In-situ polymerized ether-ester copolymer electrolytes with regulated solvation structure for quasi-solid-state lithium metal batteries

Ether-based polymer electrolytes are limited by their sluggish Li + transport kinetics and narrow electrochemical stability windows. Herein, a new P(DOX-MA) polymer electrolyte with anion-dominated solvation structure is rationally designed, which is controllably synthesized via in-situ cationic ring-opening polymerization of 1,3-dioxane (DOX) and 3-methylglutaric anhydride (MA). By integrating weakly coordinated Li-O(ester) groups and sterically hindered methyl (-CH 3 ) substituents into the P(DOX-MA) polymer backbone, the interaction between Li + and polymer is regulated. As a result, an anion-rich solvation structure is constructed in the resulting polymer electrolyte. This strategy effectively addresses the key challenges of Li + transport kinetics and electrochemical stability in polymer electrolytes. The P(DOX-MA) electrolyte delivers high Li + transference number (0.83), wide electrochemical stability window (4.98 V) and good interfacial stability. Experimental and theoretical results reveal that P(DOX-MA) electrolyte facilitates the formation of robust inorganic-rich solid electrolyte interphase (SEI) and effectively suppresses dendrite growth. As a result, the Li||Li symmetric cell achieves stable cycling for over 2000 h at 0.5 mA cm −2 , meanwhile, the Li||LiFePO 4 cells show excellent cycling stability at room temperature. This work not only elucidates the intrinsic correlations among polymer structure, solvation behavior and interfacial chemistry, but also offers a feasible and scalable design strategy for next-generation polymer electrolytes. A novel P(DOX-MA) polymer electrolyte is controllably synthesized via in-situ cationic ring-opening polymerization (CROP) of 1,3-dioxane (DOX) and 3-methylglutaric anhydride (MA). By incorporating weakly coordinated Li-O(ester) groups and sterically hindered methyl (-CH 3 ) substituents into the polymer backbone, an anion-dominated solvation structure is constructed. The P(DOX-MA) electrolyte shows a high Li + transference number (0.83) and wide electrochemical stability window (4.98 V). The anion-dominated solvation structure promotes the formation of a robust inorganic-rich SEI and effectively suppresses Li dendrite growth. As a result, the P(DOX-MA) electrolyte achieves ultra-stable cycling in Li||Li symmetric cell (over 2000 h) and excellent compatibility with both LiFePO 4 and LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) cathodes in full-cells. This work presents a scalable molecular design strategy toward high-performance quasi-solid-state lithium metal batteries. • A copolymer electrolyte is controllably synthesized, where sterically hindered methyl groups and dual Li + coordinating sites (ether and ester) are rationally integrated into the polymer backbone. • The designed molecular structure not only improves oxidative stability, but also promotes the formation of an anion-rich solvation structure, which significantly increases the Li + transference number (0.83). • The anion-dominated solvation structure induces the formation of a robust inorganic-rich SEI, thereby enabling ultra-stable cycling of symmetric Li||Li cell for over 2000 h. • Applied in full-cells, the electrolyte delivers good cycling stability with NCM811 cathode, and demonstrates excellent long-term performance (500 cycles) in Li||LiFePO 4 cell.