Electrochemical and In Situ Neutron Diffraction Investigations of La‐Ni‐Al‐H Alloys

The performance of selected LaNi{sub 5{minus}y}Al{sub y} hydride electrodes was studied by extensive electrochemical measurements and in situ neutron-diffraction measurements of the deuterated electrode (MD{sub x}) during electrochemical charge-discharge cycles. A small addition of aluminum increased the capacity tenfold under ambient conditions. Increased cell impedance and reduced capacity were noted through the cycle life of LaNi{sub 5{minus}y}Al{sub y}H{sub x}/NiO(OH) cells and were found to be associated with the corrosion and leaching of aluminum from the alloy. A high aluminum content alloy (y = 0.6), however, compensated for the corrosion loss of aluminum by achieving a longer cycle life than that of a low-aluminum-content alloy (y = 0.12). In situ neutron diffraction indicated that only alpha phase was present in the low-aluminum-content alloy, LaNi{sub 4.88}Al{sub 0.12}D{sub 1.1}, while both alpha and beta phases were present in LaNi{sub 4.4}Al{sub 0.6}D{sub 1.8}, the fully charged state. With in situ neutron-diffraction measurements, the absolute values of x in the MD{sub x} formula can be determined for various charge/discharge states, while the coulometry of cell cycling measures only the change in x.