Development ideas for high-temperature electrolytes

Development ideas for high-temperature and low-temperature electrolytes

1. High temperature type

The most widely commercialized electrolyte system currently is vinyl chloride carbonate solution. The solute LiPF6 in this system decomposes at 75 ℃, is sensitive to water, and is prone to HF corrosion on the current collector, SEI membrane, and electrode active materials, resulting in a rapid decline in battery performance. Solvents have low boiling and flash points, are prone to combustion or explosion, causing safety issues. In response to the shortcomings of existing electrolyte systems, people have developed electrolyte salts and flame-retardant solvent systems with high thermal stability starting from solutes and solvents, in order to improve high-temperature stability, solve high-temperature safety issues, and expand the application range of chlorinated vinyl carbonate in lithium-ion batteries while maintaining the room temperature performance of lithium-ion batteries.

Developing electrolyte salts with high thermal stability and flame retardant solvents can improve the high-temperature performance of electrolytes, which is of great significance for the large-scale and practical application of lithium-ion batteries.

In terms of electrolyte salts, by combining network structures or modifying functional groups, the shortcomings of existing lithium salts can be effectively overcome, and high thermal stability and electrolyte salts with good comprehensive economic performance can be developed for students.

In terms of solvent systems, chlorinated vinyl carbonate manufacturers use completely non combustible organic solvent systems such as sulfones, as well as ionic liquids due to issues with working viscosity, conductivity, price, and compatibility with electrodes. Although blending with electrolytes can partially improve these drawbacks, there is still a long way to go before practical application.

2. Low temperature type

Commercial electrolytes are easy to solidify at low temperatures and have high impedance, which limits the further use of lithium-ion batteries. The low temperature performance of lithium ion battery is affected by the speed of lithium ion in anode and cathode, the speed of lithium ion in electrolyte, the impedance of electrolyte/electrode interface facial mask and charge transfer rate.

The electrolyte not only determines the ion migration rate of the electrolyte, but also affects the formation of the SEI film on the electrode surface. Therefore, by optimizing the electrolyte suitable for the low-temperature performance of lithium-ion batteries, the ion conductivity of the electrolyte and the stability of the SEI film on the electrode surface can be improved.

The low ion conductivity, high charge transfer impedance, and small film impedance are the main reasons for the poor low-temperature performance of lithium-ion batteries.

Therefore, the focus of research on lithium salts in lithium-ion battery electrolytes is to choose a new system of lithium salts with low charge transfer impedance and wide temperature range. For low-temperature electrolyte solvents, a mixed system of EC solvents with high dielectric constant and PC solvents with low melting point should be selected. Chloroethylene carbonate can effectively alleviate the poor compatibility between PC and graphite anode by adding a small amount of EC.

For a low-temperature functional food additive, it is necessary to fully develop the combination of traditional Chinese additives and new additives. A small amount of traditional cultural organic chemical additive PS can improve the poor film-forming performance of low-temperature solvent PC.