Interplay between organic solvent geometry and divalent cation dynamics in divalent metal batteries

Abstract

This study investigates the interplay between organic solvent geometry and divalent cation dynamics in liquid electrolytes, emphasizing their relevance for energy storage systems. Using classical molecular dynamics simulations, the structural and transport properties of Mg²⁺ and Ca²⁺ were evaluated in cyclic (ethylene carbonate, EC; propylene carbonate, PC) and linear (ethyl methyl carbonate, EMC) solvents in the presence of TFSI⁻ anions across a range of temperatures. The results reveal that Mg²⁺ exhibits superior diffusion compared to Ca²⁺ due to its smaller ionic radius and weaker ion–pair interactions. Diffusion increases with temperature, following the solvent trend EC > EMC > PC. Coordination analysis showed compact solvation shells for both cations, with Ca²⁺ forming denser structures and demonstrating higher residence times compared to Mg²⁺. Solvent geometry significantly influenced solvation dynamics, with cyclic solvents enhancing ion coordination and linear solvents reducing solvation due to steric hindrance. These findings underscore the critical role of solvent structure and ion dynamics in optimizing divalent-ion battery performance, positioning Mg²⁺ as a promising candidate for sustainable energy storage solutions.