Electrochemical and Thermal Characterization of a Graphene-Based Electrochemical Double-Layer Capacitor (EDLC)

Graphene-based electrodes are of great interest for developing high performance electrochemical double-layer capacitors (EDLCs) due to their excellent electrochemical properties, low electric resistance and unique structures. Meanwhile, EDLCs have become more attractive not only to offer high power and energy densities but also to withstand a harsh temperature ranges [1]. Since temperature effects can be crucial to estimate the rational evaluation of degradation, energy efficiency and lifetime, it requires better understanding of temperature-dependent electrochemical properties especially at electrode/electrolyte interfaces. In this study, the performance of an EDLC, assembled with two identical graphene electrodes and the 1M Et₄NBF₄/PC electrolyte in a coin cell, is systemically characterized under various operating temperature conditions, ranged from -30 °C to 60 °C. Graphene deposition is carried out by using the vacuum filtration method. This method yields an electrically strong conductive and thermally stable nano-structured graphene paper [2]. Electrochemical characterization techniques including cyclic voltammetry (CV), constant charging/discharging (CCD) and electrochemical impedance spectroscopy (EIS) are performed to evaluate capacitance retention, energy and power densities, internal resistance variation and interfacial processes at the double-layer region. In addition, EIS data is simulated with the proposed electric equivalent circuit in order to investigate the temperature dependency on interfacial reactions with respects to mass transfer (diffusion) and electrode kinetics (charge transfer) [3]. Each reaction is represented by electrical resistive elements in the equivalent circuit, and its values are correlated with the activation energy to quantitatively rationalize the observed behaviour of diffusion and the charge transfer kinetics with temperature.

References:

[1] R. Kotz, M. Hahn, R. Gallay, Journal of Power Sources, 154 (2006) 550-555.

[2] H. Chen, M.B. Mueller, K.J. Gilmore, G.G. Wallace, D. Li, Advanced Materials, 20 (2008) 3557.

[3] J.W. Jinhee Kang, Shesha H. Jayaram, Aiping Yu, Xiaohui Wang, Electrochimica Acta, 115 (2014) 587-598.