- Title
- Behaviour of LiFePO₄electrodes in secondary lithium batteries utilising room temperature ionic liquid electrolytes
- Creator
- Lewandowski, Arkadiusz Piotr
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2013
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- One of the greatest challenges faced by society leading into the future is the supply of energy, with great focus put forth in providing it from renewable alternatives which can negate environmental issues caused by green-house gases, and plausibly global warming. Furthermore, many applications ranging from portable electronic devices to cars have become viable with the use of batteries, preferably, as a medium for storing electrical energy. However stringent safety and environmental guidelines need to be successfully addressed in order for a battery to become a consumer product. The advancement in consumer goods relying on batteries, now more so based on rechargeable ones, has been delayed due to materials science and the associated electrochemistry both from a safety and operational point of view. Hypothetically speaking, a rechargeable battery should provide operational longevity, quick recharge, many cycles of usage and be of minimum weight. However, devices requiring the use of batteries may require high power, energy or both, which can inadvertently increase the weight of the battery and/or recharge time. In the last decade considerable focus has been applied into lithium-based rechargeable batteries which offer relatively high energy density. However, lithium-ion batteries offer a fraction of the energy density that of which lithium metal can. In either case, suitable electrolytes and particularly cathode materials are still a prime research area. Therefore, the focus of this thesis was to investigate LiFePO₄ cathode in lithium metal-based rechargeable batteries, while also considering the use of room temperature ionic liquid electrolytes. Experimental analysis based on battery cycling indicated that it is possible to achieve 162 out of the 170 mAh/g theoretical capacity at a relatively low discharge rate (C/10). In perspective of long term cycling, it was possible to obtain over 400 cycles with relatively minimal capacity loss, while ionic liquid electrolytes generated better results instead of using the conventional carbonate-based solvents. Increasing operating temperature improved diffusion kinetics which increased capacity. Furthermore, asymmetry in the capacity was found between charging and discharging when the current was increased, with the latter showing poorer results. The effect of cathode loading indicated that when increased, concurrently with current increase, resulted in poorer results, while adequate carbon in the cathode composition improved electrochemical performance. Further analysis suggested that LiFePO₄ performance can be improved by decreasing the LiFePO₄ particle size, improving crystallinity, and creating intimate carbon coating on the surface. Particle size minimization and crystallinity allows for relatively easier lithium diffusion which predominantly occurs along the [010] direction, while intimate carbon coating allows for electrons to be transported between particles and to the current collector. There is still an ongoing debate whether lithium or electron diffusion is the more limiting physical property. However, a proposed hypothesis in conjunction with the herein results, suggested that both are intertwined and depend on several physical factors such as crystallinity, particle size and carbon content, which formed an intricate system on a cathode scale. The hypothesis suggested that both the lithium ion and the electron propagate along the [010] direction, which created a dragging-pulling dual interaction between the two that was limited when the lithium, the electron, or both, struggled to be easily de/intercalated from/into the active material. Overall the performance of LiFePO₄ in conjunction with using an ionic liquid electrolyte created positive results. Therefore, by tailoring the synthesis procedure to produce appropriate structure and optimizing the cathode composition, this material can offer safe and long lasting operation in a rechargeable lithium metal battery system.
- Subject
- lithium batteries; rechargeable; ionic liquid electrolytes; materials science
- Identifier
- http://hdl.handle.net/1959.13/941002
- Identifier
- uon:13154
- Rights
- Copyright 2013 Arkadiusz Piotr Lewandowski
- Language
- eng
- Full Text
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