阅读说明：本技术 一种软包装锂离子电池用低温电解液 (Low-temperature electrolyte for flexible package lithium ion battery ) 是由 尹晓磊 王明舟 于 2019-11-18 设计创作，主要内容包括：本发明公开了一种软包装锂离子电池用低温电解液,该电解液由电解质锂盐、有机溶剂、添加剂组成,所述添加剂为醚类化合物和N,N-二甲基甲酰胺,各组分的质量百分比如下：电解质锂盐10％-15％；有机溶剂80％-85％；醚类化合物占电解质锂盐与有机溶剂总质量的1％-5％；N,N-二甲基甲酰胺占电解质锂盐与有机溶剂总质量的1％-3％。本发明的电解质锂盐以六氟磷酸锂、双三氟甲基磺酰亚胺锂、二氟磷酸锂三种电解质锂盐合理配比(5:1:1)而成,不仅可以解决使用单一六氟磷酸锂高温分解,热稳定性差的问题,并通过在电解液中加入添加剂N,N-二甲基甲酰胺以及醚类化合物,可以使锂电池充放电过程中形成良好的SEI膜,首次效率高,且具有优良的耐低温性能和循环性能。(The invention discloses a low-temperature electrolyte for a flexible package lithium ion battery, which consists of electrolyte lithium salt, an organic solvent and an additive, wherein the additive is an ether compound and N, N-dimethylformamide, and the mass percentages of the components are as follows: 10% -15% of electrolyte lithium salt; 80% -85% of organic solvent; the ether compound accounts for 1 to 5 percent of the total mass of the electrolyte lithium salt and the organic solvent; the N, N-dimethylformamide accounts for 1-3% of the total mass of the electrolyte lithium salt and the organic solvent. The electrolyte lithium salt is prepared by reasonably proportioning (5:1:1) lithium hexafluorophosphate, lithium bistrifluoromethylsulfonyl imide and lithium difluorophosphate, so that the problems of single lithium hexafluorophosphate high-temperature decomposition and poor thermal stability can be solved, and a good SEI film can be formed in the charging and discharging processes of a lithium battery by adding additives N, N-dimethylformamide and an ether compound into an electrolyte, so that the lithium battery has high primary efficiency and excellent low-temperature resistance and cycle performance.)

1. The low-temperature electrolyte for the flexible-package lithium ion battery is characterized by comprising electrolyte lithium salt, an organic solvent and an additive, wherein the additive is an ether compound and N, N-dimethylformamide and comprises the following components in percentage by mass:

electrolyte lithium salt: 10% -15%;

organic solvent: 80% -85%;

the ether compound accounts for 1 to 5 percent of the total mass of the electrolyte lithium salt and the organic solvent;

the N, N-dimethylformamide accounts for 1-3% of the total mass of the electrolyte lithium salt and the organic solvent.

2. The low-temperature electrolyte for the flexible package lithium ion battery as claimed in claim 1, wherein the electrolyte lithium salt comprises lithium hexafluorophosphate, lithium bistrifluoromethylsulfonyl imide and lithium difluorophosphate, and the mass ratio of the lithium hexafluorophosphate, the lithium bistrifluoromethylsulfonyl imide and the lithium difluorophosphate is 5:1: 1.

3. The low-temperature electrolyte for the flexible packaging lithium ion battery according to claim 1, wherein the organic solvent is selected from the group consisting of cyclic carbonates, linear carbonates, and carboxylic esters.

4. The low-temperature electrolyte for the flexible package lithium ion battery according to claim 3, wherein the cyclic carbonate is one or two of ethylene carbonate and propylene carbonate; the linear carbonate is one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and methyl propyl carbonate; the carboxylic ester is one or more of gamma-butyrolactone, methyl formate, methyl acetate, methyl butyrate and ethyl propionate.

5. The low-temperature electrolyte for the flexible package lithium ion battery as claimed in claim 1, wherein the ether compound is one or more of dimethoxymethane, 1, 2-dimethoxyethane and diglyme, tetrahydrofuran, 2-methyltetrahydrofuran, and 1, 3-dioxolane.

Technical Field

The invention belongs to the technical field of lithium ion battery electrolyte, and particularly relates to a low-temperature electrolyte for a flexible package lithium ion battery.

Background

Since the commercialization of lithium ion batteries, lithium ion batteries have been recognized by people because of their advantages of high voltage, high volumetric specific energy and mass specific energy density, no pollution, recyclability, etc., and have been widely used in the fields of mobile phones, notebooks, digital cameras, mobile power supplies, tablet computers, electric bicycles, electric vehicles, etc., and are the preferred energy providers of current consumer products. However, the lithium ion battery has defects of the lithium ion battery, the battery discharge capacity under the low temperature condition is obviously reduced compared with the normal temperature environment, and particularly the battery capacity under the ultralow temperature (-40 ℃) environment can not be basically released. Especially for northern areas, the improvement of the low-temperature performance of the lithium ion battery is more important. There are many factors affecting the low temperature performance of lithium batteries, including the kinds of positive and negative electrode materials, the composition of the electrolyte, the manufacturing process, and the like. Among them, the electrolyte is the most important factor affecting the low temperature performance of the lithium battery because the viscosity of the electrolyte becomes high at low temperature, the ionic and electronic conductivity becomes low, the ionic transfer between the positive and negative electrodes is limited, and the activity of the battery is reduced.

Chinese patent No. CN201310031161.2 discloses a lithium ion secondary battery and an electrolyte thereof, wherein the electrolyte contains a solvent and a lithium salt, and further contains a film forming additive, the solvent includes a first solvent and a second solvent, the first solvent is composed of linear carboxylic ester and ethylene carbonate, the second solvent is one or more selected from ethyl methyl carbonate, diethyl carbonate and dimethyl carbonate propylene carbonate, and the film forming additive is one or more selected from fluoroethylene carbonate, vinylene carbonate, 1, 3-propane sultone, succinonitrile, adiponitrile, lithium bis (oxalato) borate and lithium bis (fluorooxalato) borate. According to the technical scheme, a solvent system with a high dielectric constant and a low viscosity is obtained through the collocation of linear carboxylic ester and ethylene carbonate, and the problem of poor compatibility of the linear carboxylic ester and graphite is solved through a film forming additive, so that the surface of a lithium ion secondary battery adopting the electrolyte has high power discharge capacity and excellent high-temperature cycle stability, but the capacity retention rate of constant current charging and discharging at-20 ℃ and 0.5C is only 40-45%, the low-temperature performance is poor, and the use requirement under the low-temperature condition cannot be met.

Disclosure of Invention

The invention aims to provide a low-temperature electrolyte for a flexible package lithium ion battery, which can form a good SEI film in the charging and discharging processes of a lithium battery through the combination and proportioning of organic lithium salts and the addition of an ether compound and N, N-dimethylformamide in the electrolyte, and has high first efficiency, and the prepared electrolyte has excellent low-temperature resistance and cycle performance.

In order to test the above purpose, the invention is realized by the following technical scheme:

the low-temperature electrolyte for the flexible-package lithium ion battery consists of electrolyte lithium salt, an organic solvent and an additive, wherein the additive is an ether compound and N, N-dimethylformamide.

Wherein, the weight percentage is calculated as follows:

electrolyte lithium salt: 10% -15%;

organic solvent: 80% -85%;

the ether compound accounts for 1 to 5 percent of the total mass of the electrolyte lithium salt and the organic solvent;

the N, N-dimethylformamide accounts for 1-3% of the total mass of the electrolyte lithium salt and the organic solvent.

Wherein the electrolyte lithium salt comprises lithium hexafluorophosphate LiPF₆Lithium bis (trifluoromethylsulfonyl imide) LiTFSI and lithium difluorophosphate LiPO₂F₂And lithium hexafluorophosphate LiPF₆Lithium bis (trifluoromethylsulfonyl imide) LiTFSI and lithium difluorophosphate LiPO₂F₂The mass ratio of (A) to (B) is 5:1: 1.

Wherein the organic solvent is composed of cyclic carbonate, linear carbonate and carboxylic ester.

Wherein the cyclic carbonate is any one of Ethylene Carbonate (EC) and Propylene Carbonate (PC); the linear carbonate is one or more of dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC) and dibutyl carbonate (DBC); the carboxylic acid ester is one or more of gamma-butyrolactone (GBL), Methyl Formate (MF), Methyl Acetate (MA), Methyl Butyrate (MB), and Ethyl Propionate (EP).

Preferably, Ethylene Carbonate (EC): dimethyl carbonate (DMC): ethyl Methyl Carbonate (EMC): dibutyl carbonate (DBC): the mass ratio of Methyl Acetate (MA) was 4:1:3:6: 1.

Wherein the ether compound is one or more of Dimethoxymethane (DMM), 1, 2-Dimethoxyethane (DME) and Diglyme (DG), Tetrahydrofuran (THF), 2-methyltetrahydrofuran (2Me-THF) and 1, 3-Dioxolane (DOL).

The invention has the obvious effects that:

(1) the lithium hexafluorophosphate lithium salt electrolyte is prepared by reasonably proportioning three electrolyte lithium salts, namely lithium hexafluorophosphate, lithium bistrifluoromethylsulfonyl imide and lithium difluorophosphate, so that the problems of poor thermal stability caused by the use of single lithium hexafluorophosphate can be solved, a good SEI film can be formed, the interface impedance of a battery is reduced, and the low-temperature performance and the cycle performance of the battery are improved.

(2) The carboxylic ester in the organic solvent adopted by the invention has the advantages that the freezing point is 20-30 ℃ lower than that of carbonic ester on average, the viscosity is low, and the low-temperature performance of the electrolyte can be obviously improved.

(3) The ether compound added into the electrolyte has low viscosity, high conductivity and stronger solvating capacity, and can improve the low temperature and the cycle performance of the electrolyte.

(4) The organic additive N, N-dimethylformamide has a low melting point of-61 ℃, can remarkably reduce the freezing point of a mixed solvent, and is beneficial to forming low-temperature electrolyte.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.