Zn-ion hybrid supercapacitors: Achievements, challenges and future perspectives

The newly-emerging Zn-ion hybrid supercapacitors (ZHSCs) are famed for their integration of high-capacity of Zn-ion batteries and high-power of supercapacitors (SCs), which are expected to meet the energy and power demands for both portable electronics and electrical vehicles. The practical application of ZHSCs faces serious challenges of achieving satisfactory energy density and developing suitable cathode materials and electrolytes. A systematic review on ZHSCs, the novel energy storage devices, is necessarily desired to spur the development of ZHSCs, but is still barren. This review provides a timely summary of recent advances on ZHSCs, and highlights the vital role of cathode materials and electrolyte systems in accelerating the prosperity of this kind of SCs. The ZHSCs fundamentals and the advanced engineering of various types of nanostructured cathode materials as well as their electrochemical characteristics and energy storage mechanisms are comprehensively discussed. The most recent development of electrolytes and Zn anode is also summarized and the effects of electrolyte compositions on the electrochemical performance of ZHSCs are elaborated. In the end, this review provides a detailed discussion about the existing critical challenges and presents future development perspectives on the favorable ZHSCs.