Electrophoretic deposition of a supercapacitor electrode of activated carbon onto an indium-tin-oxide substrate using ethyl cellulose as a binder

A transparent energy storage device is an essential component for transparent electronics. The increasing demand for high-power devices stimulates the development of transparent supercapacitors with high power density. A transparent electrode for such supercapacitors can be assembled via the electrophoretic deposition of an active material powder with a binder onto a transparent substrate. The properties of the binder critically influence the electrochemical behavior and performance of the resulting electrode. Ethyl cellulose (EC) is known as an eco-friendly, transparent, flexible, and inexpensive material. Here, we fabricated an electrode film with EC binder via electrophoretic deposition on an indium tin oxide (ITO) substrate instead of using the conventional polytetrafluoroethylene (PTFE) binder. The assembled electrodes with EC and PTFE were compared to investigate the feasibility of EC as a binder from different perspectives, including homogeneity, wettability, electrochemical behavior, and mechanical stability. The EC enabled the formation of a homogeneous film composed of smaller particles and with a higher specific capacitance compared with films prepared with PTFE. The annealing improved the adhesion strength of the EC because of its glass transition; however, its hydrophobic nature limited utilization of the active material for charge storage. Subsequent electrochemical activation improved the wettability of the electrode, resulting in an increased capacitance of 60 F g⁻¹. Furthermore, even with the lower wettability of EC compared with that of PTFE, better rate performance was possible with the EC electrode. The increased mechanical stability after the annealing process ensured an excellent cycle life of 95 % capacitance retention for 15,000 cycles.