Solvation Regulation of Non‐Flammable Polymer Deep Eutectic Electrolytes with Reinforced Inorganic‐Rich Interphase toward Long‐Cycle Lithium Metal Batteries

Abstract Lithium dendrites and flammable carbonate electrolytes present significant challenges to the progress of lithium metal batteries (LMBs), necessitating the urgent development of novel solid electrolytes. Herein, a non‐flammable polymer deep eutectic electrolyte (PDEE) is proposed by encapsulating N‐methylacetamide (NMA)‐based deep eutectic electrolytes within a polymer framework formed by ethoxylated trimethylolpropane triacrylate (ETPTA) via in situ polymerization. The robust Li⁺‐solvent interaction between the polar groups in NMA and lithium nitrate (LiNO₃) significantly improves the solubility of LiNO₃. Therefore, an inorganic‐rich LiF, Li_xN, and LiN_xO_y solid electrolyte interphase (SEI) is designed by introducing LiNO₃ and fluoroethylene carbonate (FEC) into PDEE. The comprehensive characterizations and simulations reveal that moderate LiNO₃ addition can modulate the solvated structure of Li⁺ and result in uniform lithium deposition. The PDEE‐2 (PDEE with 2 wt% LiNO₃) exhibits high ionic conductivity (2.5 mS cm⁻¹ at 25 °C) and high Li⁺ transference number (0.61). The Li||LiFePO4 (LFP) cells maintain cycling stability for 1700 cycles at 2 C, and Li||Ni_0.8Co_0.1Mn_0.1O₂(NCM811) cells achieve 300 cycles at 0.5 C with a capacity retention of 86.7%, one of the best results for eutectic‐based polymer electrolytes. This study presents an innovative method for producing stable polymer electrolytes and encourages the utilization of LMBs.