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

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.