Reversible kinetics and rapid tunnelling characteristics of silicon doped magnesium-titanium nanocomposites prepared by mechanical alloying route for nickel-metal hydride batteries

Abstract

Magnesium-Titanium-Silicon (Mg-Ti-Si) hybrid nanocomposites have been synthesized by using high energy ball milling. Magnesium, titanium and silicon powder mixtures are taken in the stoichiometric molar ratio of Mg0.8-xTi0.2Six (x = 0, 0.10, 0.15, 0.20 and 0.25) and mechanically milled for 30 h. The phase transformation, micro-strain and microstructural changes during mechanical alloying are examined by X-ray diffraction (XRD) and scanning electron microscope (SEM). Band gap engineering is a process done by high energy ball milling of Mg0.8Ti0.2, Mg0.8-xTi0.2Six powders, which have been tailored from 0.629 to 1.685 eV, which are obtained from the optical absorption spectra. The band gap energy is the most substantial parameter to understand the electrochemical charge-discharge activation behaviour. The high planar diffusion with high reversible reaction has been occurred only for the 30 h ball milled Mg0.70Ti0.20Si0.10 and Mg0.65Ti0.20Si0.15 powders. During the oxidation behaviour, they have been gained the higher diffusion coefficient (1.87 × 10−08 cm2 s−1 and 1.53 × 10−08 cm2 s−1), high exchange ion current density (1841 mA g−1 and 1113 mA g−1), the patronizing maximum discharge capacity (329 mAh g−1 and 307 mAh g−1), maximum energy density (0.265 Wh g−1 and 0.219 Wh g−1) with high quasi-reversible coulombic efficiency (65.80% and 61.40%) and high cyclic stability (87.23% and 82.08%) respectively. The addition of silicon concentration increases (i.e. x = 0.10–0.25) in magnesium-titanium based ball milled powders enhance the activation behaviour and robustly reduce the Gibbs free energy from −127 to −64 kJ mol−1.