Al and/or Ni-doped nanomanganese dioxide with anisotropic expansion and their electrochemical characterisation in primary Li-MnO2 batteries

Abstract

A variety of MnO2 nanorods containing one or two transition metals (M) (with M = Al and/or Ni) have been successfully synthesised via a facile hydrothermal synthesis route. The physical–chemical properties and electrochemical performance of manganese oxide were analysed by X-ray diffraction (XRD), inductively coupled plasma atomic emission spectrometry (ICP-OES), Fourier transform infrared spectrometer (FT-IR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller method (BET), galvanostatic discharge and cyclic voltammetry (CV). The result indicated that α-type MnO2 was obtained, and a small quantity of Al and/or Ni were embedded into the crystal lattice of manganese oxide instead of the partial Mn ion, which resulted in anisotropic expansion of the MnO2 unit cell. The doping of Al can strengthen Mn–O bonds in the [MnO6] octahedral and increases the specific surface area of the modified material (i.e., Al–MnO2 is 119 m2 g−1). Interestingly, MnO2 electrode co-doped with equimolar Al and Ni exhibited the highest specific capacity of 169 mAh g−1 at 0.05 mA cm−2. The substantial enhancement of the electrochemical lithium storage capacity was due to the ameliorating of integrative factors, such as high specific surface area, excellent lattice parameters and lower electrical resistance, as well as short Li+ and electron transport length. In addition, a more stable host skeleton also guaranteed an endurable Li+ intercalation behaviour during the discharge process.