Ordered macroporous metal oxides and carbonaceous composites for Li-ion and beyond Li-ion batteries

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Carroll, Aoife
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University College Cork
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This thesis provides an in-depth investigation of three-dimensional ordered macroporous materials, specifically inverse opal materials, for electrochemical energy storage systems, particularly rechargeable batteries. Exploring the potential of composite structures, this research focuses on TiO2/GeO2 nanocomposites and C/TiO2 inverse opal anodes in Li-ion batteries, and carbon inverse opal anodes in Na-ion and K-ion batteries. Employing comprehensive characterization techniques, this research studies intricate material properties and electrochemical responses inherent in these structures. The composite materials exhibit promising features such as enhanced electrolyte penetration, improved specific capacities and coulombic efficiency, and robust structural integrity during extended charge-discharge cycling. The study findings shed light on the unique advantages of inverse opal composites for application in next-generation battery technologies. Highly ordered, macroporous inverse opal structures were fabricated as TiO2/GeO2 nanocomposites with varying GeO2 content, showcasing coulombic efficiency and capacity retention. The overall capacity of these interconnected binder-free anodes was affected by the Ge content and its distribution at both slow and fast rates. Characterization techniques such as X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction, energy-dispersive X-ray spectroscopy, and electron energy loss spectroscopy were employed to analyse these anodes. The electrochemical response over 2000 cycles and at various rates elucidated the impact of the composite on key metric in battery cells. The results indicated that a composite of intercalation and alloying compounds yielded good specific capacity and excellent coulombic efficiency (>99%), even with low quantities of the GeO2. The cycling life reveals an increase in capacity with improved coulombic efficiency with suspicion that the GeO2 material becomes electrochemically active within the composite matrix, undergoing modifications during cycling. C/TiO2 composite were synthesized from sucrose as the carbon precursor to form interconnected, porous inverse opal structures. Material characterization revealed amorphous TiO2 and disordered carbon with a large pore size of ~400 nm. An atomic ratio of ~8:1 in favour of carbon yielded promising electrochemical responses with high specific capacity and capacity retention at 150 mA/g rate. Diffusion processes were shown to be the dominant contributor to current responses for all scan rates, with double-layer capacitance accounting for less than ~45 % even at the high scan rate of 1000 mV/s. When compared to individual carbon and TiO2 inverse opals the composite demonstrated improved coulombic efficiency and high-rate performance attributed to the synergistic benefits of combining these two intercalation materials. Carbon inverse opals were fabricated in a similar way from sucrose to study the effect of the macroporous structure on performance in sodium-ion and potassium-ion batteries. Composed of disordered carbon with short-range graphitic regions, the storage mechanism involved primarily diffusion processes at lower scan rate with capacitive behaviour governing the current response at faster scan rates. Structural integrity was maintained in all cells after 250 cycles showcasing impressive resistance to structural stresses. Comparing the inverse opal material to thin films of the same composition highlighted the improved capacity retention and cycling stability inherent to the three-dimensional ordered macroporous structure.
Lithium-ion battery , Anode , Macroporous , TiO2 , Metal oxide , Carbon , Batteries , Na-ion , K-ion
Carroll, A. 2023. Ordered macroporous metal oxides and carbonaceous composites for Li-ion and beyond Li-ion batteries. PhD Thesis, University College Cork.
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