Preparation Of Co₃O₄ Nanomaterial With Different Morphologies And Its Supercapacitor Properties

As a new type of e lectric energy storage device,supercapacitor s has the characteristics of high power density,long cycle life,fast charge and discharge speed,wide temperature range and environme ntal fr ie ndliness.It has become another research hotspot after lithium ion battery.Co₃O₄ has become a potentia l supercapacitors electrode materia l due to its abundant reserves,low price and high theoretica l specific capacity?3560 F/g?.The structure and morphology of the electrode materia ls are the key factors determining the perfor mance of supercapacitors.Therefore,the preparation of Co₃O₄ electrode mater ials with d ifferent morphologies is an important way to improve the perfor mance of supercapacitors.In this thesis,a variety of Co₃O₄nanomater ials with different morphologies were prepared by hydrother mal method,carbonization-reoxidation two-step method.The electrochemical properties of Co₃O₄nanomater ials with different morphologies were tested.The main contents inc lude the following three aspects:?1?Spherical Co₃O₄/carbon nano onion?Co₃O₄/CNOs?partic les were successfully prepared by direct carbonization of ionic liquids combined with oxidation.The morphology and structure were characterized by XRD,Raman,SEM,TEM and BET.The results showed that the onion-like carbon film was uniformly coated on the surface of spherical Co₃O₄ nanopartic les.Co₃O₄/CNOs was used as the supercapac itor electrode mater ial,and its specific capacitance rea ch 402.35 F/g at a current density of0.5 A/g;after 9000 cycles at 1.0 A/g,the capacita nce retentio n rate was still as high as76%.The improvement of electrochemica l performance is ma inly attrib uted to the introduction of onion-like carbon film,which not only improves the conductivity of Co₃O₄,but also the inherent gap between onion-like carbon layers can effectively alleviate the volume effect caused by the redox reaction of Co₃O₄,thereby improving the cycle stability of the electrode material.?2?The flower-like Co₃O₄ nanorods?Co₃O₄/NF?were prepared on nickel foam by hydrotherma l method using H₂O₂ as the oxidant.On the one hand,no binder was added during the electrode preparatio n process,the Co₃O₄ nanorods are directly connected to the current collector,so that the conductivity of the entire Co₃O₄/NF electrode was improved;on the other hand,there is a large gap between the flower-like Co₃O₄nanorods,and the electrolyte can fully penetrate into various parts of the electrode,increasing the contact area between the electrolyte and the Co₃O₄,thereby improving the utilization ratio of Co₃O₄.The Co₃O₄/NF was used as the electrode material of supercapacitors,the specific capacitance was as high as 2005.34 F/g at a current dens ity of 0.5 A/g.After 5000 cycles,its capacitance can still mainta in 98%of the initial capacity,ind icating that Co₃O₄/NF has excellent capacitance performance and stable cycle performance.?3?Three different morpho logies of Co₃O₄ precursors were prepared by hydrotherma l methods using NH₄F as morphological regulators.After 300o?oxidation,three different morphologies of Co₃O₄ nano materia ls were obtained.According to the evolution law o f precursor morphology in different reaction stages under different systems,a mecha nism of NH₄F affecting the morphology of precursors was proposed:NH₄F controls the phase and morpho logy of prec ursors by adjusting the pH of hydrotherma l syste m.The electroche mical properties of Co₃O₄ with three different morphologies were tested.The results show that the Co₃O₄ with both hexagona l nanosheets and needle-like nanowires has the highest specific capacita nce?1005.4 F/g?.This was ma inly due to its unique topographical structure:the needle-like nanowires are located at the edges of the hexago nal nanosheets,and the hexagonal nanosheets connected to the foamed nickel are intertwined to for m an intr icate electronic transmiss ion network;The needle-like nanowires are independent of each other,and a large gap is left between the nanowires,which is favorable for the suffic ient penetration of the electrolyte solution,thereby improving the utilizatio n ratio of Co₃O₄.