Molecular insight into nano-heterogeneity of localized high-concentration electrolyte: Correlation with lithium dynamics and solid-electrolyte interphase formation

Localized high-concentration electrolytes (LHCEs) have attracted extensive attention in light of their excellent characteristic that inherits the advantages of high-concentration counterparts and minimize their shortcomings. However, the fundamental mechanisms of nano-heterogeneity influencing the LHCE properties are still not well understood. Herein, a systematic comparison combining theoretical and experimental methods is performed to clarify the fundamental correlation between electrolyte microstructure and properties. The unique microstructure in the LHCE of high-concentration clusters surrounded by a nonsolvating diluent enables the hopping diffusion of Li+ through the anion ligand layers, which is responsible for the high transference number and fast diffusion of Li+. In addition, the anion coordinated with multiple Li+ undergoes defluorination reactions and contributes, with the diluent decomposition, to the formation of a stable and robust “LiF-rich” solid electrolyte interphase (SEI) layer on the Li metal, which is responsible for the enhanced cycling stability. These fundamental insights highlight the correlation of microstructural and dynamic heterogeneities of electrolytes with SEI formation, which should be considered in the rational design of next-generation improved electrolytes.