Modelling the ageing behaviour of supercapacitors using electrochemical impedance spectroscopy for dynamic applications

Mohammad Naim, Nur Nafisah (2015) Modelling the ageing behaviour of supercapacitors using electrochemical impedance spectroscopy for dynamic applications. PhD thesis, University of Nottingham.

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Abstract

Diagnosis of ageing mechanisms in supercapacitors is made difficult by the enforcement of various ageing factors in the current ageing tests. The thesis presents the exact determination of the ageing mechanism by separating the impacts of high temperature, current cycling and constant voltage applications in accelerated ageing tests. The state of health (SOH) of the supercapacitors are monitored periodically with electrochemical impedance spectroscopy, cyclic voltammetry and constant current test to observe the evolution of ageing.

The thesis identifies patterns of ageing from the changes at supercapacitor impedance. The thesis also presents the cause of the increase in ESR and the loss of capacitance in supercapacitors. High temperature application causes the appearance of high frequency semicircle which reflects the damage at the electrode-current collector interface. A tilt of the impedance line at low frequencies reflects modifications of electrodes and it is most sensitive to current cycling and constant voltage applications. The increase in ESR is observed to be caused by a single ageing mechanism while the capacitance loss is caused by multiple interactions of these ageing mechanisms at the same time.

The thesis develops a supercapacitor model by means of electrical equivalent circuit. The model is divided into two parts based on the changes in its SOH: the baseline model represents the early stage of the supercapacitor life and the ageing model represents the phase of ageing. The models show dynamic interactions between ageing process and supercapacitor electrical performance. The supercapacitor model, in the form of fractional-order model, reduces the number of circuit components and shows excellent electrical behaviour particularly at the open circuit voltage decay and voltage recovery period. The parameterisation of model parameters shows that aged supercapacitors experience an increase of distributed resistance in the electrode pores and an increase of diffusion impedance at high temperature.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Isa, Dino
Keywords: supercapacitors; ageing; ageing mechanism; electrochemical impedance spectroscopy; ageing model; equivalent circuit; accelerated ageing test; fractional-order; constant phase element
Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering
T Technology > TK Electrical engineering. Electronics Nuclear engineering > TK7800 Electronics
Faculties/Schools: UNMC Malaysia Campus > Faculty of Engineering
UNMC Malaysia Campus > Faculty of Engineering > Department of Electrical and Electronic Engineering
Item ID: 29169
Depositing User: MOHAMMAD NAIM, NUR NAFISAH
Date Deposited: 29 Feb 2016 12:29
Last Modified: 13 Sep 2016 15:00
URI: http://eprints.nottingham.ac.uk/id/eprint/29169

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