Using Polymeric Ionic Liquids as an Active Binder in Supercapacitors

Vitor L. Martins,Peter J. Hall,Judith Lesowiec,Roberto M. Torresi,Anthony J. R. Rennie

doi:10.1149/2.1411713jes

Vitor L. Martins, Peter J. Hall + Show 3 more

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https://doi.org/10.1149/2.1411713jes

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Abstract

Electrodes in batteries and supercapacitors generally contain inert binders to maintain their structural integrity during operation but do not participate in the storage of energy. In this paper, we demonstrate that poly ionic liquids can function as structural binders while simultaneously improving the energy storage capability of supercapacitors. Specifically, we show that when the ionic liquid N-butyl-N-methyl pyrrolidinium bis(trifluoromethanesulfonyl)imide is used as electrolyte and poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide is employed as electrode binder the permissible operating voltage of the device is enhanced to 4.0 V. This results in a substantially increased overall specific energy (80% greater) and represents a step toward the development of devices with long cycle lives and high energy densities.

Highlights

Energy storage devices are continually developing to meet the future demands of clean energy provision, with applications ranging from small portable electronics, to transport and large grid connected systems.[1,2,3,4,5,6,7,8] From the great variety of available energy storage technologies, electrochemical double-layer capacitors (EDLCs) are associated with high power densities (>10 kW kg−1), a high degree of reliability and long cycle life (>100,000), especially when compared to batteries
Our results show that binder composition plays an important role in defining the electrochemical stability of EDLC; the use of polymeric ionic liquid as binder permitted a larger maximum operating voltage compared to PVDF-HFP, which has the potential to increase the overall energy density of full devices
Fourpoint probe measurements at 25◦C show that the ionic conductivity of films increases as the proportion of ionic liquids (ILs) increases, from 3.5 10−6 mS cm−1 for pure [PDDA][Tf2N] to 0.31 mS cm−1 for the 40:60 mixture, which is in good agreement with previous work,[19] whereas the neat IL has a conductivity of 2.7 mS cm−1 (see Figure S1, in Supplementary Information (SI))

Summary

Introduction

Energy storage devices are continually developing to meet the future demands of clean energy provision, with applications ranging from small portable electronics, to transport and large grid connected systems.[1,2,3,4,5,6,7,8] From the great variety of available energy storage technologies, electrochemical double-layer capacitors (EDLCs) are associated with high power densities (>10 kW kg−1), a high degree of reliability and long cycle life (>100,000), especially when compared to batteries. The specific capacitance, CCV, was determined from the charge delivered during the discharge process, ∫ i · dt, the operating potential window, U, and the active mass of both electrodes (total mass of activated carbon in cell), m, as shown in Equation 1:

Results

Conclusion