Preventing Electrolyte Decomposition on a Ca Metal Electrode Interface Using an Artificial Solid-Electrolyte Interphase

Calcium ion batteries are gaining attention as alternatives to lithium-ion technology because they offer comparable properties at reduced cost and improved safety. However, progress has been limited because of the inability to efficiently and reversibly plate and strip Ca metal anodes in organic electrolytes. Moreover, the inorganic components of the solid-electrolyte interphase (SEI) that form via decomposition of the electrolyte often do not allow for the diffusion of Ca ions. In this work, an approach combining density functional theory and ab initio molecular dynamics (AIMD) simulations is utilized to show that the use of a preformed artificial SEI layer of amorphous Al2O3 can potentially prevent electrolyte decomposition. First, Ca is shown to be able to intercalate into an amorphous Al2O3 layer (up to Ca1.5Al2O3) and diffuse through on a reasonable time scale. Through calculation of the density of states, the system is found to remain insulating up to the equilibrium stoichiometry. Finally, AIMD simulations with a realistic organic electrolyte environment are used to show that this calcinated Al2O3 layer completely prevents the decomposition of solvent molecules. This approach can provide a route to efficient rechargeable Ca ion batteries, paving the way for cheap large-scale energy storage.