JANANI, Ronak (2019). Synthesis and characterisation of sol- gel based ionogels as electrolyte for supercapacitors. Doctoral, Sheffield Hallam University. [Thesis]
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Janani_2019_PhD_SynthesisCharacterisationSol-Gel.pdf - Accepted Version
Available under License Creative Commons Attribution Non-commercial No Derivatives.
Janani_2019_PhD_SynthesisCharacterisationSol-Gel.pdf - Accepted Version
Available under License Creative Commons Attribution Non-commercial No Derivatives.
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Abstract
With growing public demand for consumer safety regarding electronic devices,
ionogels have recently been suggested as a safe and solid replacement for the
conventional flammable and toxic organic electrolytes used for various energy
storage devices including batteries and supercapacitors. Ionogels are porous
solid scaffolds that encapsulate ionic liquids and prevent electrolyte leakage
which can otherwise be a potential hazard to the consumer or the surrounding
circuitry. In this work, sol-gel was utilised as a manufacturing technique for 1-
ethyl-3-methylimidazolium trifluoromethanesulfonate based-ionogels. Sol-gel
chemistry is a facile and industrially relevant technology that allows the formation
of solid scaffolds from homogenous precursors including a variety of silicon
alkoxides. Previous studies have used a single or a mixture of silicon alkoxides
to fabricate ionogels. In this work, four different precursors (two
tetraalkoxysilanes and two alkyltrialkoxysilanes) were utilised to explore the influence
of the type of silicon alkoxide on the reaction kinetics, thermal stability,
microstructure and the electrochemical performance of the ionogels as electrolyte
for electric double-layer capacitors (EDLCs).
Furthermore, thermally-cured 1-ethyl-3-methylimidazolium trifluoromethanesulfonate-
based ionogels have been realised for the first time in this work. The
influence of curing temperature on the structure of the ionogels and their electrochemical
performance as the electrolyte for EDLCs have been investigated.
Ionogels were synthesised via a non-hydrolytic sol-gel route and were fully
gelled post heat-treating at 125, 150, 175 and 200°C for 60 minutes with minimal
shrinkage. Charge transfer resistance (a rate-limiting parameter in cell kinetics
during charge/discharge cycles) was reduced by ∼80% via increasing the
heat-treatment temperature; this was partially attributed to the interlocking effect
at the electrode-electrolyte interface facilitated by high curing temperature. The
fast-cure fabrication process for ionogels removes one of the major hurdles in
their industrial application, their long curing and aging time, while the improved
room temperature ion transport kinetics expands the potential application of ionic
liquid-based electrochemical systems. Finally, an exploratory investigation on
the long-term stability of the fabricated EDLCs indicated that cells with 150°C cured ionogels show an improved electrochemical performance compared to
the EDLCs with ionic liquid electrolyte without the gel network.
The results gathered in this work provide an insight into sol-gel processed ionogels
as a replacement for the conventional electrolyte formulations and further
proves that, this class of materials has the potential to be a safe, solid and durable
electrolyte for EDLCs.
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