Locally Concentrated Ionic Liquid Electrolytes Enabling Low‐Temperature Lithium Metal Batteries

Lithium metal is a promising anode material for next‐generation high‐energy‐density batteries but suffers from low stripping/plating Coulombic efficiency and dendritic growth particularly at sub‐zero temperatures. Herein, a poorly‐flammable, locally concentrated ionic liquid electrolyte with a wide liquidus range extending well below 0 °C is proposed for low‐temperature lithium metal batteries. Its all‐anion Li+ solvation and phase‐nano‐segregation solution structure are sustained at low temperatures, which, together with a solid electrolyte interphase rich in inorganic compounds, enable dendrite‐free operation of lithium metal anodes at −20 °C and 0.5 mA cm−2, with a Coulombic efficiency of 98.9 %. As a result, lithium metal batteries coupling thin lithium metal anodes (4 mAh cm−2) and high‐loading LiNi0.8Co0.15Al0.05O2 cathodes (10 mg cm−2) retain 70 % of the initial capacity after 100 cycles at −20 °C. These results, as a proof of concept, demonstrate the applicability of locally concentrated ionic liquid electrolytes for low‐temperature lithium metal batteries. A locally concentrated ionic liquid electrolyte with a wide liquidus range is proposed for low‐temperature lithium metal batteries (LMBs). Its all‐anion Li+ solvation and phase‐nano‐segregation solution structure are sustained at low temperatures, which, together with a solid electrolyte interphase rich in inorganic compounds on lithium metal anodes, enable stable cycling of LMBs with high‐loading LiNi0.8Co0.15Al0.05O2 cathodes at −20 °C.