High-Throughput Processing of Nanographite–Nanocellulose-Based Electrodes for Flexible Energy Devices
Rajesh Koppolu, Nicklas Blomquist, Christina Dahlström, Martti Toivakka
Abstract
The current work aims at understanding factors that influence the processability of nanographite–nanocellulose suspensions onto flexible substrates for production of conductive electrodes. A custom-built slot-die was used in a continuous roll-to-roll process to coat the nanomaterial suspension onto substrates with varying surface smoothness, thickness, pore structure, and wet strength. The influence of a carboxymethyl cellulose (CMC) additive on suspension rheology, water release properties, and coating quality was probed. CMC addition reduced the suspension yield stress by 2 orders of magnitude and the average pore diameter of the coated electrodes by 70%. Sheet resistances of 5–9 Ω sq<sup>–1</sup> were obtained for the conductive coatings with a coat weight of 12–24 g m<sup>–2</sup>. Calendering reduced the sheet resistance to 1–3 Ω sq<sup>–1</sup> and resistivity to as low as 12 μΩ m. The coated electrodes were used to demonstrate a metal-free aqueous-electrolyte supercapacitor with a specific capacitance of 63 F g<sup>–1</sup>. The results increase our understanding of continuous processing of nanographite–nanocellulose suspensions into electrodes, with potential uses in flexible, lightweight, and environmentally friendly energy devices.