The Research Of Aluminum Stabilized α-Ni(OH)₂ As New Cathode Electrode Material

α-Ni(OH)2 substituted with different Al contents was prepared by co-precipitation in this paper, and the molar ratios of Al/Ni are 1:3, 1:4, 1:5, 1:8 and 1:10 respectively (termed asα3,α4,α5,α8,α10), with its physical and chemical properties characterized comparing to common spherical Ni(OH)2.XRD tests showed that larger space was found between NiO2 layers ofα-Ni(OH)2 due to intercalated water molecules and anion ions.α-Ni(OH)2 had better thermal stability.α-Ni(OH)2 was found to be composed of flaky and whisker structures, whose radial dimension was in nanometer range. Moreover, more structure defects were found inα-Ni(OH)2. Cyclic voltammetry tests showed thatα-Ni(OH)2 had larger proton diffusion coefficient than spherical Ni(OH)2, which increases with the increase in the aluminium content.Pureα-Ni(OH)2 and pure spherical Ni(OH)2 were applied in the preparation of AA-type MH-Ni batteries, and the electrochemical performances were measured under different conditions. Discharge specific capacity of B-α3, B-α4, B-α5 and B-α8 was 6.4%, 10.4%, 12.8% and 4.2% higher than that of B-sph under 0.2 C discharge test at room temperature. The cyclic behavior of the different nickel electrodes at 0.2C charge-discharge mode exhibited thatα-Ni(OH)2 battery had shorter activation time, and B-α3, B-α4 had better cyclic stability. Discharge specific capacity of B-α8 was geatly faded with increasing cyclic numbers, which may be due to the instability ofα8 sample during charge and discharge.Electrochemical impedance at different states of charge for MH-Ni battery indicated that electrochemical reaction resistance was decreased with increasing state of charge, for the increase of Ni3+ density and activated surface area. Electron transfer number was calculated by the Nernst equation, which exhibited that electron transfer numbers of positive electrodes of B-α3, B-α4, B-α5 and B-α8 were 1.030, 1.140, 1.183 and 1.355 respectively, however, that of B-sph was only 0.774, implying that oxidation number of Ni was above +3 in oxidation process ofα-Ni(OH)2. XRD tests of Ni(OH)2 electrodes after cycle life tests showed that main reductants of positive electrodes forα-Ni(OH)2 battery and spherical Ni(OH)2 battery wereγ-NiOOH andβ-NiOOH respectively, indicating that theα/γcouple is dominant for the positive electrode reaction ofα-Ni(OH)2, however,β(Ⅱ)/β(Ⅲ) is mainly for spherical Ni(OH)2.