Rare Earth Based Organizations And Electrochemical Properties Of The Stoichiometric Hydrogen Storage Alloys Of Re (nimmn) <sub> 5 + X </ Sub>

To improve the competition ability of AB5 type hydrogen storage electrode alloy in the market, meet the need of the Ni/ MH battery industry's development of our nation and the need for high cost performance of Ni/MH electrode alloy, this paper will lays emphasis on investigating Co-free hydrogen storage alloys and optimizing its composition. By means of over stoichiometry, composition optimization, keeping annealing at high temperature for long time, the effects of the composition on phase structure and electrochemical properties were studied systemically so as to improve the comprehensive electrochemical properties. According to reference [13], LaNi4.75Mn1.25 was choosed to be our basic composition. Through the method of 1273K 168h annealing treatment, composition optimization and reducing stoichiometry ratio of alloys, the feasibility of improving the alloy's comprehensive electrochemical properties was investigated.Neutron diffraction and electrochemical behavior of LaNi4.75Mn1.25 annealing and quenching alloys showed that the element Mn in the alloy may influence the electrochemical cycle stability of metal hydride electrode by occupying two atom site in the lattice: (1) dumbbells pairs of B-type atoms occupying the atom site 2e (2) occupation of atom site 3g , increase in amount of Mn at 3g site will do good to the cycle stability of metal hydride electrode in some extent.The capacity of over stoichiometric metal hydride electrodes is in relationship with the extent of over-stoichiometry, the atom sort and its amount. On the one hand, the amount of dumbbell pairs of B-type atoms will decreases the amount of H atom occupying interstitial site 6m; on the other hand , the difference of atom size, the influence of electron structure of alloying elements, the variation in thermodynamics and kinetics of absorption and desorption processes will all affect the electrochemical capacity.The experimental result of optimizing B-type elements of the alloy indicated using less transition elements (Cu, Fe, Cr, Sn) to substitute for Ni of alloy LaNi4.75Mn1.25 improved the cycle stability of metal hydride electrode, but some of them suffer from decrease of electrochemical capacity. Meanwhile, when using these alloying elements to substitute for element Mn will reduce the cycle stability of metal hydride electrodes greatly, but increase the maximum cycle capacity of hydride electrodes. The experimental result also indicated when substituting Ce, Pr, Nd.for Ni will improve the comprehensive electrochemical performances. Ce, Nd can benefit the cycle stability of the hydride electrodes, while Pr can improve the electrochemical capacity of hydride electrodes.The result of electrochemical measurement of LaNi4.68Mn0.93 indicated decrease in the stoichiometry of LaNi4.75Mn1.25 can increase the electrochemical capacity. The electrochemical performances of LaNi4.48Cuo.2Mn0.93 indicated that adopting lowerstoichiometry and less B-site element such as Cu substituting for Ni of LaNi4.75Mn1.25 could achieve better comprehensive electrochemical properties.