Stabilizing Interfaces in Magnesium Solid-State Batteries via High-Throughput Coating Design

To meet the growing demand for affordable and safe electrochemical energy storage systems with high energy density, all-solid-state magnesium-ion batteries (ASSMBs) have emerged as promising candidates, because magnesium is naturally abundant and offers high volumetric capacity. However, the electrochemical stability of magnesium solid electrolytes (SEs), as well as their chemical compatibility with magnesium cathodes, remains underexplored. Herein, we assess the electrochemical stability window (ESW) of magnesium SEs and evaluate their interfacial reactivity with magnesium cathodes by calculating the decomposition energy for SE-cathode pairs. Consequently, the mismatch between the ESW of magnesium SEs and cathode requirements should be addressed, underscoring the need for protective strategies. Accordingly, a high-throughput screening for relevant coating materials is conducted, identifying 14 experimentally observed candidates from 19 098 magnesium-containing inorganic compounds after thermodynamical screening. These compounds are further evaluated by computing their migration barriers for vacancy hopping, excluding seven compounds with exceptionally high vacancy-diffusion barriers and leaving seven remaining coating candidates. Following this hierarchical screening, seven Mg-containing compounds remained as particularly appealing candidates: MgBr₂, Mg₃B₇ClO₁₃, MgBHO₃, Mg₃Si(O₂F)₂, MgH₈(ClO₂)₂, Mg₃Si₄(HO₆)₂, and Mg₇P₂(HO₂)₈. This work provides fundamental insights into magnesium SEs and their interfacial stability, establishing a rational design framework to enhance overall cell performance in ASSMBs.