Phase Structure and Electrochemical Performances of La0.63Gd0.2Mg0.17Ni3.0-xCo0.3Alx (x=0.0, 0.1, 0.2, 0.3, 0.4) Alloys

The influences of Al substitution for Ni on the phase abundance, structures and electrochemical properties of La0.63Gd0.2Mg0.17Ni3.0-xCo0.3Alx (x = 0.0, 0.1, 0.2, 0.3, 0.4) alloys have been investigated. The main phase of Al-free base alloy is Ce2Ni7-type phase, Gd2Co7-type phase and CeNi3-type phase. After a little Al substitution, AB(3) phase shifts to A(2)B(7) phase. Further Al addition promotes the formation of CaCus-type phase over the A(2)B(7)-type phase. The sample of x = 0.1 (AB(3) to A(2)B(7)) increases cycling stability and its discharge capacity almost unchanged. The further addition of Al (A(2)B(7)( )to CaCus) still increases cycling stability, but decreases the maximum discharge capacity and high rate dischargeability. The substitution of Al elements increases the phase abundance of A(2)B(7)-type or CaCus-type so as to improve the cycling stability. The ability of phase pulverization resistance of the metal hydride alloy at the negative electrode appeared to be the intrinsic reason of failure mode of this series of alloys.