Molecular-Level Engineering of Gel Polymer Electrolytes in Sodiumion Batteries: A Comprehensive Computational Study

Abstract

Sodium-ion batteries (SIBs) represent promising low-cost alternatives to lithium-ion batteries (LIBs). However, critical challenges in electrolyte design -particularly in achieving both high ionic conductivity and cation transference number -must be addressed. To create a flexible and conductive polymer, we designed three novel PSO-TFSI-based polyanionic polymers with strategically positioned electronwithdrawing groups (-CF 3 ,-NO 2 ) at the 2,6-positions of the benzene ring (PSO-BTFM-TFSI, PSO-NTFM-TFSI, PSO-DN-TFSI). Using quantum mechanical calculations, we systematically evaluated cation-anion binding energies and solvent interactions, identified EC, DMSO, and DEC as optimal candidates. Molecular dynamics simulations further identified PSO-BTFM-TFSI in DEC solvent as the top performer in ionic conductivity, prompting its selection for further optimization. Subsequent optimization yielded an optimal ternary solvent ratio (EC:DEC:DMSO = 0.15:0.05:0.80) with the PSO-BTFM-TFSI polymer, achieving ionic conductivity of 2.68 ± 0.26 mS.cm -1 and 0.713 ± 0.077 cation transference number at 70 • C. This system also maintained moderate viscosity (8.84 ± 1.65 cP). We also delved deep into the diffusion mechanisms of both ionic species across the ternary solvent phase diagrams. Our work demonstrates a comprehensive design strategy for high-performance gel polymer electrolytes through targeted molecular engineering and multiscale computational screening.