Optimization Of Multicomponent Eutectic Halide Electrolyte For Thermal Batteries

The multicomponent eutectic halide?molten salt?is a nonconductive solid at room temperature,and is converted into an ionic conductor when the temperature rises above the melting point.This characteristic makes it one of the most commonly used electrolytes for thermal batteries.Since the end of the world war?,scientists have carried out a great deal of research and development on the properties of molten salts,seeking lower melting points and higher conductivity.However,the mechanism involved in the development of new eutectic halide electrolyte is rarely reported.In this study,the LiCl-LiBr-KBr-CsBr system and the LiCl-LiBr-KBr-RbCl system were prepared in an argon gas environment?glove-box?by solid-phase method.The thermal properties,conductivity,morphology and phase of each sample were tested,and some samples were selected for discharge performance tests of Li-Si/FeS₂ single cells.The mechanism of low eutectic phenomenon was analyzed,and the influence of the ratio of raw materials on the crystal structure,thermophysical property and electrical property of the material was investigated.The results show that adding CsBr or RbCl to LiCl-LiBr-KBr,a traditional ternary low melting point electrolyte,can increase the lattice distortion and reduce the melting point of the system.In addition,with the increase of additive content,grain distribution tends to be disorderly,which is conducive to reducing the stability of molten salt system.The conductivity of molten salts is positively correlated with the content of lithium ion in raw materials.The crystal structure types of LiCl,LiBr,KBr and RbCl all belong to B1 type and the ion radius is close to each other,while the cell of CsBr is B2 type and the ion radius is large,resulting in no complete eutectic in the LiCl-LiBr-KBr-CsBr system,and the LiCl-LiBr-KBr-RbCl system can achieve eutectic.With the increase of lithium ion content,the performance at high temperature of the single cell was significantly improved,but the Performance at low temperature was decreased due to the influence of electrolyte segregation.