Study On Performance Optimization Of Activated Carbon Electrode Doped MnO₂ In Supercapacitors

In this article, various of composite electrodes have been obtained by adding Mn O2 powders into activated carbon electrode. As is known, the activated carbon with high electrical conductivity is a promising material for electrical applications, as well as the Mn O2 with high specific capacity. In our study, three types of manganese dioxide(Mn O2) powder: A Mn O2, B Mn O2 and C Mn O2, with specific crystalline structure and morphology, have been obtained under different processes. The influence of the addition of different Mn O2 powders on the electrochemical behavior of the electrode was discussed. Moreover, the crystalline structure, morphology of Mn O2 powders; and the electrochemical behavior of composite electrodes were studied by scanning electron microscope(SEM), X-Ray Diffraction(XRD), cyclic voltammetry and constant current charge-discharge.As a result, when the electric flow was 5 m A, B Mn O2 preformed the highest specific capacity of 157 F/g, with a honeycomb structure(β-Mn O2). Under the same condition, A Mn O2 preformed a nano-scale grainy structure with a 99 F/g of specific capacity(α-Mn O2). Otherwise, the specific capacity of C Mn O2 was 112 F/g, and its structure was nanowire, which intertwined with each other(γ-Mn O2). Respectively, the internal resistance of A Mn O2, B Mn O2, C Mn O2 was 4.4 Ω, 6.4 Ω and 3.2 Ω.In addition, the electrochemical behavior of composite activated carbon electrodes were studied by controlling the ratio of different Mn O2 powders. When A Mn O2 has been added, the optimum ratio of A Mn O2 for the composite electrode was 70%, with 151 F/g of specific capacity. On the other hand, 172 F/g and 141 F/g of specific capacity can be obtained, which the ratio of B Mn O2 and C Mn O2 was 60% and 50% respectively.B Mn O2 performed the highest specific capacity of the three powders, but C Mn O2 performed the minimum internal resistance. Thus, composite electrods with B Mn O2, C Mn O2 and activated carbon have been further studied. The results showed a composite electrod with 191 F/g of specific capacity, 0.11 Ω of internal resistance and 91% of charge-discharge efficiency, which the ratio of B Mn O2, C Mn O2 and activated carbon was 3:3:4.By using previous composite electrode, a supercapacitor has been obtained as well. The initial capacitance of this supercapacitor was 85.3 F. With 99% of charge-discharge efficiency for every single text, 79.2 F of capacitance can be maintained after 8000 times of galvanostatic charge-discharge tests. Meanwhile, the internal resistance for each unit of the supercapacitor was only 0.32 Ω, and the energy density of it was 2.36Wh/Kg.