Molecular insights into the effect of graphene surface functionalization on the properties of PEO-based solid polymer electrolytes.

The effects of graphene nanofillers and their surface functional groups on the structural, dynamic, and mechanical properties of poly(ethylene oxide) (PEO)-based solid polymer electrolytes were investigated using molecular dynamics simulations. Graphene nanofillers, regardless of surface functionalization, had minimal influence on polymer chain conformation, packing, and Li+-PEO coordination. However, Li+ mobility strongly depended on both the presence of graphene and the nature of the surface functional groups. Graphenes bearing highly polar groups (e.g., -COOH and -OH) exhibited strong adsorption to PEO chains, reducing polymer dynamics and suppressing Li+ transport. In contrast, pristine graphene enhanced the mobility of both polymer chains and Li+ ions. Li+-graphene interactions also significantly affected ion transport. Pristine graphene and G-CH3 interacted weakly with Li+, whereas G-NH2 showed stronger Li+ binding despite its lower polarity compared with G-COOH and G-OH. These results indicate that Li+ mobility is governed by the combined effects of polymer-graphene and Li+-graphene interactions. Deformation simulations further revealed that graphene nanofillers improve the tensile strength of PEO-based electrolytes, with increasingly polar functional groups producing higher elastic moduli through stronger interfacial interactions. These findings provide molecular-level insights for designing graphene-enhanced polymer electrolytes with balanced ionic conductivity and mechanical performance.