Beyond Composition: Optimizing Ion Transport in Solid-State Composite Polymer Electrolytes through Pathway Engineering

Composite polymer electrolytes (CPEs), composed of a polymer matrix and inorganic nanoparticles, are promising for solid-state batteries. While most studies focus on compositional factors such as filler type and polymer structure, mesoscale connectivity between polymer coordination sites represents a crucial, yet underexplored, factor influencing ion transport. Here, using coarse-grained Monte Carlo simulations, we explored how coordination site connectivity governs transport. The polymer chain connectivity is quantified as a proxy for coordination site connectivity, and we found that repulsive nanoparticles enhance chain connectivity, particularly at high weight ratio and strong repulsion. Structural analysis shows that this enhancement extends throughout the polymer. These predictions were validated experimentally using CPEs composed of poly(ethylene oxide) and silica nanoparticles of tunable surface chemistry. CPE with strong repulsive silica nanoparticles exhibited improved room-temperature ionic conductivity by up to 5-fold and a significant reduction in effective activation energy under a suboptimal condition. Our findings demonstrate that connectivity restructuring critically enhances ionic transport, offering a new design paradigm for CPEs based on mesoscale connectivity control.