Polymer-Metal Oxide Cluster Co-Crystallization for the Synergy of Superionic Conduction and Mechanical Robustness

Solid polymer electrolytes (SPEs) promise high safety for next-generation energy storage, but practical applications are bottlenecked by the coupling of ion transport with sluggish polymer segmental dynamics. Herein, polymers are co-crystallized with sub-nm anionic metal oxide clusters (MOCs) using Li⁺ counterions, achieving synergistic superionic conduction and mechanical robustness. Mixing MOC (Li₄SiW₁₂O₄₀) and poly(ethylene glycol) (PEG) affords face-centered cubic crystalline structures at high MOC loadings (≥ 60 wt.%). The crystalline framework imposes spatial nanoconfinement that favors a pronounced shift of PEG chains toward densely packed zigzag-like conformations. Relaxation-dynamics studies reveal substantial decoupling between Li⁺ transport and PEG segmental relaxation, thereby enabling a superionic transport regime. The optimized composite achieves an ionic conductivity of 1.1 mS cm^-1 at 110°C with an apparent activation energy of 0.32 eV. Since the long-range mobility of SiW₁₂ ^4- is constrained, the electrolyte exhibits pronounced single-ion-conducting character with a high lithium-ion transference number (0.79). Furthermore, the composition with inorganic Li₄SiW₁₂O₄₀ enhances the mechanical modulus (25.04 MPa) and thermal stability with intrinsic flame retardancy. Solid-state symmetric supercapacitors fabricated from the electrolyte exhibit predominantly electric-double-layer capacitive behavior with a high specific capacitance (76 F g^-1) and excellent rate capability (87.16%).