Recently, researchers from the Gwangju Institute of Science and Technology clarified critical changes in the thermal properties of energy storage devices during operation, paving the way towards better thermal management.
Effectively managing the thermal properties of energy storage devices is the key to avoiding thermal runaway and ensuring safety. The scientists uncovered key changes to the thermal properties of electric double-layer capacitors (EDLCs) during charging and discharging.
Modern energy storage devices, such as supercapacitors and batteries, have highly temperature-dependent performance. If a device get too hot, it become susceptible to “thermal runaway.”
Thermal runaway—or uncontrolled overheating—can ultimately result in explosions or fires. Adopting a well-informed thermal management strategy is necessary for the stable and safe operation of devices. To do this, it is important to understand how certain thermal properties, like heat capacity (Cp), dynamically change during charging and discharging.
Electric double-layer capacitors are a type of supercapacitor with high power and long life.
“Using the 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 the adsorption and desorption of ions,” Professor Hun Seol said, who led the study.
The research team conducted experiments both in situ (under static conditions) and operando (during charging). They found that the temperatures of the positive and negative electrodes changed by 0.92 per cent and 0.42 per cent during charging, which corresponded to 9.14 per cent and 3.91 per cent reductions in their respective Cp.
“According to thermodynamic theory, the ionic configuration entropy (a measure of randomness) of a system decreases during adsorption, i.e., charging. This also affects the free energy of the system. Together, this leads to a decrease in Cp,” Seol said.
The team also varied the concentration of the electrolyte, potassium hydroxide, to see how it affected EDLC performance. They found that the EDLC displayed maximum capacitance and Cp reduction 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 alters Cp of EDLCs,” Seol said. “These findings will extend our understanding of the underlying thermal physics of EDLCs.”
These results could be a major step towards future effective thermal management strategies, which will create safer and more reliable energy storage devices.
The study was published in Volume 188, Issue 122632 of International Journal of Heat and Mass Transfer on 1 June.