Insights into the Solvation Structure of Multi-Valent Ions for Multivalent Battery Applications

Multivalent batteries, such as those based on divalent Mg²⁺ ions, have the potential to provide significant gains in energy storage density, at lower cost and with enhanced safety compared to Li-ion devices. However, the development of Mg-ion battery technologies require innovation not only in the design of novel electrode materials but also in electrolytes that facilitates transport and charge transfer of the doubly-charged Mg ion.Thus, a fundamental understanding of the intrinsic interactions in these novel electrolytes is imperative for design of liquids systems with improved electrochemical stability as well as charge transfer properties. Using the high-throughput capability of the Materials Project (www.materialsproject.org), we are able to rapidly screen electrolyte systems for suitable properties. In this work, we present molecular dynamics simulations coupled with first-principles calculations for a range of Mg salts in common solvents, benchmarked against available experimental information on radial distribution function and diffusion coefficient. The results are also compared to similar studies available for Li-ion systems. In the comparison, it is obvious that the inter-molecular solvation structure for multivalent ions is very different from the one we are used to in well-performing monovalent ion (e.g. Li and Na) electrolytes and hence points to a design metric for future electrolyte work.