Improved supercapacitors by implanting ultra-long single-walled carbon nanotubes into manganese oxide domains

Abstract

Ultra-long single-walled carbon nanotubes (SWCNTs) are implanted into thicker manganese oxide (MnO2) domains for enhancing the ultimate energy density of the MnO2 based supercapacitors. The implanted SWCNTs form a nano-meshed jungle-gym wherein the MnO2 domains are densely packed. Functioned as templates, MnO2 domains have been divided into nano-sized particles during the electrochemical deposition of the thicker MnO2 domains. Functioned as conductive paths, electrons transferred under lower resistances via the SWCNT networks during the charge/discharge. The ultimate thickness of the resultant SWCNT-MnO2, which is established on the cell-walls of nickel foams (NF; NF served as current collectors) can reach to 13.3 μm while the electrochemical performance of the SWCNT-MnO2@NF electrode remains excellent (1898 mF cm−2 capacitances; 101.9% specific capacitance retention ratios, after 10,000 times of charge/discharge). We also assembled asymmetric supercapacitor cells and obtained high energy densities (734.1 μWh cm−2) and high power densities (18.47 mW cm−2 at 277.1 μWh cm−2). Electrochemical data are analysed based on Dunn's method, new insights into the capacitive behaviours of the SWCNT-MnO2@NF are observed.