Microstructural analysis of the ageing of pseudo-binary (Ti,Zr)Ni intermetallic compounds as negative electrodes of Ni-MH batteries

Ageing of Ti1.02−xZrxNi0.98 (0 ≤ x ≤ 0.48) compounds during the electrochemical cycling in aqueous KOH electrolyte has been investigated. Microstructural and chemical characterisation, mostly conducted by transmission electron microscopy, show that for all electrodes their activation results from calendar KOH corrosion. After activation, Zr substituted compounds attain much higher capacity (∼350 mAh g−1) than the binary TiNi compound (∼150 mAh g−1) but their cycle-life is poor. The mechanism of electrode degradation differs for the binary and the substituted compounds. For TiNi, degradation is due to KOH corrosion whereas, for substituted compounds, it mainly results from the loss of electrical contact due to particle pulverisation. For all electrodes, KOH corrosion produces a double surface layer formed by an inner two-phase (Ni–NiO) nanocrystalline layer and an outer (Ti,Zr)O2 amorphous layer.