Engineering of MnO2-based nanocomposites for high-performance supercapacitors

Supercapacitors have emerged as one of the most attractive electrochemical storage systems with unique characteristics featuring high power delivery and long-term cycling stability. Manganese oxides (MnO2) have particularly received increasing attention owing to their high specific capacitance, low cost, natural abundance, and environmental benignity. Nanoscale MnO2 structures should incorporate highly porous and electrically conductive materials to form hybrid or composite nanostructures in order to maximize their capabilities and electrochemical performance. The rapid development of MnO2-based nanocomposites for high-performance supercapacitors in recent years has been reviewed in terms of the charge storage mechanism, materials science, and smart cell assembly. This review article aims to summarize the latest progress in MnO2-based nanocomposite electrodes to provide guidance for the design, manufacturing, and assembly of high-performance supercapacitors. The review starts with the discussion of charge storage mechanisms of MnO2-based materials. Subsequent emphasis is placed on the significant progress of MnO2-based heterogeneous nanocomposites, followed by the development of asymmetric supercapacitors assembled with the MnO2-based nanocomposites. Finally, perspectives and challenging issues regarding the rational design and synthesis of MnO2-based nanocomposites for high-performance supercapacitors are discussed.