Ion-transport phenomena in concentrated PEO-based composite polymer electrolytes D. Golodnitsky * , G. Ardel, E. Peled School of Chemistry, Sackler Faculty of Exact Science, Tel Aviv University, Tel Aviv, 69978, Israel Received 30 July 2001; received in revised form 10 December 2001; accepted 12 December 2001 Abstract The enhancement of the ionic conductivity of Li – P(EO) n -based polymer electrolytes by the addition of finely divided inorganic oxides is the subject of considerable discussion. The increase in ionic conductivity in concentrated composite solid polymer electrolytes (CSPE) is related both to the suppression of the formation of crystalline PEO and PEO-salt phases and to interfacial conduction. In the case of polycrystalline or polyparticle solid electrolytes, however, grain-boundary (GB) resistance, which is associated with the crossover of ions from particle to particle across grain boundaries orthogonal to the direction of current flow (or parallel to the field lines), must be considered. The conduction across grain boundaries in polymer appears to be ignored so far. In this work, we provide SEM and ECS experimental data on LiI – P(EO)– Al 2 O 3 CSPEs. The effects of plasticizers, doping by CaI 2 , change in Li/EO ratio, and nanosize alumina concentration on the interior grain ionic conductivity and on the resistance of the orthogonal grain boundaries are addressed. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Ion-transport phenomena; Composite solid polymer electrolytes; Conduction; Plasticizers 1. Introduction The great majority of studies on batteries over the last two decades has been directed toward the develop- ment of highly conductive solid polymer electrolytes because of their promising applications in all-solid- state rechargeable lithium or lithium-ion batteries. A central aspect of research on these electrolytes deals with the mechanism of ion transport. Theoretical models for the conduction mechanism have been proposed [1,2]. Despite this activity, the exact con- duction mechanism in polymer electrolytes is still a matter of some controversy, but it is generally agreed that above the melting point of the eutectic (T m ), the effective ionic conduction occurs mainly in the molten phase and that both ionic species are mobile. It has been demonstrated by several research groups [3 –16] that dispersion of small-size ceramic powders in the polymer matrix produces composite polymer electrolytes (CPE) that show consistent improvements in both interfacial and transport proper- ties. On the basis of DSC, SEM, XRD, NMR, and conductivity data [11,12], we have suggested that the addition of 15-nm-size aluminum and magnesium oxides increases the degree of local crystal disorder of the PEO – LiI complex by preventing agglomera- tion of the chains. This is followed by enhanced segmental motion. Laboratory prototypes of mono- and bipolar lithium/pyrite long-cycle-life batteries 0167-2738/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0167-2738(01)01036-0 * Corresponding author. E-mail address: golod@post.tau.ac.il (D. Golodnitsky). www.elsevier.com/locate/ssi Solid State Ionics 147 (2002) 141 – 155