Enabling uniform Li deposition behavior by introducing a NO3−-based ionic liquid additive into carbonate electrolyte for high-voltage Li metal batteries

The nonuniform lithium deposition behavior and low deposition/dissolution reversibility are the most significant obstacles for practical high-energy-density lithium metal batteries (LMBs). Herein, a novel 1-ethyl-3-methylimidazolium nitrate ionic liquid ([EMIm][NO3] IL) is proposed to incorporate into the conventional carbonate electrolyte with a small amount of 1,2-dimethoxyethane (DME) as the cosolvent. A high solubility of 0.5 M [EMIm][NO3] in the carbonate electrolyte is achieved for high-voltage LMBs by replacing traditional lithium nitrate with [EMIm][NO3] IL, where the DME cosolvent with high donicity enables the solvation of NO3− in the electrolyte system. Benefitting from the electrochemical reduction of NO3− anions, the designed electrolyte promotes the formation of highly conductive and stable solid electrolyte interface abundant with N-containing species and achieves stable Li stripping/plating behavior. As a result, the IL-modified electrolyte enables excellent electrochemical performances with improved Coulombic efficiency (>98.5%) in Li|Cu cell and stable cyclability (900 h) in Li|Li symmetric cell, respectively. More importantly, a Li|LiNi0.8Co0.1Mn0.1O2 pouch-type battery composed of high mass loading cathode (20 mg cm−2) and thin Li foil (50 μm) maintains an impressive cycling lifespan of 100 cycles. The exploration of NO3− containing IL as a novel electrolyte additive offers a promising opportunity for achieving high-performance Li metal batteries.