Operando Raman Spectroscopy for Evaluating Concentration Changes in Li- and Na-Based Solid Polymer Electrolytes

Abstract

The solid polymer electrolytes (SPEs) can apply to all-solid-sate batteries using various cations as the carrier species. Herein, we performed operando Raman spectroscopy to evaluate the concentration changes with ionic transport in the Li- and Na-based SPEs composed of ether-based host polymer and MN(SO2CF3)2 (M = Li, Na; MTFSA), with the aim of extracting differences in behavior under electrochemical operation. In the [Li | Li-based SPE | Cu] cell, the integrated intensities of TFSA anions changed near the working electrode (WE) and counter electrode (CE) sides during cyclic voltammetry measurements, revealing changes in the anion concentration. Then, operando Raman spectroscopy was conducted for the [M | Li- or Na-based SPE | M (M = metallic Li or Na)] symmetric cells during chronoamperometry measurements. The cell using Li-based SPE exhibited increasing and decreasing integrated intensities for TFSA at the WE and CE sides, respectively, before reaching a steady state. In contrast, the integrated intensities of TFSA required a longer time to reach a steady state in the Na-based SPE system, suggesting that the solvation/desolvation of Na+ is more difficult during ionic transport. Overall, operando Raman spectroscopy contributed to elucidating the differences in ionic transport properties between Li- and Na-based SPEs during electrochemical processes.