Lithium-Bond-Based Deep Eutectic Electrolyte Solutions for High-Temperature Lithium Metal Batteries

Achieving long-term cycling stability in high-temperature lithium metal batteries (LMBs) demands both efficient ion transport and stable electrode interfaces. However, the molecular polarity and strong ionic interactions of conventional electrolytes hinder ion mobility and compromise interfacial stability. In this study, we developed a deep eutectic electrolyte based on Li-bond (Li-DEE) comprising tetraethylammonium nitrate and lithium bis(fluorosulfonyl)imide, which is different from the traditional hydrogen bonding or lithium ionic bonding electrolyte. The Li-bond network within the Li-DEE enables rapid lithium-ion transport (6.5 × 10^{- 3} S cm^-1 at 100 °C) while forming a stable electrode interface rich in Li₃N and LiF. As a result, the Li-DEE enables an LMB to deliver a high capacity retention of 80% over 635 cycles at 0.5 C and a capacity of 84.4 mAh g^-1 after 1500 cycles at 2 C and 100 °C. This study provides valuable insights for designing next-generation electrolytes that function under extreme operating conditions.