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

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||LiNi_0.8Co_0.1Mn_0.1 and 4.9 V-class Li||LiNi_0.5Mn_1.5O₄ cells. Notably, the Li||LiNi_0.5Mn_1.5O₄ cell maintains its electrochemical activity at high temperature (100 °C) and even in flame without fire or explosion.