Engineering a Novel AgMn₂O₄@Na_0.55Mn₂O₄ Nanosheet toward High-Performance Electrochemical Capacitors

Manganese oxides, as a type of two-dimensional (2D) material with high specific area and low cost, are considered promising energy storage materials. Here, we report novel AgMn₂O₄/Na_0.55Mn₂O₄ nanosheets created by a popular liquid precipitation method with different AgNO₃ contents, and their corresponding physical and electrochemical characterizations are performed. The results show that the ultra-thin Na_0.55Mn₂O₄ nanosheets were combined with the AgMn₂O₄ nanoparticles and an enhancement in their specific capacity was observed compared to the pristine sheets. This electrode material displays a peak specific capacitance of 335.94 F g^-1 at 1 A g^-1. Using an asymmetric supercapacitor (ASC) assembled using a positive electrode made of AgMn₂O₄/Na_0.55Mn₂O₄ nanosheets and a reduced graphene oxide (rGO) negative electrode, a high energy density of 65.5 Wh kg^-1 was achieved for a power density of 775 W kg^-1. The ASC showed good cycling stability with a capacitance value maintained at 90.2% after 10,000 charge/discharge cycles. The excellent electrochemical performance of the device was ascribed to the heterostructures and the open space formed by the interconnected manganese oxide nanosheets, which resulted in a rapid and reversible faraday reaction in the interface and further enhanced its electrochemical kinetics.