Fabrication of 10-meter Rolls of Paper Electrodes for Energy Storage on a Pilot-Scale Paper Machine

Cellulose-based electrodes for the use in energy storage devices have been demonstrated in numerous publications over the past decades. Although cellulose is an electrical insulator, properties such as electrochemical stability and an amphiphilic nature make it an excellent material for acting as a hosting material for conducting and/or electroactive materials. Perhaps the most compelling opportunity with cellulose-based electrodes is the vision of a fast, cheap, and green production of energy storage materials on paper machines. While paper-based energy storage is not expected to compete with high-end solutions in terms of performance, the presumed low cost and recyclability of such devices should be preferable in applications such as grid energy storage or to power smart paper packaging. However, as most such investigations have been done on nanocellulose composites, the majority of the reported material concepts are not applicable to the existing production assets.<br/><br/>To meet this challenge, it is important to investigate material systems based on cellulose-rich pulp fibers in paper-making settings. The present investigation was carried out on a pilot paper machine with the aim to fabricate supercapacitor electrodes. Activated carbon (AC) was selected as the main charge-storing material. Process parameters and fiber properties, in combination with the electrical characteristics of the formed electrode papers, have been analyzed to establish the relationship between the manufacturing process, raw material characteristics and the product performance.<br/><br/>The results showed a positive relationship between the electrode conductivity and the measured specific capacitance. This stresses the importance of introducing good conductors in the electrode along with the charge-storing AC, and indeed motivated the investigation of using such additives. Post-impregnation of the electrode papers with small amounts of the conductive polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) indicated a synergetic effect with the AC in terms of conductivity. The impregnation lead to conductivity increases which exceeded the separate conductivities of AC-loaded and PEDOT:PSS-impregnated papers alone, with an observed corresponding increase in charge storage capacity.<br/><br/>The pilot paper machine trials resulted in several 10-meter-long rolls of paper electrodes. With a measured electrode specific capacitance of about 50 F/g and a specific capacitance per mass unit of loaded AC of more than 80 F/g, this demonstrates the feasibility of using paper making techniques for supercapacitor electrode fabrication. Along with the knowledge provided about important aspects in their material and process design, this work advances the technological readiness of paper-based energy storage.