Electrochemical hydrogenation of LaY2Ni9 anode at C/3 and C/10 discharge rates for nickel-metal hydride batteries

The electrochemical hydrogenation of the LaY₂Ni₉ alloy as a negative electrode material of a nickel-metal hydride accumulator has been investigated at C/3 and C/10 rates. For this case, several electrochemical methods such as the galvanostatic charging and discharging (chronopotentiometry), the constant potential discharge (chronoamperometry), and the cyclic voltametry were used to investigate the hydrogen absorption-desorption and electrochemical properties. The decrease of the discharge rate makes the maximum discharge capacity greater and activation cycle number smaller. The evolution of the potential difference with the decrease of the discharge rate can be correlated with both the maximum discharge capacity and the cycle number of activation. The electrochemical discharge capacity undergoes an important increase during first cycles attributed to the activation of the alloy, then it decay gradually with increasing cycling. This decreasing becomes more important with C/3 rate. The evolution of the redox parameters and the diffusion coefficient (D_H/a²) is correlated with the activation phenomenon which confirm the good results obtained by the C/10 rate, knowing that the cycling plays a role of stripping the surface of the electrode, that is to say the removal of a continuous manner of oxides from the surface of the electrode, engendering a reduction of its thickness.