Development of All‐Solid‐State Lithium Metal Batteries Using Polymer Electrolytes Based on Polycarbonate Copolymer with Spiroacetal Rings

All‐solid‐state lithium metal batteries (ASSLMBs) using lithium as anode are candidates for safe and high energy batteries. Lithium metal is an ideal anode because of its high theoretical storage capacity and low standard electrode potential, but nonuniform Li deposition induces short circuits and safety issues. The development of ASSLMBs having stable charge and discharge cycles remains a challenge. ASSLMB‐type cells based on the branch ‐P(DMC/TEG/SPG) electrolyte is demonstrated using LiFePO 4 cathode and Li anode provide stable battery performance. branch ‐P(DMC/TEG/SPG) is a polycarbonate‐based copolymer with poly(decamethylene carbonate) [P(DMC)], pentaerythritol (PE), triethylene glycol (TEG), 3,9‐bis(1,1‐dimethyl‐2‐hydroxyethyl)‐2,4,8,10‐tetraoxaspiro[5.5]undecane (spiroglycol, SPG). Solid polymer electrolyte (SPE) based on this polymer exhibits electrochemically and mechanically stability, as it is reported previously. Cells with the branch ‐P(DMC/TEG/SPG) electrolyte have good discharge capacities at 125, 126, and 106 mAh g −1 with high coulombic efficiency (>99%) after the 30th cycle of at 0.01, 0.05 and 0.1 C, respectively. X‐ray photoemission spectroscopy analysis shows that a moderately thick and LiF‐rich cathode electrolyte interphase (CEI) gives rise to stable battery performance. The branch ‐P(DMC/TEG/SPG) electrolyte having viscoelastic nature and high concentration of Li‐salt forms the stable CEI. These results further the development of ASSLMBs with long‐life and stable performance.