Study On The Preparation Of3D Flower-like Metal Oxides Nanomaterials And Their Electrochemical Performance

Metal oxide nanomaterials have many advantages, such as high capacity, lowcost, good stability and so on, which are widely used as lithium ion battery a nd supercapacitor electrode materials, furthermore, they are becoming the most promisingcandidates in future instead of carbon materials used for lithium storage andcapacitance. Performance of metal oxide nanomaterials depends largely on theirmorphology and size, so it can improve their performance to a certain extent bycontrolling the synthesis of nanoscale size and different shapes. In this paper, wesynthetized nanomaterials through a simple hydrothermal method. And we used twoways to improve the performance of lithium ion batteries and supercapacitors, throughcontrolling nanoscale morphology structure and the synthesis of multivariatecomposite metal materials. Our research work mainly is as these following aspects.In chapter3, we synthesized the3D flower-like Ni(OH)2hierarchicalarchitectures by using nickel acetate, ethanol amine, and deionized water as rawmaterials. SEM and TEM show3D flower-like Ni(OH)2hierarchical architecturesconsisting of many thin self-assembly nano-layers, whose diameters were about2.5to5μm and thickness of nano-slice was about20nm. Our experiments have proved thatthe form of a complete3D flower-like hierarchical architectures lie in the choice ofalkali and the control of concentration, then we put forward a kind of acceptableformation mechanism of3D flower-like hierarchical architectures. In2M KOHsolution, nickel foam as conductive base, in current density of2A g-1and voltagerange of0-0.65V for performance of supercapacitor tests, which exhibit areal specificcapacitance value of around1.51F cm-2, and mass specific capacitance value of725Fg-1. Then mass specific capacity can still keep retention of about96%after about2000cycles in current density of5A g-1.In chapter4,3D flower-like Ni(OH)2precursor was firstly synthesized througha common simple hydrothermal method, and then porous3D flower-like NiOhierarchical architectures can obtain after high temperature pyrolysis of Ni(OH)2precursor. SEM and TEM show these petals of3D flower-like NiO hierarchicalarchitectures distribute many irregular holes, at the same time, the BET analysisshows that the nano holes become larger, specific surface area decreases and thecrystalline also unceasingly to enhance by XRD analysis with increas ing annealing temperature (300,400,500℃). Used as negative electrode material of lithium ionbatteries, these NiO nanomaterials annealed at three different temperature displaydifferent lithium storagy properties, which shows that the performance of mat erialmainly depends on their structure, crystalline and specific surface area.In chapter5, NiCo2O4flower-like microspheres were prepared by using binarymixed salt consisted of nickel acetate and cobalt acetate as main raw materialsthrough a low temperature hydrothermal method. And SEM shows that themorphology of flower-like microspheres are relatively uniform, whose diameterdistribution range from3to4μm. Quite a lot of holes on the piece of microspherescan be clearly observed after annealed at300℃and no collapse occurs of thesemicrospheres. The nanometer materials are abtaind after annealed and applied assupercapacitors electrode materials, they show good electrochemical performance,when in the current density of2A g-1, mass specific capacity is up to1339F g-1,corresponding to the areal specific capacitance value of1.71F cm-2. Then massspecific capacity can still keep retention of about75%after more than1200cycles incurrent density of5A g-1, and the coulombic efficiency is close to100%.