Solvation, Speciation, and De-Solvation Penalties in Multivalent Battery Electrolytes

Abstract

Although substantial effort has been applied to the development of new multivalent liquid electrolytes for next generation batteries, an improved understanding of how the solvation environment controls the properties of these electrolytes is needed. Most working electrolytes for Mg2+ and Ca2+ systems utilize low permittivity solvents, namely ethers, which enable the high charge density of the divalent cation to exert significant influence on the surrounding solvation environment. These effects lead to non-intuitive concentration-dependent speciation and significant ion correlations even when employing “weakly coordination” anions. In this presentation we describe the solvation environments of critical exemplar systems based on Ca2+, Mg2+, and Zn2+ working cations using complementary techniques, including dielectric relaxation spectroscopy and modeling. In select cases we connect these solvation details to electrochemical desolvation barriers through temperature-dependent impedance spectroscopy. Through these investigations we address critical questions regarding the magnitude and tunability of the dication desolvation penalty during metal deposition and/or cathode insertion.Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.