| With increasing requirements for the high-performance secondary batteries withno environmental pollution, the Ni/MH batteries industry underwent a rapiddevelopment in recent years. As required, the performance of the nickel electrodes inNi/MH batteries should be improved. Based on the review of nickel electrodes, anickel hydroxide/carbon composite was synthesized by co-precipitation method. Themicrostructure, morphology and electrochemical properties of the synthesizedmaterials were discussed. In addition, the effects and mechanisms of some additiveson the nickel electrodes were investigated.In chapter 3, nickel hydroxide/carbon composite was synthesized byco-precipitation method. X-ray diffraction (XRD) showed that the as-synthesizedNi(OH)2 had aβ-type crystal structure. SEM investigation showed that the nickelhydroxide powders were spherical with unique three-dimensional petal shape. Athigh-rate discharge conditions, the Ni(OH)2/C composite presented excellent cyclingstability, high discharge capacity and high mean voltage of discharge. The dischargecapacity and the mean discharge voltage of Ni(OH)2/C composite were about 281mAh/g and 0.303V (vs. Hg/HgO) at 1 C-rate, 273 mAh/g and 0.296 V at 5 C-rate,250 mAh/g and 0.292 V at 10 C-rate, respectively. The cyclic voltammetry (CV)measurements and the electrochemical impedance spectroscopy (EIS) revealed thatthe Ni(OH)2/C composite exhibited good electrochemical reversibility and theformation ofγ-NiOOH during the charge/discharge processes was prevented.In chapter 4, cobalt sulfate heptahydrate (CoSO4·7H2O, CSH) was used as theadditive of the nickel electrode (β-Ni(OH)2) of nickel-metal hydride battery. Theresults showed thatβ-Ni(OH)2 electrodes with CSH had better redox reversibility,much lower oxidation potential of Ni(Ⅱ) and much higher reduction potential than thecorresponding oxidation state, as compared to the electrodes without additive. XRDmeasurements showed that COSO4·7H2O was transformed into CoOOH aftercharge/discharge cycles, which not only lowered the ohmic resistance of the electrode,but also improved the utility ofβ-Ni(OH)2 active materials. The electrochemicalimpedance spectroscopy (EIS) revealed that the charge transfer resistance and theproton diffusion resistance were reduced with the addition of CSH. With the additionof CSH inβ-Ni(OH)2 electrodes, the electrochemical performances including thedischarge capacity and cycle life were improved significantly. It was found that 18.7wt％CSH was a proper amount. In Comparison with CoO additive, CSH may be a promising substitute for CoO in construction of Ni/MH battery with low cost.In chapter 5, some additives for nickel electrode operating under hightemperature were investigated by cyclic voltammetry (CV) measurements. It showedthat TiO2, ZrO2 increased oxygen evolution potential and improved the performanceof nickel hydroxide electrode at high temperature. |
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