Graphene-Based All-Solid-State Supercapacitor with Ionic Liquid Gel Polymer Electrolyte
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Graphene-Based All-Solid-State Supercapacitor with Ionic Liquid Gel Polymer Electrolyte
G. P. Pandey1 and A. C. Rastogi1,2 1
Center for Autonomous Solar Power (CASP), Binghamton University, State University of New York, Binghamton, NY, 13902, USA 2
Department of Electrical and Computer Engineering, Binghamton University, State University of New York, Binghamton, NY, 13902, USA
ABSTRACT Graphene-based all-solid-state supercapacitors the using ionic liquid gel polymer electrolyte have been fabricated and characterized. The gel polymer electrolyte has been prepared by immobilizing ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4) with poly(vinylidene fluoride-hexafluoropropylene). Cyclic voltammetry studies show highly capacitive behavior under fast scan rates. Impedance analysis show nominal charge transfer and ion diffusion at pores related resistance contributions. The graphene-based solid-state supercapacitor shows optimum capacitance of 80 mF cm-2 (equivalent to the single electrode specific capacitance of 76 F g-1). This corresponded to the specific energy of 7.4 Wh kg-1 and specific power of 4.5 kW kg-1. The supercapacitor cell shows stable cyclic performances for up to 5000 cycles and possibly beyond. INTRODUCTION Electrical double layer capacitors (EDLCs) are the most studied class of supercapacitors based on different kinds of porous carbon electrodes such as activated carbons, carbon nanotubes, carbon xerogels, carbon nanofibers, carbide-derived carbons etc. [1-5]. In recent years, graphene, two-dimensional layers of sp2-bonded carbon, has emerged as an extremely promising electrode material for the next generation supercapacitors. Graphene possesses many attractive properties such as high specific surface area up to 2675m2/g, excellent electrical conductivity and remarkable mechanical stiffness [6]. Most of the graphene electrode based supercapacitors reported so far are based on the liquid electrolytes (aqueous, organic and pure ionic liquid) [6-8]. There are many practical limitations of the liquid electrolyte based devices such as leakage of electrolytes, bulky design, corrosion of electrodes/cases of the devices, etc. The gel polymer electrolytes, generally prepared by immobilizing liquid electrolyte in a host polymer matrix, offer a viable substitute for the liquid electrolytes and they are being used for flexible and solid-state electrochemical devices, e.g., batteries and supercapacitors. However, their poor thermal and electrochemical properties as well as volatile organic constituents limit the performance characteristic of gel polymer electrolytes [9]. Recently, room temperature ionic liquids (RTILs) have emerged as an attractive alternative to the aprotic organic solvents due to their unique properties like excellent chemical and thermal stability, nonvolatility and wider electrochemical potential window [10]. The ionic
liquid based gel polymer electrolytes have been used in various electrochemical applications including rechargeable batteries and supercapacitors [5,10]. W
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