MnO2 nanoparticles anchored on carbon nanotubes with hybrid supercapacitor-battery behavior for ultrafast lithium storage

Abstract

Developing hybrid supercapacitor-battery energy storage devices for applications in electric vehicles is attractive because of their high energy density and short charge/discharge time. In this study, flexible MnO2 nanoparticle-coated air-oxidized carbon nanotube (MnO2/aCNT) electrodes are fabricated by the in situ redox reaction of KMnO4 and aCNTs at room temperature. The MnO2 nanoparticles have diameters of ∼10 nm. There is a strong chemical interaction between the MnO2 active material and aCNTs as a result of the Mn–O–C linkage. The flexible aCNT network can alleviate the strain from the MnO2 volume change and maintain the electrode integrity during rapid charge/discharge. The aCNT framework also provides a continuous and rapid electron pathway and ensures uniform dispersion of the MnO2 nanoparticles. The presence of MnO2 nanoparticles provides short pathways for Li-ion diffusion and allows interfacial capacitive lithium storage for ultrafast and reversible lithium storage. We report the best high-current performance to date for MnO2/C electrodes, of 395.8 mA h g−1 at 10 A g−1, and 630.2 mA h g−1 after 150 cycles at 2 A g−1. The excellent electrochemical performance, combined with the capacitive dominating process of the electrode, will further the design of high-performance hybrid supercapacitor-battery energy storage devices.