N-methyl-2-pyrrolidone (NMP)-solvated LiNO3 in carbonate electrolyte and the synergistic effects of LiNO3, NMP and fluoroethylene carbonate on lithium electrodes

The implementation of rechargeable high-energy lithium metal batteries is hindered by the instability of lithium electrodes. The electrolyte additive, LiNO₃, can significantly improve the stability of lithium electrodes. However, LiNO₃ has very low solubility in carbonate electrolytes which are widely used in commercial lithium-ion batteries. Herein, we introduce N-methyl-2-pyrrolidone (NMP) as a carrier solvent into diethyl carbonate (DEC)-based electrolyte to solvate and dissolve LiNO₃. It is found that, in LiFSI/DEC electrolytes, interactions between LiNO₃, NMP, and fluoroethylene carbonate (FEC) reorganize the solvation structure: DEC, FEC, NMP, and NO₃^– are involved in coordination interactions, while FSI- ions mainly remain free. This unique configuration induces synergistic effects, achieving a Coulombic efficiency (CE) of 98.4%. Surface analysis reveals a composite solid electrolyte interphase (SEI) layer comprising Li₂CO₃, RCO₂Li, Li_xN, LiF, and a rarely reported F-containing strong ionic compound. Such an SEI layer is found to be more protective and more favorable for improving the CE and kinetics.