Scaling Analysis of Thermal Behavior of Electrical Double Layers

Charging of electric double layer capacitors (EDLCs) may cause significant heat generation. The resulting elevated temperatures lead to shortened cell life and increased self-discharge rates and cell pressure. Better understanding and accurate modeling of the fundamental physical phenomena involved are needed for developing thermal management strategies and for designing and optimizing the next generation of EDLCs. Existing thermal models of EDLCs rely on experimentally measured heat generation rates or cell electrical resistances. This makes them unsuitable for assessing new and untested designs. The present study aims to develop a physical model accounting for the dominant transport phenomena taking place in EDLCs. It accounts for the presence of the Stern layer, finite ion size, ion diffusion, and Joule heating. It solves the modified Poisson-Nernst-Planck model with a Stern layer and the heat diffusion equation. A dimensional analysis was performed and six dimensionless parameters governing electrodiffusion coupled with heat transfer were identified and physically interpreted. The scaling analysis was successfully validated numerically.