Application of binder-free TiOxN1−x nanogrid film as a high-power supercapacitor electrode

Binder-free TiOxN1−x nanogrid films with high conductance, high specific surface area, and high electrochemical stability can meet the demand for high-performance supercapacitor materials. A metal-phase TiOxN1−x nanogrid film was prepared by a simple hydrothermal-nitrification method. The TiOxN1−x nanogrid film showed higher specific surface area (75.9 m2 g−1) and lower impedance than nanosheet, nanowire, and nanoribbon films. As a result, the TiOxN1−x nanogrid electrode showed the highest specific capacitance (8.28 mF cm−2), the highest capacitance retention (95.8%) after 10,000 galvanostatic charge/discharge cycles, and the highest operating frequency (398 Hz). To improve the power density and energy density of the supercapacitor, an organic electrolyte (1 mol L−1 tetraethylammonium tetrafluoroborate in acetonitrile, TEA-BF4/AN) and a room temperature ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, EMIM-TFSI) were applied to enlarge the voltage range to 0-2.5 V and 0-3.5 V, respectively, compared with the 0-0.8 V of a KCl aqueous electrolyte. The EMIM-TFSI supercapacitor reached the highest energy density, 15.0 Wh kg−1, while the highest power density with the TiOxN1−x nanogrid electrode, 166.1 kW kg−1, was achieved by the TEA-BF4/AN supercapacitor, which is much larger than not only the 45.1 kW kg−1 determined in 1 mol L−1 KCl aqueous electrolyte but also the 144.1 kW kg−1 measured in EMIM-TFSI.