Polymer electrolytes with a dual-phase structure composed of poly(acrylonitrile- co-butadiene)/poly(styrene- co-butadiene) blend films impregnated with lithium salt solution

Abstract

Dual-phase polymer electrolytes that possess good mechanical strength and high ionic conductivity were prepared by mechanically mixing a poly(acrylonitrile- co-butadiene) rubber (NBR) and poly(styrene- co-butadiene) rubber (SBR) binary solution and casting polymer blend films. The films were swollen with lithium salt solutions (e.g. 1 M LiClO 4 in γ-butyrolactone) to obtain dual-phase polymer electrolyte films. As the mixing rate increases, the average domain size of the NBR and SBR in the film decreased, levelling off at a mixing rate of > 10 000 rev min −1 as it approached the value of 5 μm. A mechanically strong film was obtained by reducing the domain size to less than one-fifth of the film thickness. On the other hand, the ionic conductivity depended on the fraction of NBR in the NBR/SBR matrix rather than on the domain size of the film. Thus high ionic conductivity (> 10 −4 S cm −1) could be achieved with an NBR weight fraction of over 50% (w/w). Additionally, transmission electron microscope observation and differential scanning calorimetric analysis showed evidence that a dual-phase structure was created, in which the NBR phase provided an ion-conductive pathway and the SBR acted as a mechanically supportive matrix. Quantitative analysis of ionic conductivity suggested that a ‘free’ lithium salt solution absorbed in the matrix caused the high ionic conductivity of the polymer electrolyte.