Solvation structure and ion transport in mixed ethylene carbonate and dimethyl carbonate electrolytes for sodium-ion batteries: a molecular dynamics study

초록

We present a molecular dynamics study of sodium hexafluorophosphate (NaPF6) electrolytes in mixed ethylene carbonate (EC) and dimethyl carbonate (DMC) solvents across a wide range of compositions. By analyzing radial distribution functions, coordination numbers, mean squared displacements, diffusion coefficients and viscosity, we elucidate how solvent composition governs the solvation structure and ion transport. EC-rich systems exhibit stronger coordination with Na+ and enhanced salt dissociation, while DMC-rich systems offer lower viscosity and higher diffusivity. Notably, an EC:DMC volume ratio of 1:1 maximizes solvation efficiency, Na+ relative mobility, and structural stability. A diffusion inversion is observed at high EC content, where EC molecules diffuse faster than DMC, attributed to confinement effects. Relative mobility analysis reveals that Na+ and PF6- become increasingly decoupled as EC content increases, with distinct transport behavior emerging for each ion. These findings highlight the interplay between solvation, viscosity and mobility and provide insights for the rational design of mixed-solvent electrolytes for sodium-ion batteries.

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