Synthesis, Characterization And Electrochemical Properties Of Cobalt Base Material, Carbon Material And Their Composite Materials

In this dissertation, LiCoO>2concaved cuboctahedrons were hydrothermally prepared in low temperature reaction kettle, the forming process and phase composition of the product were discussed, they were studied as cathode materials in the charge/discharge experiments of lithium ion batteries. LiNi1/3Co1/3Mn1/3O2/carbon core-shell structure and Ca9Co12O28nano-materials were synthesized by the improved Pechini method, we preliminary studied the advantage and scalable in the preparation of nano-materials by this synthesis method. We also systematic studied the effects such as nanometer size, uniform coating of carbon, carbon layer thickness and calcining temperature on the electrochemical performances. In addition, hollow carbon octahedra and four kinds of carbon nanosheets with different morphologies were prepared in the autoclave. We discussed their possible formation mechanism, studied the influence such as reaction time, ratio of raw materials on the final morphologies, and studied their performance as lithium ion battery and supercapacitor, respectively. The main works were summarized as follows:1. LiCoO2concaved cuboctahedrons with size about1.0μm were hydrothermally prepared from COCO3and LiOH·H2O at150℃. Field-emitting scanning electron microscope (FESEM) images show that the cuboctahedrons consisted of four hexagonal plates, with angles70.5°in neighboring plates. Electrical diffractions (ED) of the hexagonal plates show (100) diffraction of LiCoO2in rhombohedral phase and (220) diffraction in spinel phase. which means LiCoO2concaved cuboctahedrons are intergrown by two phases. The electrochemical performance of these concaved cuboctahedron of LiCoO2at0.5C rate demonstrated first run charge/discharge capacities at155and141mAh/g and a stable discharge capacity at114mAh/g after100circles. After that, FESEM images show the LiCoO2concaved cuboctahedrons no significant change. As the temperature was120℃and kept the same condition, only small amount of LiCoO2concaved cuboctahedron appeared. As the temperature rose to180℃, flower-like LiCoO2microstructures with size about1.0μn constructed by irregular plates were formed. The electrochemical performance of the products prepared at120℃and180℃present less stability than that of LiCoO2concaved cuboctahedrons. The above results of research have been published in the international journal of Dallon Transactions in 2011.2. LiNi1/3Co1/3Mni/3O2/carbon core-shell nanocomposites with sizes of～100nm and the thickness of carbon shell of～6nm are obtained by a modified Pechini process, in which process LiNi1/3Co1/3Mn1/3O2are synchronously formed together with carbon coating in the presence of Polyethylene Glycol-600. Electrochemical measurements show that the nanocomposites deliver a stable discharge capacity of175mAh/g at1C and a capacity decay rate of <3%after100cycles. The effects of synthesis temperatures on the electrochemical performance of the nanocomposites are examined, which show that the discharge capacities increase from154to175mAh/g as the temperature increasing from800to1000℃. Meanwhile, the electrochemical performances of the nanocomposites with carbon content vary from0to20.8%are examined. Among these composites,15.5%carbon content in the composite exhibits the most high and stable discharge behaviour at1C for100cycles. The above results of research have been published in the international journal of RSC Advances in2012.3. Ca9Co12O28nanopaticles with size of about25nm were prepared by Pechini process at850℃for4h. The as-obtained nanopaticles demonstrated initial charge/discharge capacities of908and816mAh/g and a stable discharge capacity of210mAh/g after50cycles. Different morphologies of Ca9Co12O28as multilayer structure and micro-plates were also obtained by solid-state reaction and coprecipitation-precursor technique at850℃for20h. When they were studied in the charge/discharge experiments of lithium ion batteries, the initial discharge capacities reached values of762,790mAh/g, together with stable discharge capacities of141,151mAh/g after50cycles, respectively, which were both lower than those of nanoparticles. The above results of research have been published in the international journal of Materials Letters in2012.4. Hollow carbon octahedra with an average size of300nm and a shell thickness of2.5nm were prepared by a reaction starting from ferrocene and Mg(CH3COO)2-4H2O at700℃for10h. They became compressed and turned into deflated balloon-like octahedra when the reaction time was increased to16h. It was proposed that the gas pressure generated during the reaction process induced the transformation from broken carbon hollow octahedra into deflated balloon-like compressed octahedra. X-ray powder diffraction and Raman spectroscopy indicate that the as-obtained carbon products possess a graphitic structure and high-resolution transmission electron microscopy images indicate that they have low crystallinity. Their application as an electrode shows revesible capacity of353mAh/g after100cycles in the charge/discharge experiments of secondary lithium ion batteries. The above results of research have been published in the international journal of Materials Research Bulletin in2012.5. Carbon nanoplates with diameter up to～1.2μm and the thickness of～18nm were prepared by a reaction using CaC2, ferrocene and NH4HCO3as starting materials at600℃for10h. These carbon nanoplates form aggregates which have a specific surface area up to831m2/g and have a specific capacitance up to184F/g at a scanning rate of10mV/s in a3mol/L H2SO4solution. Without using NH4HCO3, hexagonal carbon nanoplates with an average edge length of500nm and the thickness of～22nm were obtained with a specific capacitance up to42F/g. If NaN3or NaHCO3was used instead of NH4HCO3, carbon nanoplates with a curved surface, or irregular circular carbon nanoplates were obtained with respective specific capacitances of87and36F/g. The above results of research have been published in the international journal of European Journal of Inorganic Chemistry in2010.