Ionic liquid electrolyte for room to intermediate temperature operating Li metal batteries: Dendrite suppression and improved performance

Abstract

Lithium metal is considered to be the ultimate negative electrode material to maximize the energy density of lithium secondary batteries based on its high theoretical specific capacity and low redox potential. Despite these outstanding features, lithium metal is facing difficulties in overcoming of dendritic lithium growth, low coulombic efficiency, and poor cycle performance. In this study, the Li[FSA]-[1-ethyl-3-methylimidazolium][FSA] (FSA⁻ = bis(fluorosulfonyl)amide) ionic liquid system is proposed to be an electrolyte for wide temperature operable Li metal batteries. The ionic liquid presents unique properties of suppressing Li dendrite growth, dead Li accumulation, and long-life cycling performance across 25 and 90 °C. Full-cell tests with Li₂FeP₂O₇ positive electrode and this ionic liquid electrolyte demonstrate the feasibility of operating lithium metal batteries from room to intermediate temperature. The full cell retained 99.1% of its initial capacity after 200 cycles with an average coulombic efficiency of 99.97%.