Annealing Temperatue on Structural and Electrochemical Property of Mg-free La-Y-Ni Based A₂B₇-type Hydrogen Storage Alloys

Effects of annealing temperature on the microstructure and electrochemical properties of A(2)B(7)-type La0.33Y0.67Ni3.25Mn0.15Al0.1 hydrogen storage alloys were systematically investigated by XRD, SEM, EDS, and electrochemical measurements. Results showed that the alloy was composed of CaCu5-type, 2H-Ce2Ni7-type, 3R-Gd2Co7-type and 3R-Ce5Cu19-type phases. Both abundance and unit cell volume of Ce2Ni7-type phase increased gradually with the anneale temperature increase when the annealing temperature was lower than 950V. CaCu5-type and Gd2Co7-type phases disappeared at 950 degrees C, but both abundance and unit cell volume of the Ce2Ni7-type phase maximized When annealing temperature was higher than 950 degrees C, Ce2Ni7-type phase decreased while Ce5Co10 type phase increased. The alloy, annealed at 950 V had the lowest hydrogen desorption platform pressure (0.0192 similar to 0.087 atm), maximum hydrogen storage capacity (1.35 wt%) and high electrochemical discharge capacity (371 mAh/g) with the maximum capacity retention S(100 )at 89% after 100 cycle. The high rate discharge ability (HRD) of the annealed alloys were significantly improved, the alloy annealed at 950 degrees C had the best performance and HRD 900 was up to 83.4%. These well performances demonstrated that it is the hydrogen diffusion in the alloys that controls the high rate discharge.