Layered coating of ultraflexible graphene-based electrodes for high-performance in-plane quasi-solid-state micro-supercapacitors.

To meet the demand of rapid development of portable and wearable electronic devices, in-plane quasi-solid-state micro-supercapacitors (QSS MSCs) have great potential as miniaturized energy storage devices. However, their ultralow areal capacitance and poor flexibility limit their practical applications. Here, we demonstrate a new strategy for the fabrication of ultraflexible MnO2@reduced graphene oxide (rGO) films (MGFs) for high-performance planar QSS MSCs through a facile layer-by-layer coating and a laser engraving method. Benefiting from conductive and flexible rGO films reduced by HI, the MGF based symmetrical QSS MSC exhibits a high areal capacitance (31.5 mF cm-2 at 0.2 mA cm-2), excellent flexibility (no capacity degradation at a bending radius from ∞ to 0 cm), and outstanding cycling stability (retaining 77.0% of its initial capacity after 6000 cycles). Most importantly, the electrochemical performance of QSS MSCs can be multiplied by simply adding more MGF layers. By adding up to 5 MGF layers, the MSC can deliver an ultrahigh areal capacitance of 144.3 mF cm-2 at 0.3 mA cm-2, and a superior energy density of 13.9 mW h cm-3 at 34.7 mW cm-3. Therefore, this work offers versatile quasi-solid-state MSCs and provides an impressive strategy to enhance electrochemical performance which will greatly enrich the design and fabrication of MSCs.