Electrolyte evaluation and engineering for the performance enhancement of electrochemical capacitors
Doctoral thesis, 2021
Besides a general discussion about ECs, the main objective of this thesis is to identify and address the above-mentioned critical challenges, and to propose and demonstrate corresponding solutions. Firstly, it is revealed that utilizing a redox-active KBr electrolyte can enhance both operating voltage and capacitance, and hence increases energy density without sacrificing power density or cycle life. Secondly, an evaluation of elevated temperature influence on the capacitive performance of ECs containing ionic liquid (IL) electrolyte demonstrates a high working temperature beyond 120 °C. Thirdly, a systematic investigation of ECs containing IL at elevated temperatures shows a significant increase of the self-discharge rate with temperature and pinpoints the underlying mechanisms; at lower initial voltages the self-discharge rate is dominated by diffusion of electrolyte ions rather than charge redistribution. Fourthly, the addition of a small amount of liquid crystals (LC) in neutral electrolyte shows a reduction of self-discharge and leakage current due to slower diffusion of ions in the device, which is proposed to originate from the anisotropic properties of LC. Finally, by utilizing the thermocapacitive effect, a thermal charging of ECs containing IL is demonstrated, where a high voltage of more than 900 mV could be recovered when two devices in series are exposed to a 60 °C temperature environment.
Mohammad Mazharul Haque
Chalmers, Microtechnology and Nanoscience (MC2), Electronics Material and Systems Laboratory
Redox enhanced energy storage in an aqueous high-voltage electrochemical capacitor with a potassium bromide electrolyte
Journal of Power Sources,; Vol. 348(2017)p. 219-228
Thermal influence on the electrochemical behavior of a supercapacitor containing an ionic liquid electrolyte
Electrochimica Acta,; Vol. 263(2018)p. 249-260
Self-discharge and leakage current mitigation of neutral aqueous-based supercapacitor by means of liquid crystal additive
Journal of Power Sources,; Vol. 453(2020)
Identification of self-discharge mechanisms of ionic liquid electrolyte based supercapacitor under high-temperature operation
Journal of Power Sources,; Vol. 485(2021)
Haque, M. Abdurrokhman, I. Idström, A. Li, Qi. Rajaras, A. Martinelli, A. Evenäs, Lars. Lundgren, P. Enoksson, P. Exploiting low-grade waste heat to produce electricity through supercapacitor containing carbon electrodes and ionic liquid electrolytes
As for today, there are two main types of electrical energy storage devices: rechargeable batteries and electrochemical capacitors (ECs). Rechargeable batteries are by far the most popular and widely used alternative in all kinds of applications, from electronic devices to transportation. However, typically rechargeable batteries based on Faradaic reactions suffer from two main limitations: long charging time, and limited cycle life. On the contrary, due to the unique electrostatic charge storage mechanism, ECs can charge in minutes (if not seconds) and have a nearly unlimited cycle life. These features make them immensely attractive for a wide range of emerging applications like regenerative braking for the electric vehicle, uninterruptible power supply, wearable electronics just to name a few.
However, there are some key limitations of ECs that need to be addressed before they can enter the market with their full potentials. First and foremost is their low energy density, meaning that their operation time between charging cycles is limited. They also tend to self-discharge faster than batteries when not in use. In certain applications, ECs need to operate in a wide temperature range which makes it very critical to select durable and compatible structural components and maintain a good performance.
In this thesis, we address the aforementioned challenges and provide potential solutions/improvements/suggestions to achieve high-performing ECs and expanding their range of usability.
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VINNOVA, 2017-11-10 -- 2021-05-01.
Areas of Advance
Other Materials Engineering
Chalmers Materials Analysis Laboratory
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4971
Chalmers University of Technology
Kollectorn, Kemivägen 9, Göteborg
Opponent: Professor Ncholu Manyala, University of Pretoria, South Africa