| dc.description.abstract | Sodium-ion batteries (NIBs) are appealing as post-lithium energy storage devices, especially for large-scale energy storage applications owing to its abundance and global distribution. However, NIBs are still in the early stages of development. There have been many decent breakthroughs in developing stable and low-cost cathodes, with the performance being close to that of Lithium-ion batteries (LIB) cathodes. Finding a suitable anode is comparatively challenging since the commonly used LIBs graphite anode has poor Na+ storage capability. Recently, tin oxide (SnO2) has attracted much attention as the NIB anode because it is chemically stable, readily available, and environmentally benign, and has ability to deliver a very high theoretical specific capacity of 1398 mA h g?1. However, this anode currently encounters four major obstacles, which are low first-cycle coulombic efficiency, unsatisfactory charge–discharge capacities, poor high rate performance, and insufficient cyclic stability.
This thesis is focused on the development of high-performance SnO2 anode through optimization of electrolytes, carbon supports, and binders. The sole objective of the thesis is to overcome the limitations of SnO2 anode. The third chapter of the thesis deals with the systematic study to optimize the electrolyte formulation for a SnO2/graphene anode, which is prepared via a supercritical-CO2-assisted synthesis method. Herein, we study various electrolytes like propylene carbonate (PC), PC/fluoroethylene carbonate (FEC), PC/ethylene carbonate (EC), and PC/EC/FEC electrolytes (with NaClO4 salt) to clarify the effects of FEC and EC on the columbic efficiency, reversible capacity, rate capability, and cycle life of a SnO2/graphene. Moreover, the above properties are compared to those of an N-Propyl-N-methylpyrrolidinium (PMP)–FSI ionic liquid (IL) electrolyte. The temperature effects (25 and 60 °C) for both the carbonate-based and IL electrolytes are also examined. The results obtained point out the importance of the electrolyte formulation, which affects the charge–discharge performance of the electrode to a great extent.
The fourth chapter of the thesis deals with the development of unique carbon support for SnO2. Nanosized SnO2 particles (~2 nm in diameter) are embedded in ordered mesoporous CMK-8 carbon with three-dimensional interconnected pore channels. With the unique SnO2/CMK-8 architecture, exceptional reversible capacity (800 mA h g?1), rate capability (delivering 330 mA h g?1 in ~10 min.), and cyclic stability (80% retention after 300 cycles) is achieved. Also, the SnO2?Sn conversion reaction and Sn?Na alloying reaction were effectively promoted. The proposed microstructure/architecture of the electrode material is highly effective in boosting Na+ storage properties and should be applicable to other anodes and cathodes in various battery applications.
The fifth chapter deals with the optimization of binders for SnO2/CMK-8. Herein, we employed polyvinylidene difluoride (PVDF), sodium carboxymethylcellulose (NaCMC), sodium polyacrylate (NaPAA), and NaCMC/NaPAA mixed binders to enhance the electrode sodiation/desodiation properties. Synergistic effects between NaCMC and NaPAA lead to the formation of an effective protective film on the electrode. This coating layer not only increases the charge–discharge Coulombic efficiency, suppressing the accumulation of solid-electrolyte interphases, but also keeps the SnO2 nanoparticles in the CMK-8 matrix, preventing oxide agglomeration and falling off upon cycling. With NaCMC/NaPAA binder, exceptional electrode capacities of 850 and 425 mA h g–1 are obtained at charge–discharge rates of 20 and 2000 mA g–1, respectively. After 300 cycles, 90% capacity retention is achieved. The thermal reactivity of the sodiated electrodes is studied using differential scanning calorimetry. The binder effects on NIB safety, in terms of thermal runaway, are investigated. | en_US |