Recent research of core–shell structured composites with NiCo2O4 as scaffolds for electrochemical capacitors

Abstract With the rapid development of novel electrodes towards electrochemical capacitors, new materials with reasonable compositions and unique structures are intensively studied in order to achieve a high energy density. NiCo2O4 has been considered as an excellent electrode material due to its high activity and electronic conductivity. The core–shell structured composites with NiCo2O4 as core are designed and synthesized, and the composites usually can deliver higher specific capacitance than pure NiCo2O4. In this work, the recent progress of core–shell composites using NiCo2O4 as scaffolds is comprehensively reviewed. The shell materials of the core–shell configurations including metal oxides, hydroxides, sulfides as well as conductive polymers are summarized and discussed in detail. The core–shell structures grown on conductive substrates can avoid the aggregation of materials and facilitate the penetration of electrolytes. The NiCo2O4 cores serve as conductive pathways for the shell materials to ensure synergistic contribution and the shell materials act as protective coatings to keep NiCo2O4 stable. Some possible development directions and opportunities for the NiCo2O4 core–shell structured electrodes are also discussed.