A Concentrated Ternary-Salts Electrolyte for High Reversible Li Metal Battery with Slight Excess Li

Li metal can potentially deliver much higher specific capacity than commercially used anodes. Nevertheless, because of its poor reversibility, abundant excess Li (usually more than three times) is required in Li metal batteries, leading to higher costs and decreased energy density. Here, a concentrated lithium bis(trifluoromethane sulfonyl) imide (LiTFSI)-lithium nitrate (LiNO3)-lithium bis(fluorosulfonyl)imide (LiFSI) ternary-salts electrolyte is introduced to realize a high stable Li metal full-cell with only a slight excess of Li. LiNO3 and LiFSI contribute to the formation of stable Li2O-LiF-rich solid electrolyte interface layers, and LiTFSI helps to stabilize the electrolyte under high concentration. Li metal in the electrolyte remains stable over 450 cycles and the average Coulombic efficiency reaches 99.1%. Moreover, with 0.5 x excess Li metal, the Coulombic efficiency of Li metal in the LiTFSI-LiNO3-LiFSI reaches 99.4%. The electrolyte also presents high stability to the LiFePO4 cathode, the capacity retention after 500 cycles is 92.0% and the Coulombic efficiency is 99.8%. A Li metal full-cell with only 0.44 x excess Li is also assembled, it remains stable over 70 cycles and 83% of the initial capacity is maintained after 100 cycles.