A symmetrical ionic liquid/Li salt system for rapid ion transport and stable lithium electrochemistry

Abstract

Contrary to the accepted wisdom that avoids cation symmetry for the sake of optimum electrolyte properties, we reveal outstanding behaviour for the diethylpyrrolidinium cation ([C₂epyr]), in combination with the bis(fluorosulfonyl)imide (FSI) anion and Li[FSI]. The equimolar [C₂epyr][Li][FSI]₂ is a liquid with high conductivity, high Li transference number and >90% lithium metal cycling efficiency. The high level of performance for these electrolytes invites consideration of a new class of electrolytes for lithium batteries.