Researchers have uncovered critical changes in the thermal properties of energy storage devices during operation, paving the way for better heat management.
Modern energy storage devices, such as supercapacitors and batteries, have highly temperature-dependent performance. If a device becomes too hot, it becomes susceptible to “thermal overclocking”. Thermal acceleration – or uncontrolled overheating – can eventually lead to dangerous explosions or fires. Adopting a well-informed heat management strategy is necessary for the stable and safe operation of the devices. To do this, you need to understand how certain thermal properties, such as heat capacity (Cp), change dynamically during charging and discharging.
Researchers at the Gwangju Institute of Science and Technology (GIST) recently studied the thermal properties of electric dual-layer capacitors (EDLC) – a type of high-power, long-life supercapacitor – for a technical basis in thermal measurement and revealed significant information. “Using 3ω hot wire method, we were able to measure the change in heat capacity of EDLCs in real time in a microscopic electrode-electrolyte volume, which is an active site for ion adsorption and desorption, ”explains Prof. Jae Hun Seol, who led the study.
The study was submitted online on February 5, 2022 and will be published in Volume 188, Number 122632 of International Journal of Heat and Mass Transfer on June 1, 2022
The research team conducted experiments on both on the spot (under static conditions) and operand (during charging). They found that the temperatures of the positive and negative electrodes changed by 0.92% and 0.42% during charging, corresponding to a 9.14% and 3.91% reduction in their respective Cp. According to thermodynamic theory, the entropy of the ionic configuration (a measure of chance) of the system decreases during adsorption, ie. when charging. This also affects the free energy of the system. Together, this leads to a reduction in Cp“, Explains Prof. Seol.
The team also changed the concentration of the electrolyte, potassium hydroxide, to see how it affected EDLC performance. They found that EDLC showed maximum capacity and a decrease in Cp when the electrolyte concentration was 8 M. They attributed this to variations in the degree of hydration of ions and their ionic mobility.
“An important aspect of this study is that charging and discharging also changes Cp of EDLC “, says Prof. Seol. “These findings will broaden our understanding of the basic thermal physics of EDLC.”
In fact, these results can be considered a major step towards future effective heat management strategies that will create safer and more reliable energy storage devices.
Reference: “In situ and operando thermal characteristics in aqueous electric two-layer capacitors using 3ω Hot Wire Method ”by Yeongcheol Park, Jaehoon Kim, Changho Kim, Seung-Mo Lee, Chul Kang and Jae Hun Seol, February 5, 2022, International Journal of Heat and Mass Transfer.
DOI: 10.1016 / j.ijheatmasstransfer.2022.122632