Developing High-Performance Flexible Zinc Ion Capacitors from Agricultural Waste-Derived Carbon Sheets

A rechargeable zinc ion capacitor (ZIC) employing a metallic anode, nature-abundant materials-derived high-performance cathode, and an aqueous electrolyte represents an interesting combination of high capacitance, high power, safety operation, and overall a sustainable and economic system, which make them a leading power source to portable consumer electronics. However, it is often a challenge to fabricate a large-area flexible device with a metallic anode due to the characteristic rigidity of the metal. Herein we present a high-performance aqueous ZIC based on abundant agricultural waste biomass ( Areca Catechu sheath)-derived high-surface-area (2760 m 2 /g) mesoporous multilayer-stacked carbon sheets as the capacitive electrode in 1 M ZnSO 4 electrolyte. In coin cell configuration, the ZIC showed a high specific capacitance of 208 F/g at 0.1 A/g, a good rate capability, and an outstanding cyclic stability with 84.5% capacitance retention after 10 000 cycles at a current density of 5 A/g. We also demonstrate an easy and scalable strategy to fabricate a large-area flexible zinc ion capacitor with laser-scribed carbon (LSC@PI), scribed on a polyimide film with customizable area as the flexible current collector for both anode and cathode. Electrodeposition of zinc onto LSC@PI as anode showed a very low plating stripping overpotential, and the flexible sandwich-type ZIC with an electrolyte-soaked paper separator exhibited excellent flexibility and a high areal capacitance of 128.7 mF/cm 2 at 100 mA/cm 2 current when bended at an angle of 110°, corresponding to an energy density of 32.6 μW h/cm 2 . When the current was increased by 20 times, the flexible device under bending condition could provide an energy density of 11 μW h/cm 2 at a high power density of 1.906 W/cm 2 . The synthesized materials were characterized by X-ray diffraction (XRD), RAMAN, Field Emission Scanning Electron Microscope (FESEM), and Brunauer–Emmett–Teller (BET) analysis, whereas the electrochemical performances were measured in terms of cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and Electrochemical impedance spectroscopy (EIS) analysis.