Investigating LiFePO 4 electrode degradation in water-in-salt electrolyte

Abstract

International audienceLithium-ion battery safety can be enhanced by replacing the flammable organic-electrolyte by a water based one. Unfortunately, electrochemical stability window of water is limited (1.23 V) but can be enhanced with water-in-salt electrolyte (WISE) where water activity is drastically reduced. However, during cycling, several issues occur all linked to the release of free water molecules, which leads to poor electrochemical performance. We decided, to investigate the impact of WISE on LiFePO4 positive electrode materials prior cycling. LiFePO4 electrodes were soaked during 24 h in WISE at different concentration and investigated by several techniques such as X-ray photoelectron spectrometry, X-ray absorption spectroscopy and contact angle measurement. Results tend to indicate an early decomposition of the active materials with oxidation of Fe. These same electrodes were cycled in half-cell (i.e. vs Li metal) with classic organic-based electrolyte, and shows different OCV and premature electrochemical fading confirming soaked electrodes in WISE suffer decomposition