A team of researchers at the University of Minnesota and Northwestern University, USA, have developed a printing method to produce flexible graphene micro-supercapacitors with a planar architecture suitable for integration in portable electronic devices.
The new process, referred to as ‘self-aligned capillarity-assisted lithography for electronics’ (SCALE), begins with the creation of a polymer template, generated by stamping a UV-curable polymer with a PDMS mold. High-resolution inkjet printing is then used to deposit a graphene ink into the template, which is annealed using a xenon lamp to form the electrodes. In the final step, a polymer gel electrolyte is printed onto the template over the electrodes to complete the configuration.
The graphene ink is formulated from pristine graphene, shear-mix exfoliated from graphite flakes using a polymer stabilizer. A cyclohexanone/terpineol/di(ethylene glycol) methyl ether solvent system is used to provide a shear viscosity of just 8–12 mPa s, ensuring good capillary channel wicking of the ink during printing. The PDMS stamp can be used multiple times, and there is the potential for scalable roll-to-roll processing of graphene electronics, including complex interdigitated architectures, using this technique.
Arrays of micro-supercapacitors were printed onto a flexible PET film and their electrochemical performance was tested. It was reported that all printed devices were found to be functional, and it was determined that fewer electrode fingers provided a higher specific capacitance value, with larger energy and power densities.