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

Abstract

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(trifluoromethyl 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 (σ ∼1.53 × 10−3 S cm−1 at room temperature) and wide enough electrochemical stability window, ESW (∼3.1 V versus Ag). Addition of Li-salt in the gel polymer electrolyte improves the electrochemical properties (σ ∼2.87 × 10−3 S cm−1 and ESW ∼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 (∼255 F g−1, ∼20 Wh kg−1 and ∼55.7 kW kg−1, respectively) than the cell with electrolyte without Li-salt (∼244 F g−1, ∼19 Wh kg−1 and ∼39.3 kW kg−1, respectively). The EDLC (with Li-salt electrolyte) exhibits 96–100% Coulombic efficiency and almost stable specific capacitance for ∼20,000 charge-discharge cycles after only ∼11% initial fading. The capacitor gives stable performance for a wide temperature range from −30 to 90 °C.