UBC Theses and Dissertations
Engineering high performance electrodes for energy storage devices from low-cost, sustainable and naturally abundant biomaterials Watson, Timothy
With the increased global push towards sustainable energy utilization, the need for advanced energy storage technologies has become increasingly important as countries seek to integrate rapidly advancing renewable energy technologies like wind and solar. At the same time, the burgeoning electric vehicle and wearable electronics industries are fuelling demand for lower-cost energy storage devices with high energy capacities and longer cycle lives. Currently, despite huge leaps in performance of Li-Ion batteries in recent years, the technology is approaching its predicted limits and new solutions will be needed to keep up with the demand of current and future electrical devices. At a time where scientific applications of nanomaterials and nanofabrication is on the rise, there exists an opportunity to take advantage of our increased understanding of nanotechnology to significantly improve existing energy storage devices and to unlock the potential of next-generation energy storage technologies. In this work, binder-free and porous graphitic nanofibre electrodes produced from low-cost and sustainable softwood kraft lignin are devised and proposed as a platform for the development of high-performance energy storage devices. Motivated by difficulties facing some key energy storage technologies, scalable electrospinning of lignin and polyethylene oxide (PEO) precursor materials, followed by a hydrothermal treatment and carbonization in an inert atmosphere yields free-standing interconnected nanofibre electrodes with tunable porosity, high conductivity and superior electrochemical performance. Electrical impedance spectroscopy measurements of the optimized porous nanofibre electrodes demonstrate a conductivity reaching 18.39 S cm-¹, while Brunauer-Emmett-Teller specific surface area measurements yield a specific surface area as high as 1258.41 m² g-¹. Supercapacitor devices revealed highly symmetric cyclic voltammetry results which demonstrated a gravimetric capacitance approaching 112 F g-¹ at a voltage scan rate of 5 mV s-¹. Galvanostatic charge/discharge experiments show reversible supercapacitor behaviour, a high capacity even at elevated voltage scan rates up to 200 mV s-¹ and exhibit excellent cyclic stability, retaining 91% of their initial capacity after 6000 cycles. This work demonstrates the use of sustainable and abundant softwood Kraft lignin as source for porosity-tunable electrodes with high capacitance and stability as a demonstration of nature sourced and high performance electronic devices.
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