Superacid Anhydride Additive to Enhance the Solubility and Interfacial Reactivity of Lithium Nitrate in Carbonate-based Electrolytes

Abstract

The limited solubility of lithium nitrate (LiNO3) in carbonate-based electrolytes has long impeded its application in lithium metal batteries (LMBs), despite its well-known ability to form robust and ionically conductive solid electrolyte interphases (SEIs). Here, we introduce trifluoromethanesulfonic anhydride (Tf2O) as a superacid additive that enables the dissolution of LiNO3 and simultaneously promotes favorable interfacial chemistry on lithium metal. In the presence of Tf2O, LiNO3 is converted into soluble lithium triflate (LiOTf) and triflyl nitrate (TfONO2) species and, upon contact with the lithium metal surface, the LiNO3-Tf2O pair undergoes spontaneous interfacial reactions to form an inorganic-rich SEI that effectively suppresses electrolyte decomposition and dendritic lithium deposition. Spectroscopic analyses reveal that this additive pair restructures the Li+ solvation shell from a solvent-dominated to anion-associated configuration, markedly increasing the Li+ transference number while selectively enhancing Li+ transport. As a result, Li

Cu cells exhibit high Coulombic efficiency with reduced nucleation overpotential, and Li

Li symmetric cells show substantially extended cycling with low interfacial resistance. In full cells, NCM622

Li and NCM622

Li configurations both deliver markedly improved capacity retention and durability compared with the baseline carbonate-based electrolyte. This work demonstrates a simple yet effective strategy to unlock the benefits of LiNO3 in carbonate systems and provides design guidelines for long-life and high-energy LMBs.