Modeling of yarn-shaped supercapacitors - Unraveling its length dependent output

Abstract

Yarn-shaped energy-storage devices are promising power sources for electronic textiles, since they carry the possibility to be seamlessly integrated into various fabrics. The energy/power outputs of these devices are inevitably a function of their lengths, the dependence on which is yet to be thoroughly explored. Despite numerous research on yarn-shaped supercapacitors (YSCs) and batteries, the correlation between yarn length and their electrochemical output remains ambiguous, and sometimes even controversial. Herein, a dual transmission-line model for YSCs is created and used to fit the electrochemical impedance spectra (EIS) of YSCs ranging from 10 cm to 300 cm in length. The evolution of equivalent series resistances, electrolyte diffusion resistances and capacitances of YSCs as yarn length increases is investigated. Given the structure and components of YSCs used in this study, a favorable length range of 40–60 cm has been identified to achieve the best electrochemical performance, including the lowest internal resistance and the highest specific capacitance, where the highest energy and power densities sit. The mathematical model introduced in this work provides a reasonable description of the electrochemical behaviors of YSCs in different yarn lengths, offering a theoretical foundation to guide the design of these devices for specific application scenarios.