Effect of Annealing Treatment on Structure and Electrochemical Properties of New Mg-free Y0.7La0.3Ni3.25Al0.1Mn0.15 Hydrogen Storage Alloys

Mg-free A(2)B, type Y0.7La0.3Ni3.25Al0.1Mn0.15 alloy of La-Y-Ni system was prepared by arc melting and annealed for 24 h in high purity Ar atmosphere at 800-1050 degrees C . X-ray diffraction ( XRD ) , neutron diffraction( ND) , scanning electron microscopy and energy dispersive spectroscopy ( SEM/EDS ) and electrochemical test methods were used to research the influence of annealing temperature on the structure and properties of the alloys. Structural analysis shows that as-cast alloy consists of CaCu5 , Ce5Co19 , Gd2Co7 and Ce2Ni7. As the annealing temperature increases, CaCu5 , Ce5Co19 and Gd2Co7 gradually decrease to disappear, while the phase abundance of Ce2Ni7 main phase increases gradually. When annealing at 900-950 degrees C , the alloy is single-phase Ce2Ni7 structure. When annealing temperature continues to rise, a small amount of PuNi3 phase appears in the alloy. The maximum discharge capacity of the alloy electrodes increases first and then decreases as the annealing temperature increases. It increases from 307. 6 mA . h/g for the as-cast alloy to 393. 1 mA . h/g at the nnealing temperature of 900 degrees C , and then decreases to 366. 4 mA . h/g at the nnealing temperature of 1050 degrees C . The electrochemical cycle stability of alloy electrodes increase with the increase of annealing temperature. After 100 cycles, the electrochemical capacity retention rate ( S-100 ) increases from 66% 14 the as-cast alloys to 88. 5% at the nnealing temperature of 1050 degrees C . When annealing at 900-950 degrees C , the alloy electrodes have better comprehensive electrochemical properties.