a flame retardant additive.
2. The method and the technique for preparing a high-safety lithium ion battery electrolyte according to claim 1, wherein the molar concentration of the electrolyte in the organic solvent is 0.8 to 1.5 mol/L.
3. A method and a technique for preparing a high-safety lithium ion battery electrolyte according to claim 2, wherein a preferred concentration of the electrolyte in the organic solvent is from 1 to 1.2 mol/L.
4. The method and the technology for preparing a high-safety lithium ion battery electrolyte according to claim 1, wherein the high flash point solvent is a fluorocarbon solvent, a sulfone solvent, or a cyclic carboxylic acid ester solvent. One or several.
5. A method and a technique for preparing a high-safety lithium ion battery electrolyte according to claim 4, wherein the fluorinated solvent is preferably fluoroethylene carbonate (FEC), 1, 1, 2, 2 - tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether or the like, and the sulfone solvent is preferably sulfolane (TMS), dimethyl sulfite (DMS) or the like, and the cyclic carboxylic acid ester is preferably γ- Butyrolactone (BL).
6. The method and the technology for preparing a high-safety lithium ion battery electrolyte according to claim 1, wherein the film forming additive of the additive of the present invention is: vinylene carbonate, vinyl ethylene carbonate, One of fluoroethylene carbonate.
7. The method and the technique for preparing a high-safety lithium ion battery electrolyte according to claim 6, wherein the weight percentage of the film-forming additive in the electrolyte is 1-2%.
8. The method and the technology for preparing a high-safety lithium ion battery electrolyte according to claim 1, wherein the flame retardant additive is trimethyl phosphate, triphenyl phosphate or hexamethylphosphazene. One.
9. The method and the technical method for preparing a high-safety lithium ion battery electrolyte according to claim 8, wherein the weight percentage of the flame retardant additive in the electrolyte is 5 to 8%.