Insight into the solvation and dynamic behaviors of lithium salt in water-in-bisalt electrolytes

Abstract

Through a combination of molecular dynamics simulations and experimental approaches, the solvation structure and diffusion behavior of Li+ was investigated in water-in-bisalt electrolytes formed by introducing a second lithium salt (LiBF4, LiNO3, LiOAc) into the LiTFSI aqueous electrolyte. The calculation and experimental results indicate that nanostructures of water-in-bisalt electrolytes include “water-rich” and “anion-rich” domains. When LiBF4 is added, Li+ is mostly located in the water-rich domain, effectively increasing the diffusion coefficient of Li+. This electrolyte exhibits a higher conductivity and a much lower price compared to mono-LiTFSI electrolytes, On the contrary, with the addition of LiOAc, OAc− will strongly coordinate with Li+ to change the solvation structure of solvent separated ion pairs (Li+(H2O)4) to aggregates, which results in the decrease of Li+ diffusion coefficient. These fundamental insights highlight the correlation of microstructural and dynamic heterogeneities of water-in-bisalt electrolytes, which are expected to trigger rational design of solvation and dynamic behaviors of advanced aqueous electrolytes.