Li‐ion hopping conduction enabled by associative Li‐salt in acetonitrile solutions

Abstract

AbstractTo date, ionic conduction in nonaqueous electrolytes has been explained through the vehicle‐type migration mechanism. Yet, new research hints at another conduction mode: ion‐hopping, seen in highly concentrated solutions with multi‐coordinating solvents. Our research uncovers that Li‐ion hopping conduction also occurs in monodentate acetonitrile (AN) electrolytes, enabled by a highly associative Li‐salt. Using techniques like pulse‐field gradient NMR, Raman spectroscopy, and dielectric relaxation spectroscopy, we examined AN solutions with lithium trifluoroacetate (LiTFA) and lithium bis(fluorosulfonyl)imide (LiFSI). Results showed that Li‐ion diffusion in LiTFA‐AN was faster due to an anion‐bridge structure formed by the associative nature of LiTFA. In contrast, the LiFSI‐AN solution demonstrated slower Li‐ion movement. In practical applications, like LiFePO4 symmetric cells, 4 M LiTFA‐AN outperformed 1 M LiTFA‐AN in rate performance, despite its lower ionic conductivity. This challenges the belief that associative Li‐salts are unsuitable for battery electrolytes and prompts reconsideration of other associative Li‐salts.