Multiscale modelling of supercapacitors with hierarchical structure

Structural supercapacitors (SSCs) are a class of multifunctional composites that simultaneously provide load-carrying and energy storage capacities. This paper presents a physics-based continuum multiscale electrochemical model aimed at understanding the influence of design decisions on the electrochemical performance of mechanically robust supercapacitors (SCs). The approach was exemplified by considering carbon aerogel-modified carbon fibre-reinforced multifunctional electrodes in a room-temperature ionic liquid (RTIL) electrolyte. The new pseudo 4D (P4D) multiscale model integrates a 3D macroscopic dynamic model to solve the charge transport while coupling a 1D microscopic equilibrium electric double layer (EDL) model to determine the local voltage-dependent double layer capacitance of the porous structural electrode. The numerical model was evaluated to simulate the conventional electrochemical device characterisation methods: cyclic voltammetry, galvanostatic charging and discharging, and electrochemical impedance spectroscopy. The model achieved prediction errors below 10 % for specific energy and capacitance, and around 20 % for specific power. Additionally, an asymmetrical electrochemical behaviour was predicted on the symmetric cell, exhibiting an unbalanced potential window and capacitance at the negative and positive electrodes. Overall, the proposed P4D multiscale electrochemical model provides a powerful tool for analysing, developing, and optimising SSCs and more general SCs with porous electrodes.