Nickel metal hydride batteries (MH-Ni) with high specific energy and excellent performance are widely used in electronics, communications, computers and other industries, and will also be widely used in the field of electric vehicles. As a positive active substance, the performance of nickel hydroxide is the key to determine the overall performance of MH-Ni batteries. In this paper, nanometer nickel hydroxide is studied comprehensively from the following four aspects: First, nanometer nickel hydroxide is prepared by grinding micron grade nickel hydroxide by hand and ball mill, and the influence of grinding on the structure and properties of nickel hydroxide is studied by X-ray diffractometer, scanning electron microscope, transmission electron microscope and cyclic voltammetry curve testing device. The results show that during the grinding process, the nickel hydroxide crystal is broken along (0001): slip system under the action of shear stress, and the grain size along the C-axis decreases continuously. When the mechanical grinding intensity is not large, the lattice constant c value of nickel hydroxide cell gradually decreases with the extension of time, and under high intensity mechanical grinding, not only the lattice constant c value of nickel hydroxide changes with time, but also the a value decreases. High intensity mechanical grinding results in lattice distortion and increases the electrochemical activity of Ni(OH)_2 materials. With the grinding process, the grain size and particle size of the sample decrease, the specific surface area of the material increases, the diffusion path of proton H~+ is shortened, the conductivity of the electrode is improved, the reaction impedance of the electrode is reduced, and the insertion and removal of proton H~+ in Ni(OH)_2 are promoted, and the reversibility of the electrode is improved. However, when the intensity and time of mechanical grinding increase to a certain extent, with the continuous reduction of the grain size of nickel hydroxide, the grain boundary resistance of the proton transfer process in the electrode reaction will increase, and the electrochemical performance of the material will deteriorate. The increase of electrode conductivity also promoted the oxygen evolution reaction of the electrode, reduced the difference between the oxygen evolution peak potential and the oxidation peak potential, and reduced the charging efficiency of the nickel hydroxide electrode and the utilization rate of active substances. Mechanical grinding does not cause the reaction between zinc and copper additives and nickel hydroxide, after grinding, each component in the sample maintains its own independent structure, but their grain size and particle size decrease with the increase of grinding time and intensity. Adding appropriate amount of zinc powder and copper powder can inhibit the oxygen evolution reaction of nickel hydroxide electrode, improve the charging efficiency of electrode and the utilization rate of active substance. At the same time, copper can also improve the reversibility of the electrode reaction and improve the electrochemical activity of nickel hydroxide. Second, nanometer nickel hydroxide was prepared by microemulsion method. The influence of synthesis conditions on the structure and properties of nickel hydroxide was studied by X-ray diffraction, transmission electron microscopy and cyclic voltammetry. The synthesis conditions were optimized by orthogonal experiment. The experimental results show that β-type nickel hydroxide with particle size from 3 nm to 15nm can be synthesized by microemulsion method. The grain size of nickel hydroxide will change with the change of pH, temperature, reactant concentration, stirring time and stirring intensity during synthesis. With the decrease of grain size, the grain boundary resistance of proton H~+ increases, and the reversibility of nickel hydroxide electrode reaction decreases. Conversely, the reversibility is improved, and the electrochemical properties of nickel hydroxide are improved. The optimum conditions for preparing nanometer β-type nickel hydroxide were as follows :pH 10, temperature 60℃, sodium hydroxide concentration 4mol/ dm-3, nickel sulfate concentration lmoFdm3, synthesis stirring time 30min and synthesis stirring intensity medium to strong. Nano nickel hydroxide with similar grain size and particle size can be prepared by mechanical grinding and microemulsion method, but the nano nickel hydroxide synthesized by microemulsion method has serious lattice distortion, which is beneficial to the transfer of proton H+ in the electrode material, promote the electrode reaction, and thus improve the electrochemical activity of nickel hydroxide. Therefore, the microemulsion method is an advantageous method for the synthesis of nanometer nickel hydroxide for batteries. Third, the effects of zinc and calcium additives on the structure and properties of nanoscale nickel hydroxide were studied by X-ray diffraction, transmission electron microscopy, cyclic voltammetry and constant current charge-discharge experiments. The results show that the zinc added by mechanical mixing coexists with nickel hydroxide in the form of metal element, and the structure of nickel hydroxide is not affected. Because zinc is a good conductor, the addition of zinc improves the electrical conductivity of nickel hydroxide, improves its electrochemical performance, and also increases the specific discharge capacity. When zinc was added by coating and co-precipitation, Zspear-Z + replaced part of Niz+ into the nickel hydroxide structure, forming P-Ni,-x Znx(oH)2. The addition of zinc distorted the crystal structure, promoted the transfer of proton H+ in the electrode material, improved the reversibility of the nickel hydroxide electrode reaction, and increased the specific discharge capacity. With the increase of zinc addition, the defects of nickel hydroxide crystals increase, which is more conducive to the transfer of proton H 10. The electrochemical properties of nickel hydroxide are constantly improved, and the specific discharge capacity of the electrode is also increased. However, when the amount of zinc increases to a certain limit, the performance of nickel hydroxide will be deteriorated and the specific discharge capacity will be reduced due to the excessive reduction of the active component of nickel. The optimum amount of zinc added by coprecipitation is 2.5%. Adding CaO and CaCO3 in the way of “pre-precipitation” and “post-precipitation” does not affect the structure of nickel hydroxide, but Cao and CaCO3 mixed in nickel hydroxide will cause defects in the crystal, promote the transfer of proton H+ in the electrode material, improve the reversibility of the nickel hydroxide electrode reaction, and increase the specific discharge capacity. When the addition of Cao and CaCO3 is greater than 1%, the performance of nickel hydroxide deteriorates and the specific discharge capacity decreases due to the reduction of the effective composition of nickel. Mechanical mixing of CaO and CaCO3 can increase the grain size of the composite, reduce the grain boundary resistance during proton H 10 transfer, improve the electrochemical performance of nickel hydroxide, and increase the specific discharge capacity. Fourthly, the electronic structures of nickel hydroxide and doped nickel hydroxide were studied by DV Xa method in quantum chemistry, in order to theoretically understand the structural characteristics of nickel hydroxide and the influence of doped elements on its structure and properties. It is found that nickel, oxygen and hydrogen atoms in nickel hydroxide are only partially charged, indicating that nickel hydroxide is not a typical ionic crystal, and the chemical bonds in its structure have strong covalence. Nickel hydroxide is formed mainly by the strong interaction between nickel atoms and oxygen atoms, and the hydrogen atom is not tightly bound to the system, so it can be freely removed and embedded. The removal of hydrogen does not cause the structure of nickel hydroxide to change, but can still maintain the original layered hexagonal structure, and the net charge number of nickel atoms increases.
13
6月
