Nitrile Electrolyte Strategy for 4.9 V-Class Lithium-Metal Batteries Operating in Flame

Abstract

Challenges facing high-voltage/high-capacity cathodes, in addition to the longstanding problems pertinent to lithium (Li)-metal anodes, should be addressed to develop high-energy-density Li-metal batteries. This issue mostly stems from interfacial instability between electrodes and electrolytes. Conventional carbonate- or ether-based liquid electrolytes suffer from not only volatility and flammability but also limited electrochemical stability window. Here, we report a nitrile electrolyte strategy based on concentrated nitrile electrolytes (CNEs) with co-additives. The CNE consists of high-concentration lithium bis(fluorosulfonyl)imide (LiFSI) in a solvent mixture of succinonitrile (SN)/acetonitrile (AN). The SN/AN solvent mixture is designed to ensure high oxidation stability along with thermal stability, which are prerequisites for high-voltage Li-metal cells. The CNE exhibits interfacial stability with Li metals due to the coordinated solvation structure. Lithium nitrate (LiNO3) and indium fluoride (InF3) are incorporated in the CNE as synergistic co-additives to further stabilize solid-electrolyte interphase (SEI) on Li metals. The resulting electrolyte (CNE + LiNO3/InF3) enables stable cycling performance in Li||LiNi0.8Co0.1Mn0.1 and 4.9 V-class Li||LiNi0.5Mn1.5O4 cells. Notably, the Li||LiNi0.5Mn1.5O4 cell maintains its electrochemical activity at high temperature (100 °C) and even in flame without fire or explosion.