Deciphering the Structural Transformations during Nickel Oxyhydroxide Electrode Operation

The phases present in the positive nickel oxyhydroxide electrode (NOE) under standard operation conditions, that is, β-Ni(OH)2 and β-NiOOH, were studied by powder diffraction using the Rietveld method extended to handle a range of microstructural models and high-resolution transmission electron microscopy under mild conditions. The results highlight that, contrary to what was believed, a change in the oxygen layers stacking sequence along the c-axis in β-NiOOH (ABCA) compared to β-Ni(OH)2 (ABAB) takes place, which indicates that battery positive electrode material undergoes reversible structural transformations during the nickel battery charge and discharge processes.