Engineering a Novel AgMn 2 O 4 @Na 0.55 Mn 2 O 4 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 AgMn 2 O 4 /Na 0.55 Mn 2 O 4 nanosheets created by a popular liquid precipitation method with different AgNO 3 contents, and their corresponding physical and electrochemical characterizations are performed. The results show that the ultra-thin Na 0.55 Mn 2 O 4 nanosheets were combined with the AgMn 2 O 4 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 AgMn 2 O 4 /Na 0.55 Mn 2 O 4 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.