Mn₃O₄ based materials for electrochemical supercapacitors: Basic principles, charge storage mechanism, progress, and perspectives

The captivating properties of supercapacitors (SCs) such as high power and reasonably high energy densities made them stand up as a versatile solution to emerging energy storage applications. Thus, everyone is in pursuit of improvisation of the energy storage characteristics of SCs. Hausmannite or manganese oxide (Mn₃O₄) is a widely studied electrode material considering its fascinating features such as high theoretical capacitance (1370 F/g), variable oxidization states, prominent Jahn-Teller effect, broad potential window, environmentally benign and cost-effectiveness. A lot of research has been carried out on this material to unfold and improve its electrochemical aspects. In this review, comprehensive knowledge and innovative attempts taken to improve its energy storage of Mn₃O₄ material are discussed. Firstly, the basic properties concerned with electrochemical charge storage such as valance states, crystal structure, band diagram and energy storage mechanism are discussed, followed by putting forth the limitations of Mn₃O₄. Later on, various strategies adopted to improve the electrochemical attributes of Mn₃O₄ such as making composite with carbon-based materials, metal-based materials, polymers or doping metal atoms are thorough. Finally, remarks on key scientific points and perspectives for further development of energy storage in Mn₃O₄ conclude this review.