Effects of ammonolysis and of sol-gel titanium oxide nitride coating on carbon fibres for use in flexible supercapacitors

Smooth titanium oxide nitride coatings have been deposited on carbon fibres using a non-oxide sol–gel method based on self-condensation of titanium alkylamide species. Both the coating and a nitridation of the fibres resulting from the coating process increase the capacitance of the fibres measured in aqueous acid conditions, with significant redox capacitance contributions. When flexible symmetric capacitors were made from the coated fibres and an acid gel electrolyte they provided competitive energy and power densities. Their capacitance was retained very effectively on bending up to 180°.

Fig. S1 SEM image (left) and Ti EDX map (right) of carbon fibres coated with a sol produced in the same way as CF-TiN-5 (see experimental) but using THF rather than hexane as the solvent.S1.
Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A. This journal is © The Royal Society of Chemistry 2018   The specific capacitance of a single electrode in the three-electrode configuration was calculated from cyclic voltammetry curves and the galvanostatic charge-discharge curves using the following equations: Where  is the discharge current (A), melectrode is the weight of the electrode (g),  is the scan rate (mV s -1 ) Δ is the potential window (V), Δ is the discharge time (s).
The specific capacitance of the gel electrolyte SCs (two-electrode system) was determined from their charge-discharge curves by the following equation: Where  is the discharge current (A), Δ is the discharge time (s), Δ is the potential window (V), mcell is the weight of two electrodes (g).Note 2 Calculation of power density and energy density in Fig. 11 The volumetric energy density (Ev) and power density (Pv) of the cell based on the electrodes could be calculated by the following equations: (4) , =     (5) Where 1 g of CF-TiN-1 contains 0.783 g of carbon fibers, 0.148g of TiN, 0.040 g of Rutile TiO2, and 0.029 g of Anatase TiO2, the densities of carbon fibers, TiN, Rutile TiO2, and Anatase TiO2 are 1.78 g cm -3 , 5.22 g cm -3 , 4.23 g cm -3 and 3.78 g cm -3 , respectively,   is the density of CF-TiN-1 (g cm - 3 ),  , is the volumetric capacitance of the device (F cm -3 ), Δ is the potential window (V), Δ is the discharge time (s), Cv,cell is the volumetric capacitance of the device (F cm -3 ), EV is the volumetric energy density (mWh cm -3 ) and PV is the volumetric power density (w cm -3 ) of the device.

Fig. S2
Fig. S2 Rietveld fit to diffraction data collected on a Ti(O,N)-coated carbon fibre sample (CF-TiN-2).Refined parameters are shown in TableS1.

Fig. S3
Fig. S3 XRD pattern of the white residue after oxidation of Ti(O,N)-coated carbon fibres (CF-TiN-5) in the TGA.

Table S1
Phase fractions, lattice parameters and profile weighted reliability factors derived from Rietveld fitting of the XRD data (Fig.S2) for Ti(O,N)-coated carbon fibres.
Determination of electrochemical performance of SCs