Freestanding Three-Dimensional Graphene/MnO₂ Composite Networks As Ultralight and Flexible Supercapacitor Electrodes

TLDR

Flexible energy‑storage devices demand lightweight, efficient solutions, and graphene‑based supercapacitors are promising candidates due to their unique properties. The study develops freestanding, ultrathin 3D graphene networks loaded with MnO₂ as flexible supercapacitor electrodes and optimizes MnO₂ loading to maximize capacitance. The electrodes are fabricated by electrodepositing MnO₂ onto 0.75 mg cm⁻², <200 µm thick, 55 S cm⁻¹ 3D graphene networks, and a symmetrical device is assembled from two such networks separated by a membrane and encapsulated in PET. The composite achieves an area capacitance of 1.42 F cm⁻², a specific capacitance of 130 F g⁻¹, and a lightweight (<10 mg), ~0.8 mm thick symmetrical supercapacitor with excellent electrochemical performance, offering a low‑cost, environmentally friendly energy‑storage solution.

Abstract

A lightweight, flexible, and highly efficient energy management strategy is needed for flexible energy-storage devices to meet a rapidly growing demand. Graphene-based flexible supercapacitors are one of the most promising candidates because of their intriguing features. In this report, we describe the use of freestanding, lightweight (0.75 mg/cm(2)), ultrathin (<200 μm), highly conductive (55 S/cm), and flexible three-dimensional (3D) graphene networks, loaded with MnO(2) by electrodeposition, as the electrodes of a flexible supercapacitor. It was found that the 3D graphene networks showed an ideal supporter for active materials and permitted a large MnO(2) mass loading of 9.8 mg/cm(2) (~92.9% of the mass of the entire electrode), leading to a high area capacitance of 1.42 F/cm(2) at a scan rate of 2 mV/s. With a view to practical applications, we have further optimized the MnO(2) content with respect to the entire electrode and achieved a maximum specific capacitance of 130 F/g. In addition, we have also explored the excellent electrochemical performance of a symmetrical supercapacitor (of weight less than 10 mg and thickness ~0.8 mm) consisting of a sandwich structure of two pieces of 3D graphene/MnO(2) composite network separated by a membrane and encapsulated in polyethylene terephthalate (PET) membranes. This research might provide a method for flexible, lightweight, high-performance, low-cost, and environmentally friendly materials used in energy conversion and storage systems for the effective use of renewable energy.