Supercapacitors are energy storage devices, which store energy at the electrode and electrolyte interface based on electrical adsorption of ions. Carbon electrodes with high surface area and pore volumes enhance the capacitance while Ionic liquid (IL) electrolytes with high voltage windows increase the energy density compared to organic and aqueous electrolytes. But the polymer precursors and the IL electrolytes are expensive and the ionic conductivity of the ILs is low. Therefore, we fabricated high surface area carbon electrode with a low cost and IL with high conductivity. Lignin is the second most abundant natural polymer and is less expensive compared to other polymer precursors of carbon electrodes. Free standing, flexible and binder free carbon electrodes were fabricated using Kraft lignin together with polyvinyl alcohol (PVA):PVA as a sacrificial polymer. Lignin:PVA with different compositions were prepared in water and solutions were subjected to electrospinning. Electrospun mats were stabilized at 250 oC in air, carbonized at 1000 oC in inert environment and activated at 800 oC in CO2. CO2 activated lignin derived carbon nanofibers for supercapacitor electrodes is first reported in this study. Pyr14TFSI:PC:EC IL electrolyte system was prepared optimizing the IL and solvents ratios, in order to obtain highest ionic conductivity. SEM, Raman, TGA, FTIR and surface area analysis were carried out to analyze the structure and morphology of the carbon electrode material and the electrolyte was analyzed for its conductivity. Coin cell supercapacitors were assembled and then performance was evaluated with Cyclic voltammetry, galvanostatic charge discharge and electrochemical impedance spectroscopy. Lignin:PVA 90:10 mass ratio composition showed 71 F/g capacitance at 10 mV/s scan rate which was 92% of retained at 100 mV/s scan rate with an energy density of 27 Wh/kg at 1 A/g. This shows an improved performance in supercapacitors when compared to the reported studies on carbonized lignin:PVA nano fiber mats.

Lignin based electrospun carbon nanofiber electrodes for high performance supercapacitors in ionic liquid electrolytes

254th National Meeting (2017)

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