Highly Stable Lithium Metal Batteries by Regulating the Lithium Nitrate Chemistry with a Modified Eutectic Electrolyte

Lithium nitrate is widely used as an additive in electrolytes to regulate the solid electrolyte interphase (SEI). However, the application of LiNO3 in lithium metal batteries (LMBs) is limited by its extremely low solubility in conventional carbonate-based electrolytes. In this study, a non-flammable deep eutectic solvent (DES) with lithium bis(trifluoromethanesulfonyl)imide and N-methylacetamide (NMAC) as the main components is chosen as the LMB electrolyte. Using theoretical calculations and experiments, the strong interaction between NMAC and LiNO3 is proved to be effective in increasing the solubility of LiNO3 (up to 4 wt%) and realizing stable anion-rich SEI layers. DES synergizes with LiNO3 to produce Li-F, LixN, and LiNxOy enriched SEI layer, which improves the uniformity of lithium deposition. In particular, the NCM622||DES-2||Li full cells achieve 84% capacity retention after 600 cycles at 0.5 C, far exceeding that of conventional carbonate electrolytes (56%). Consequently, this study provides a new strategy for employing LiNO3 in LMBs, in addition to its potential application in other alkali metal batteries and anode-free batteries.