The Study Of Electrochemical Properties Of Ni（OH）₂and Its Composite Materials

Supercapacitor is a new type of energy storage devices environmentally friendly,filling the gap between electrostatic capacitor and battery and have become the hotspot inthe study of new types of energy storage devices. Because of its special structure andmorphology, Ni(OH)2has superior performance in charge storage. But it is asemiconductor， so as the electrode material， Ni(OH)2should be improved in itsconductivity firstly. The study prepared Ni(OH)2with different morphology andcrystallinity through different ways and used expanded graphite (EG) to improve it. XRD,SEM and EDS techniques were used to characterize the phase and structure of thematerials. Cyclic Voltammegry, AC Impedance and Chronopotentiometry technologywere used to investigate its electrochemical properties. Details were as follows:(1) With urea, sodium hydroxide and ammonia as precipitants and usingmicrowave-hydrothermal synthesis method to synthesize Ni(OH)2, we got the porous lobestructure Ni(OH)2with high specific area by urea and the Ni(OH)2of axiolitic, nanowiremixing nanorod structure by sodium hydroxide and ammonia with different sizes.Prepared by chemical precipitation method with ammonia as precipitant, Ni(OH)2hadnanorod structure. The Ni(OH)2synthesized by microwave-hydrothermal synthesismethod had smaller size than chemical precipitation method. Electrochemical testsshowed that: as electrode materials, Ni(OH)2presented the pseudo capacitance propertiesmainly; The specific capacitance of Ni(OH)2with lobe structure reached up to820F/g, andits impedance was smaller. The highest specific capacitance of Ni(OH)2of axiolitic,nanowire (nanorod) structure was639F/g. Ni(OH)2with lobe structure had a longer timeof discharge than that with acicular structure.(2) Using the hydrothermal method, splat cooling precipitation and single-modemicrowave synthesis respectively, the disorder of Ni(OH)2in turn increased.Electrochemical tests showed that: the higher the disorder degree of Ni(OH)2was, thegreater the specific capacitance was and the longer the discharge time was. The maximumof specific capacitance was649F/g. (3) Ni(OH)2was deposited on the surface of expanded graphite by chemicalprecipitation. We got Ni(OH)2/EG composite materials with different amount of Ni(OH)2by changing the precursor solution concentration. Electrochemical tests showed that: withthe increase of the Ni(OH)2loading, the specific capacitance increased and the specificcapacitance of the composite was on a declining curve after reaching its extreme value.The reason was that EG couldn’t play the role of electric conduction. The specificcapacitance of Ni(OH)2/EG composite materials could reach up to1432F/g. It was1.75times as large as the highest value of Ni(OH)2. Obviously, EG played an important role inthe improvement of the electrochemical performance of Ni(OH)2.