Electrochemical hydrogen storage properties of Mg _2-xAl _xNi (x = 0, 0.3, 0.5, 0.7) prepared by hydriding combustion synthesis and mechanical milling

Mg _2-xAl _xNi (x = 0, 0.3, 0.5, 0.7) hydrogen storage alloys used as the negative electrode in a nickel-metal hydride (Ni-MH) battery were successfully prepared by means of hydriding combustion synthesis (HCS) and the selected alloy Mg _1.5Al _0.5Ni was further modified by mechanical milling (MM). The structural and electrochemical hydrogen storage properties of Mg _2-xAl _xNi alloys have been investigated in detail. XRD results show that a new phase Mg ₃AlNi ₂ that possesses an excellent cycling stability is observed with the substitution of Al for Mg. A short-time mechanical milling has a significant effect on improving the discharge capacity of the HCS product of Mg _1.5Al _0.5Ni. The maximum discharge capacity of Mg _1.5Al _0.5Ni ascends with increasing mechanical milling time and reaches the maximum 245.5 mAh/g when milled for 10 h. The alloy milled for 5 h shows the best electrochemical kinetics, which is due to its smaller mean particle size and uniform distribution of the particles. Further increasing in mechanical milling time could not bring about better electrochemical kinetics, which might be attributed to the agglomeration of the alloy particles and thus the charge-transfer reaction and hydrogen diffusion are restrained. It is suggested that the novel method of HCS + MM is promising to prepare ternary Mg-based intermetallic compound for electrochemical hydrogen storage.