All-in-one inks for one-step printing of solid-state graphene micro-supercapacitors on cellulose substrates

Printable graphene inks, widely developed for micro-supercapacitors (MSCs), facilitate the fabrication of microscale graphene electrodes with complex interdigitated structures. However, dense graphene flake packing in printed electrodes hinders electrolyte penetration, reducing the electrode/electrolyte interface for the electric double layer and thereby limiting the capacitance. Here, all-in-one inks are introduced to print electrodes and electrolytes simultaneously for graphene MSCs. The inks are prepared based on graphene flakes coated with polypropylene carbonate (PPC) and an ionic liquid (IL). Printing these inks through an appropriately designed stencil on cellulose substrates forms interdigitated graphene electrodes along with solid-state PPC/IL layers that enable ion transport between the electrodes. Furthermore, the IL deposited with graphene flakes in the printed electrodes enhances the electrode/electrolyte interface, promoting the formation of the electric double layer. The resulting graphene MSCs exhibit exceptional areal capacitance, exceeding 4 mF cm⁻². This one-step printing method also allows the fabrication of graphene MSCs in parallel or series connections, which extends operating time or voltage, offering a streamlined and scalable approach for the production of high-performance solid-state graphene MSCs.