Tuning a Solvation Structure of Lithium Ions Coordinated with Nitrate Anions through Ionic Liquid‐Based Solvent for Highly Stable Lithium Metal Batteries

Abstract Rational design of promising electrolyte is considered as an effective strategy to improve the cycling stability of lithium metal batteries (LMBs). Here, an elaborately designed ionic liquid‐based electrolyte is proposed that is composed of lithium bis(trifluoromethanesulfonyl)imide as the lithium salt, 1‐ethyl‐3‐methylimidazolium nitrate ionic liquid ([EMIm][NO 3 ] IL) and fluoroethylene carbonate (FEC) as the functional solvents, and 1,2‐dimethoxyethane (DME) as the diluent solvent. Using [EMIm][NO 3 ] IL as the solvent component facilitates a special Li + ‐coordinated NO 3 − solvation structure, which enables the continues electrochemical reduction of solvated NO 3 − and the formation of remarkably stable and conductive solid electrolyte interface. With FEC as another functional solvent and DME as the diluent solvent, the formulated electrolyte delivers high oxidative stability and ionic conductivity, and endows improved electrochemical reaction kinetics. Therefore, the formulated electrolyte demonstrates exceedingly reversible and stable Li stripping/plating behavior with high average Coulombic efficiency (98.8%) and ultralong cycling stability (3500 h). Notably, the high‐voltage Li|LiNi 0.8 Co 0.1 Mn 0.1 O 2 full cell with IL‐based electrolyte exhibits enhanced cyclability with a capacity retention of 65% after 200 cycles under harsh conditions of low negative/positive ratio (3.1) and lean electrolyte (2.5 µL mg −1 ). This study creates the first NO 3 − ‐based ionic liquid electrolyte and evokes the avenue for practical high‐voltage LMBs.