CONDUCTION MECHANISMS IN CONCENTRATED LII POLYETHYLENE OXIDE AL2O3-BASED SOLID ELECTROLYTES

The ionic conductivity of concentrated LiI-polyethylene oxide P(EO)(x) high surface area oxide composite polymer electrolytes has been inves tigated. Two different Arrhenius dependences felt concentrated composi te polymer electrolytes (CPEs) have been identified. The first one is characterized by an inflection point at about 80 degrees C, and the se cond, by a conductivity jump. We have suggested that in CPEs, where 3 < n < 9, the solid phase is major contributor to the overall ionic con ductivity at temperatures above, but close to the melting point of the eutectic (T-m < T < T-k), where T-k is the knee temperature. It is im portant to note that at T < T-k the apparent activation energy of cond uction (Ea) for composite solid electrolytes (CSEs, n less than or equ al to 3), is about 40% of that for CPEs. We believe that the preferred conduction path in even more concentrated CPEs, which are defined as CSEs, is interfacial conduction. Differential scanning calorimetry (DS C), scanning electron microscopy (SEM), and x-ray data, presented in t his communication are evidence supporting our view. The effects of sev eral parameters including type and content of oxide matrix, Li salt to ethylene oxide (EO) ratio, copolymers, and solvents on polymer electr olyte conductivity (especially at T > T-k or T-jump) and on Ea have be en studied (T-jump is a temperature of the conductivity jump). The add ition of small quantities of ethylene carbonate (EC), poly(methyl meth acrylate), and polyacrylonitrile were found to be beneficial while pol y(methyl acrylate), poly(butyl acrylate), and poly(vinylidene fluoride ) additions made the polymer electrolyte stiffer and less conductive. MgO, Al2O3, and potassium aluminosilicate muscovite mica based CSEs ha ve similar conductivity DSC and SEM results clearly demonstrated the d epression of CPE crystallinity by addition of fine Al2O3 powder, ethyl ene carbonate, and poly(ethylene glycol) dimethyl ether. This is in ag reement with the conductivity enhancement of the CPE.