Effect Of Elemental Y And Zr Substitution And Heat Treatment On Microstructure And Properties Of AB₅ Type Hydrogen Storage Alloys

AB₅ type hydrogen storage alloy is the mainstream product on the market at present.It takes up the majority of the market share of nickel metal hydride battery anode material.Cobalt is one of the main elemental composition of the AB₅ type hydrogen storage alloy,the cycle stability of the alloy is improved greatly by addition of cobalt.But the price of Co is expensive and the price of cobalt has a rising trend.In order to meet the market needs of nickel-metal hydride batteries and enhance competitiveness,La_0.75Ce_0.25-xZr_x?Ni Mn Al?_5.6?x=0,0.01,0.02,0.03?and(La_0.75Ce_0.25-xY_x)?Ni Mn Al?_5.6?x=0,0.03,0.06,0.09?alloys were prepared by induction melting.The microstructures,activation properties,discharge capacity,cycle life and high rate discharge properties of the alloy were studied by XRD and battery test system.Then the heat treatment process matching the optimum composition was studied.While a low-cost product which meeting the customer's technical specifications?0.2C capacity>320mAh/g,1C cycle capacity retention rate>80%?was finally developed.The results of the study are as following:After the substitution of Zr for Ce,the structure of the alloy did not change,the unit cell volume decreased gradually,and the half-peak width gradually increased.The material cost of x=0.01 sample in the unheated(La_0.75Ce_0.25-xZr_x)?Ni Mn Al?_5.6?x=0,0.01,0.02,0.03?alloys is 82.19 Yuan/kg.The capacity was 332.6 mAh/g,and the capacity retention rate increased from 39.7%to 57.8%after 200 cycles.The alloy has the most advantages in terms of overall cost and performance.The effects of heat treatment temperature and time on the structure and electrochemical properties of the alloy were studied.It was found that the structure of the alloy did not change after the heat treatment,but the degree of crystallization and the lattice parameters of the alloy were slightly different.The alloy has the best performance under the heat treatment condition of 1000°C for 6 h:the capacity of the alloy is 333 mAh/g,the capacity retention rate reaches83.05%after 200 cycles,and the HRD value reaches 88.41%at 5C rate,which meets the customer's performance index.After the substitution of Y for Ce,the phase structure of the alloy remains LaNi5phase,and the half-peak width of the alloy increases first and then decreases.The cost of materials for x=0.03 samples in(La_0.75Ce_0.25-xY_x)?Ni Mn Al?_5.6?x=0,0.03,0.06,0.09?series alloys after heat treatment at 1000?for 8 hours is 83.1 yuan/kg.The capacity of x=0.03 alloy is 333.4 mAh/g,and the high rate discharge performance is optimal.The remaining capacity after 240 cycles is increased from 200.7 mAh/g of the unsubstituted alloy to 241.2 mAh/g.Considering the cost and performance,the x=0.03 alloy is expected to reach the customer's performance index.Therefore,the optimum heat treatment temperature and time of the alloy were studied.It was found that the properties of the alloy reached the optimum after holding for 8 hours at 1000 C.The capacity reached 330 mAh/g,the capacity retention rate reached 80.55%after 240 cycles,and the HRD reached 82.66%at 5C ratio,which meets the customer's performance index.