Molecular Understanding of Heat Transfer in Ionic-Liquid-based Electric Double Layers

Electric double layer capacitors(EDLCs)as promising electrical energy storage devices are faced with thermal management issues,which concern the performance and lifetime of the devices.Heat transfer at the solid-liquid interface has a crucial impact on the thermal management of EDLCs.In this work,the interfacial thermal resistance(Kapitza resistance)of the interface between ionic liquid(IL)and graphite electrode is determined,and the heat transfer resistance in the uncharged/charged system with different temperatures is investigated via molecular dynamics simulations.It is found that Kapitza resistance near the negative-charged interface decreases by 23%compared to that in the uncharged system,while the temperature effect on Kapitza resistance is little in our simulation.The unique ion layer structure of ILs formed at the interface may influence the thermal transport performance.Simulations are performed to investigate the effects of surface charge and working temperature on the heat transfer resistance of interfacial ILs from three aspects:ionic spacing,inter-ion interaction,and heat capacity.With the influence of surface charge,ionic spacing in the electric double layer is found to decrease while the inter-ion interaction and heat capacity increase,leading to the reduction in thermal resistance of interfacial ILs.However,rising temperature has small effects on the three thermal properties,with a slight tendency to increase the thermal resistance of ILs.