Nickel sulfide-based energy storage materials for high-performance electrochemical capacitors

Supercapacitors are favorable energy storage devices in the field of emerging energy technologies with high power density, excellent cycle stability and environmental benignity. The performance of supercapacitors is definitively influenced by the electrode materials. Nickel sulfides have attracted extensive interest in recent years due to their specific merits for supercapacitor application. However, the distribution of electrochemically active sites critically limits their electro-chemical performance. Notable improvements have been achieved through various strategies such as building synergetic structures with conductive substrates, enhancing the active sites by nanocrystallization and constructing nanohybrid architecture with other electrode materials. This article overviews the progress in the reasonable design and preparation of nickel sulfides and their composite electrodes combined with various bifunctional electric double-layer capacitor (EDLC)-based substances (e.g., graphene, hollow carbon) and pseudocapacitive materials (e.g., transition-metal oxides, sulfides, nitrides). Moreover, the corresponding electrochemical performances, reaction mechanisms, emerging challenges and future perspectives are briefly discussed and summarized.