436 Ionics 10 (2004) Evidence of Ion Pair Breaking by Dispersed Polymer in Polymer Gel Electrolytes Rajiv Kumar and S.S. Sekhon Department of Applied Physics, G. N. D. University, Amritsar - 143005, INDIA Abstract. Non-aqueous polymer gel electrolytes containing trifluoromethanesulfonic acid (HCF3SO3) and polyethylene oxide (PEO) as the gelling polymer has been studied. The increase in conductivity observed with the addition of PEO to liquid electrolytes has been explained to be due to the breaking of ion aggregates present in electrolytes at higher acid concentrations. The increase in free H + ion concentration upon breaking of ion aggregates has also been observed in pH measurements and viscosity of gel electrolytes has been found to increase with PEO addition. Polymer gel electrolytes containing dimethylacetamide (DMA) have o~ 10.2 S/cm at room temperature and are stable over -50 to 125 ~ range of temperature. Gels based on propylene carbonate (PC) and ethylene carbonate (EC) are stable in the -50 to 40 ~ temperature range and loose their gelling nature above 40 ~ 1. Introduction Polymer gel electrolytes are receiving much attention due to their increasing use in lithium batteries, proton exchange membrane fuel cells and other devices. They possess high value of conductivity (102 - 10-3 S/cm) at moderate temperatures alongwith good chemical and elec-trochemical stability and having wide range of compositions and hence wider control of properties [1- 4]. The variation of conductivity of these electrolytes with salt concentration shows a maxima which suggests the presence of two competing phenomena simulta- neously. While the increase in conductivity at low concentrations is due to the availability of more free mobile ions provided by the salt, the decrease in conductivity at higher concentrations is due to an increase in viscosity of the electrolytes alongwith the presence of ion aggregates which do not take part in the conduction process [5-6]. The presence of ion aggregates at higher salt concentrations in electro-lyres containing lithium salts has been experimentally studied by diffe- rent workers [7-10]. The addition of polymer to liquid electrolytes in- creases the mechanical stability of the polymer gel electrolytes. The increase in viscosity observed with polymer addition shall lower mobility and as a result conductivity shall decrease. The decrease in conductivity observed with the addition of different polymers in lithium ion conducting polymer gel electrolytes is generally small which suggests that the polymer does not play an active role in the conduction process and acts as a stiffener only [l 1-12]. However recently it has been reported that in some gel electrolytes the addition of polymer to liquid electrolytes results in an increase in conductivity and gels with conductivity higher than the corresponding liquid electro-lytes have been obtained [13-16]. This is very interesting behaviour where the increase in conductivity takes place despite an increase in viscosity alongwith a decrease in salt concentration both of which results in a decrease in conductivity. This increase in conductivity with the addition of polymer has not been clearly understood and needs further inves- tigations. The present work has been undertaken to study the role of polymer in conductivity enhancement in poly- mer gel electrolytes. Polymer gel electrolytes containing HCF3-SO 3 with PEO as the gelling polymer and propylene carbonate (PC), ethylene carbonate (EC) and dimethylacetamide (DMA) as solvents have been chosen. The variation of conductivity with acid con- centration, polymer concentration and temperature has