Microscopic Understanding of the Ionic Networks of “Water-in-Salt” Electrolytes with Synchrotron X-Ray Scattering

Abstract

Many recent reports have investigated the structures of highly concentrated LiTFSI aqueous electrolytes. However, the solvation behaviors at different concentrations and temperatures are not entirely understood. To fully understand the solvation structure, we systemically changed the LiTFSI concentrations and measured them with SAXS. According to SAXS results, LiTFSI aqueous solutions can be divided into three concentration regimes: low concentration, medium concentration, and high concentration. At a low concentration solution regime, only TFSI- solvated structures exist at room temperature. However, the TFSI- networks can be formed with increasing temperature. For a medium concentration solution regime, two structures (TFSI- solvated structure and TFSI- network) co-exist. There is only one structure at room temperature at a high concentration solution regime, TFSI- network, where all TFSI- have been involved in forming TFSI- networks. TFSI- network structure at high temperature even improves the electrochemical high-temperature stability.