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 (C-areal) values up to 1.324 mF cm(-2) (5.296 mF cm(-2) for a single electrode), corresponding to an outstanding volumetric capacitance (C-vol) 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 mu Wh 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 degrees). 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.