| Nickel hydroxide is widely used as the positive electrode material of MH-Ni, Cd-Ni, Fe-Ni and Zn-Ni secondary alkaline batteries. The further improvement on the performance of MH-Ni batteries is limited by several problems such as volume expansion and low theoretical capacity inβ-Ni(OH)2. In order to improve the performance of the nickel electrode, nickel hydroxide was modified by the doping of some metal elements such as Mn, Al and Bi, and the effects of the compositions and structures of the samples on their electrochemical performance were investigated in detail.In the third chapter of this thesis, the Mn-substituted Ni(OH)2 samples were prepared by a coprecipitation method, and their structure were characterized by X-ray diffraction(XRD). Their electrochemical performance was also investigated by various electrochemical techniques. The results of XRD indicated that the Ni(0H)2 samples with the Mn contents less than 20% mainly consist ofβ-phase, and the sample with a pure alpha structure can be obtained when the Mn content reaches 28.3%. The results of the electrochemical experiments showed that the Mn-substituted Ni(OH)2 samples manifest high electrochemical cycling stability, and the samples with lower manganese contents exhibit larger discharge capacity and higher discharge potential. It was also found that the doping of Mn obviously increases the oxygen evolution potential and leads to the formation of proton deficiency.In the forth chapter, the Al-substituted Ni(OH)2 samples with various Mn contents were prepared by a coprecipitation method. The samples with Mn display typicalα-phase, and the samples with larger Mn contents have better structural stability in strongly alkaline medium. The doping of Mn improves the charging efficiency, cycle stability and discharge capacity of the Al-substituted Ni(OH)2 electrodes. The sample with Mn 9.3 % shows the highest discharge capacity during the whole electrochemical cycle, and its capacity reaches to 260 mAh g-1 (NEE is 1.1) at the 300th cycle. The ohmic and electrochemical polarizations of the electrodes are markedly decreased by the doping of Mn in Al-substituted Ni(OH)2, and the samples with larger Mn contents show lower electrode polarization.In the fifth chapter of this thesis, the effects of Bi on the electrochemical performance of Mn-substituted Ni(OH)2 were investigated. The results of electrochemical tests showed that the addition of Bi increases the discharge potential and the oxygen evolution potential, and the charging efficiency is also improved. Moreover, it was found that the physical addition of Bi has more obvious effects on the improvement of the electrochemical performance of the samples. The results of EIS showed that the doing of Bi in Mn-substituted Ni(OH)2 increases the ohmic polarization of the electrodes, but effectively decreases their electrochemical polarization.
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