Effect of calendering and coating formulations on conductivity in paper-based electrodes

The paper industry together with the printing industry has the ability to produce large areas. In many technologies, for example solar-cells, displays and energy storage, there is a need for at least one electrically conductive electrode in order to make a device. We have investigated a system of conductive coatings, containing nano-graphite, graphene and a conductive carbon black to make "paper" electrodes. Cellulose nano-fibrils were used as a binder in the coatings. Rheological measurements of the system show strong interactions, giving coating colours at low solids content processable viscosities and resulting in coatings with high porosities. This was confirmed from SEM images. Conductive carbon black is the standard solution to get high conductivity in graphitic battery electrodes. Our intention was to fill the graphene/nano-graphite coatings with small conductive carbon black particles to produce denser coatings with higher conductivity. However, there was a decrease in electrical conductivity rather than the desired increase. Calendering, a common papermaking technology, gave on the other hand a very positive effect on the electrical conductivity. Calendered samples had resistance as low as 1.6 Ohm/sq at 15 gsm coat weight.