Optimizing Yolk–Shell ZnCo2S4 Nanoparticles for Enhanced Supercapacitor Performance: Failure Mechanism Analysis and Material Design

Ternary metal sulfides hold the potential to deliver electrochemical supercapacitors with theoretically high power and energy densities, as well as an extended cycle life. However, the novel bimetallic ternary metal sulfides suffer from rapid loss of their specific capacitance and poor cycle life because their electrochemical reactions involve multiple redox steps, volume expansion, and irreversible structural changes. Thus, understanding the failure mechanisms in terms of the material chemistry is important for designing novel energy materials with high electrochemical stability during long‐term cycling. In this study, yolk–shell ZnCo2S4 (ZCS) nanoparticles are synthesized and modified with either a carbon shell (ZCS@C) or a polypyrrole (PPy) coating (ZCS@PPy) to explore the failure mechanism of yolk–shell ZCS nanoparticles via the decomposition of their shells. The optimal ZCS@C addresses these issues, producing high capacitance (171 F g−1 at 2 A g−1) with high retention (78% after 5,000 cycles). Therefore, we comprehensively report this investigation on the effects of the physical chemistry and electrochemistry of ZCS materials on the performance of electrochemical supercapacitors, aiming to design ZCS@C electrochemical materials that effectively address the proposed failure mechanisms.