It is imperative to develop alternative battery technologies based on naturally abundant elements, with competitive performance as lithium-ion batteries. Sodium has a natural abundance 1000 times more than lithium with both lithium and sodium-ion batteries having similar chemistry. Sodium-ion batteries are potentially an alternative that can achieve such competitive performance, given that electrode and electrolyte materials of high rate and long-term electrochemical performance are being developed. This thesis investigates the rate capability and long-term performance of bulk bismuth electrodes containing varying carbon content. The electrodes were cycled in cells with glyme-based electrolytes: diglyme and tetraglyme. Scanning electron microscopy and energy dispersive spectroscopy showed the morphology and elemental mapping of pristine and cycled bismuth electrodes. The result demonstrates the evolving porosity as the electrode cycled. The galvanostatic cycling of half-cells showed two plateaus each for sodiation and desodiation. Also, two peaks are seen in cyclic voltammetry suggesting a two-phase reaction. When cycled between -0.6 to 0.6 V in a symmetrical cell, the bismuth electrode showed an appreciable rate capability at a current rate of 770 mA/g in diglyme. In tetraglyme, it showed a poor rate capability, even at a current rate of 308 mA/g. The rate performance in a full cell cycled between 0.1 to 3.2 V also showed a good rate capability at a current rate of 770 mA/g in diglyme. Tetraglyme showed poor rate capability at the same current rate. The capacity retention was higher in the symmetrical cells, with 79 % and 78 % capacity retention relative to the initial charge capacity after 100 cycles for diglyme and tetraglyme. At the same current rate and more than 70 cycles, the full cells showed capacity retention of 58 % in diglyme and 44.8 % in tetraglyme. The capacity retention varied slightly for the two different electrode composites. The superior performance in the symmetrical cell is due to the narrow voltage window. Evaluating the stability of the solid electrolyte interphase via galvanostatic cycling suggests some stability issues. The full cells showed growing resistance with an increasing number of cycles.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:uu-449075 |
| Date | January 2021 |
| Creators | Nwafornso, Tochukwu |
| Publisher | Uppsala universitet, Strukturkemi |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | UPKEM E ; 93 |
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