UV-cured polymer electrolyte membranes for Li-cells: Improved mechanical properties by a novel cellulose reinforcement J.R. Nair a , C. Gerbaldi a, * , A. Chiappone a , E. Zeno b , R. Bongiovanni a , S. Bodoardo a , N. Penazzi a a Department of Materials Science and Chemical Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Turin, Italy b Centre Technique du Papier (CTP), Domaine Universitaire, B.P. 251, 38044 Grenoble Cedex 9, France article info Article history: Received 19 May 2009 Received in revised form 15 July 2009 Accepted 16 July 2009 Available online 18 July 2009 Keywords: Cellulose hand-sheet UV-curing Gel-polymer electrolyte Mechanical property Li-cells abstract One of the main drawbacks that restricts the practical application of gel-polymer electrolytes is the inferior mechanical performance compared to other available systems. In this work, we have reinforced UV-cured methacrylic membranes with cellulose. To enhance its compatibility with the polymer matrix, cellulose is modified by UV-grafting poly(ethylene glycol) methyl ether methacrylate on it. Excellent mechanical properties are obtained and good ionic conductivity values are observed, enlightening that this kind of membrane is an interesting candidate for future applications as thin gel-polymer electrolyte in flexible lithium batteries. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Today, special attention is focused on polymer systems showing high ionic conductivity at ambient and/or sub ambient tempera- tures, since they find unique practical applications, such as separa- tors in high power, versatile, rechargeable Li-based batteries. Although a commercial reality, these power sources are still the object of intense R&D aiming to improve their performances for high-end applications [1,2]. High performing innovative electrolyte materials should be capable of high ionic conductivity even at ambient temperature, with good mechanical and interfacial prop- erties and stable performances. Moreover, they should be low cost, ecologically friendly and safe. Thermo-set membranes prepared by free radical photo-polymerisation (UV-curing) could be an inter- esting alternative to existing polymer electrolytes. Methacrylic-based thermo-set gel-polymer electrolytes (GPEs) obtained by free radical photo-polymerisation (UV-curing) used for lithium battery application have been already illustrated and discussed [3–5]. The preparation process is very easy, reliable and rapid; the obtained membranes show good behaviour in terms of ionic conductivity, interfacial stability with the Li-metal elec- trode and cyclability in lithium cells. Though the membranes are flexible, self standing and easy to handle, there is room for improv- ing mechanical strength, in particular if application in flexible bat- teries is taken into consideration. In the present communication, we present and discuss our preliminary results regarding the improvement of the mechanical properties of GPE prepared by UV-curing using modified cellulose hand-sheets, specifically pre- pared and modified by UV grafting [6]. Such modification would make these hybrid organic, green, cellulose-based composite poly- mer systems a strong contender in the field of flexible Li-based power sources. The promising perspectives of such kind of GPEs are illustrated by the experimental data on the electrochemical re- sponse of a lithium polymer cell. 2. Experimental 2.1. Cellulose hand-sheets preparation and modification Kraft pulp, bleached and refined at 35 °SR (Schopper–Riegler degree [7]), was used as a raw material for hand-sheets prepara- tion. A hard-wood (HW) to soft-wood (SW) combination of 60:40 w/w was re-pulped and blended using a high speed blender and made into desired concentration of 3 g L À1 . It was later made to a suspension of 1.5 g L À1 which was introduced into a retention sheet-former (FRET) of 1500 RPM. The filtrate on copper wires was then dried at 90 °C under high vacuum to give a hand-sheet of 1.5 g with an average thickness of 100 lm. The hand-sheets were modified by photo-grafting technique using poly(ethylene glycol) methyl ether methacrylate (PEGMA, average M n = 475, Aldrich), and benzophenone (Aldrich) as photo- initiator. In this grafting procedure, derived from Stachowiak et al. [6], the paper was swelled into a solution of benzophenone 1388-2481/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2009.07.021 * Corresponding author. Tel.: +39 0115644638; fax: +39 0115644699. E-mail address: claudio.gerbaldi@polito.it (C. Gerbaldi). Electrochemistry Communications 11 (2009) 1796–1798 Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom