Research On The Technique For Producing Spherical Nickel Oxy-hydroxide

In this thesis, two techNiques-electrochemical oxidation and chemical oxidation, for synthesis NiOOH from Ni(OH)₂, which was an important cathode active material for some primary batteries, e.g. Zn/NiOOH, were investigated systematically. The emphasis was put(?) upon the production of spherical NiOOH by electrolytic oxidation Ni(OH)₂ in the caustic alkali electrolyte. The effects of technology parameters, e.g. the nature and concentration of caustic alkali electrolyte, the electrolyte temperature, the duration of electrolysis time and so on , upon the properties of the produced NiOOH, e.g. oxidation degree, bulk density, tap density, crystal structure etc. were probed by using several methods, such as, powder X-ray diffraction (XRD), scanNing electron microscope (SEM), cyclic voltammetray (CV), chemical analysis, and charge and discharge feature of experimental battery, etc. The main conclusions were as below:1. Comparing with other cell, a divided two compartment cylinder cell separated by membrane with stirring equipment, was more suitable for electrolyzing Ni(OH)₂ to produce NiOOH. The adhesive bonded vinylon fabric cloth could meet the requirement of membrane.2. The impurities toxic to battery performance could not be introduced, using Ni(OH)₂ as source material. The speeds of electrochemical oxidation of Ni(OH)₂ to NiOOH were accelerated by adding some Co(OH)₂ powder in Ni(OH)₂, and it was favor for preventing the formation of γ-NiOOH.3. The nature and concentration of electrolyte affected the crystal structure of the produced NiOOH sigNificantly. When KOH solutions were used as electrolyte, if the concentration was lower than 5.0mol/L, the final product by electrochemical oxidation was 6-NiOOH; while the final product was γ-NiOOH if the concentration was higherthan 5.0mol/L. When NaOH solutions were used as electrolyte, if the concentration was lower than 7.0mol/L, the final product was 6-NiOOH; while the final electrochemical oxidized product was y-NiOOH if the concentration was higher than 7.0mol/L.4. Three components electrolyte contaiNing NaOH, KOH and liOH, has a good conductivity and could prevent the formation of y-NiOOH. The products produced using this electrolyte mainly appeared as B-NiOOH. The determined optimum component was: 4-5mol/LKOH + 4-5mol/LNaOH +20g/LLiOH5. The rates of electrochemical oxidation of Ni(0H)2 to NiOOH were accelerated by pre-immersing Ni(0H)2 in electrolyte before electrolysis. The duration time meeting the requirement of immersion was 1-2 hours.6. As the temperature of the electrolytic process get higher( = SCPC), the electrolytic oxidation speed of the system which use NaOH as electrolyte can get higher gradually. But the electrolytic oxidation speed of the system which use KOH as electrolyte get lower if the temperature of the electrolyse process exceed 6(^0. As the current density get higher, the oxidation speed get higher accordingly, but the current efficiency get lower.7. The result of SEM shown that, spherical 8-NiOOH could be produced by electrochemical oxidizing spherical B-Ni(0H)2. Even at a proper high oxidation degree, using this method, the spherical grain shape ofB-Ni(OH)2 could be preserved quite well in the product of B-NiOOH. Because of the cell volume expansion appeared during the formation of y—NiOOH from the over oxidation of B-NiOOH, the grain shape of spherical y—NiOOH were destroyed greatly.8. Because it is difficult to control the oxidation degree of NiOOH, using chlorine and hypochlorate to oxidize Ni(0H)2, the products produced by chemical oxidation could be easily transformed to y—NiOOH from B-NiOOH. The grains of the product with an irregular shape were easily assembled as colloidal sediment, leading a difficulty for washing.