W. Peng et al., ELECTROCHEMICAL AND IN-SITU NEUTRON-DIFFRACTION INVESTIGATIONS OF LO-NI-AL-H ALLOYS, Journal of the Electrochemical Society, 144(11), 1997, pp. 3836-3844
The performance of selected LaNi5-yAly hydride electrodes was studied
by extensive electrochemical measurements and in situ neutron-diffract
ion measurements of the deuterated electrode (MDx) during electrochemi
cal charge-discharge cycles. A small addition of aluminum increased th
e capacity tenfold under ambient conditions. Increased cell impedance
and reduced capacity were noted through the cycle life of LaNi5-yAlyHx
/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 ach
ieving 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, LaNi4.88Al0.12D1.1, wh
ile both alpha and beta phases were present in LaNi4.4Al0.6D1.8, the f
ully charged state. With in situ neutron-diffraction measurements, the
absolute values of x in the MDx formula can be determined for various
charge/discharge states, while the coulometry of cell cycling measure
s only the change in x.