Sand‐Milling Exfoliation of Structure Controllable Graphene for Formulation of Highly Conductive and Multifunctional Graphene Inks

Abstract Conductive graphene inks have shown a great potential for the manufacturing of high‐performance flexible wearable electronics. However, the lack of cost‐effective, straightforward, and facile routes to formulate multifunctional graphene aqueous inks with excellent conductivity and high apparent viscosity have greatly limited their applications, particularly in high concentration processing and additive‐manufacturing. Here, the high‐concentration graphene aqueous inks based on structure controllable, sand‐milling exfoliation of raw graphite is reported. Such a route yields 62.8% graphene dispersed in water with a high concentration up to 25.1 mg mL −1 , which can be formulated into aqueous inks with excellent printability. As such, the screen printing of the viscous graphene inks into film‐heating devices and micro‐supercapacitors (MSCs) is further demonstrated. Due to its excellent conductivity (up to ≈870 S cm −1 after annealing), the graphene film showcases a fast ramping temperature (171.9 °C) at 8 V in 75 s in the heating device, and a high areal capacitance (1.36 mF cm −2 ) in the MSCs, respectively. It is thus believed that the mechanical‐exfoliated graphene inks hold great promise in scalable production of high‐performance printable wearable electronics.