Design strategy and research progress in positive electrode materials for zinc-ion capacitors

Zinc-ion capacitor is a hybrid supercapacitor consisting of a battery-type negative electrode and a capacitor-type positive electrode, which has the advantages of high energy density, high power density, high safety, and low cost. Its energy density is still limited by the energy storage capacity of the positive electrode material. Therefore, how to design the positive electrode material with high specific capacitance is the key issue to improve the energy density of zinc-ion capacitors. Firstly, the development history, device structure and principles of zinc-ion capacitors were briefly summarized. Moreover, the reasons that limit the application of zinc-ion capacitors were analyzed. Secondly, the device performances, advantages, and shortcomings of typical carbon-based materials and pseudocapacitive materials as positive electrode materials were systematically summarized. Subsequently, the representative research work was chosen to summarize the design strategies and research progress of the positive electrode materials, including nanostructure design, composite material construction, and heteroatom doping. Finally, the development prospects of the positive electrode materials were discussed. It is pointed out that specific research directions are presented, including in-depth research and discovery of new electrochemical mechanisms, the development of new high-performance positive electrode materials, the exploration of effective modification strategies of carbon materials, and the development of functional such as flexible electrode materials. These perspectives can provide important ideas for the preparation of positive electrode materials with excellent electrochemical performance.