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.