Thesis (M. Sc. (Chemistry)) -- University of Limpopo, 2019 / Nano-architecture structures of LixTiO2 are very promising as anode materials for
lithium rechargeable batteries due to their ability to accommodate more lithium atoms
and its ability to withstand high temperatures at atomistic level through charging and
discharging. In these studies, we investigated how nano-architectured structures of
LixTiO2 behave at high temperatures through the process of amorphisation and
recrystallisation. A computational method of molecular dynamics (MD) simulation was
employed to recrystallise the amorphous LixTiO2 nano-architectures of bulk,
nanosheet, nanoporous and nanosphere, where x depicts the fraction of lithium ions,
i.e. 0.03, 0.04 and 0.07. The main objective of this study was to go beyond the previous
inserted lithium atoms on TiO2 and understand the effects of concentrations,
temperature, defect chemistry and charge storage properties/capacity on the overall
lithium transport to improve lithium ion battery performance.
Recrystallisation of all four nanostructures from amorphous precursors were
successfully achieved and was followed by the cooling process towards 0 K and finally
we heated all four nano-architectures at temperature intervals of 100 K up to 500 K.
The variation of configuration energies as a function of time, was used to monitor the
crystal growth of all nanostructures. Calculated Ti-O radial distribution function, were
used to confirm the stability interaction after cooling. Calculated X-Ray Diffraction
(XRD) spectra where used to characterise and compare their patterns at cooled and
above high temperatures, using the model nanostructures, and they showed
polymorphic nanostructures with LixTiO2 domains of both rutile and brookite in accord
with experiment. Amorphisation and recrystallization showed good results in
generating complex microstructures. In particular, bulk structures show few zigzag
tunnels (indicative of micro twinning) with 0.03 Li but 0.04 Li and 0.07 Li show complex
v
patterns indicating a highly defected structure. While 0.03 and 0.04Li nanospheres
show, zigzag and straight tunnels in accord with experiment, the one with 0.07 Li has
melted. Lastly, nanoporous and nanosheet structures have pure straight and zigzag
patterns that are well in accord with our XRD patterns at all concentrations of lithium
atoms and temperatures. The lithium transport was analysed using diffusion
coefficient, calculated as a function of temperature in order to confirm the mobility
above the given temperatures. An increase in temperature shows an increase in
diffusivity of lithium at all lithium concentrations in nanoporous and nanosheet
structures. The same trend was observed in bulk but only with 0.03 and 0.07 Li ion
concentrations. / National Research
Foundation (NRF)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/3169 |
| Date | January 2019 |
| Creators | Rikhotso, Blessing Nkateko |
| Contributors | Ngoepe, P. E., Matshaba, M. G. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | xiii, 116 leaves |
| Relation | Adobe Acrobat Reader |
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