Pinecone-derived porous activated carbon for high performance all-solid-state electrical double layer capacitors fabricated with flexible gel polymer electrolytes

We report a novel configuration of electrical double layer capacitors (EDLCs), fabricated with porous activated carbon electrodes derived from bio-waste pinecone and plastic crystals-based gel polymer electrolytes. Different activated carbons have been produced by activating raw pinecone powder employing different amount of activating agent ZnCl2. Optimization of morphology, structure and porosity parameters of activated carbons has been performed by scanning electron microscopy, x-ray diffraction, Raman and porosity analyses. Mixed (micro-and meso-) porous interiors in activated carbon show optimum characteristics of EDLCs. Gel polymer electrolyte comprising mixture of non-ionic plastic crystal and organic ionic plastic crystal (succinonitrile and 1-ethyl-1-methyl pyrrolidinium bis(tri-fluoromethyl sulfonyl) imide, respectively) entrapped in poly(vinylidene fluoride-co-hexafluoropropylene) has been found suitable to fabricate EDLCs owing to their flexible nature, high ionic conductivity (sigma similar to 1.53 x 10(-3) S cm(-1) at room temperature) and wide enough electrochemical stability window, ESW (similar to 3.1 V versus Ag). Addition of Li-salt in the gel polymer electrolyte improves the electrochemical properties (sigma similar to 2.87 x 10(-3) S cm(-1) and ESW similar to 3.8 V) and found to influence the performance of the EDLCs, particularly, the specific power, significantly. The EDLC cell with Li-salt containing electrolyte offers higher values of specific capacitance, energy and power (similar to 255 F g(-1), similar to 20 Wh kg(-1) and similar to 55.7 kW kg(-1), respectively) than the cell with electrolyte without Li-salt (similar to 244 F g(-1), similar to 19 Wh kg(-1) and similar to 39.3 kW kg(-1), respectively). The EDLC (with Li-salt electrolyte) exhibits 96-100% Coulombic efficiency and almost stable specific capacitance for similar to 20,000 charge-discharge cycles after only similar to 11% initial fading. The capacitor gives stable performance for a wide temperature range from -30 to 90 degrees C. (C) 2019 Elsevier Ltd. All rights reserved.