The Preparation And Electrochemical Performance Research Of Al-substituted Nickel Hydroxide As Electrode Material

Nickel hydroxide has attracted considerable attentions because of its excellentelectrochemical properties and potential applications in rechargeable Ni-based alkalinebatteries. Based on its high theoretical specific capacitance, good cyclic stability, lowenvironmental pollution and so forth, nickel hydroxide is recognized as a promisingelectrode material for electrochemical capacitors. In this paper, the electrochemicalproperties of Ni（OH）₂in the MH-Ni battery and electrochemical capacitors arecomprehensively studied.In this study, different small contents of Al-substituted Ni（OH）₂directly grown onnickel foam were prepared via an in situ method by using a mixed aqueous solution ofnickel nitrate, aluminum nitrate and ammonia. Their structure，composition and surfacemorphology are characterized by X-ray diffraction （XRD）, scanning electron microscopy（SEM） and transmission electron microscopy （TEM）. The results show that7%Al-containing Ni（OH）₂exists α and β phases with the average crystallite size of15nm. Thenanosheets are composed of a large number of thin slices with the thickness of100nm andthey are staggered vertically to form an open and microporous network structure. The actualAl contents of the different samples are measured by Energy dispersive X-ray spectrum（EDS） and inductively coupled plasma mass spectrometry （ICP-MS）. The results show theactual Al contents of the different samples are consistent with the Al contents in initialreaction solution in the range of allowable error.When different contents of Al-substituted Ni（OH）₂are applied in MH-Ni battery, theirelectrochemical performances are investigated by cyclic voltammetry, electrochemicalimpedance spectroscopy and galvanostatic charge-discharge tests. The results show that7%Al-containing Ni（OH）₂exhibits highest discharge specific capacity of324.5mAh·g-1，306.7mAh·g-1and297.4mAh·g-1at the charge-discharge rate of0.1C,1C and2C, respectively.The discharge specific capacity maintains298mAh·g-1after200cycles at1C. The dischargecapacity of as-prepared7%Al-containing Ni（OH）₂electrode can overtake the theoreticalspecific capacity of289mAh·g-1for MH-Ni battery. Therefore, a drastic improvement in thecapacitive characteristics by the addition of Al probably benefits from a mixture structurewith α and β phases. When different contents of Al-substituted Ni（OH）₂are applied in electrochemicalcapacitors, the performances are studied by electrochemical methods. Results show that thesample with7%（in mol） Al substitution shows pseudocapacitive behavior with maximumspecific capacitance of2358.4F·g-1at a current density of1A·g-1, while specificcapacitance is593.5F·g-1at a current density of20A·g-1. The specific capacitance is closeto theoretical specific capacitance of2601F·g-1of β-Ni（OH）₂. After500cycles at1A·g-1,the specific capacitance maintains1791.5F·g-1with capacitance retention of77.9%. Hence,after the addition of Al, the specific capacitance can significantly improve than pureβ-Ni（OH）₂phase.