Moderately concentrated electrolyte enabling high-performance lithium metal batteries with a wide working temperature range

The electrolyte integrated with lithium metal anodes is subjected to the issues of interfacial compatibility and stability, which strongly influence the performances of high-energy lithium metal batteries. Here, we report a new electrolyte recipe viz. a moderately concentrated electrolyte comprising of 2.4 M lithium bis(fluorosulfonyl)imide (LiFSI) in a cosolvent mixture of fluorinated ethylene carbonate (FEC) and dimethyl carbonate (DMC) with relatively high ion conductivity. Owing to the preferential decomposition of LiFSI and FEC, an inorganic-rich interphase with abundant Li2O and LiF nanocrystals is formed on lithium metal with improved robustness and ion transfer kinetics, enabling lithium plating/stripping with an extremely low overpotential of ∼ 8 mV and the average CE of 97%. When tested in Li||LiFePO4 cell, this electrolyte provides long-term cycling with a capacity retention of 98.3% after 1000 cycles at 1 C and an excellent rate performance of 20 C, as well as an areal capacity of 1.35 mA h cm−2 at the cathode areal loading of 9 mg cm−2. Moreover, the Li||LiFePO4 cell exhibits excellent wide-temperature performances (-40 ∼ 60 ℃), including long-term cycling stability over 2600 cycles without visible capacity fading at 0 ℃, as well as extremely high average CEs of 99.6% and 99.8% over 400 cycles under −20 ℃ and 45 ℃.