Insights into Ionic Liquid Electrolyte Transport and Structure via Operando Raman Microspectroscopy

18 October 2021, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Ionic liquid electrolytes (ILEs) have become popular in various advanced Li-ion battery chemistries because of their high electrochemical and thermal stability, and low volatility. However, due to their relatively high viscosity and poor Li+ diffusion, it is thought large concentration gradients form, reducing their rate capability. Here, we utilised operando Raman microspectroscopy to visualise ILE concentration gradients for the first time. Specifically, using lithium bis(fluorosulfonyl)imide (LiFSI) in N-propyl- N-methylpyrrolidinium FSI, its "apparent" diffusion coefficient, lithium transference number, thermodynamic factor, ionic conductivity and resistance of charge-transfer against lithium metal, were isolated. Furthermore, the analysis of these concentration gradients led to insights into the bulk structure of ILEs, which we propose is composed of large, ordered aggregates.

Keywords

transport properties
ionic liquid electrolyte
concentration gradients
operando Raman mictrospectroscopy

Supplementary materials

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