Decoupling Li⁺ Transport via in Situ Semi-Interpenetrating Polymer Electrolytes for High-Performance and Practical...

Solid polymer electrolytes are considered a promising route toward next-generation lithium metal batteries (LMBs), yet they have long been constrained by the trade-off between mechanical strength and ionic conductivity. This work develops a high-performance semi-interpenetrating polymer network (SIPN) electrolyte through LiFSI-initiated in situ cationic ring-opening polymerization of 1,3-dioxolane (DOL). By incorporating a rigid poly(N, N'-methylenebisacrylamide) (PMBA) backbone and cyclobutanesulfonic acid (SL) plasticizer, the resulting SIPN electrolyte (SIPN-3) effectively decouples ion transport from polymer chain motion. SIPN-3 exhibits outstanding ionic conductivity of 4.14 mS cm^{- 1} at room temperature, a high Li⁺ transference number of 0.71, and a broad electrochemical stability window exceeding 5.0 V. Mechanistic studies reveal that the synergistic effect between optimized LiFSI concentration and SIPN structure promotes the formation of a stable, inorganic-rich SEI. Consequently, LiFePO₄||Li batteries employing SIPN-3 maintained a capacity retention of 76.4% after 1000 cycles, while high-voltage NCM811||Li batteries achieved 93.6% capacity retention after 100 cycles. Furthermore, assembled ternary lithium metal pouch cells successfully illuminated an LED and drove a small fan, validating their practical applicability. This work provides a robust strategy for designing polymer electrolytes with high conductivity and high-voltage stability, suitable for practical high-energy-density lithium metal batteries.