A temperature-dependent solvating electrolyte for wide-temperature and fast-charging lithium metal batteries

High safety and stable wide-temperature operation are essential for lithium metal batteries (LMBs). Herein, we designed an amide-based eutectic electrolyte composed of N-methyl-2,2,2-trifluoroacetamide (NMTFA) and lithium difluoro(oxalato)borate, enabling LMBs’ wide-operating temperature range and fast-charging performance. In addition to high thermal tolerance and non-flammability, our designed electrolyte (AEEs-5) triggers a temperature-dependent Li solvation structure due to the thermal motion of polar NMTFA, ensuring appropriate Li-ion de-solvation kinetics at 25°C–100°C. Moreover, the AEEs-5-induced solid electrolyte interphase (SEI) with high inorganic contents and thermal stability greatly reduces the parasitic reactions of LMBs. As a result, the AEEs-5-based LiFePO4||Li cells deliver not only a good 2 C-rate cycling at 25°C but also a better capacity retention (82.79%) after 1,000 cycles (20 C-rate) at 100°C, and the operating temperature for these LMBs can exceed 150°C. This work provides a deep understanding of Li solvation chemistry, taking temperature into consideration.