J Solid State Electrochem DOI 10.1007/s10008-014-2731-5
ORIGINAL ARTICLE
Flexible electric double-layer capacitors fabricated with micro-/mesoporous carbon electrodes and plastic crystal incorporated gel polymer electrolytes containing room temperature ionic liquids Mohd. Suleman & Yogesh Kumar & S. A. Hashmi
Received: 8 May 2014 / Revised: 12 August 2014 / Accepted: 29 December 2014 # Springer-Verlag Berlin Heidelberg 2015
Abstract Novel configuration of symmetrical electric doublelayer capacitors (EDLCs) comprising plastic crystalline succinonitrile (SN)-based gel polymer electrolytes, incorporated with ionic liquids 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPTFSI) and 1-ethyl-3methylimidazolium trifluoromethanesulfonate (EMITf) immobilized in a host polymer poly(vinylidine fluoride-cohexafluoropropylene) (PVdF-HFP), have been fabricated and characterized. The cost-effective activated carbon powder containing a large proportion of mesoporosity has been derived from coconut shell to use as the capacitor electrodes. The high ionic conductivity (∼10−3 S cm−1 at room temperature) and good electrochemical stability render the gel polymer electrolyte films suitable candidates for the fabrication of EDLCs. The performance of the EDLCs has been tested by electrochemical impedance spectroscopy, cyclic voltammetry, and charge–discharge studies. Performance of the capacitor cell with EMITfbased gel electrolyte in terms of specific capacitance, specific energy, pulse, and continuous power densities (which are respectively ∼254 F g−1, 35 Wh kg−1, 10.3 kW kg−1, and 12 kW kg−1) is found to be better than the EDLC fabricated with BMPTFSI-based gel electrolyte. The superior performance of the EMITf-based cell is correlated with smaller sizes of EMITf component ions, responsible for easy ion migration and switching through even smaller pores of activated carbon. Keywords Electric double-layer capacitor . Supercapacitor . Activated carbon . Gel polymer electrolyte . Succinonitrile . Ionic liquid M. Suleman : Y. Kumar : S. A. Hashmi (*) Department of Physics and Astrophysics, University of Delhi, Delhi 110007, India e-mail:
[email protected]
Introduction Electric double-layer capacitors (EDLCs), also referred as supercapacitors, belong to an emerging class of power sources [1]. From the technological research point of view, these are attractive devices as they possess high specific capacitance, moderate specific energy with high specific power, and long cycle life [1–4]. In general, EDLCs employ various forms of carbon including activated carbon powder/fibers/fabrics/ aerogels, carbon nanotubes (CNTs), carbon nanofibers (CNFs), graphene, etc. as electrode materials [1–9]. The activated carbon, being a predominantly microporous material with larger surface area (∼1000–2500 m2 g−1), has the ability to offer larger value of specific capacitance (100–350 F g−1) as compared to low surface area mesoporous carbons, e.g., CNTs, CNFs, fullerene, etc. [9]. The cost-effective activated carbons have been reported to be derived from various natural resources, e.g., coconut shell [10, 11], poplar wood [12], tea leaves [13], seed hulls [14], etc. The porosity of such carbons can be controlled by specific chemical and physical activation processes. Hu et al. [10] systematically characterized the activated carbons prepared from coconut shell with different proportions of microporosity (pore size
