Hydrothermal Synthesis And Electrochemical Properties Of Cobaltite With Spinel Structure

Due to high initial capacity, good thermal stability and electrochemicalperformance，low cost and lower toxicity than Co3O4, cobaltite with spinel structurecould be a promising anode material for lithium-ion batteries in future applications. Inthis paper, nanosized-MnCo₂O₄、CuCo₂O₄、ZnCo₂O₄have been synthesized viahydrothermal method, the crystalline phase, the morphology and the valences of thecompositions elements of the resultant samples were characterized by X-raydiffraction （XRD）, transmission electron microscopy （TEM）, scanning electronmicroscopy （SEM） and X-ray photoelectron spectrometry （XPS）, respectively. Theelectrochemical properties of the resultant samples were studied by cyclicvoltammetry （CV）, galvanostatic charge-discharge tester, as well as electrochemicalimpedance spectroscopy （EIS）. Futher, the relationship between various factors andelectrochemical properties were summarized and analyzed by the characterizationresults.In chapter1, the development, the components and working principle oflithium-ion battery were described. The structure, synthesis and electrochemicalperformance of lithium-ion battery electrode material were summarized, futher, thedevelopment of cobaltite with spinel structure as lithium-ion battery anode material inthe future was also outlook.In chapter2, the working process and applied areas of the related apparatuseswere described, and also, the processes of preparing electrode and assembling thecells were mentioned.In chapter3, nano-MnCo₂O₄synthesized via hydrothermal method and itselectrochemical performance was studied. The influence of different calcinationstemperature on the product was investigated. XRD figure showed that the preparedsamples under600℃was pure phase with spinel structure, a cubic crystal system,space group Fd3m, with a good crystal form, a high degree of crystallinity. XPS dataof the sample exhibit that the valence of Mn and Co were+4and+2, respectively.SEM and TEM results showed that the nanoparticles were obtained, particle size of11¹7nm, uniformly distributed, high resolution transmission electron microscopy（HRTEM） was characterizatied, the result show that, MnCo₂O₄nanoparticles weregrowth along the specific crystal planes （311）, with a high degree of crystallinity. Theelectrochemical performance of MnCo₂O₄as the anode of lithium-ion batteries wastested. It showed that the first discharge capacity can reach a very high value of1448mA h g－1. The reaction mechanism between lithium and MnCo₂O₄was also discussed based on the results of electrochemical performance. The EIS result showedthat the product has smaller surface impedance, which is only46In chapter4, nano-CuCo₂O₄synthesized via hydrothermal method and itselectrochemical performance was studied. The XRD result showed that the proceedsCuCo₂O₄particles with spinel structure, was cubic crystal system, space group Fd3m,with a good crystal form, and a high degree of crystallinity, accompanied by a smallamount of CuO. XPS data of the sample exhibit that the valence of Cu and Co were+2and+3, respectively. TEM result showed that the nanoparticles were obtained,particle size of22²6nm, uniformly distributed. The electrochemical performance ofCuCo₂O₄as the anode of lithium-ion batteries was tested. It showed that the firstdischarge capacity can reach a very high value of1509mA h g^－1. The reactionmechanism between lithium and CuCo₂O₄was also discussed based on the results ofelectrochemical performance.In chapter5, different morphologies ZnCo₂O₄synthesized via hydrothermalmethod and its electrochemical performance was studied. XRD figure showed that allthe prepared samples was pure phase with spinel structure, a cubic crystal system,space group Fd3m, with a good crystal form, a high degree of crystallinity. SEM andTEM results showed that four kinds of different morphologies were obtained, therewere nanorods, the one-dimensional structure, hexagonal flakes and porousnanoparticles, among them, nanorods with lengths of150nm an20nm in diameter.The HRTEM result showed that, the proceeds ZnCo₂O₄nanoparticles were growthalong the specific crystal plane （311）, with a high degree of crystallinity, theformation mechanism of nanorod was also discussed. The EIS result showed that thesurface impedance of product was198. The electrochemical performance ofZnCo₂O₄as the anode of lithium-ion batteries was tested. It showed that the firstdischarge capacity can reach as high as1376¹559mA h g－1. The reactionmechanism between lithium and ZnCo₂O₄was also discussed based on the results ofelectrochemical performance.