Effect of Ionic Liquid Anion Type in the Performance of Solid Polymer Electrolytes Based on Poly(vinylidene fluoride-trifluoroethylene)

Solid polymer electrolytes (SPEs) or ionic conductors were proposed by Gray in 1997 and are typically composed by polymer with salts in its constitution, finding applications in the areas of batteries, sensors/actuators and supercapacitors, among others. Recently, salts have been substituted by ionic liquid (ILs) due to their excellent properties, including  high ionic conductivity (~10^-3 – 10^-2 S.cm^-1), almost null volatility, null flammability, thermal stability, wide electrochemical windows (~4-6 V) and being environmental friendly [1-2].

The excellent properties of poly(vinylidene fluoride-co-trifluoroethylene), P(VDF-TrFE), as solid polymer electrolyte with (N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide, [N_{111 2(OH)}][NTf₂] where demonstrated in [3], where the addition of the ILs affects the microstructure, thermal stability and ionic conductivity of the polymer membrane.

In this work, the effect of different anions within the ionic liquid for the development of SPE based on P(VDF-TrFE) has been investigated. 1-ethyl-3-methylimidazolium acetate, [C₂mim][OAc], 1-ethyl-3-methylimidazolium triflate, [C₂mim][(CF₃SO₃)₃], 1-ethyl-3-methylimidazolium lactate, [C₂mim][Lactate], 1-ethyl-3-methylimidazolium thiocyanate, [C₂mim][SNC]   and 1-ethyl-3-methylimidazolium hydrogen sulphate [C₂mim][HSO₄] have been used for this purpose and the SPE were prepared by thermaly induced phase separation (TIPS). The thermal and electrical properties of the SPE strongly depend on the selected IL through their different interactions with the polymer matrix. The room temperature ionic conductivity increasing in the following way for the different anions: [SNC] > [CF₃SO₃)₃] > [HSO₄] > [Lactate] > [OAc].

 

Acknowledgments

This work was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/FIS/UI607/2011, PEST-C/QUI/UI0686/2013, PEST-OE/EQB/LA0004/2011, and grants SFRH/BD/68499/2010 (C.M.C.) and SRFH/BD/90366/2012 (R.L.). The authors also thank funding from Matepro –Optimizing Materials and Processes”, ref. NORTE-07-0124-FEDER-000037”, co-funded by the “Programa Operacional Regional do Norte” (ON.2 – O Novo Norte), under the “Quadro de Referência Estratégico Nacional” (QREN), through the “Fundo Europeu de Desenvolvimento Regional” (FEDER). The authors thank Solvay for kindly supplying the high quality materials.

References

[1] F.M. Gray, Solid Polymer Electrolytes: Fundamentals and Technological Applications, VCH Publishers Inc., 1991.

[2] J.M. Tarascon, M. Armand, Nature 414 (2001) (6861) 359.

[3] R. Leones, C.M. Costa, A.V. Machado, J.M.S.S. Esperança, M.M. Silva, S. Lanceros-Méndez, Solid State Ionics 253 (2013) 143.