Physicochemical properties and electrochemical performance of Al-substituted α-Ni-(OH)2 with additives for Ni-metal hydride batteries

Al-substituted alpha-Ni(OH)(2) coprecipitated with the additives Mg2+ and Co2+ was prepared by a complexation-coprecipitation method. The physical properties of Al-substituted alpha-Ni(OH)(2) samples containing different amounts of Mg2+ or Co2+ were examined by X-ray diffraction, AES and ICP. The effects of Mg2+ and Co2+ on the electrochemical performance of Al-substituted alpha-Ni(OH)(2) such as charge-discharge and diffusion coefficient of the proton (DH+) measured by current pulse relaxation and cycle life were investigated. The results show that the addition of Mg2+ increases the crystal cell parameters and the charge and discharge potentials and decreases the electrochemical polarization. A higher charge efficiency and cycle life are obtained by the addition of Co2+. The addition of both Mg2+ and Co2+ improves DH+ and the stability in alkaline solution at high temperature. The DH+ and R-t of alpha-Ni(OH)(2) electrode reach their maximum and minimum values at about 50% depth of discharge (DOD) and 75% DOD, respectively. (C) 2003 The Electrochemical Society.