Synthesis and characterization of layered materials for electrochemical capacitors and batteries
Date
2018
Authors
Melchior, Sharona Ashira
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The energy storage performance of one of the lightest but less researched
MXenes, Ti2CTx, combined with other materials, was investigated for improved
electrodes in electrochemical capacitors (ECs) and lithium-ion batteries (LIBs).
This work investigated: (i) Ti2CTx combined with carbon nanospheres (CNS) as a
symmetric electrode system in an aqueous electrolyte (1M Li2SO4); (ii) Ti2CTx
combined with electrolytic manganese dioxide (EMD) as an anode for LIB. The
structure, composition, morphology and electrochemical properties of the
synthesized materials were studied. The combined MX/CNS material
demonstrated a higher specific capacitance compared to the individual
components. The material was fabricated with relatively high (1.87 mgcm-2) and
low (0.17 mgcm-2) mass loadings and assembled into a symmetric device.
Specific capacitance, power and energy for the lower electrode mass loading of
180 Fg-1, 37.6 kWkg-1 and 14.1 Whkg-1 were all higher than 86 Fg-1, 20.1
kWkg-1 and 6.7 Whkg-1 for the higher mass loading. A wide voltage window of
1.5 V, which is larger than the window reported in works involving MXene as
symmetric supercapacitor electrodes in an aqueous electrolyte (<1.0 V), was
obtained, but with limited long-term cycling behaviour. Mathematical modelling
and simulation of the supercapacitor showed good correlation with the
experimental results, validating the model. The cell performance was
demonstrated by lighting an LED. This reveals the potential of the Ti2CTx to be
employed as a viable energy storage system for applications requiring low mass.
In the study of MXene combined with EMD, three different ratios were examined
as anodes for LIB in a half-cell configuration. Results showed that the combined
MXene/EMD material has a greater capacity, rate capability and cycling stability
compared to the EMD. The best ratio was found to be MXene:EMD=80:20. The
capacity obtained for this material after 200 cycles is 460 mAhg-1 at a current
density of 100 mAg-1. The Li-ion accessibility was found to improve with
cycling. This study provides a first insight into the viability of using a
light-weight MXene/EMD composite for improved LIB anodes. EMD is a low
cost and abundant material, thus provides great opportunities for improved
capabilities for light-weight applications at an affordable cost
Description
A thesis submitted to the Faculty of Engineering and the Built
Environment, University of the Witwatersrand, Johannesburg, in
fulfilment of the requirements for the degree of Doctor of Philosophy.
Johannesburg, September 2018
Keywords
Citation
Melchior, Sharona Ashira. (2019). Synthesis and characterization of layered materials for electrochemical capacitors and batteries. University of the Witwatersrand, https://hdl.handle.net/10539/26597