Lithium metal batteries capable of stable operation at elevated temperature

Rechargeable lithium metal batteries have attracted wide attention due to high theoretical energy density. For practical applications, high-temperature performance of lithium batteries is essential due to complex application environments, in terms of safety and cycle life. However, it's difficult for normal operation of lithium metal batteries at high temperature above 55–60 °C using current lithium hexafluorophosphate (LiPF6) electrolyte systems. Herein, a kind of new electrolyte system is designed by adding two thermal-stable lithium salts together (i.e. lithium bis(trifluoromethanesulfonimide) (LiTFSI) and lithium difluoro(oxalato)borate (LiDFOB)) into carbonate solvents with high boiling/flashing point (i.e. ethylene carbonate (EC) and propylene carbonate(PC)). Small amount of LiPF6 is also added to prevent the corrosion of aluminum current collector. The results indicate that the new electrolyte possesses superior high-temperature performance, meanwhile, it effectively suppresses the formation of lithium dendrite by synergy effects of salts and solvents. Li/LiCoO2 cells with high LiCoO2 real capacity (2.4 mAh/cm2) using this kind of new electrolyte shows excellent cycling performance at elevated temperature up to 80 °C. Such performance is achieved for the first time for rechargeable Li metal battery using liquid organic electrolytes. It overcomes the operation temperature upper limit of traditional Li-ion batteries (i.e. 55–60 °C), which would effectively reduce thermal runaway risk and simplify the thermal management of Li metal batteries in reality.