Study On Nano-scale Nickel Hydroxide Used As Electrode Material

Metal hydride nickel (MH-Ni) batteries with high energy density and excellent properties, was widely used in many fields such as electronic industry, communication, computer and electric vehicles. As a positive active material, the performance of nickel hydroxide was the key deciding entire property of MH-Ni batteries. In this paper, nano-scale nickel hydroxide was studied comprehensively from the following four aspects.Firstly, nano-scale nickel hydroxide was prepared with grinding micro Ni(0H)2 byhandwork and ball mill respectively, the effect of grinding on its structure andelectrochemical properties was measured and investigated through X-ray diffraction,TEM, SEM and cyclic voltammetry. Results showed that during grinding nickelhydroxide crystal slipped and broke along (0001) <1120> slip system under shearingstress. Meanwhile the size of crystalline grain decreased along c axis direction. It wasfound that under gentle mechanical grinding, only the crystal lattice constant c value ofnickel hydroxide decreased gradually with time prolonging, under strong mechanicalgrinding, both the crystal lattice constant c value and a value of nickel hydroxidechanged with time. Strong mechanical grinding caused the distortion of crystal latticeand thus increased the electrochemical properties of nickel hydroxide material. Stronggrinding also increased the surface area of synthesis samples, shortened diffuse distanceof protons H+, improved the electric conductivity of electrode material, reduced theimpedance of electrode reaction, and enhanced the reversibility of electrode with theaccelerated intercalation and de-intercalation of protons H+ in nickel hydroxide.However, if the strength and performing time of mechanical grinding were increased tosome degree, the resistance of crystal interface of protons H+ transfer process inelectrode reaction was increased and electrochemical performance of the materialdeclined. The high electric conductivity of electrode caused by grinding accelerated theoxygen evolution reaction and thus reduced the difference between the evolutionoxygen potential and the oxidation potential. As a result, the charge efficiency ofelectrode decreased and the utilization of active material were suffered. Although zincand copper additives did not react with nickel hydroxide during mechanical grindingand each ingredient of samples maintained its own independent structure, the size ofcrystalline grains and grains decreased along with the increase of strength and time ofmechanical grinding. By adding appropriate amount of zinc and copper powder, the oxygen evolution reaction could be inhibited and the charge efficiency of electrode and utilization of active material could be improved. At the same time, the reversibility of electrode reaction was enhanced and the electrochemical performance was improved by doping metal copper powder.Secondly, nano-scale nickel hydroxide was synthesized with micro-emulsion method. By the aid of X-ray diffraction, TEM, SEM, cyclic voltammetry, the effect of the preparation condition of micro-emulsion method on the structure and properties of nickel hydroxide was investigated and the preparation process was optimized by orthogonal test. The result of test showed that Ni(0H)2 of elliptical spheroid form, with the size of grain within 3-15nm, could be gained through micro-emulsion method. The size of crystalline grain could be altered with changing pH value, the consistency of reacting substance, stirring time and stirring degree. The decrease of the crystalline grain size increased the resistance of crystal interface of protons H+ transfer process and reduced the reversibility of electrode reaction of nickel hydroxide, whereas the increase of the crystalline grain size improved the reversibility and the electrochemical performance of nickel hydroxide. The optimal preparation condition of nano-scale -Ni(0H)2 obtained by orthogonal test was that pH value was 10, temperature was 60, the consistency of NaOH was 4mol/dm3, the consistency of NiSO4 was lmol/dm3, preparative stirring time was 30m...