Investigation On The Structrue And Electrochemical Properties Of AB_3.5-3.8-type R-Y-Ni System Hydrogen Storage Alloys

In order to i mprove the cycle stability of R-Y-Ni hydrogen storage alloys,the A₂B₇-and A₅B₁₉-type hydrogen storage alloys are used as research objects.Different rare earth ele ments are used to optimize the A-ter minal co mposition of the alloy.A large number of materials research methods and electroche mical test methods are used to study the structural and electrochemical properties of the alloys.The influence of the average atomic radius of the A-side element on the structure and electroche mical properties of the alloy is studied.First,a hydrogen storage alloy of A₂B₇-type R_0.3Y_0.7Ni_3.25Mn_0.15Al_0.1?R=Y,La,Pr,Ce,Nd,Gd,Sm?is prepared by vacuum smelting and annealing heat treatment under a high purity Ar atmosphere at 1173K.From the results of the study,the series of annealed alloys are mainly composed of Ce₂Ni₇-type and YNi₃-type phases.Rare-earth elements with different atomic radii have a significant influence on the alloy phase composition and cell volume,and the unit cell volume and Ce in the Ce₂Ni₇-type phase alloy.The regularity of the average atomic radius of the A-side ele ments is the sa me;the phase abundance of the main phase Ce₂Ni₇-type is the highest when the La ele ment par tially replaces the Y element is 90.6%.In addition to the alloy with R=Ce,the a mount of hydrogen absorbed by other alloys increases,the pressure plateau becomes flatter and wider,and the ma ximum electroche mical discharge capacity and cycle stability of the alloy electrode are significantly improved.Whe n R=La,the maxi mum discharge capacity of the alloy electrode is 389.2 mAh/g,and the capacity retention rate S₁₀₀ is 85.72%after 100 cycles of charge and discharge,and its overall electroche mical performa nce is good.Partial substitution of rare earth ele ments with Y can substantially increase the high rate discharge performance of the alloy.Secondly,taking R-Y-Ni A₅B₁₉ hydrogen storage alloy as the research object,we try to use different lanthanide rare earth eleme nts instead of the A ter minal part of the Yele ment.Thephasestructureandelectroche micalpropertiesof R_0.45Y_0.55Ni_3.5Mn_0.2Al_0.1?R=Y,La,Pr,Nd,Sm?series annealed alloys are syste matically studied.The results show that the microstr ucture of the annealed alloys is a multiphase structure mainly composed of Ce₅Co₁₉-type phase,Ce₂Ni₇-type phase and La Ni₅-type phase;The abundance of Ce₅Co₁₉-type phase is the highest when the ele ment is present,and the La Ni₅-type phase is present in the alloy when there is a part of the Nd element at the A terminal.Electrochemical studies show that the addition of lanthanide rare earth eleme nts can obviously increase the discharge capacity and cycle stability of the alloy electrode;when R=La,the maxi mu m discharge capacity of the alloy electrode is 389 mAh/g;when R=Nd,the alloy electrode has the most With good cycle life,the capacity retention rate S₁₀₀ can reach90.0%after 100 cycles of charge and discharge,and it has a good overall electrochemical performance.Partial substitution of yttrium-based rare earth ele ments greatly improves the high rate discharge performance of the alloy.Finally,aiming at the particularity of La element and Nd element in hydrogen storage alloy,an alloy with composition La_0.1Nd_xY_0.9-xNi_3.25Mn_0.15Al_0.1?x=0⁰.6?is designed,and different Nd eleme nts are syste matically studied.The results show that the microstructure of the annealed alloy is a multiphase structure.When x=0⁰.3,the alloy mainly consists of Ce₂Ni₇-type phase and La Ni₅-type phase.Whe n x=0.4⁰.6,the alloy mainly consists of Ce₂Ni₇-type phase and PuNi₃-type phase.The phase abundance of the main phase Ce₂Ni₇-type is the highest at x=0.4.Electroche mical performa nce of the alloy electrodes show that with the increase of rare earth element Nd,the capacity retention rate of the alloy electrode is higher than that of the alloy electrodes without Nd ele ment;when x=0.4,the maxi mum discharge capacity of the alloy electrode is 377.7 m Ah/g and The higher capacity retention rate is 84.16%.At the sa me ti me,the alloy has the best high-rate discharge performance and exhibits excellent overall electrochemical performance.