Conversion-type cathode materials for high energy density solid-state lithium batteries

Solid-state lithium batteries (SSLBs) are regarded as an essential growth path in energy storage systems due to their excellent safety and high energy density. In particular, SSLBs using conversion-type cathode materials have received widespread attention because of their high theoretical energy densities, low cost, and sustainability. Despite the great progress in research and development of SSLBs based on conversion-type cathodes, their practical applications still face challenges such as blocked ionic-electronic migration pathways, huge volume change, interfacial incompatibility, and expensive processing costs. This review focuses on the advantages and critical issues of coupling conversion-type cathodes with solid-state electrolytes (SSEs), as well as state-of-the-art progress in various promising cathodes (e.g., FeS₂, CuS, FeF₃, FeF₂, and S) in SSLBs. Furthermore, representative research on conversion-type solid-state full cells is discussed to offer enlightenment for their practical application. Significantly, the energy density exhibited by the S cathode stands out impressively, while sulfide SSEs and halide SSEs have demonstrated immense potential for coupling with conversion-type cathodes. Finally, perspectives on conversion-type cathodes are provided at the material, interface, composite electrode, and battery levels, with a view to accelerating the development of conversion-type cathodes for high-energy–density SSLBs.