Effects of particle size and type of conductive additive on the electrode performances of gas atomized AB5-type hydrogen storage alloy

• We study structure and state of gas atomized LaNi4.5Al0.5 powders of three fractions.
• Electrodes of powders of all the fractions show high electrochemical characteristics.
• Hydrogen diffusion coefficients in electrodes of all powder fractions are calculated.
• We propose charge/discharge mechanism and equivalent circuit model for МН electrodes.

The phase composition, morphology, structure, and state of the surface of gas atomized LaNi4.5Al0.5 alloy powders constituting a fine (≤50 μm), a medium (160–316 μm), and a coarse (630–1000 μm) fraction have been investigated. The electrochemical and storage characteristics of electrodes made from these powders with addition of electrolytic copper powder or a carbon composite (1 wt.% carbon nanotubes + 7 wt.% nanosized carbon black) as a conductive additive have been studied. In the work, X-ray diffraction, scanning electron microscopy, electron-probe microanalysis, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and several electrochemical methods have been used. It has been established that, in the initial state, the coarse-fraction gas atomized powders show a better kinetics of the hydrogen exchange reactions and higher discharge capacity (∼300 mA h/g). It is shown that electrodes made from the powders of all the fractions have a good high-rate discharge capability. Hydrogen diffusion coefficients during discharge of the electrodes made from the alloy powders of all the fractions and conductive additives have been calculated. It is shown that, for LaNi4.5Al0.5 alloy electrodes with the composite carbon additive, the hydrogen diffusion coefficients during discharge computed from data obtained by the electrochemical impedance spectroscopy method agree well with those calculated from cyclic current–voltage curves (2–4 × 10−9 cm2/s).