Electrochimica Acta 54 (2009) 5660–5665 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Highly conductive ionic liquid based ternary polymer electrolytes obtained by in situ photopolymerisation Izabela St ˛ epniak ∗,1 , Ewa Andrzejewska Poznan University of Technology, Faculty of Chemical Technology, Piotrowo3, PL 60-965 Poznan, Poland article info Article history: Received 6 February 2009 Received in revised form 27 April 2009 Accepted 4 May 2009 Available online 13 May 2009 Keywords: Ionic liquids Polymer electrolytes Photopolymerisation Conductivity VTF abstract New ternary polymer electrolytes based on a commercial cross-linking resin dianol diacrylate (DDA), tetramethylene sulphone (TMS) as a compatibilizing solvent and ionic liquids (ILs) were prepared by in situ photopolymerisation. The electrolytes containing two polymer-to-TMS-to-IL ratios, 20:30:50 and 20:20:60 by weight, respectively and six various ILs were investigated. The obtained materials were flex- ible, self-standing with good mechanical properties and a long-term stability. They showed high ionic conductivities, in the range of ca. 7 × 10 -3 to 3 × 10 -2 S cm -1 at 25 ◦ C. A very important result is that the conductivities of all the prepared polymer electrolytes exceeded the conductivities of the correspond- ing neat ILs by 2–3.5 times. The temperature dependence of the ionic conductivity correlates with VTF equation. All the materials prepared were characterized by a broad electrochemical stability window (3.3–3.7 V). © 2009 Elsevier Ltd. All rights reserved. 1. Introduction Ionic liquids (ILs) are compounds consisting of an organic cation and an organic or inorganic anion, with melting points below the boiling point of water. When they are liquid at room temperature, they are called room temperature ionic liquids (RTILs). ILs have unusual properties including non-volatility, non-flammability, high ionic density, conductivity, chemical and electrochemical stabil- ity, etc. [1]. These attractive properties have led many scientists to exploit ILs as electrolytes in batteries [2–5], in double-layer capac- itors [6–8], fuel cells [9,10], dye-sensitive solar cells [11–15] or numerical displays with conducting polymers [16]. In contrast to conventional polymer electrolytes, which are solid solutions of electrolyte salts in polymers (e.g. polyethylene oxides) [17], the IL-based polymer electrolytes belong to gel polymer elec- trolytes, which consist of polymer matrix and liquid electrolyte. The latter serves both as the charge carrier and a plasticizer. Sometimes a non-volatile solvent (like carbonates) is added to plasticize and to dissolve IL in the system [18]. IL-based solid polymer electrolytes can be prepared by: (i) dissolution of a polymer and an IL in a volatile solvent and then vaporization of the latter [19,20], ∗ Corresponding author. Tel.: +48 616652317; fax: +48 616652571. E-mail address: izabela.stepniak@put.poznan.pl (I. St ˛ epniak). 1 ISE member. (ii) in situ polymerisation of a monomer-IL mixture (alternatively ionic liquids with vinyl groups): • induced by thermal radical initiators, • induced by UV (or visible) light in the presence of suitable photoinitiators. Preparation of polymer electrolytes in the polymerisation process induced by thermal initiators usually needs relatively high temperatures (∼70–80 ◦ C) and long reaction times (2–24 h) [21–26]; such conditions are the main drawbacks of the method. On the other hand, the light-induced polymerisation seems to be especially useful due to the short polymerisation time (min- utes or seconds) and low reaction temperature (room or ambient). Moreover, it enables the full control of the process because the poly- merisation starts when the light is switched on and stops when the light is cut off. This technique is still one of the most rapid growing polymerisation methods as it offers a broad application spectrum in the industrial area, including coatings, printing inks, stereolithogra- phy, dental materials, optical devices, medicine, microelectronics, etc. [27]. Only in several works (in this number those from our group) photochemical reactions were used for preparation of solid polymer electrolytes [28–37]. IL-containing solid polymer elec- trolytes were based mainly on poly(meth)acrylates. The usage of popular methacrylate and acrylate monomers often results in poor mechanical properties of the resulting conducting film [38]. Another difficulty in application of the in situ method is limited miscibility of monomers with ILs. The conducting film can be useful in practice when its ionic conductivity is above 10 -3 S cm -1 . For the IL-based polymeric 0013-4686/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2009.05.004