Opportunities and challenges of conversion type cathodes in zinc sulfur and zinc iodine batteries

Conventional cathode materials for zinc-ion batteries (ZIBs) predominantly rely on ion-insertion electrochemistry, which inherently limits their specific capacity and restricts the full realization of ZIBs' performance potential. In contrast, cathode materials based on conversion reactions offer a promising pathway toward achieving higher energy densities. Among them, zinc-sulfur (Zn-S) and zinc-iodine (Zn-I₂) batteries have attracted considerable attention for their commercial viability, yet targeted reviews addressing their reaction mechanisms, recent advances, and current challenges remain relatively scarce. To address this gap, this review provides a concise overview of the reaction mechanisms and battery configurations pertinent to conversion-type cathodes in Zn-S and Zn-I₂ systems. Furthermore, it critically examines the fundamental physicochemical and structural challenges inherent to these materials, along with an evaluation of engineered solutions and emerging technological innovations designed to overcome these limitations. Finally, it outlines prospective research directions and development opportunities for advancing conversion-type cathodes in next-generation ZIBs.