Comparative electrochemical study of new poly(oxyethylene)–Li salt complexes

Abstract

The high ionic conductivity of alkali-metal salts complexed with poly(oxyethylene)(POE) has stimulated wide research on solid polymer electrolytes. Differential scanning calorimetry (DSC), cyclic voltammetry and conductivity measurements have been used to explore the fundamental electrochemical characteristics of two new promising Li salts: Li[(CF₃SO₂)₂N](LiTFSI) and Li[(CF₃SO₂)₃C](LiTriTFSM). A study of the ionic conductivity of membranes containing various concentrations of lithium salts as a function of temperature reveals that, when compared with all the other salts used so far, these new compounds markedly improve the conductivities, essentially as a consequence of lower crystallinity. The voltammograms between –0.2 and 3.9 V vs. Li⁺/Li° show that the three anhydrous complexes POE–LiTFSI, POE–LiTriTFSM and POE–50%LiTFSI–50%LiTriTFSM have a wide electrochemical stability window.