Phase behavior and electrochemical properties of solid lithium electrolytes based on N-ethyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide and PVdF composites

Abstract

Organic ionic plastic crystals (OIPCs) are a class of solid-state electrolyte material with good thermal and electrochemical stability and higher safety due to their non-flammability and non-volatility. N-ethyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide, [C2mpyr][FSI] is an organic ionic plastic crystal that has previously shown promising electrochemical performance for Li metal batteries. Free standing solid-state composite electrolytes can be prepared by combining an OIPC with an apparently inert polymer such as PVdF. In this work, the effect of PVdF morphology, either in the form of electrospun fibres or nanoparticles, on the LiFSI/[C2mpyr][FSI] electrolyte phase and electrochemical behavior is discussed. In both cases, the PVdF interacts with the electrolyte mixtures at a molecular level, altering the phase behavior and electrochemical properties of 50 mol% LiFSI - [C2mpyr][FSI] and, to a lesser extent, with 10 mol% LiFSI - [C2mpyr][FSI]. Comparison of Li | LiNi1/3Mn1/3Co1/3O2 electrochemical cell performance using the 50 mol% LiFSI - [C2mpyr][FSI] electrolyte with different PVdF morphologies shows the dependence of cell stability on physical aspects of the composite.