NEUTRON POWDER DIFFRACTION OF OPERATING ELECTROCHEMICAL CELLS CONTAINING LaNi_5-yAl_yD_x ELECTRODES G. L. Burr(IPNS), J. W. Richardson(IPNS), J. M. Carpenter(IPNS), W. Peng(CMT), L. Redey(CMT), A. N. Jansen(CMT), Argonne National Laboratory. Argonne, IL 60439, USA

Lanthanum-nickel hydride(LaNi₅D_x) has been of interest as a battery material because of the ability of the intermetallic alloy to absorb large amounts of hydrogen(deuterium). It has been shown that substitution of some of the nickel with aluminum will increase the capacity of the electrode ten-fold. Rietveld profile refinements of neutron powder diffraction data on operating electrochemical cells have been performed to gain insight into the relationship between structural and electrochemical phenomena.

Our neutron powder diffraction studies on the aluminum substituted alloy indicate that aluminum preferentially substitutes into one available nickel site. Also, the addition of aluminum into the alloy leads to significant strain, as determined from the difference in peak broadening over that of the LaNi₅ alloy.

The working cell consists of a rolled LaNi_5-yAl_y electrode with a NiO(OD) counterelectrode, positioned outside of the neutron beam, in a KOD/D₂O electrolyte solution, all in a quartz tube. Contributions from the electrolyte and quartz tube are modeled by the Rietveld program.

Refinement of deuterium occupancy in a LaNi_5-yAl_y electrode indicates that the alpha phase(where x is small) in LaNi_4.88Al_0.12D_x can accept much more deuterium than the alpha phase for LaNi₅D_x(x = 1.2 versus 0.5 for LaNi₅D_x). No additional detuerium sites were identified. This is indicative of the aluminum contibuting additional stability to deuterium in present sites. The Rietveld refinement was able to show that the deuteriums were preferentially loaded in sites near the aluminum.

A slow and steady decrease in the deuterium concentration(x) during a discharging cycle of a LaNi_4.88Al_0.12D_x cell was observed. Also cell volume in the same cycle also illustrated a similar decrease. The stress associated with the added aluminum is also present in the deuterated samples.

This presentation will focus on several LaNi_5-yAl_y alloys and how the structure effects the electrochemical loading of deuterium. The structural results observed in each step of the deuterium loading will also be presented.