Modelling and optimization of electrodes utilization in symmetric electrochemical capacitors for high energy and power Innocent S. Ike a,b,c,d, *, Iakovos Sigalas a,b,c , Sunny E. Iyuke a a School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Private Bag 3, Johannesburg, South Africa b Materials for Energy Research Group (MERG), University of the Witwatersrand, Private Bag 3, Johannesburg 2050, South Africa c DST/NRF Centre of Excellence in Strong Materials (COE-SM), University of the Witwatersrand, Private Bag 3, Johannesburg 2050, South Africa d Department of Chemical Engineering, Federal University of Technology, Owerri, Nigeria A R T I C L E I N F O Article history: Received 3 November 2016 Received in revised form 21 March 2017 Accepted 11 May 2017 Available online xxx Keywords: Electrode thickness Current density Effective conductivity Modelling and simulation Electrode utilization Potential drop A B S T R A C T Expressions and guidelines for determination of electrode's effective thickness, optimum charging current density and electrode utilization in device with certain electrode's and electrolyte's effective conductivity were developed, and systematically used to study the performance of electrochemical capacitors (ECs). Effective thickness of electrode increases along with increase in effective conductivity of electrolyte and decreases as charging current density is increase. It was seen that every current density applied to device of specific electrode's and electrolyte's effective conductivity has corresponding effective thickness of electrode, and when charged at current density higher than its maximum current density, materials (electrodes) utilization was less than 100%. Also, when device with electrode's thickness higher than the effective thickness was charged at its maximum current density, materials (electrodes) utilization reduced below 100%. Materials utilization decreases along with increase in charging current density and electrode thickness, but increases as effective conductivity of electrode and electrolyte are increase. Therefore, optimum/effective thickness of electrode and optimum current density must be employed in charging device of given electrode's and electrolyte's effective conductivity for maximum materials utilization and performance (with minimum or no potential drop). Optimum current density beyond which energy density decays increases along with increase in electrode's and electrolyte's effective conductivity and decrease in electrode thickness. Use of optimum current density and effective electrode's thickness to maximize energy and power densities is inevitable, because increase in current density results in increase in power density and decrease in energy density. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction Electrochemical capacitors (ECs), also known as supercapaci- tors or ultracapacitors, have drawn reasonable attention in academia as well as industry, due to some easily distinguishable merits like higher power density, long cycle, fast charge and discharge rates, low cost, and environmental friendliness when compared with batteries and fuel cells [1–5]. ECs have attracted considerable interest in different areas of applications demanding high power density. Nevertheless, the major challenge for existing ECs is the energy density that is usually much less than those of batteries and fuel cells, even for pseudocapacitors and hybrid capacitors. The low energy density of existing ECs cannot completely serve the growing demand of applications that needs high energy density, and therefore, limits their general application [4,6–9]. In order to prevail over this challenge, substantial study has been dedicated to improve the energy density of ECs [10,11], so as to enlarge the scope of their application. Modern ECs with high operation voltage and energy density without compromising their advantages of high power capability and cyclability are inevitable. According to the expression for determining energy density of ECs given asE ¼ CV 2 2 , the effective approach to enhance the energy density (E) is by increasing either or both specific capacitance (C) and the cell operating voltage (V), which is decided by the structure and properties of electrode materials and nature of electrolyte employed [12]. This energy density enhancement can be achievable via development of electrode materials with high capacitance, electrolytes with large operating potential range, and desegregated structures with novel and optimized system [13,14]. * Corresponding author at: School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Private Bag 3, Johannesburg, South Africa. E-mail address: innocent.ike@students.wits.ac.za (I.S. Ike). http://dx.doi.org/10.1016/j.est.2017.05.006 2352-152X/© 2017 Elsevier Ltd. All rights reserved. Journal of Energy Storage 12 (2017) 261–275 Contents lists available at ScienceDirect Journal of Energy Storage journa l home page : www.e lsevier.com/loca te/est