Preparation and Electrochemical Properties of Al3+-Doped δ-MnO2

Al3+-doped delta-MnO2 nano-powders with different doping ratios were synthesized by hydrothermal method. The influence of Al3+-doping on the d-MnO2 crystal structure and electrochemical performance was characterized by X-ray diffraction,scanning electron microscopy,transmission electron microscopy,X-ray photoelectron spectroscopy, cyclic voltammetry,electrochemical impedance spectroscopy and galvanostatic charge-discharge. The results suggested that Al3+ ions entered into the crystal lattice of delta-MnO2 to replace some Mn3+ and Mn4+ ions,which enhanced the electrical conductivity and structural stability of delta-MnO2,and thus significantly improved the electro- chemical performance. When the molar ratio of Al3+/Mn2+ in the precursor was 0.45,the synthesized product (A0.45M)showed the best electrochemical performance. A0.45M delivered a specific capacitance of 207.61 F/g at a current density of 1 A/g,which was 2.4 times the capacitance of the pure delta-MnO2 (A0M). Moreover,A0.45M could maintain a high specific capacitance of 100.81 F/g even after 10000 cycles at 10 A/g,with capacity retention ratio of 81.33%.