A design-based predictive model for lithium-ion capacitors

Recent years have seen substantial developments of lithium-ion capacitor (LIC) technology. However, there has been little research in physics-based models to predict the performance of LICs. Existing models have focused upon cell degradation over time or equivalent circuit models to describe laboratory work. Experimentalists have determined that LICs' energy storage capabilities are inversely proportional to their charge or discharge current. This study developed a physics-based model in Simulink to predict this relationship as a function of a LIC's constituent materials' properties, charge current, and their effects upon the LIC's internal temperature in accordance with the Butler-Volmer equation. The Butler-Volmer temperature increase and the LIC's exchange current in turn affected the capacitance of the LIC. Once these relationships were understood, the model was able to predict energy storage as a function of charge power. Additionally, the model was able to estimate LIC voltage and therefore state of charge. This is the first known physics-based model to predict an LIC's energy storage as a function of its charge current.