High-performance hierarchical MnO2/CNT electrode for multifunctional supercapacitors

Supercapacitors possessing multiple functions other than storing energy, such as bearing mechanical loads, are a promising technology for a wide range of applications. However, achieving both energy storage efficiency and mechanical strength/stiffness requires structurally strong electrolytes and high-capacitance electrodes. Herein, we report a novel method of synthesizing a high-mass loading of MnO2 on carbon nanotube (CNT) mats to create nanocomposite electrodes of high capacitance and mechanical properties. With CNTs acting as structural reinforcement for the pseudocapacitive MnO2 matrix, the resulting nanocomposite electrodes exhibited an ultrahigh areal capacitance of 2579 mF/cm2 at a current density of 1 mA/cm2 and excellent mechanical properties. These electrodes were then used to fabricate flexible and mechanically strong structural supercapacitors by infusing with a PVA gel electrolyte and a PEGDGE solid electrolyte, respectively. The resulting flexible supercapacitors yielded a high areal capacitance of 947 mF/cm2 while the structural supercapacitors gave a high tensile modulus of 6.1 GPa. These results demonstrated that the hierarchical MnO2/CNT electrodes could provide both excellent energy storage capability and structural stiffness and strength, expanding their applications beyond mono-functional supercapacitors.