Multi-Solid-Electrolyte Systems for All-Solid-State Batteries: Current Status and Future Prospects

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All-solid-state batteries (ASSBs) are considered a groundbreaking solution to next-generation energy storage, offering enhanced safety, higher energy density, and longer cycle life than conventional lithium-ion batteries (LIBs). A key component of ASSBs are single-solid-electrolyte systems, which include sulfide-, oxide-, halide-, and hydride-based solid electrolytes. However, these single solid electrolytes often fail to simultaneously meet all of the necessary criteria, such as sufficient ionic conductivity, strong chemical stability, and robust interfaces with both high-voltage cathodes and low-voltage metal anodes. Therefore, multi-solid-electrolyte systems, which integrate two or more solid electrolytes to overcome these limitations, have been gaining increasing importance. When solid electrolytes are strategically combined, multi-solid-electrolyte systems can effectively mitigate interfacial reactions, enhance ionic transport, and improve electrochemical performance. Approaches include coating the cathode with a solid electrolyte, using solid electrolytes as the catholyte and anolyte, and employing mixed and multilayered solid electrolytes. These methods have been proven to reduce side reactions at both electrodes and enable stable cycling at high voltages and with metallic anodes. Furthermore, future perspectives focus on refining interfacial engineering and optimizing design strategies to fully unlock the potential of multi-solid-electrolyte systems. These advancements will provide deeper insights into the fundamental mechanisms governing ion transport and interfacial stability, thereby guiding the further development of next-generation ASSBs.