Non-corrosive asymmetric fluorinated aryl sulfonimide lithium salt for high-temperature and high-voltage lithium metal batteries.

Electrolyte for high-temperature and high-voltage lithium metal batteries face challenges of thermally decomposition of lithium salt and interfacial corrosiveness with aluminum current collectors/cathode materials. Herein, we report a non-corrosive asymmetric lithium salt, i.e., lithium fluorinated aryl sulfonimide (LiFAS). Due to the fluorinated aryl substituent on the bis-sulfonylimide anion, the LiFAS exhibits several desirable physiochemical properties for high-temperature and high-voltage applications, i.e. high thermal stability (decomposition temperature ~388 °C), high voltage tolerance (anodic decomposition potential ~5.5 V vs. Li/Li+), and a high Li+ transference number of 0.62. Moreover, the LiFAS is able to efficiently inhibit the notorious Al-corrosion issue by forming a dense Al(FAS)3/AlF3 passivation layer on the surface of Al current collector. In addition, LiFAS could also promote the formation of inorganic-rich interphases on the cathode and anode. The unique advantages of LiFAS endow Li||NCM811 full cells great cycling stability and capacity retention at harsh cycling conditions (81% after 230 cycles at 60 °C and 4.5 V, 0.5 C charge/1 C discharge). This work inspires molecular engineering strategy for designing functional lithium salts to enhance the cycle life of LMBs under high-temperatures and high-voltages.