The influence of Mg substitution on the phase structure and electrochemical properties of Nd1−xMgxNi3 (x = 0.10-0.50) alloys

In this paper, Nd1−xMgxNi3 (x = 0.10-0.50) alloys as anode electrode materials of nickel metal hydride batteries were prepared by the powder sintering method. The solid solubility of Mg and electrochemical properties of the Nd1−xMgxNi3 (x = 0.10-0.50) alloys were studied. It is found that when x increases from 0.1 to 0.36, the multiphase structure with Ce2Ni7-, PuNi3- and MgCu4Sn-type phases of the alloy changes to PuNi3-type single-phase structure. As x further increases to 0.5, the extra Mg can not further enter into the PuNi3-type structure and forms an MgNi2 secondary phase. It indicates that the maximum solid solubility of Mg in the PuNi3-type (Nd,Mg)Ni3 phase is 0.36 at 1183 K. Electrochemical studies show the PuNi3-type single-phase Nd0.64Mg0.36Ni3 alloy exhibits good discharge capacity, close to 341 mAh g−1, and superior high rate dischargeability, which remains 151 mAh g−1 at a current density of 1800 mA g−1, respectively. Especially, the single-phase alloy exhibits excellent cycling property, which 288 mAh g−1 retained after cycling 100 cycles. The content of Mg is a key factor that affects the phase structure and electrochemical properties for Nd-Mg-Ni-based alloy. Less than or more than the maximum solid solubility value of Mg are disadvantageous to the cycling stability of the alloy due to the formation of impurity phase in the alloys.