Relationship Between Liquidus And Valence Electron Structure Of Electrolytes For Liquid Metal Batteries

It is necessary to reduce the consumption of fossil fuels for achieving the goal of carbon neutrality,but,which causes a huge requirement for power energy,and the development of novel green energy is the only way to resolve this issue.Thus,the novel energy storage technology should be explored for meeting with a huge demand of energy storage.Both mechanical and electromagnetic energy storages have unique advantages and good prospects,but they are currently limited by natural conditions and application ability,which cannot be used to product with a large scale.Currently,chemical energy storage is the most effective way to meet the requirement of energy storage.Liquid metal battery(LMB),which is one of chemical energy storage technologies,has the potential application in the grid due to its many advantages such as long cycle life,good capacity scalability,simple assembly,and low cost.However,Liquid metal battery currently operate at high temperature,it is required to reduce the operating temperature of LMB for enhancing its operating stability and safety,and decreasing effectively energy consumption during operating.The molten salts with low melting temperature,which is used as electrolyte for LMB,is helpful for reducing the operating temperature.Lithium halide molten salt is one of hot topics in electrolyte due to its excellent electrical performance.The melting temperature of electrolyte can significantly decrease by replacement of pure lithium halide by multi-component lithium halides.However,the mechanism is not studied yet.In this study,the empirical electron theory(EET)of solid and molecular is used to investigate the melting temperatures of multi-component lithium halide molten-salt according to their valence electron structures,and designs the refined compositions of quaternary lithium halides with low melting temperature for electrolyte.The melting model in EET is built based on the parameters of valence electron structures in real space,which is totally different from those of the first-principle and its developed semi-empirical theories in reciprocal space.EET is used to study systematically the melting point of pure LiX(X=halide group),eutectic point of binary LiX system,melting temperature and liquidus phase curves of ternary LiX system.The theoretical bond-lengths and melting temperature match the experimental ones well.The melting mechanism is revealed by the valence electron structure.In ternary system,the liquidus phase curves are modulated by the valence electron structure dependence on the composition of multi-component molten-salts.The liquidus phase lines of ternary lithium halide decreases with increasing the number of covalent electrons nc in high temperature region,however,goes up with increase of nc in low temperature region.It reveals that the bonding energy of the strongest X-Li bond is related to the melting temperature,the melting of ternary lithium halides needs more thermal vibrating phonons for breaking X-Li bond at low temperature region.In valence electron structure,the electron transition from p electron to s electron,which induces the enhancement of X-Li bond ability.The melting model is introduced in the quaternary lithium halides,the calculated melting temperatures are very close to the temperature of the first absorption peak in differential scanning calorimetry(DSC)measured curves.It is suggested to exist two phases in quaternary lithium halides,and the EET calculation results correspond to the melting temperature and valence electron structures of the low melting phase.