Impact of Anion Mixing on Li+ Coordination and Transport Properties in Pyrrolidinium-Based Ionic Liquid Electrolytes

Abstract

A series of pyrrolidinium-based ionic liquid electrolytes were investigated to explore the potential benefits of incorporating mixed anions, here bis(fluorosulfonyl)imide and bis(trifluoromethylsulfonyl)imide. The effect of mixing anions on fundamental physicochemical properties was investigated, with particular emphasis on transport properties and lithium-ion coordination. More specifically, the electrolytes were systematically characterized in terms of phase behavior, density, viscosity, transport properties (ionic conductivity and self-diffusion), and intermolecular interactions. The results show that mixing anions modifies the nature of intermolecular interactions, which in turn alters the coordination of the Li⁺ to its counterions. In the case of (LiFSI)_0.2(Pyr₁₄TFSI)_0.8 sample, this resulted in improved thermal and transport properties, anticipating an improved performance in lithium-ion batteries.