Nitrogen plasma activation of cactus-like MnO2 grown on carbon cloth for high-mass loading asymmetric supercapacitors

Abstract

The electrochemical performance of high theoretical capacitance MnO2 is usually restricted to low mass loading electrode due to the slower electron/ion diffusion kinetics in dense electrodes. Defect engineering has been supposed to an effective way to improve the capacitive performance of transition metal oxides. Herein, cactus-like structure MnO2 was grown on carbon cloth (CC) and treated with N2-plasma to obtain the N-MnO2 electrode with high mass loading of 12 mg cm−2. Benefiting from the hierarchical structure and rich oxygen vacancies, the as-prepared N-MnO2 electrode delivered a high mass specific capacitance of 443F g−1 and a high areal capacitance of 5320 mF cm−2. Furthermore, the N-MnO2 electrode released an excellent rate capability with 71.8% capacitance retention at 20 mA cm−2 as well as gratifying cycling life with 96 % capacitance retention after 8 000 cycles at 20 mA cm−2. Moreover, an asymmetrical supercapacitor device assembled by N-MnO2 and activated CC can achieve a high energy density of 0.56 mWh cm−2 (46 Wh kg−1) at the power density of 5.14 mW cm−2 (420 W kg−1) with good cycle stability. Such facile N2-plasma treatment for defect engineering shows great potential in the rational design for advanced supercapacitor electrodes with high mass loading.