Synthesis, structure, magnetic, electrical and electrochemical properties of Al, Cu and Mg doped MnO2

Pure and doped manganese dioxides were prepared by wet-chemical method using fumaric acid and potassium permanganate as raw materials. X-ray diffraction patterns show that pure and Al, Cu and Mg doped manganese dioxides (d-MnO2) crystallized in the cryptomelane-MnO2 structure. Thermal analysis show that, with the assistance of potassium ions inside the 2 × 2 tunnel, the presence of Al, Cu and Mg doping elements increases the thermal stability of d-MnO2. The electrical conductivity of d-MnO2 increases in comparison with pure MnO2, while Al-doped MnO2 exhibits the lower resistivity. As shown in the magnetic measurements, the value of the experimental effective magnetic moment of Mn ions decreases with introduction of dopants, which is attributed to the presence of a mixed valency of high-spin state Mn4+/Mn3+. Doped MnO2 materials show good capacity retention in comparison with virgin MnO2. Al-doped MnO2 shows the best electrochemical results in terms of capacity retention and recharge efficiency.