Atomic-Scale Mechanisms of Li-Ion Transport Mediated by Li ₁₀ GeP ₂ S ₁₂ in Composite Solid Poly(Ethylene Oxide) Electrolytes

Polymer electrolytes incorporating Li10GeP2S12 (LGPS) nanoparticles are promising for solid-state lithium batteries due to their potential for enhanced ionic conductivity; yet, the atomistic mechanisms driving this enhancement remain debated. Here, we systematically investigate the relationship between LGPS nanoparticle loading, poly(ethylene oxide) microstructure, and Li-ion transport using a combination of molecular dynamics (MD) simulations, experimental ionic conductivity measurements, and density functional theory (DFT) calculations. MD simulations and experiments reveal good agreement on ionic conductivity as a function of LGPS concentrations of up to 10 wt % (x %), exhibiting a volcano-like curve with ionic conductivity increasing 5-fold from the low concentrations and can be accounted for by a classical transport mechanism governed by polymer segmental dynamics and interface effects. However, at more than 10% LGPS, experiments show further conductivity enhancement that cannot be accounted for by MD simulations, indicating a shift to another transport mechanism. DFT calculations elucidate that, at the polymer| LGPS interface, Li-ion migration proceeds via vacancy-driven hopping, with barriers sensitive to local atomic composition-low-barrier pathways are possible when S atoms dominantly occupy the sites on the interface to facilitate Li-hopping, while pathways involving Ge act as obstacles to Li transport. These results establish that optimized interfacial chemistry and electrolyte structure enable efficient, barrier-lowering migration channels that are distinct from bulk polymer or ceramic behavior. Our approach reconciles experiments with classical simulations at low LGPS concentrations and quantum chemical interface calculations, highlighting design criteria for maximizing the performance of these types of solid composite polymer electrolytes and guiding the development of advanced lithium batteries.