Balancing Carbon Percolation and MnO 2 Pseudocapacitance in a Few-Layer Graphite/Carbon Black Waterborne Ink for Screen-Printed Planar Microsupercapacitors

Waterborne conductive inks for screen-printed planar microsupercapacitors (MSCs) must reconcile low-cost processing, print fidelity, electronic conduction, and electrochemical activity. Graphite/carbon black (CB) networks provide scalable conduction but limited charge storage, whereas excessive manganese dioxide (MnO2) can disrupt electron and ion pathways. Here, we identify a practical composition window, within the tested range, for a ternary few-layer graphite (F-GT)/CB/MnO2 ink prepared by high-speed dispersion and planetary ball milling. F-GT forms the long-range conductive scaffold, CB bridges interflake junctions, and MnO2 supplies pseudocapacitive sites without dominating the percolated carbon network. The optimized ink exhibited shear-thinning behavior and reproduced fine patterns on paper and PET. At an F-GT/CB/MnO2 mass ratio of 5:1:3, screen-printed MSCs with a PVA/LiCl gel electrolyte delivered 19.7 mF cm–2 and 9.95 F cm–3 and 1.34 F g–1 at 0.05 mA cm–2 and 2.73 μWh cm–2 at 0.025 mW cm–2. The devices retained 83.7% of their capacitance after 5000 charge–discharge cycles and 90.5% after 1000 bending cycles. Three series-connected devices operated at 3 V and powered a green light-emitting diode. These results show how MnO2 loading can add oxide-based charge storage while preserving a low-cost graphite-derived conductive framework for flexible printed energy storage.