Multivalent ion batteries (MVIB), or those utilizing Mg, Ca, Zn, and Al, are garnering increasing attention as alternatives to Li-ion batteries in applications where portability is not an issue owing to their high energy density, cost efficiency, and abundance. However, the lack of suitable electrolytes allowing for the reversible plating of metallic anodes has limited the development of MVIBs, especially those involving Ca. This is primarily due to the fact that the solid-electrolyte interphase (SEI), a passivating layer which forms between the electrolyte and anode, often does not allow for the migration of ions in MVIBs. [1,2] In this work, we develop an understanding of the SEI in MVIB 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 Li, Ca, and Al surfaces 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. Finally, we investigate the decomposition of these electrolytes in the presence of external electric fields to more fully understand these reactions in electrochemical systems. We anticipate the promising new electrolytes proposed in this work will help guide experimentalists in the development of rechargeable MVIBs.
J.Y. and M.S. were supported by funds from Binghamton University. DFT calculations were performed on the Spiedie cluster at Binghamton University, as well as the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by NSF Grant No. ACI-1053575, under allocations TG-DMR170127 and TG-DMR180009.
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