Boosting the Electrochemical Storage Properties of CoO Nanowires by the Mn Doping Strategy with Appropriate Mn Doping Concentrations.

High specific capacitance, high energy density, and high power density have always been important directions for the improvement of electrode materials for supercapacitors. In this paper, CoO nanowire arrays with various Mn doping concentrations (Mn:Co molar ratio = 1:11, 1:5, 1:2) directly grown on nickel foam (NF) were prepared by a simple hydrothermal method and annealing process. The influence of Mn doping on the morphology, structure, and electrochemical behaviors of CoO was investigated. The results show that partial substitution of Co ions with Mn ions in the spinel structure does not change the nanowire morphology of pure CoO but increases the lattice parameter and decreases the crystallinity of cobalt oxide. Electrochemical measurements showed that Mn doping in CoO could effectively enhance the redox activity, especially CoO with a Mn doping ratio of 1:5, which exhibits the most excellent electrochemical performance, with the maximum specific capacitance of 1210.8 F·g at 1 A·g and a rate capability of 33.0% at 30 A·g. The asymmetric supercapacitor (ASC) device assembled with the optimal Mn-CoO (1:5) and activated carbon (AC) electrode performs a high specific capacitance of 105.8 F·g, a high energy density of 33 Wh·kg at a power density of 748.1 W·kg, and a capacitance retention of 60.2% after 5000 cycles. This work indicates that an appropriate Mn doping concentration in the CoO lattice structure will have great potential in rationalizing the design of spinel oxides for efficient electrochemical performance.