3.1 Production of an energy-storage electrode paper using a pilot-scale paper machine
The global efforts in electrifying our society requires an enormous capacity of electrical energy storage. This drives the demand for low-cost and sustainable solutions, where electrode materials of various kinds are key components. In the present work, all-organic supercapacitor electrodes have successfully been demonstrated, which were produced in a pilot-scale paper machine, thereby showing the feasibility of large-scale production of “paper-based” energy technology. The material concept was based on activated charcoal as the active charge-storage material combined with cationized cellulose pulp, the latter having small amounts of electrostatically adsorbed PEDOT:PSS which provides a percolating conducting network. In a pre-trial lab experiment, it became evident that even a small amount of 1wt% PEDOT:PSS gave a large increase in capacitance . In the pilot trials, the addition of carboxymethylated cellulose nanofibrils and/or carbon black was further investigated. The different additives significantly affected several critical paper properties, where the nanofibrils improved mechanical properties while the carbon black enhanced both the in-plane conductivity and specific capacitance of the activated charcoal. The achieved specific capacitance of the activated charcoal of 67 F/g along with the mass loading of 44% in the paper gave an electrode specific capacitance up to 29.4 F/g, which is comparable to commercial supercapacitor electrodes. The successful production of several 10-meter-long rolls of supercapacitor paper electrodes shows the feasibility of producing energy storage devices with “classical” papermaking methods, and the work as a whole provides valuable insights on how to further advance bio-based energy storage solutions for large-scale applications.