Electrochemical Properties and Applications of Ionically and Electronically Conducting Polymers
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ELECTROCHEMICAL PROPERTIES AND APPLICATIONS OF IONICALLY AND ELECTRONICALLY CONDUCTING POLYMERS FAUSTO CROCE, STEFANIA PANERO AND BRUNO SCROSATI Dipartimento di Chimica, Universita' di Roma 'La Sapienza', Italy.
Rome,
ABSTRACT. Various types of polymeric materials with enhanced electrical properties have been characterized recently. Many of these conducting polymers are of specific interest in solid state electrochemistry and in solid state ionics since they act as novel electrode and electrolyte materials. Indeed, these materials are currently used as improved polymer electrolytes and polymer electrodes for the development of advanced-design electrochemical devices. However, there are still some problems which prevent the wide utilization of these conductors. In this paper we attempt to identify the nature of these problems and discuss their possible solutions.
POLYMER ELECTROLYTES. Complexes between metal salts and high molecular weight polymers , such as lithium salt- poly(ethylene oxide), PEO, behave as polymer electrolytes having both cation and anion transport. These electrolytes may be easily constructed in form of thin films so they permit construction of thin-layer, plastic-like batteries. Rechargeable lithium batteries, are presently under development in various industrial and academic laboratories [1-5]. However, the use of PEO-based electrolytes, such as the PEOLiCIO 4 complexes, requires temperatures operating higher than ambient to assure good conductivity. This may not be a serious drawback if the polymer electrolytes are directed to the development of high rate batteries - as, for instance those designed for electric vehicle utilizationwhere the necessary heat is provided by internal ir dissipation. However, a temperature of operation above ambient is a limitation in power sources for the consumer electronic market. Therefore, the low ambient conductivity is the first and, perhaps the most discussed drawback of PEO electrolytes. Various and diversified- attempts are in progress to identify polymer-salt
Mat. Res. Soc. Symp. Proc. Vol. 210. 91991 Materials Research Society
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combinations which would result in polymer electrolytes having high conductivity at moderate and low temperatures. The most straightforward strategy is the use of modified polymer hosts having lower glass transition temperature than linear PEO. To achieve this goal, we have synthesized and characterized electrolytes formed by lithium perchlorate complexed with a series of crosslinked, comb-shaped polyvinylethers in which the basic structure contains short ethylene oxide side chains attached to a supporting inactive backbone chain [6,7]. Effectively, polymer electrolytes obtained by this combination (here simply identify as PVE-LiCIO 4 ) proved to have enhanced conductivity (as induced by the amorphous condition) combined with acceptable mechanical properties (assured by the crosslinking).
.-3
EIE
PE
-9.
2.4
2.8
1500/T
3.2
3.6
(1/K)
FIGURE I- Conductivity of polymer electrolytes formed by LiCIO4 with various pol
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