A Highly-Fluorinated Lithium Borate Main Salt Empowering Stable Lithium Metal Batteries

Traditional lithium salts are difficult to meet practical application demand of lithium metal batteries (LMBs) under high voltages and temperatures. LiPF6, as the most commonly used lithium salt, still suffers from notorious moisture sensitivity and inferior thermal stability under those conditions. Here, we synthesize a lithium salt of lithium perfluoropinacolatoborate (LiFPB) comprising highly-fluorinated and borate functional groups to address the above issues. It is demonstrated that the LiFPB shows superior thermal and electrochemical stability without any HF generation under high temperatures and voltages. In addition, the LiFPB can form a protective outer-organic and inner-inorganic rich cathode electrolyte interphase on LiCoO2 (LCO) surface. Simultaneously, the FPB- anions tend to integrate into lithium ion solvation structure to form a favorable fast-ion conductive LiBxOy based solid electrolyte interphase on lithium (Li) anode. All these fantastic features of LiFPB endow LCO (1.9 mAh cm-2)/Li metal cells excellent cycling under both high voltages and temperatures (e.g., 80 % capacity retention after 260 cycles at 60 degrees C and 4.45 V), and even at an extremely elevated temperature of 100 degrees C. This work emphasizes the important role of salt anions in determining the electrochemical performance of LMBs at both high temperature and voltage conditions. A highly-fluorinated lithium borate main salt of lithium perfluoropinacolatoborate (LiFPB) is designed to enhance cycling performance of practical lithium metal batteries (LMBs). The superior stability of LiFPB and the as-formed favorable CEI/SEI endow LMBs (50 mu m of lithium anode) excellent cycling stability even under high temperature (100 degrees C) and voltage (4.5 V vs. Li/Li+) conditions without any generation of HF.+ image