| In this paper, in order to improve the cycling life of the alloy electrode, and strengthen the balanced use of rare earth resources, established the Re-Mg-Ni based A2B7type alloys as the research target by maens of optimizing furtherly the A side components of Re-Mg-Ni based hydrogen storage alloys. A series of research and testing methods were applied to carry out the microstructure, hydrogen storage properties,electrochemical and kinetics properties of alloys. The research mainly focused on the influence from the content of A side mixture rare earth elements, the associated changes between A side mixture rare earth and magnesium element and heat treatment process.A2B7-type Lao.83-o.5x(Pro.1Ndo.1Smo.1Gd0.2)xMg0.17Ni3.1Coo.3Al0.1(x=0～1.66) hydrogen storage alloys were prepared by annealing treatment at1173K in He+Ar atmosphere. The effect of the partial substitution mixed rare earth for La on the structure and electrochemical properties of the alloys were systematically investigated by XRD, SEM and electrochemical measurement. Phase structure analyses showed that the annealed alloys mainly consisted of Ce2Ni7-type and Gd2Co7-type phases accompanied by minor CaCu5-type and PuNi3-type phase and the influence of the substituted mixed rare earth content x in alloys on the phase constitute and structure was great. With the increase of x value, the main phase abundance of A2B7-type (Ce2Ni7-type and Gd2Co7-type) gradually increased and the unit cell parameters of the main phase decreased. The partial substitution the mixed rare earth for La benefited the formation of Gd2Co7-type phase, indicating that the atoms with smaller radius favored the formation of the Gd2Co7-type phase. The electrochemical measurement results showed that the activation performance was influenced little but the discharge capacity and the cycle stability of the alloys were all first increased and then decreased with the increase of x value. When x value was equal to0.4, the maximum discharge capacity exhibited the maximum electrochemical discharge capacity (389.8mAh·g-1) and the best cyclic stability (Sioo=92.82%). The high rate discharge ability of alloys presented a increasing trend with the increase of x value. The appropriate substitution the mixed rare earth for La provided the alloy electrodes with preferable comprehensive electrochemical properties.On the basis of previous work, establishing the alloy whose comprehensive electrochemical property was the best of all the alloys as the research target, annealled heat treatment for A2B7type Lao.43(Pro.1Ndo iSmo.1Gdo.2)o.4Mg0.17Ni3.1Co0.3Al0.1alloy and AB3.3type La0.8-x(Pro.1Ndo.1Sm0.1Gd0.2)0.4MgxNi29Co0.3Al0.1(x =0.15,0.17,0.15) alloy respectively under four conditions which was (1173K,8h),(1203K,8h),(1223K,8h) and (1273K,6h). The results proved that microstructure and change rules of the phase abundance were different under the two ingredients.The former only changed with different annealed conditions and the latter changed with both the annealed conditions and the magnesium element composition.These difference were reflected in the hydrogen absorption/desorption performance and the electrochemical properties of alloys, which showed that heat treatment conditions and composition of A side all had a great influence on the electrode performance.Finally, aim at the question that the influence tules on alloy electrode properties of mixed rare earth composition and magnesium element composition of A side were similar,designed the La0.7-0.35x(Pro.1Ndo.1Sm0.1Gdo.2)x Mgo.3-0.15x Ni3.1Coo.3Al0.1(x=2.0,1.0,0.5,0.3,0.0,) alloy electrodes.The results showed that the alloy microstructure consisted by Pr5Co19type,2H-Ce2Ni7type,3R-Gd2Co7type and PuNi3type phase, with the decrease of the x, namely the increase of the content of magnesium element and the non-lanthanum mixed rare earth content reduced, the Pr5Co19type phase in the alloy increased before they decreased, the PuNi3type phase gradually reduced, the2H-Ce2Ni7type phase first increased then decreased,and the3R-Gd2Co7type phase gradually increased. In just the right amount of mixed rare earths and magnesium content, alloy had higher2H-Ce2Ni7type phase abundance.Alloy electrode platform pressure decreased firstly and then increased, hydrogen absorption capacity first increased and then decreased. Alloy electrodes can be fully activated among1～3times charge and discharge cycle, the maximum discharge capacity was387.6mAh·g-1. The discharge capacity of alloy electrode was increased firstly and then decreased and the cycle life was first increased then decreased, these changes of alloy electrodes electrochemical properties related to the changes of alloy microstructure and phase abundance. The high rate dischargeability(HRD) performance of alloy electrodes showed a trend of slowly rised firstly and then rapidly declined, the peak value was92.76%, the exchange current density was the main factor to determine the high rate dischargeability performance of alloy electrodes. |
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