Manganese oxide based materials for supercapacitors

Manganese oxides, as an environmentally friendly material with various oxidation states, have a long history as an electrode material for batteries. Recently, a new energy storage system, supercapacitor, with its unique power density and energy density range, has been put in the focus. With a vast number of ongoing researches in exploring the MnOx as the electrode materials for supercapacitors, this article provides a comprehensive review on the recent findings in this area. Different approaches to synthesise and the electrochemical behaviours of various forms of pure and composite MnOx were presented. Important parameters that can influence the electrochemical behaviour of manganese oxides based materials are summarised. The state of the art of engineering of MnOx into composites or specific nanostructures with improved electrochemical performance is reviewed. A brief survey on the performance of symmetric and hybrid supercapacitors with MnOx as electrode material is given and appropriate cell configuration has been proven to be necessary for the optimisation of the capacitive performance. Moreover, the essential difference of charge storage mechanism between battery and supercapacitor for MnOx electrode is stated. Based on these literature findings, MnOx is believed to be a type of promising and competitive electrode material for applications in supercapacitors.