Phase transformation in the charge-discharge process and the structural analysis by synchrotron XAFS and XRD for nickel hydroxide electrode

Abstract

The detailed phase transformation in the charge-discharge process for the nickel hydroxide electrode have been examined by using the high-energy synchrotron X-ray absorption fine structure (XAFS) and X-ray diffraction (XRD). The structural refinement for the ß-Ni(OH)2 and the ß-NiOOH have been done successfully on the basis of two phase models of the ideal and fault phases. At 0% of SOC, it was found that the sample consisted of 80% of the ideal ß-Ni(OH)2 phases and 20% of the fault ones. At 100% of SOC, the ideal and fault (3-Ni(OH)2 phases were transformed to the ideal and fault p-NiOOH phases, respectively. It was found that the fault phases contained a larger amount of intercalated potassium ions and H2O (OH-) than the ideal ones. At 150% of SOC, the only ideal ß-NiOOH phases was transformed to the ideal γ-NiOOH phases, accompanied by further intercalation of the potassium ions and H 2O (OH-) into the interlayer.