Electrochemically Exfoliated Chlorine‐Doped Graphene for Flexible All‐Solid‐State Micro‐Supercapacitors with High Volumetric Energy Density

Graphene-constructed micro-supercapacitors (MSCs) have received considerable attention recently, as part of the prospective wearable and portable electronics, owing to their distinctive merits of well-tunable power output, robust mechanical flexibility, and long cyclability. In the current work, the focus is on the fabrication of high-quality and solution-processible chlorine-doped graphene (Cl-G) nanosheets through a handy yet eco-friendly electrochemical exfoliation process. The Cl-G is characteristic of the large lateral size of ≈10 µm, abundant nanopores with sizes of as small as 2 nm, as well as numerous steps from the rugged surface. Arising from the rich chemical functionalities and structure defects, the all-solid-state MSC built by using Cl-G via a facile mask-assisted method delivers a large reversible capacity and ultrasteady charge/discharge performance, with the capacitance being maintained at 98.1% even after 250 000 cycles. The Cl-G-MSC with EMIMBF₄ /PVDF-HFP as the electrolyte displays a large volumetric capacitance up to 160 F cm^-3 at the scan rate of 5 mV s^-1 and high volumetric energy density of 97.9 mW h cm^-3 at the power density of 3.4 W cm^-3 . The device can also output a high voltage up to 3.5 V and robust capability with 94.8% of capacitance retention upon 10 000 cycles.