| Summary: | 碩士 === 元智大學 === 化學工程與材料科學學系 === 105 === The dissertation investigates the electrochemical performance of electrode materials synthesize with co-precipitation method for lithium-ion and magnesium-ion batteries. This study can be qualitatively divided into two parts: (i) MgCo2O4/Li4Ti5O12 (ML) for lithium-ion batteries, (ii) MgCo2O4/Graphite (MG) for magnesium-ion batteries.
(i) MgCo2O4/Li4Ti5O12 for lithium-ion batteries
In the present work, MgCo2O4 (MCO)/Li4Ti5O12 (LTO) composites with different MCO contents are synthesized by a co-precipitation method in order to partially replace expensive Co with Mg as well as to exploit advantages of MCO and LTO as anode materials for Li-ion batteries. X-ray diffraction patterns of as-prepared materials confirm successful fabrication of the MCO/LTO composites. The average particle size of MCO nanoparticles of the three samples are 38.1, 56.9 and 58.5 nm. Electrochemical results show that MCO/LTO anode offers a discharge capacity of 300 mAh g-1, which is two times higher than that achieved by pristine LTO. In addition, cyclic stability test reveals that the composite anode retains 86.1% of its initial capacity after 50 cycles. Electrochemical Impedance spectrum indicates that the electronic conductivity of MCO/LTO electrodes is significantly higher than that of LTO. The superior performance of the composite electrodes can be attributed to its improved conductivity as well as to the formation of active sites of MCO on LTO.
(ii) MgCo2O4/Graphite for magnesium batteries
This study uses co-precipitation method to synthesize MCO nanocrystals, followed by the formation of MG cathode by using mechanical mixing method. The weight ratios of MCO to graphite are set at 7:3(M7G3), 5:5(M5G5), 3:7(M3G7), according to different proportion can be divided into M7G3, M5G5 and M3G7. Through the method, MCO nanoparticles are uniformly coated over the graphite. The coin cells fabricated with the hybrid anodes were systematically investigated by CV and charge-discharge cycling test at different C rates. The current density of MG is found to have an increasing function of the loading of graphite. The maximal specific capacity of M3G7 cathode is up to 180 mAh g-1, which is two times higher than M7G3. The electrochemical impedance spectroscopy shows that the resistance of M7G3, M5G5 and M3G7 are 250.1 , 158.2 and 82.3 , respectively. On the basis of the results, the improved performance is attributed to the high conductivity of MCO and graphite which enhance the number of active sites and reduce the resistance during the electrochemical reaction. The MG cathode displays high specific capacity and low inner resistance, showing a promising feasibility for Mg-ion battery applications.
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