Deposition of MnO2 on KOH-activated laser-produced graphene for a flexible planar micro-supercapacitor

Abstract

The rapid development of flexible supercapacitors has been impeded by the difficulty of preparing flexible electrodes. We report the fabrication of a highly flexible and conductive microporous graphene-based substrate obtained by direct laser writing combined with KOH activation, which we call activated laser-produced graphene (a-LPG), which is then decorated with electrochemically deposited MnO₂ to form a flexible a-LIG/MnO₂ thin-film electrode. This hybrid electrode has a high areal capacitance of 304.61 mF/cm² at a current density of 1 mA/cm² in a 1 mol/L Na₂SO₄ aqueous electrolyte. A flexible asymmetric supercapacitor with a-LIG/MnO₂ as the anode, a-LIG as the cathode and PVA/ H₃PO₄ as a gel electrolyte was assembled, giving an areal energy density of 2.61 μWh/cm² at a power density of 260.28 μW/cm² and an ultra-high areal capacitance of 18.82 mF/cm² at 0.2 mA/cm² with 90.28% capacitance retained after 5 000 cycles. It also has an excellent electrochemical performance even in the bent state. This work provides an easy and scalable method to design high-performance flexible supercapacitor electrodes and may open a new way for their large-scale fabrication.