Capacity loss in Ni-Cd pocket plate batteries. The origin of the second voltage plateau

Electrical testing of batteries, voltammetry and surfaces analysis by X-ray diffraction (XRD) and Fourier transformation infrared (FTIR) were used to investigate the origin of the second voltage plateau. The electrical testin g results show that there is a direct coupling between graphite loss and th e appearance of the second voltage plateau. The graphite loss was shown to increase for float charging at elevated temperatures and high potentials. T he effect of graphite particle size distribution was also investigated Volt ammetry of discharged material, Ni(OH)(2), and charged material, beta-NiOCI H and gamma-NiOOH, in carbon paste showed that the second voltage plateau d id not originate from the redox properties of the material, or the presence of carbonate in the material or in the electrolyte. Therefore, the second voltage plateau is believed to appear whenever an inc.:eased internal resis tance arises, may it be due to graphite loss, swelling or some other factor . (C) 2000 Elsevier Science S.A. All rights reserved.