Different additives-substituted α-nickel hydroxide prepared by urea decomposition

Pure Ni(OH)(2), Al-substituted, Co-substituted, Al and Co co-substituted alpha-Ni(OH)(2) were prepared by homogeneous precipitation from nickel nitrate solution in the presence of urea. The physical properties of the samples with different additives were examined by XRD and SEM. The XRD results show that the Ni(OH)(2) samples with different additives prepared by this method are typical a-phases. The SEM results show that the pure Ni(OH)(2) and Co-substituted sample display spherical particles with some degree of agglomeration. However, Al-substituted sample and Al and Co co-substituted sample are the aggregates of irregularly shaped particles. The results of galvanostatic charge-discharge experiments show that the addition of Co2+ decreases the discharge potential, but the addition of Al3+ and co-doping of Al3+ and Co2+ increase the discharge potential. The cycle stability of Al and Co co-substituted alpha-Ni(OH)(2) is obviously improved compared with Al-substituted alpha-Ni(OH)(2). The results of diffusion coefficient of proton (DH+) experiment show that the DH+ values at different depth of discharge (DOD) are increased markedly by the doping of Al3+ or the co-doping of Al3+ and Co2+ and decreased by the doping of Co2+. The electrochemical transfer resistance (R-t) value of Co-substituted sample increases at first and then decreases with the increase of DOD. However, R-t increases with the increase of DOD for other samples. (C) 2004 Elsevier Ltd. All rights reserved.