Rechargeability improvement of δ-type chemical manganese dioxide with the co-doping of Bi and Ni in alkaline electrolyte Original Research Article

δ-MnO2 with the doping of Ni and Bi was prepared through a simple chemical precipitation/oxidation method. Its structure was confirmed by the X-ray diffraction tests. The results of cyclic voltammetry and galvanostatic charge–discharge tests showed that both the doping of Bi and Ni benefited the electrochemical activity of the MnO2 electrode. Compared to the un-doped electrode, the Bi-doped one showed larger discharge capacity and the Ni-doped one showed higher discharge potential and better cycleability. With the co-doping of 5 wt% Bi and 10 wt% Ni, the discharge capacity of the MnO2 electrode reached 252 mA h g−1 at a 0.2C rate and 116 mA h g−1 at a 1C rate, respectively. Its capacity remained in 105 mA h g−1 after 50 cycles at a 1C rate, but the capacity of a commercial electrolytic MnO2 electrode was only 37 mA h g−1.