Ionic conductivity in crystalline–amorphous polymer electrolytes – P(EO) 6 :LiX phases Wesley A. Henderson a,b, * , Stefano Passerini b a Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA b Ente Per le Nuove Tecnologie, l’Energia e l’Ambiente, IDROCOMB, Centro Ricerche Casaccia, Via Anguillarese 301, Rome 00060, Italy Received 14 May 2003; accepted 22 May 2003 Published online: 16 June 2003 Abstract Recent reports have indicated higher ionic conductivities in crystalline polymer electrolytes consisting of isostructural P(EO) 6 :LiX(X ¼ PF 6 ,AsF 6 ,SbF 6 )phasesrelativetotheanalogousamorphousmaterials.Thesereportschallengetheconventional wisdom in polymer electrolyte research that amorphous electrolytes are much more conductive than crystalline ones. The higher conductivity in the crystalline materials was attributed to the structures in which Li þ cations are located within PEO cylinders uncoordinated by the anions. The conductivity and crystallinity of P(EO) n –LiClO 4 (EO/Li ¼ 6 and 10) electrolytes have been ex- aminedhere.Incontrasttotherecentreports,muchlowerconductivitiesarefoundfortheisostructuralP(EO) 6 :LiClO 4 crystalline electrolyte relative to the same fully amorphous electrolyte. Ó 2003 Elsevier Science B.V. All rights reserved. Keywords: PEO; Conductivity; Crystallinity; LiClO 4 ; LiAsF 6 1. Introduction Ionically conducting polymer electrolytes – polymer membranes with dissolved salts – are currently being researched worldwide for the development of devices suchasall-solid-statelithiumbatteries.Suchelectrolytes would ideally combine the properties of high ionic conductivity (>10 3 S cm 1 at 25 °C), flexibility and mechanical integrity with an absence of volatile or reactive additives. The first commercial lithium–metal– polymer (LMP) battery manufacturing plant was inau- gurated by AVESTOR in September 2002. Such batteriesuse ÔdryÕ polymerelectrolytesasopposedtothe ÔgelÕ polymer electrolytes with liquid additives used in commercial lithium batteries. The need to further im- prove the ionic conductivity of such dry polymer elec- trolytes remains critical, however, for high power battery applications such as portable electronics and electric vehicle propulsion systems. Recently, Bruce and coworkers [1,2] have reported results which contradict the widely accepted view that ionic conductivity in polymer electrolytes always pre- dominates in amorphous rather than crystalline mate- rials.Theseauthorshaveindicatedthatthreecrystalline poly(ethylene oxide) polymer electrolytes, P(EO) 6 :LiX (X ¼ PF 6 ,AsF 6 ,SbF 6 ),haveahigherionicconductivity than the analogous amorphous phases. This is no small matter since the research on both new polymers and salts intended for polymer electrolyte applications has been driven for the past 25 years by the goal of pre- paring fully amorphous electrolytes with favorable me- chanical properties to optimize the ionic conductivity [3,4]. The authors have further suggested that the ex- ploration of other crystalline polymer electrolytes may be a worthwhile endeavor for improving the ionic con- ductivity of electrolytes beyond that found for fully amorphousmaterials.Beforesuchresearchisembarked upon, however, the validity of such claims should be examined. Electrochemistry Communications 5 (2003) 575–578 www.elsevier.com/locate/elecom * Corresponding author. Tel.: + 39-06-3048-4985; fax: +39-06-3048- 6357. E-mail address: wesley.henderson@casaccia.enea.it (W.A. Hender- son). 1388-2481/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S1388-2481(03)00131-0