COMPOSITION EFFECTS IN POLYETHERURETHANE-BASED SOLID POLYMER ELECTROLYTES

Nuclear magnetic resonance spectroscopy (n.m.r.), dynamic mechanical t hermal analysis (d.m.t.a.) and AC impedance techniques have been used in combination to probe the effect of electrolyte composition in an ar chetypal solid polymer electrolyte (SPE). A series of solid polymer el ectrolytes (SPEs) based on a urethane-crosslinked trifunctional poly(e thylene glycol) polymer host containing dissolved ionic species (LiClO 4 and LiCF3SO3) have been studied. D.m.t.a. has established that incre asing LiClO4 concentration causes a decrease in the polymer segmental mobility, owing to the formation of transient crosslinks via cation-po lymer interaction. Investigation of the distribution of mechanical/str uctural relaxation times for the LiClO4/polymer complex with d.m.t.a. reveals that increasing LiClO4 concentration causes a slight broadenin g of the distribution, indicating a more heterogeneous environment. Re sults of n.m.r. Li-7 T-1 and T-2 relaxation experiments support the id ea that higher salt concentrations encourage ionic aggregation. This i s of critical importance in determining the conductivity of the materi al since it affects the number of charge carriers available. Introduct ion of the plasticiser tetraglyme into the LiClO4-based SPEs suppresse s the glass transition temperature of the SPE, and causes a significan t broadening of the relaxation time distribution las measured by d.m.t .a.). (C) 1998 Elsevier Science Ltd. All rights reserved.