Computational Understanding of Solid-Electrolyte Interphase Formation in Ca-ion Batteries

Multivalent ion batteries (MVIB) have garnered attention as alternatives to Li-ion batteries in applications where portability is not an issue, as they are energy dense, cost efficient, and utilize Earth-abundant elements. However, the development of MVIBs, especially Ca-ion, has been limited by the lack of suitable electrolytes that can reversibly plate metallic anodes. This is due to the fact that the passivating layer which forms between the electrolyte and anode (the solid-electrolyte interphase, SEI) does not allow for the migration of Ca²⁺ ions. In this work, we develop an understanding of the SEI in Ca-ion systems using a computational approach combining density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. We first identify the principle components of the SEI by studying the decomposition of the solvents and salts comprising various electrolytes on a Ca surface using AIMD. Following this, we identify electrolytes which can be used with a Ca metal anode by investigating the diffusion of Ca ions through the likely inorganic compounds produced using DFT. We anticipate the promising new electrolytes proposed in this work will help guide experimentalists in the development of rechargeable Ca cells.