Nonflammable Nitrile Deep Eutectic Electrolyte Enables High-Voltage Lithium Metal Batteries

Nonflammable functional electrolytes with remarkably interfacial compatibility toward both lithium anodes and high-voltage cathodes are considered as the ultimate pursuit for rechargeable lithium metal battery. For this target, we report a dual-anion deep eutectic solution (D-DES) based on elaborately selected combination of nitrile and functional lithium salts. The interactions of succinonitrile with cation/anion are highlighted by in situ/ex situ measurements, which endow D-DES with excellent ionic conductivity and significantly enhanced interface stability. By using this D-DES, constant Li|Li cycling over 1 year (>10,000 h) under a Li capacity of 5 mA h cm–2 can be achieved. The capacity retention is still over 70% with a high charging voltage of 4.7 V for 500 cycles in LiCoO2|Li battery. Pouch cells with high areal capacity close to practical application also deliver superior safe performance. This study paves a new pathway for designing high-safety electrolyte and boosts the practical application of high-voltage lithium metal battery.