Lithium Nitrate as a SEI-Stabilizing Additive in Single-Ion Conducting Polymer Electrolytes for Lithium–Metal Batteries

Single-ion conducting polymer electrolytes (SIPEs) are among the most promising candidates for lithium-metal batteries, which commonly suffer from the risk of lithium dendrite growth and continuous electrolyte decomposition at the lithium-electrolyte interface. Herein, we report the introduction of lithium nitrate (LiNO₃) as an additive into an SIPE based on a poly(ethylene oxide) backbone and grafted perfluorosulfonate anions. By comparing SIPEs with and without LiNO₃ concerning the charge transport, electrochemical stability, reversibility of the lithium stripping/plating process, electrode morphology, and surface composition, it appears that the introduction of LiNO₃ yields a thinner, but more robust solid electrolyte interphase, which greatly benefits the eventual performance, Coulombic efficiency, and reversibility of lithium stripping and plating. The advantageous effect of LiNO₃ is finally confirmed in Li|SIPE|LFP solid-state battery cells, providing a substantially longer cycle life.