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Carbon and Metal Oxide Based Electrode Materials for Sodium Ion Batteries and Sodium Ion Capacitors
- Author / Creator
This thesis is focused on the design and fabrication of carbon-based electrode materials for sodium-ion batteries (NIBs) and sodium-ion capacitors (NICs), as well as metal oxide (SnO2) based anode material for NIBs and lithium-ion batteries (LIBs).
Na ion based energy storage systems are attracting significant interest as a potential lower cost alternative to Li ion based systems due to the geographically democratic reserves of the sodium metal. In its infancy, there is a strong demand for suitable electrode materials. In our first attempt, we created carbon materials (CPM-A) as NIB anodes, which exhibited many attractive electrochemical properties, similar to graphite as a LIB anode. An abundant wild plant, peat moss was chosen as the carbon precursor. The highly cross-linked polymer tissue of peat moss suppressed the nucleation of equilibrium graphite phase at high temperatures, instead transforming into highly ordered pseudographitic domains with substantially larger interlayer spacing (0.388nm) than that of graphite (0.335nm). These domains can provide Na intercalation sites analogous to the Li storage sites in graphite. By inheriting the unique cellular structure of peat moss leaves, CPM-A were composed of 3D macroporous frameworks of carbon nanosheets, which not only provided facile electrolyte access pathways but also greatly reduced the Na bulk diffusion distances. Benefiting from all these superiorities, the best CPM-A anode exhibited many highly desirable features, including low capacity voltage, negligible voltage hysteresis, high Coulombic efficiency, good cycling retention and high rate capacity. Based on this set of CPM-A specimens with tunable graphitic order, surface area and heteroatoms level, we also discovered the inner correlation between the physical/chemical properties of carbon and the galvanostatic voltage profile of the corresponding NIB anode, which provided important guidance for future carbon NIB anode design and preparation.
In our second attempt, we built a Na-ion based hybrid capacitor device (NIC) which has spanned the energy-power divide between the traditional batteries and supercapacitors. Both the anode carbon and cathode carbon were entirely derived from a highly economical biowaste: peanut shell. By skillfully utilizing the heterogeneous tissue of peanut shell, an adsorption cathode carbon (PSNC) and an intercalation anode carbon (PSOC) were prepared using the outer and inner skin of peanut shell, respectively. The cathode carbon has a high surface area, a high level of oxygen doping and a unique hierarchically porous architecture, which all positively contribute to the excellent capacitive performance. On the contrary, the anode carbon is highly ordered with low surface area and low heteroatom doping, and thus provides large intercalation capacity in the low voltage region. By pre-sodiating the anode, the working voltage windows of both the cathode and anode in the full NIC cell were optimized. In more detail, the cathode swung within a wide voltage window from 1.5 to 4.2V hence the high adsorption capacity of PSNC was fully utilized. The anode was restricted within the low voltage region (below 0.1V), in order to achieve the largest possible working voltage window for the full device. Benefiting from the excellent electrochemical properties of electrode materials and the optimized working style of the electrodes, the resultant NIC devices can offer a state-of-the-art cyclically stable combination of energy and power densities, even comparable to the performances of previously reported Li-ion capacitors (LICs).
In the third attempt, we tried to develop anode materials with high volumetric capacity for NIBs. SnO2 was chosen as the active material. A glucose mediated self-assembling method was employed to prepare a novel SnO2-carbon nanocomposite, which exhibited very promising cyclability and rate behavior as both a NIB and LIB anode. In addition to the advanced material synthesis, we also made systemic investigation on the fundamental energy storage mechanism of SnO2 anodes. Combining characterization methods of TEM, XRD and XPS, the phase transformations of SnO2 during the sodiation/desodiation, lithiation/delithiation processes have been studied in detail. These analyses have revealed the inner cause of the capacity discrepancy for SnO2 anode between Li and Na systems, which although frequently observed has never been explained. The much lower capacity of SnO2 anode against Na is due to the kinetic difficulty of Na-Sn alloying reaction to reach the terminal Na15Sn4 intermetallic. Therefore, a large portion of the active material only shuffles between SnO2 and Sn+NaO2. The characterization data also revealed a critical difference in the conversion reactions between the two systems. LiO2 is reduced directly to SnO2 and Li, whereas the NaO2 to SnO2 reaction proceeds through an intermediate SnO phase. These fundamental findings have great significance for future SnO2 anode development.
- Graduation date
- Fall 2015
- Type of Item
- Doctor of Philosophy
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.