Electrochemical Performance Of La Doped Zn/Al-substituted α-Ni(OH)₂ Prepared By Homogeneous Precipitation Method With Urea

This paper summarized the present research situation of the electrode material Ni(OH)2 as positive electrode active material of the MH-Ni battery systemly. Based on the unique electron configuration of rare earth element materials and the 4f electron moving features and some electrochemical functional characteristics of the metal positive ions, through the homogeneous precipitation method with urea, this article studied the technological conditions and the behavior rule of nickel electrode active materialα-Ni(OH)2 prepared by rare earth La doped Zn/Al-substituted. Moreover, the sample material structural features, electrochemical activity and the electrochemical performance were studied. Simultaneously the electrochemical action effect mechanism of the samples as electrode materialα-Ni(OH)2 was discussed.In this paper, we investigated the influence on the performance of electrode material by single factor with the urea content, reaction temperature, reaction time and dispersant. The results show that optimum process conditions of homogeneous precipitation method are that the molar ratio of urea: metal salt is 30:1, the reaction temperature is 90±1℃, and the time of the reaction is 3h, and the drying temperature is 60℃.Zn/Al-substitutedα-Ni(OH)2 samples with doping different La contents were synthesized at optimum processing conditions. The research experimental result indicates that the morphology of samples is the adhesions of numerous sheet and spherical particles with more porous. The microstructure is characterized by the methods such as XRD, Raman, IR, and TG-DSC. The results show that comparing with only Zn/Al-substitutedα-Ni(OH)2, the La doped Zn/Al-substitutedα-nickel hydroxide electrode material have more structure defect and much bigger interlayer distance, and there are much more water molecular and the thermal stability becomes stronger. When the samples power of La doped Zn/Al-substituted were made as the nickel electrode active material, then assembled the MH-Ni simulation battery, the charge/discharge test shows that 5% La doped Zn-substituted sample has a relative high specific capacity (382.85mAh·g-1 at rate of 0.1C), the value of the middle discharge voltage reaches 1.2943V, while the discharge specific capacity reaches 359.85mAh/g at 1.0C and the capacity still remains 91.04% after 30 cycles. In addition, the material electrode of 5% molar ratio La doped Al-substituted sample whose middle discharge voltage 1.2968V is higher, the discharge specific capacity reaches 404.95 mAh/g at 0.1C. And the charge/discharge at the rate of 1.0C test shows that after 30 cycles the capacity still remains 92.14% and it has better structural stability and cycle life at high-rate discharge condition.The research on the electrochemical activity and the electrochemical action effect mechanism of the La doped Zn/Al-substitutedα-nickel hydroxide samples discovery that the number of electrons transferred of the electrode materials are 1.247e and 1.328e in the electrode process, and there are much better charge acceptance and discharge capacity of electron transferred, electrical conductivity and activation performance. Furthermore, the cyclic reversibility of the electrode reaction improves after doping La and the rare earth La has good effect in inhibiting the oxygen evolution reaction of sample electrode, reducing the electrode reaction of the electrochemical polarization and ohmic resistance, and increasing the discharge voltage.