CN109888391B

CN109888391B - Low-temperature lithium ion battery electrolyte

Info

Publication number: CN109888391B
Application number: CN201910180499.1A
Authority: CN
Inventors: 沈剑
Original assignee: Hefei Guoxuan High Tech Power Energy Co Ltd
Current assignee: Hefei Gotion High Tech Power Energy Co Ltd
Priority date: 2019-03-11
Filing date: 2019-03-11
Publication date: 2020-09-04
Anticipated expiration: 2039-03-11
Also published as: CN109888391A

Abstract

The invention discloses a low-temperature lithium ion battery electrolyte, which is characterized in that: consists of a non-aqueous organic solvent, lithium salt, a low-temperature additive and other functional additives; the low-temperature additive adopted by the invention has a remarkable improvement effect on the low-temperature performance of the electrolyte, wherein the silicon oxygen radical reacts with HF and water in the electrolyte, so that the acidity and the moisture in the electrolyte are reduced, and the purity of the electrolyte is improved; pyrrole and unsaturated bond polymerization and silicon-oxygen base adsorption are generated at the interface of the electrolyte and the electrode to form a protective film, the synergistic effect of the pyrrole and unsaturated bond polymerization and the silicon-oxygen base adsorption improves the lithium ion conduction rate of the interface and reduces the interface impedance, the compatibility of the positive/negative electrode interface and the electrolyte is well improved, and the low-temperature cycle performance and the high-temperature stability of the lithium ion battery are guaranteed.

Description

Low-temperature lithium ion battery electrolyte

Technical Field

The invention relates to the technical field of lithium batteries, in particular to a low-temperature electrolyte added with pyrrole silicon-based derivatives.

Background

The lithium ion secondary battery gradually establishes a wide market by virtue of the advantages of high working voltage, long cycle life, high charging and discharging speed and the like, and plays an important role in the fields of small electronic products such as mobile phones, computers, electric tools and the like. However, under extreme conditions (high temperature and low temperature), the problems of battery cycle, safety and the like become prominent, and particularly, the viscosity of the electrolyte increases at low temperature, so that lithium ions cannot normally migrate and be inserted into the negative electrode, and a lithium precipitation phenomenon occurs, which affects the service life and safety of the battery. Therefore, how to improve the low-temperature cycle performance of the electrolyte is a problem which needs to be solved urgently in the lithium ion battery at present.

In order to solve the problem, a low-temperature lithium ion battery electrolyte and a lithium ion battery (CN103107364A) disclose a methyl acetate-containing electrolyte, and the lithium ion battery has remarkable low-temperature discharge performance.

The electrolyte has the advantages that the consumption of methyl acetate is large, the low-temperature performance can be obviously improved, but the situation of deterioration of the high-temperature performance of the lithium ion battery inevitably occurs, and the low-temperature cycle performance and the high-temperature stability of the lithium ion battery are finally affected mainly because methyl acetate is unstable and easy to decompose at high temperature, so that special additives are needed to be designed, and the electrolyte not only has the low-temperature performance but also has good high-temperature stability.

Disclosure of Invention

The invention aims to provide a low-temperature lithium ion battery electrolyte which can remarkably improve the low-temperature cycle performance and the high-temperature stability of the electrolyte.

In order to achieve the purpose, the invention adopts the following technical scheme:

the electrolyte of the low-temperature lithium ion battery consists of a non-aqueous organic solvent, lithium salt, a low-temperature additive and other functional additives, wherein the structural formula I of the low-temperature additive is as follows:

wherein R is selected from methyl or ethyl.

Further, the non-aqueous organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate.

Further, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis oxalate borate and lithium difluoro oxalate borate.

Further, the other functional additive is selected from one or more of vinylene carbonate, trimethyl phosphate, tri (trimethylsilyl) borate and tri (trimethylsilyl) phosphate.

Further, the low-temperature additive accounts for 0.1-5% of the total mass of the electrolyte.

Further, the low-temperature additive accounts for 2% of the total mass of the electrolyte.

Further, the percentage of the other functional additives in the total mass of the electrolyte is 0.01-2%.

The invention has the following beneficial effects: the pyrrole silicon-based derivative with the structural formula I is added into the electrolyte, and the low-temperature additive has a remarkable improvement effect on the low-temperature performance of the electrolyte, wherein the silicon-oxygen base reacts with HF and water in the electrolyte, so that the acidity and the moisture in the electrolyte are reduced, and the purity of the electrolyte is improved; pyrrole and unsaturated bond polymerization and silicon-oxygen base adsorption are generated at the interface of the electrolyte and the electrode to form a protective film, the synergistic effect of the pyrrole and unsaturated bond polymerization and the silicon-oxygen base adsorption improves the lithium ion conduction rate of the interface and reduces the interface impedance, the compatibility of the positive/negative electrode interface and the electrolyte is well improved, and the low-temperature cycle performance and the high-temperature stability of the lithium ion battery are guaranteed.

Drawings

FIG. 1 is a graph showing the low-temperature cycle of the electrolytes of examples 1, 2, 3, 6 and 7 of the present invention.

FIG. 2 is a graph showing the results of high-temperature storage of the electrolytes of examples 1, 2, 3, 6 and 7 of the present invention.

Detailed Description

The present invention will be further described in detail with reference to the following specific examples:

preparation of low-temperature additive I1:

adding 33mmol of pyrrole into 100mL of anhydrous n-hexane, then slowly dropwise adding butyl lithium (36mmol), slowly stirring for 24 hours in an inert atmosphere to generate white precipitated lithiated pyrrole; then, 50mL of (chloromethyl) dimethoxy (methyl) silane (31mmol) toluene solution is slowly dripped into the solution, and the solution is stirred for 12 hours at room temperature after the dripping is finished; filtration followed by recrystallization from toluene gave 3.52g of product I1 in 61.2% yield.

The structural formula of the product I1 is as follows:

preparation of low-temperature additive I2:

33mmol of pyrrole was added to 100mL of anhydrous n-hexane, followed by slow dropwise addition of butyl lithium (36mmol), and the mixture was stirred slowly for 24 hours under an inert atmosphere to give a white precipitated lithiated pyrrole. To this solution was slowly added dropwise a 50mL toluene solution of (chloromethyl) diethoxy (methyl) silane (31mmol), and after completion of the dropwise addition, the mixture was stirred at room temperature for 12 hours. Filtering, recrystallizing with toluene to obtain product I₂It was 3.76g, and the yield was 56.9%.

The structural formula of the product I2 is as follows:

example 1

In an inert atmosphere glove box with the water content of less than 10ppm and the oxygen content of less than 5ppm, preparing organic solvents of Ethylene Carbonate (EC), diethyl carbonate (DEC) and Ethyl Methyl Carbonate (EMC) into a mixed solvent according to the mass ratio of 3:2:5, selecting lithium hexafluorophosphate as lithium salt, adding vinylene carbonate accounting for 2% of the total mass of the electrolyte, and fully stirring and uniformly mixing to obtain the electrolyte.

Taking out a proper amount of the prepared electrolyte in a drying room, and injecting the electrolyte into a lithium iron phosphate battery, wherein the anode is lithium iron phosphate, and the cathode is natural graphite; the cell design capacity was 3 Ah. The battery is formed according to the following steps: the voltage is charged to 3.65V by 0.02C constant current and 3.65V by 0.1C constant current. Aging the formed battery, then vacuumizing and sealing, and grading the capacity according to the following steps: charging the battery to 3.65V at a constant current and a constant voltage of 0.3C, discharging the battery to 2.0V at a constant current of 0.3C, and performing the following two tests on the obtained battery respectively after the charge and discharge cycle is performed for 2 times:

firstly, placing the material into a charging and discharging detection cabinet for low-temperature cycle test: the testing temperature is-10 ℃, and the testing steps are as follows: 0.2CC/0.5CD, 2.0V-3.65V.

Secondly, performing high-temperature storage test: and (3) carrying out constant volume at normal temperature of 1C for 3 weeks in a charging and discharging detection cabinet, after the constant volume is finished, placing the battery into a thermostat at 55 ℃ for 7 days, then carrying out constant volume at normal temperature of 1C for 3 weeks, and calculating the capacity retention rate and the capacity recovery rate after the battery is placed.

Example 2

In an inert atmosphere glove box with the water content of less than 10ppm and the oxygen content of less than 5ppm, preparing organic solvents of Ethylene Carbonate (EC), diethyl carbonate (DEC) and Ethyl Methyl Carbonate (EMC) into a mixed solvent according to the mass ratio of 3:2:5, selecting lithium hexafluorophosphate as lithium salt, adding vinylene carbonate accounting for 2 percent of the total mass of the electrolyte and 1 percent of low-temperature additive I1, and fully stirring and uniformly mixing to obtain the electrolyte.

The subsequent operation was the same as in example 1.

Example 3

In an inert atmosphere glove box with the water content of less than 10ppm and the oxygen content of less than 5ppm, preparing organic solvents of Ethylene Carbonate (EC), diethyl carbonate (DEC) and Ethyl Methyl Carbonate (EMC) into a mixed solvent according to the mass ratio of 3:2:5, selecting lithium hexafluorophosphate as lithium salt, adding vinylene carbonate accounting for 2 percent of the total mass of the electrolyte and a low-temperature additive I2 accounting for 5 percent of the total mass of the electrolyte, and fully stirring and uniformly mixing to obtain the electrolyte.

The subsequent operation was the same as in example 1.

Example 4

In an inert atmosphere glove box with the water content of less than 10ppm and the oxygen content of less than 5ppm, preparing organic solvents of Ethylene Carbonate (EC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC) and Propylene Carbonate (PC) into a mixed solvent according to the mass ratio of 3:2:4.5:0.5, wherein lithium hexafluorophosphate and lithium tetrafluoroborate are selected as lithium salts, vinylene carbonate and trimethyl phosphate accounting for 2% of the total mass of the electrolyte and a low-temperature additive I1 accounting for 0.1% of the total mass of the electrolyte are added, and the mixed solvent is fully stirred and uniformly mixed to obtain the electrolyte.

The subsequent operation was the same as in example 1.

Example 5

In an inert atmosphere glove box with the water content of less than 10ppm and the oxygen content of less than 5ppm, preparing organic solvents of Ethylene Carbonate (EC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC) and dimethyl carbonate (DMC) into a mixed solvent according to the mass ratio of 3:2:4.5:0.5, selecting lithium hexafluorophosphate and lithium bis (oxalato) borate as lithium salts, adding vinylene carbonate and tris (trimethylsilyl) borate accounting for 2% of the total mass of the electrolyte, and fully stirring and uniformly mixing 0.5% of a low-temperature additive I2.

The subsequent operation was the same as in example 1.

Example 6

In an inert atmosphere glove box with the water content of less than 10ppm and the oxygen content of less than 5ppm, preparing organic solvents of Ethylene Carbonate (EC), diethyl carbonate (DEC) and Ethyl Methyl Carbonate (EMC) into a mixed solvent according to the mass ratio of 3:2:5, selecting lithium hexafluorophosphate and lithium difluorooxalato borate as lithium salts, adding vinylene carbonate and tris (trimethylsilyl) phosphate accounting for 2% of the total mass of the electrolyte, and fully stirring and uniformly mixing 2% of a low-temperature additive I1.

The subsequent operation was the same as in example 1.

Example 7

In an inert atmosphere glove box with the water content of less than 10ppm and the oxygen content of less than 5ppm, preparing organic solvents of Ethylene Carbonate (EC), diethyl carbonate (DEC) and Ethyl Methyl Carbonate (EMC) into a mixed solvent according to the mass ratio of 3:2:5, selecting lithium hexafluorophosphate as lithium salt, adding vinylene carbonate accounting for 2 percent of the total mass of the electrolyte and 2 percent of low-temperature additive I2, and fully stirring and uniformly mixing.

The subsequent operation was the same as in example 1.

After the preparation of the electrolytes of examples 1 to 7, the ionic conductivities of the electrolytes were measured at-10 ℃ by a conductivity meter, and the results are shown in Table 1.

Table 1:

from table 1, the ionic conductivity of the electrolyte added with the pyrrolylsilyl derivative is improved, wherein the ionic conductivity of the electrolyte is improved to the maximum extent in example 7.

FIG. 1 is a low temperature cycle curve for examples 1, 2, 3, 6 and 7, with a test temperature of-10 ℃ and test steps of: 0.2CC/0.5CD, 2.0V-3.65V; the results show that the low-temperature additives I1 and I2 can effectively improve the low-temperature cycle performance of the battery, wherein the low-temperature cycle performance improvement effect of example 7 (adding the low-temperature additive I2 accounting for 2% of the total mass of the electrolyte) is the best.

FIG. 2 is a graph of the results of high temperature storage for examples 1, 2, 3, 6 and 7 showing: the embodiment added with the low-temperature additive improves the low-temperature cycle performance and simultaneously does not reduce the high-temperature stability, and the capacity retention rate and the recovery rate respectively reach more than 97 percent and 98 percent.

The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solution of the present invention by those skilled in the art should fall within the protection scope defined by the claims of the present invention without departing from the spirit of the present invention.

Claims

1. The low-temperature lithium ion battery electrolyte is characterized in that: the lithium salt battery pack is composed of a nonaqueous organic solvent, a low-temperature additive and other functional additives, wherein the structural formula I of the low-temperature additive is as follows:

wherein R is selected from methyl or ethyl.

2. The low-temperature lithium ion battery electrolyte according to claim 1, wherein: the non-aqueous organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate.

3. The low-temperature lithium ion battery electrolyte according to claim 1, wherein: the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis (oxalate) borate and lithium difluoro (oxalate) borate.

4. The low-temperature lithium ion battery electrolyte according to claim 1, wherein: the other functional additive is selected from one or more of vinylene carbonate, trimethyl phosphate, tri (trimethylsilyl) borate and tri (trimethylsilyl) phosphate.

5. The low-temperature lithium ion battery electrolyte according to claim 1, wherein: the low-temperature additive accounts for 0.1-5% of the total mass of the electrolyte.

6. The low-temperature lithium ion battery electrolyte according to claim 1, wherein: the percentage of the low-temperature additive in the total mass of the electrolyte is 2%.

7. The low-temperature lithium ion battery electrolyte according to claim 1, wherein: the percentage of the other functional additives in the total mass of the electrolyte is 0.01-2%.