Synthesis And Research Of Electrochemical Performance Of Spherical α-Ni（OH）₂

As an important green secondary energy source,nickel-metal hydride（Ni/MH）batteries have the characteristics of safety,environmental protection,low price and high capacity,which are widely used in civilian and military industries.As a positive electrode material for nickel-metal hydride batteries,β-Ni（OH）₂has been industrialized because of its stable chemical properties and convenient synthesis.It has also been widely studied and applied in the fields of batteries and electrocatalysis.β-Ni（OH）₂can be converted toβ-Ni OOH during the charging process.At this time,only 1 mol of electrons are transferred,so its theoretical capacity is only 289 m Ah/g.Forα-Ni（OH）₂,it can be converted toγ-Ni OOH during charging,the electron transfer number is 1.67 mol,and the theoretical capacity is as high as 482 m Ah/g.However,due to the shortcomings of the material itself,such as instability and weak conductivity,restrict the commercial application of the material.Therefore,research and development of stableα-Ni（OH）₂cathode materials will be important for the further improvement of the performance of nickel-hydrogen batteries.In this paper,nickel nitrate and urea are used as basic raw materials,α-Ni（OH）₂is synthesized by hydrothermal method,andα-Ni（OH）₂is monoatomically doped with single metal elements（Co,Zn and Mn）are explored.The influence of single metal elements doping onα-Ni（OH）₂crystal form,morphology,interlayer ions and electrochemical properties.The study found that the doping of different ions has a significant impact on the crystal shape,morphology and electrochemical properties of the final product,and the doped product maintains the structure of the pureα-Ni（OH）₂crystal structure,and all samples have a good spherical morphology.（1）Co element itself has good conductivity.When it enters the Ni（OH）₂crystal lattice,and construct a good conductive network,thereby effectively reducing the internal resistance of the material itself and effectively improving the utilization of Ni atoms.We found that with the addition of Co,the resistance value（Rct）of the product has a significant downward trend,and the discharge capacity of 7 mol%Co-dopedα-Ni（OH）₂at 1 C can reach 363.5 m Ah/g,and after cycling to 350 cycles,its discharge capacity can still maintain 273.3 m Ah/g.（2）When Zn enters the nickel hydroxide crystal lattice,it will effectively strengthen the Ni–O bond in the nickel hydroxide crystal lattice,thereby enhancing the stability of the material itself,making it difficult to occurα/βphase structure transition for the nickel hydroxide electrode to be cycled,thereby enhancing the cycle life of the electrode material.Studies have shown that:compared toα-Ni（OH）₂that is not doped or doped with other metal elements,α-Ni（OH）₂doped with Zn has a better discharge system or discharge current density under the same discharge system or current density.High discharge voltage.Among them,α-Ni（OH）₂doped with 3 mol%Zn has a higher discharge voltage platform（1.26V）.This advantage can make this material has a higher level working power in actual use.（3）A group of sphericalα-Ni（OH）₂with Mn instead of Ni was synthesized by hydrothermal method.The difference between the morphology of this group of materials and the first two groups of materials is that the Mn-dopedα-Ni（OH）₂is nanoneedles nucleate first and then grow into balls.Among them,the spherical product doped with 5mol%Mn dopedα-Ni（OH）₂has a larger specific area（200.39 m²/g）,which increases the electroactive sites of the material itself and avoids a large amount of agglomeration of nickel hydroxide,which increases the contact area between electrolyte and electrode material,shortening the OH^–diffusion path during the charge and discharge process,thereby improving its electrochemical performance.When the discharge system is 0.2 C,the sample Ni–Mn5 is assembled into an electrode material,and its discharge capacity can reach 353 m Ah/g.The kinetic test research shows that compared with theα-Ni（OH）₂that is not doped with metal elements.To a certain extent,the electrochemical impedance of the doped with metal elements itself is reduced,and increase the proton diffusion coefficient D,Thereby improving the rate discharge performance ofα-Ni（OH）₂.