Computational Development of an Artificial Solid Electrolyte Interphase for Rechargeable Multivalent Ion Batteries

Multivalent ion batteries (MVIB), or those utilizing Mg, Ca, Zn, and Al, are garnering increasing attention as alternatives to Li-ion batteries in non-portable applications such as grid storage, as they are energy dense, cost efficient, and safe. The development of such MVIBs, however, has been hindered by the inability of existing electrolytes to reversibly plate and strip metallic anodes. This is a particular problem in Ca ion batteries, as the the solid-electrolyte interphase (SEI, the passivating layer which forms between the electrolyte and anode) does not allow for the migration of Ca²⁺ ions. In this work, we develop an understanding of this SEI using a computational approach combining DFT and ab initio molecular dynamics (AIMD) simulations. First, we show that AIMD can be utilized to predict the decomposition products making up the SEI in a variety of systems containing different anodes and electrolytes. Second, we demonstrate that the use of an amorphous Al₂O₃ layer between the Ca metal anode and organic electrolyte prevents decomposition while allowing for the transport of Ca ions. We propose that this strategy can aid in the development of rechargeable Ca ion batteries by completely avoiding the formation of an ionically insulating SEI from electrolyte decomposition.