Supercapacitors with lithium-ion electrolyte: an experimental study and design of the activated carbon electrodes via modelling and simulations

Electrochemical double layer capacitors (EDLCs) are investigated with activated carbon electrodes and a lithium-ion electrolyte, in anticipation of potential future applications in hybridised battery-supercapacitor devices and lithium ion capacitors. An experimental study of a symmetric electrochemical double layer capacitor (EDLC) with activated carbon (AC) electrodes on aluminium foil current collectors and electrolyte 1 M LiPF6 in EC:EMC 50:50 v/v concludes a stability window to a maximum potential of 3 V, an equivalent in series resistance of 48 Ω for 1 cm2 cell area (including the contact resistance between electrode and current collector) and an average specific electrode capacitance of 50.5 F g−1. Three AC electrode materials are assessed via computer simulations based on a continuum ion and charge transport model with volume-averaged equations, considering the pore size distribution for each electrode material and, depending on pore size, transport of tetrahedral solvated or flat solvated Li+ ions and solvated or desolvated PF6− ions. The computer simulations demonstrate that the best electrode material is an AC coating electrode with a hierarchical pore size distribution measured in the range of 0.5–180 nm and bimodal shape, and specific surface area BET = 808 m2 g−1.