Sand-Milling Fabrication of Screen-Printable Graphene Composite Inks for High-Performance Planar Micro-Supercapacitors

Rational engineering and simplified production of printable graphene inks are essential for building high-energy and flexible graphene micro-supercapacitors (MSCs). However, few graphene-based MSCs show impressive areal capacitance and energy density, especially based on additive-manufacturing, cost-effective, and printable inks. Herein, a new-style and solution-processable graphene composite ink is ingeniously formulated for scalable screen printing MSCs. More importantly, the as-formulated inks consist of interwoven two-dimensional graphene and activated carbon nanofillers, which are delaminated by one-step sand-milling turbulent flow exfoliation. Notably, embedding the activated carbon nanoplatelets into graphene layers drastically boosts the electrochemical performance of screen-printed micro-supercapacitors (denoted as Gr/AC-MSCs), such as an outstanding areal capacitance of 12.5 mF cm–2 (about 20 times than pure graphene). The maximum energy density, maximum power density, and exceptional cyclability are 1.07 μW h cm–2, 0.004 mW cm–2, and 88.1% after 5000 cycles, respectively. As such, the as-printed MSCs on paper display high resolution and pronounced energy-storage performance. Furthermore, the packaged and optimized Gr/AC-MSCs showcase remarkable mechanical flexibility even under highly folded and excellent water resistance, maintaining 91.8% capacitance retention after being washed for 90 min. The versatile methodology highlights the promise of graphene and analogous 2D nanosheet functional inks for scalable fabrication of flexible energy-storage devices.