Stamping Fabrication of Flexible Planar Micro-Supercapacitors Using Porous Graphene Inks

Abstract

High performance, flexibility, safety, and robust integration for micro-supercapacitors (MSCs) are of immense interest for the urgent demand for miniaturized, smart energy-storage devices. However, repetitive photolithography processes in the fabrication of on-chip electronic components including various photoresists, masks, and toxic etchants are often not well-suited for industrial production. Here, a cost-effective stamping strategy is developed for scalable and rapid preparation of graphene-based planar MSCs. Combining stamps with desired shapes and highly conductive graphene inks, flexible MSCs with controlled structures are prepared on arbitrary substrates without any metal current collectors, additives, and polymer binders. The interdigitated MSC exhibits high areal capacitance up to 21.7 mF cm^-2 at a current of 0.5 mA and a high power density of 6 mW cm^-2 at an energy density of 5 µWh cm^-2. Moreover, the MSCs show outstanding cycling performance and remarkable flexibility over 10 000 charge-discharge cycles and 300 bending cycles. In addition, the capacitance and output voltage of the MSCs are easily adjustable through interconnection with well-defined arrangements. The efficient, rapid manufacturing of the graphene-based interdigital MSCs with outstanding flexibility, shape diversity, and high areal capacitance shows great potential in wearable and portable electronics.

Keywords: areal energy density; graphene inks; micro‐supercapacitors; stamping.

Figure 1

a) Schematic of the stamping fabrication of the flexible planar MSCs. b) MSCs stamped on a leaf. c) MSCs patterned with the text of “TUC.” d–f) Optical images of interdigital MSCs upon bending. g–j) Optical images of nine serially connected MSCs under flat (g), bending (h), spiral (i), and knotted (j) states.

Figure 2

a) SEM images of porous graphene. b) AFM image and c) height profile of porous graphene flakes on a silicon wafer. d) Raman spectra of hexagonal porous graphene at different locations. e) Nitrogen adsorption–desorption isotherms and pore size distribution of porous graphene. f) C1s XPS spectrum of porous graphene. g–j) TEM images of hexagonal porous graphene.

Figure 3

Electrochemical properties of the interdigital MSCs. a) Illustration of charge storage mechanism of the graphene‐based MSC. b) CV curves of MSCs tested at various potential windows. c) CV curves of MSCs tested at different scan rates. d) GCD curves of MSCs measured at various current densities. e) Areal capacitance at different current densities. Inset shows the photograph of the MSCs in series lighting a LED. f) Ragone plot of graphene‐based MSC. g) Cycling performance of the MSCs. Inset shows the first and final 10 GCD curves of the 10 000 cycles. h) Electrochemical impedance spectra of the MSCs after different charge–discharge cycles.

Figure 4

Electrochemical stability of graphene‐based MSCs during bending tests. a) Schematic illustration of the bending test. b,c) Photographs of bending supports with different bending radii. d–f) Representative photographs of MSCs bending at bending radii from 1.5 to 5 mm. g,h) CV curves tested at a scan rate of 100 mV s⁻¹ for different bending radii (g) and different bending angles (h). i) Capacitance retention as a function of bending cycles.

Figure 5

a) CV curves at a scan rate of 100 mV s⁻¹ and b) GCD curves at a current of 1 mA of integrated graphene‐based MSCs with different numbers of devices connected in series. c) CV curves at a scan rate of 100 mV s⁻¹ and d) GCD curves at 1 mA of different integrated graphene‐based MSCs connected in parallel. e) Schematic of the MSCs bridging solar cells for solar energy storage. f) Charging curve (black) of the MSCs charged by commercial solar cells, and discharging curves (blue and red) of the MSCs at different current. Inset shows a LED lightened by the energy stored in MSCs.