| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 93 === ABSTRACT
The purpose of this study is to develop high rate capability and high cyclability of layered cathode material for an advanced lithium-ion batteries (LiBs). In order to achieve the goal, we have employed a novel synthesis process that can produce high density spherical particles and their surface was modified further by coating with appropriate metal oxides to obtain the cathode materials with high reversible capacity, high rate capability and better cycleability.
The LiNi1/3Co1/3Mn1/3O2 electrode is the most promising cathode for rechargeable lithium batteries owing to its high reversible capacity at higher potential. We have prepared LiNi1/3Co1/3Mn1/3O2 material by co-precipitation and spray drying process and the resulted electrode powder was modified by coating with ZrO2, TiO2, Al2O3 and AlPO4 on its surface. The phase purity, elemental analysis, particles size and surface morphology and the nature of coating on the electrode surface of the bare and modified electrodes were determined, respectively, by employing the X-ray diffraction (XRD), inductively coupled plasma - Atomic emission spectrometer (ICP-AES), Scanning electron microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques. Further, we have evaluated the thermal stability of the bare and the modified electrodes by means of Differential Scanning Calorimetry (DSC) and also the existence of chemical states of transition metals (Ni, Co and Mn) were determined by Electron Spectroscopy for Chemical Analysis (ESCA).
The XRD pattern analysis revealed that the LiNi1/3Co1/3Mn1/3O2 of both bare and modified by coating with ZrO2, TiO2, Al2O3 and AlPO4 electrode materials were found to be single phase and layer structure. The SEM micrographs of the bare and the modified electrode powder showed partial nanopore and the coating layer on the surface of the modified electrode was found to be uniform as evidenced from TEM micrographs. The chemical states of Ni, Co and Mn were determined as Ni2+, Co3+ and Mn4+ from the ESCA analysis.
The electrochemical cycle performance of the LiNi1/3Co1/3Mn1/3O2 electrode was determined at various C-rates (0.1 ~ 1.0 C) in the potentials at 3.0 ~ 4.5 V at ambient temperature in order to evaluate the rate capability of the bare and the modified electrode materials. The LiNi1/3Co1/3Mn1/3O2 electrode modified by coating with ZrO2 was capable of delivering the best electrochemical characteristics of reversible capacity, rate capability and cyclability among the studied bare and modified electrodes. The improved electrochemical characteristics of the modified electrode by coating with ZrO2 may improve the surface properties of the modified electrode thereby smaller polarization as evidenced from polarization analysis. we have also determined the thermal stability of the various electrodes at the end of charged state (4.5 V) and the DSC analysis showed that the electrode modified by coating with various metal oxides released lower heat compared to that of the pristine as well as commercial LiCoO2 cathode which indicates that the higher safety of the battery that can be operated at higher potentials.
Based on various experimental results, we have concluded that the LiNi1/3Co1/3Mn1/3O2 electrode modified its surface by coating with ZrO2 was found to exhibit the best electrochemical characteristics of reversible capacity, rate capability and cyclability. The improved electrochemical properties suggest that the modified electrode can be used as a potential cathode in the lithium-ion batteries for the next generation power source.
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