Combining electrochemical, molecular simulation and operando techniques to investigate the stability of electrodes and organic electrolytes used in EDLCs

Abstract

A comprehensive study involving Electrochemical, Mass Spectrometry, Raman & FT-IR operando analyses, and Molecular Dynamics Simulations is present to evaluate the stability of electrodes and electrolytes used in organic-based EDLCs. In this sense, we present some directions to correctly determine the maximum stable cell voltage, specific capacitance, energy, and power, as well as the equivalent series resistance. Multi-walled carbon nanotubes and activated carbon electrodes are contrasting in symmetric devices filled with 1.0 M LiTFSI and TEABF4 salts dissolved in AN, PC, and EC:DMC electrolyte. We observed anomalous transport caused by adsorption effects in the electrical double-layer in all electrochemical studies due to the defective nature of the ionic channels in the presence of displacement of finite-sized charge carriers. This behavior is unequivocally verified from the impedance analysis using a double-channel transmission line model representing the macrohomogenous behavior of the electrochemical system. The residual gas analysis suggested a maximum stable voltage of 3 V to avoid electrolyte degradation. The carbon-based electrodes remain stable in all cases, as evidenced by the Raman & FT-IR operando studies. We verified that the AC/TEABF4-PC/AC system is auspicious for further studies aiming to develop EDLC prototypes with high specific capacitance, energy, and power characteristics. The derivative analysis method involving the galvanostatic findings permitted us to verify the different dynamics regarding the charge-storage process in macro and microporous structures as a function of the applied current. Computational simulations indicated that [TEA]+ has a high affinity for the carbon electrodes, which is related to the higher electrochemical stability of TEABF4-PC.