5 - Polymer electrolytes I: General principles

Summary

Background

Polymer electrolytes are the newest area of solid ionics to receive wide attention for applications in electrochemical devices such as batteries and electrochromic windows. Unlike inorganic glass or ceramic electrolytes, the polymer electrolytes are compliant and this property makes it possible to construct solid state batteries in which the polymer conforms to the volume changes of the electrodes that typically occur during discharge and charging cycles. The potential utility of polymer electrolytes has stimulated the synthesis of new polymer electrolytes, physical studies of their structure and charge transport, and theoretical modelling of the charge transport processes. The rapid progress in this field has led to many reviews (Armand, 1986; MacCallum and Vincent, 1987, 1989; Ratner and Shriver, 1988; Vincent, 1989; Tonge and Shriver, 1989; Cowie and Cree, 1989; Bruce and Vincent, 1993; Linford, 1987, 1990).

The structures and charge transport mechanisms for polymer electrolytes differ greatly from those of inorganic solid electrolytes, therefore the purpose of this chapter is to describe the general nature of polymer electrolytes. We shall see that most of the research on new polymer electrolytes has been guided by the principle that ion transport is strongly dependent on local motion of the polymer (segmental motion) in the vicinity of the ion.