Li-ion Mobility and Solvation Structures in Concentrated Poly(ethylene carbonate) Electrolytes: A Molecular Dynamics Simulation Study

With the rapid global growth of digital devices and electric vehicles, solid polymer electrolytes (SPEs) have emerged as promising candidates for all-solid-state batteries. They are expected to resolve safety concerns and overcome the limitations of energy density and charging speed found in traditional Li-ion batteries with liquid electrolytes. However, a limited understanding of the ionic conduction mechanisms remains a significant barrier to their further development and practical application. In this study, we employed molecular dynamics simulations to investigate the static and dynamic properties of poly(ethylene carbonate) (PEC) electrolytes at various salt concentrations. Key analyses included the radial distribution function, solvation free energy, and mean-square displacement (MSD) of individual Li cations. Based on their MSD data, Li cations were categorized into "faster" or "slower" groups, corresponding to conductivity levels above or below the average in each model. Our findings reveal that, at higher concentrations, a smaller fraction of faster Li cations contributes disproportionately more than slower Li cations to the overall mobility, indicating that the faster ions dominate ion transport more significantly in concentrated electrolytes. Additionally, changes in coordination number and solvation free energy for both faster and slower Li cations suggest the existence of three different solvation patterns as salt concentration increases. These insights provide a deeper understanding of ionic transport and solvation structures in PEC electrolytes, with potential implications for the design of more efficient all-solid-state batteries.