Scalable Production of Graphene Inks via Wet‐Jet Milling Exfoliation for Screen‐Printed Micro‐Supercapacitors

The miniaturization of energy storage units is pivotal for the development of next‐generation portable electronic devices. Micro‐supercapacitors (MSCs) hold great potential to work as on‐chip micro‐power sources and energy storage units complementing batteries and energy harvester systems. Scalable production of supercapacitor materials with cost‐effective and high‐throughput processing methods is crucial for the widespread application of MSCs. Here, wet‐jet milling exfoliation of graphite is reported to scale up the production of graphene as a supercapacitor material. The formulation of aqueous/alcohol‐based graphene inks allows metal‐free, flexible MSCs to be screen‐printed. These MSCs exhibit areal capacitance (Careal) values up to 1.324 mF cm−2 (5.296 mF cm−2 for a single electrode), corresponding to an outstanding volumetric capacitance (Cvol) of 0.490 F cm−3 (1.961 F cm−3 for a single electrode). The screen‐printed MSCs can operate up to a power density above 20 mW cm−2 at an energy density of 0.064 µWh cm−2. The devices exhibit excellent cycling stability over charge–discharge cycling (10 000 cycles), bending cycling (100 cycles at a bending radius of 1 cm) and folding (up to angles of 180°). Moreover, ethylene vinyl acetate‐encapsulated MSCs retain their electrochemical properties after a home‐laundry cycle, providing waterproof and washable properties for prospective application in wearable electronics. Single‐/few‐layer graphene flakes, produced via scalable wet‐jet milling exfoliation of graphite, are used as the active material for micro‐supercapacitors (MSCs). The formulation of aqueous‐alcohol graphene inks, as well as the addition of carbon nanotubes, allows for the interdigitated structure to be screen‐printed on plastic substrates for metal‐free, flexible, solid‐state, and washable MSCs with high areal performance.