Computational Design of Double-Layer Cathode Coatings in All-Solid-State Batteries

All-solid-state lithium-ion batteries have great potential for improved energy and power density compared to conventional lithium-ion batteries. With extensive research efforts devoted to the development of inorganic superionic conductors, lithium thiophosphates stand out due to their high ionic conductivity and room‐temperature processability. However battery rate performance still suffers from increased impedance attributed to the interfacial reactions between thiophosphate electrolyte and oxide electrodes. Stabilizing the interfaces with a protective coating layer has been proposed as a solution to the interfacial problem, but it is rare for a material to simultaneously exhibit fast ionic conductivity and chemical stability at battery interfaces. Here, we propose a double-layer coating design comprising a sulfide-based layer adjacent to the thiophosphate electrolyte accompanied by a layer that is stable against the oxide cathode. Based on a high-throughput thermodynamic stability screen and active learning molecular dynamics simulations, we identify several sulfide + halide couples that potentially outperform the known coating materials in interfacial stability as well as ionic conductivity. Several halides we identify have been recently identified as novel solid electrolyte candidates. We highlight the integration of room-temperature fast ionic conductors Li5B7S13 (137 mS cm−1), Li7Y7Zr9S32 (6.5 mS cm−1), and Li(TiS2)2 (0.0008 mS cm−1) which potentially reduces interfacial reactivity with minor loss of charge transfer rate through the thiophosphate electrolyte.