Study on the ionic conductivity of polyether network polymer electrolytes: effect of the preparation method

In preparing the network polymer electrolytes, two different methods were taken in the incorporation of salt into the polymer network. In one method, the network polyether was dipped into the lithium salt solution with or without plasticizer, and in the other method the network formation was proceeded in the presence of the lithium salt in the reaction medium with or without plasticizer. We designated the former as the network polymer electrolyte (NPE), the latter as the salt added network polycondensate electrolyte (SNPE). For the NPEs, the ionic conductivities increased with decreasing the cross-linking degree, which was mainly attributed to the increase of the free ion fraction with the decrease in the cross-linking degree that was evidenced by Li-7 NMR relaxation studies. For the NPEs plasticized with MPEG(7), the conductivities increased with increase of the MPEG(7) content, which was largely due to the increase of the mobility of the free ions. The ionic conductivity of the SNPE was higher than that of the NPE, which resulted from the lower microviscosity of the SNPE due to the larger amount of the contained linear polyether and the lower cross-linking degree. (C) 1999 Published by Elsevier Science B.V. All rights reserved.