Study of the structural, thermodynamic and electrochemical properties of LaNi3.55Mn0.4Al0.3(Co1−xFex)0.75 (0 ≤ x ≤ 1) compounds used as negative electrode in Ni-MH batteries

This study concerns the influence of iron for cobalt substitution on the structural, thermodynamic and electrochemical properties of the hydrides of poly-substituted LaNi_3.55Mn_0.4Al_0.3(Co_1?xFe_x)_0.75 (0 ≤ x ≤ 1) alloys used as material for negative electrode in Ni-MH batteries. The Fe substitution leads to an increase of the cell parameter, this increase is linear according to the rate of substitution, and a decrease of the equilibrium pressure in agreement with the geometric law. Nevertheless, it is observed that the Fe substitution leads to a deviation from the linear variation between the logarithm of the pressure and the cell volume observed for Co, Mn and Al for Ni substitution. The Fe for Co substitution leads also to a decrease of the solid–gas and electrochemical capacity.