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Electrochimica Acta 45 (2000) 1203 – 1209 www.elsevier.nl/locate/electacta

Polymer electrolytes comprising organometallic compounds
Z. Florjanczyk, E. Zygadl ´ *o-Monikowska *, W. Bzducha
Warsaw Uni6ersity of Technology, Faculty of Chemistry, ul. Noakowskiego 3, 00 -664 Warsaw, Poland Received 30 November 1998; received in revised form 29 March 1999; accepted 12 April 1999

AbstractComposite polymeric electrolytes based on PEO complexes and ethyl aluminum alkoxides have been studied. The addition of the aluminum compounds causes a considerable reduction in the PEO crystalline phase content and provides very good mechanical and thermal stability up to 140°C. The glass transition temperatures of blends are low, falling within the − 64 to −29°C range. The ionic conductivity of suchsystems reaches the value of 10 − 5 S cm − 1 at ambient temperature and that of 10 − 3 S cm − 1 at 60 – 70°C. Impedance studies show that these systems form a passive layer with a lithium electrode, which protects this electrode from corrosion processes. © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Poly(ethylene oxide); Composite polyelectrolytes; Inorganic fillers; Organoaluminumcompounds; Ionic conductivity

1. Introduction The formation of composites with various ceramic materials is an extremely simple and at the same time efficient method of modifying the mechanical and conducting properties of solid polymeric electrolytes based on poly(ethylene oxide) (PEO) complexes. The addition of certain inorganic substances such as g-LiAlO2, zeolites, Al2O3, B2O3/Li2O/Li2SO4glass powder or TiO2 [1–7] of particle size of the order of nanometers considerably limits the PEO crystallization. This causes that the ionic conductivity of such systems at below 60°C (i.e. melting point of the PEO crystalline phase) is several orders of magnitude higher with respect to the PEO/salt complex and reaches ambient temperature values of the order of 10 − 5 S cm − 1. Nanocomposite polymerelectrolytes are characterized by good mechanical properties, which result from the possibility of complex formation between the basic polyether chains and the inorganic filler particles, the surface of which exhibits properties of a Lewis acid, forming a spatial physical net structure.
* Corresponding author.

Good compatibility with the lithium metal electrode is an additional advantage ofthis type of composite electrolytes, although the mechanism and role of the inorganic additive in the formation of a stable passive layer are not well understood yet. The use of ceramic particles as components of electrolytes is connected, however, with some problems resulting from the homogeneous distribution of heterogeneous materials in the polymeric matrix, the stiffening of the matrix, and alsothe presence of OH groups on the surface of the ceramic component which leads to initial passivation of the electrodes. In order to avoid these problems we propose the use of appropriate organometallic compounds as protecting agents, which dissolve well in solvents used for the obtaining of films with PEO and which easily react both with water and impurities of an acidic character (often presentin lithium salts) and the basic character typical for commercially available polyethers. From our studies it results that the diethylalkoxyaluminum compound obtained from the reaction of triethylaluminum and poly(ethylene glycol) methyl ether is a suitable component of the composite.

0013-4686/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 3 - 4 6 8 6 ( 99 ) 0 0 3 8 2 - 5

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Z. Florjanczyk et al. / Electrochimica Acta 45 (2000) 1203–1209 ´

Al(C2H5)3 +CH3(OCH2CH2)n OH “ 1/x[CH3(OCH2CH2)n OAl(C2H5)2]x +C2H6
A

(1)

n= x=

2 2

3 1.5

7 1.5

This compound clearly improved the ambient temperature conductivity of PEO complexes and could be used directly in an atmosphere of dry air. The simple method of synthesis along with...