Highly Conductive, Oriented Polymer Electrolytes for Lithium Batteries† D. Golodnitsky*, E. Livshits, A. Ulus and E. Peled School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel ABSTRACT WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW In semicrystalline complexes of poly(ethylene oxide) (PEO) with different salts, such as lithium iodide, lithium trifluoromethanesulfonate (LiTF) and lithium trifluoromethanesulfonimide (LiTFSI), stretching in- duced longitudinal DC conductivity enhancement was observed, in spite of the formation of more ordered polymer electrolyte (PE) structure. It was found that the more amorphous the PE, the less its lengthwise conductivity is influenced by stretching. The results of our investigation suggest that ionic transport occurs preferentially along the PEO helical axis, at least in the crystalline phase, and that the rate-determining step of the lithium ion conduction in LiI:P(EO) 20 , LiTF: P(EO) 20 polymer electrolytes below T m is ªinterchainº hopping. Understanding ion transport processes is clearly a fertile field for research and development in the synthesis of new rigid polymers with ordered channels and composition appropriate for enhanced ionic conductivity. Copyright  2003JohnWiley&Sons,Ltd. KEYWORDS: polymer electrolyte; ion transport mechan- ism INTRODUCTION WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW The words ªlithium±polymerº have become synon- ymous with advanced battery technology [1]. A dry polymer design of the battery offers simplifications with respect to fabrication, durability, safety and thin profile. There is less flammability risk because no liquid electrolyte is used. Unfortunately, the dry lithium±polymer systems suffer from poor con- ductivity at ambient temperatures. The internal resistance is too high and cannot deliver the current pulses needed for powering modern communica- tion devices and spinning up the hard drives of mobile computing equipment [1]. Most of the research on new polymer electro- lytes (PE) has been guided by the principle that ion transport is strongly dependent on local motion of the polymer in the vicinity of the ion. Ions are thought to be transported by quasi-random motion of short polymer segments. A strong coupling between ionic motion and relaxation of the polymer host was formalized by Angel [2]. The conductivity was generally observed to rise with increasing flexibility of the chains and rapid relaxation of the host polymer. Charge-carrier motion is considered as a thermally activated mechanism. Three ways to increase ionic conduction were suggested in [3]: (a) the simple addition of more salt, increasing the number of mobile ions; (b) a facilitating of polymer relaxation by decreasing the glass transition tem- perature (T g ), and thus increasing the amorphicity; (c) increasing the conductivity by a decoupling diffusion from relaxation of the host. In this case, the aim is to create structures in which ions can move through static pathways independent of host polymer relaxation. As of now, ionic conductivity in practice is improved by plasticizing the polymer electrolytes with organic and nano-size inorganic compounds [4±8]. Modification of the polymer electrolyte architecture by crosslinking and the POLYMERS FOR ADVANCED TECHNOLOGIES Polym. Adv. Technol. 13, 683±689 (2002) Published online in Wiley InterScience (www.interscience.wiley.com). DOI:10.1002/pat.266 Received 11 December 2001 Revised 1 March 2002 Accepted 1 April 2002 *Correspondence to: D. Golodnitsky, School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel. E-mail: golod@post.tau.ac.il † This paper was presented at PAT 2001±Eilat, Israel. Copyright  2003 John Wiley & Sons, Ltd.