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

Abstract 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.