| Summary: | 碩士 === 國立高雄應用科技大學 === 化學工程與材料工程系 === 97 === In this study, the iron oxide (α-Fe2O3) active materials are synthesized by electrochemical deposition and chemical precipitation methods, respectively. In addition, the iron oxide was coated on the surface of carbon fiber (VGCF) to form α-Fe2O3/VGCF composite electrode as an anode material for high-capacity Li-ion batteries.
In the first part, the iron oxide film and α-Fe2O3/VGCF composite electrodes are prepared by electrochemical deposition method. The effects of different deposition current densities (0.025 and 0.125 mA cm-2) on the material characteristics and electrochemical performances of iron oxide electrode are investigated. According to the SEM analysis, the iron oxide film deposited at low-current density (0.025 mA cm-2) is rod-like morphology and that deposited at high-current density (0.125 mA cm-2) is sheet-like morphology. During the first charge-discharge process, the reversible capacity of films deposited at 0.025 and 0.125 mA cm−2 are 1390 and 1275 mAh g-1, respectively; At 10 C rate, the reversible capacity are 803 and 797 mAh g-1, respectively. The synthesized anode materials have a higher capacity than the graphite material for lithium storage. The SEM and XRD results indicate that iron oxide films are uniformly coated on the surface of carbon fiber by means of electrochemical deposition process. Compared with iron oxide electrode (deposited at 0.125 mA cm-2), the reversible capacity of α-Fe2O3/VGCF composite electrodes are increased by 17.9 % in first charge-discharge process and 12 % at 10 C rate. The results show that carbon fiber can improve the electrochemical performance of the composite electrodes effectively.
In the second part, the iron oxide powder is synthesized by chemical precipitation method and is deposited onto the stainless steel substrate by electrophoretic deposition to form iron oxide film and α-Fe2O3/VGCF composite electrodes. The effects of different precursors [Fe(NH4)2(SO4)2．6H2O and FeCl3．6H2O] on the material characteristics and electrochemical performances of the iron oxide electrode is investigated. According to the SEM analysis, when the precursors are Fe(NH4)2(SO4)2．6H2O and FeCl3．6H2O, the morphologies of resulting iron oxide powder are nanorod and nanoparticles, respectively. The TG-DTA and XRD results indicate that FeOOH is fully converted into α-Fe2O3 when the annealing temperature is elevated to 400℃. During the first charge-discharge process, the reversible capacity of films for Fe(NH4)2(SO4)2．6H2O and FeCl3．6H2O are 1390 and 1275 mAh g-1, respectively; At 10 C rate, the reversible capacity are 713 and 503 mAh g-1, respectively. Compared with iron oxide electrode [Fe(NH4)2(SO4)2．6H2O], the reversible capacity of α-Fe2O3/VGCF composite electrodes are increased by 16.2 % in first charge-discharge process and 11.8 % at 10 C rate.
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