| In our previous work, based on the (Ti Cr)0.497V0.42Fe0.083 alloy for the matrix, by adding 30%(wt) of rare earth alloy A2B7 La0.63 R0.2Mg0.17 Ni3.1 Co0.3 Al0.1 for catalytic activity materials, adopting echanical ball mill modification for 5h, the electrochemical properties of the materials were improved.The maxmum discharge capacity of the composite electrode is 425.8 mA·h/g and the discharge capacity retention rate C100/Cmax after 100 charge–discharge cycles is 97%, which exhibits a good cycle stability.In this thesis,(TiCr)0.497V0.42Fe0.083+x(wt%)(LaRMg)2(NiCoAl)7(x=550) were prepared by mechanical milling process for 5h. The changes in hydrogen storage characteristics, microstructure and electrochemical properties of the milled composites were investigated systematically. The milled composite (TiCr)0.497V0.42Fe0.083+30(wt%) (LaRMg)2(NiCoAl)7 were further modified by changing the milling process and annealing ,and the alloying element content in alkaline solution after different cycle number was also studied. The conclusions are as follows:P-C-T analysis showed that with the increase of A2B7 alloys, absorption plateau pressure decreased, absorption plateau slope increased and the absorption capacity decreased; discharge efficiencyηincreased gradually by 53.2% to 92.9%; the discharge efficiency of (TiCr)0.497V0.42Fe0.083+30(wt%(LaRMg)2(NiCoAl)7 is 92.5%,ΔHΘis 26.165KJ/mol,ΔSΘis 88.96j/k/mol,which is fit for negative electrode for high-energy MH/Ni batteries.XRD and SEM analysis showed that the A2B7 alloy particles were uniformly dispersed and encapsulated on the surface of the V-based alloy particles and the encapsulated area enhanced with the increasing x. Compared with vanadium-based alloy, the crystal parameters a and cell volume V of solid solution BCC phase in the composite decreased observably. The electrochemical measurements showed that the maximum discharge capacity of the milled composite electrodes first increased then decreased with increasing x.When x≧ 5, the discharge capacity of the milled composites were 280433.2 mA·h/g and the discharge capacity retention rate C100/Cmax were 91.9%-98.9% after 100 charge–discharge cycling, which exhibited a better cycle life than that of the A2B7 type alloy electrode. Among all of the alloys, the composite (x=30) had the best electrochemical properties. Chemical composition analysis in electrolyte showed that the surface coating, the corrosion resistance of A2B7 type alloy, and the dissolution behavior of element V had an important effect on the electrochemical cycling stability of the composites.The high rate discharge ability(HRD) and exchange current density I0 increased but the hydrogen diffusion coefficient decreased, and the electrochemical kinetic properties was improved obviously with increasing x, indicating that the electrochemical kinetic properties of the milled composite were mainly controlled by the electrocatalytic activity.Compared with the milled composite alloys under argon atmosphere, the particle size under hydrogen atmosphere is much smaller and the particle lubricity increased which lead to a low cladding; the cyclic stability and discharge capacity were much poor but the electrical catalytic activity increased. After changing the milling process, the discharge capacity improved but the cyclic stability was still poor.The distinction of the electrochemical properties of the composite electrodes with different annealing temperature was larger.There was no phase change after 200℃annealing, the discharge capacity and the high rate discharge ability(HRD) decreased slightly, the cyclic stability improved largely.When the annealing temperature≥400℃, there were complicated phase change and the discharge capacities were relatively low.
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