Molecular insights into temperature oscillation of electric double-layer capacitors in charging-discharging cycles

Electric double-layer capacitors (EDLCs) are promising electric energy storage devices for increasing global energy demand. During charging-discharging cycles, the generated heat results in temperature variation inside EDLCs, but its intrinsic molecular mechanism remains unclear. Most of existing models are based on fluid continuum hypothesis, neglecting the EDL layering structure, which causes large deviation in temperature profile from experimental observations. To tackle this problem, herein we propose a theoretical framework for the microscopic heat transfer coupled with the local fluid structure from non-equilibrium statistical mechanics, which precisely captures the layering effect of EDL structure on thermal transport in EDLCs. With the inclusion of molecular interactions, strong temperature oscillation is observed when periodically voltages are applied, accompanied by the formation/desorption of EDL. Several factors regulating the EDL structure and the local temperature are evaluated. We observe that the decrease of applied voltage and ionophilicity weakens the electrode-fluid interactions and suppresses the temperature oscillation, leading to a slower temperature promotion. This work offers a molecular perspective into the thermal transport in EDLCs, and provides a theoretical guidance for realizing the directional thermal management of electrochemical devices.