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

## TL;DR

This study explores how the shape of organic solvents affects the movement of divalent cations in batteries, showing that solvent geometry and cation type influence battery performance.

## Contribution

The study reveals how solvent geometry and cation dynamics interact, offering insights for designing better divalent metal batteries.

## Key findings

- Mg2+ diffuses faster than Ca2+ due to smaller size and weaker ion-pair interactions.
- Cyclic solvents like EC enhance ion coordination, while linear solvents like EMC reduce solvation.
- Ca2+ forms denser solvation shells with higher residence times compared to Mg2+.

## 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.

Elucidating the local structure and the dynamic nature of divalent cations under different solvent geometries.