Effect of coolant on the thermal management performance for the supercapacitors by immersion cooling

Supercapacitors generate great amount of heat inside during operation at high current density, causing the rapid and high temperature rise. Immersion cooling shows great potential for thermal management of supercapacitor due to low contact thermal resistance and high heat dissipation efficiency. The coolant is a critical factor of immersion cooling. When the operating temperature exceeds 82.5 °C, the acetonitrile-based electrolyte begins to boil and the supercapacitor will fail. In this work, the cooling performance of supercapacitor immersed in different coolants of water-ethylene glycol solution (WG, 50/50 vol%), fluorinated liquid (FL), mineral oil (MO), and silicone oil (SO) are investigated. Results show that after 90 cycles at 200 A, the average temperatures of supercapacitor in WG, FL, SO, and MO are reduced to be 35.2 °C, 45.4 °C, 49.0 °C and 48.8 °C with temperature differences of 5.3 °C, 8.5 °C, 9.7 °C and 5.7 °C, respectively, compared to that of 65.3 °C and 33.9 °C for air cooling after only 17 cycles. WG immersion exhibits best cooling capability due to high convective heat transfer coefficient and specific heat capacity. However, voltage retention after immersed in WG for 10 h is only 93.5 % due to relative high conductivity. SO immersion shows poor cooling efficiency owing to low convective heat transfer coefficient and specific heat capacity. FL immersion exhibits favorable cooling and electrochemical performance, but it suffers from a high cost. This study offers guidelines for coolant selection in supercapacitor immersion thermal management systems.