Recent Advances of Asymmetric Supercapacitors

Asymmetric supercapacitors (ASCs) have attracted significant attentions worldwide owing to their wider voltage window compared with symmetric supercapacitors (SCs). Through combinations of two electrodes with different charge storage mechanisms or different redox reactions, extended operating voltage window can be realized for ASCs. In this article, first the ASCs are classified into two types based on different charge storage mechanisms: electric double-layer capacitive (EDLC)//pseudocapacitive-type ASCs and EDLC//battery-type hybrid SCs. For the EDLC/pseudocapacitive-type ASC, carbon materials are adopted as anode and transition metal oxides including MnO2, RuO2, etc., are utilized as cathodes. For EDLC//battery-type hybrid SCs, carbon materials as anode are combined with metal oxide/hydroxide such as NiO, and Ni(OH)(2), etc., as cathode. Recently, Li-ion-based ASCs composed of carbon materials and Li-ion battery-type electrode materials with a Li-containing organic electrolyte show great potentials to be promising alternatives. Some metal oxides/nitrides including InO2, Bi2O3, Fe3O4, Fe2O3, and VN can work in a negative potential range. By coupling another battery/pseudocapacitive electrode, all redox-type ASCs are assembled and their electrochemical performances are widely studied. Then, based on the above categories recent advances of ASCs are summarized. Finally, the challenges and prospects for the development of ASCs are pointed out from perspectives of this study.

Automated summary

This article introduces the structure and material compositions of asymmetric supercapacitors, which are classified into two types: electric double-layer capacitor//pseudocapacitive-type and electric double-layer capacitor//battery-type hybrid, using carbon materials and different metal oxides/hydroxides as anodes and cathodes. Recent advances show that Li-ion-based ASCs have great potential, and the challenges and prospects for the development of ASCs are pointed out.