title: Increasing the conductivity of crystalline polymer electrolytes.
abstract: Polymer electrolytes consist of salts dissolved in polymers (for example, polyethylene oxide, PEO), and represent a unique class of solid coordination compounds. They have potential applications in a diverse range of all-solid-state devices, such as rechargeable lithium batteries, flexible electrochromic displays and smart windows. For 30 years, attention was focused on amorphous polymer electrolytes in the belief that crystalline polymer:salt complexes were insulators. This view has been overturned recently by demonstrating ionic conductivity in the crystalline complexes PEO6:LiXF6 (X = P, As, Sb); however, the conductivities were relatively low. Here we demonstrate an increase of 1.5 orders of magnitude in the conductivity of these materials by replacing a small proportion of the XF6- anions in the crystal structure with isovalent N(SO2CF3)2- ions. We suggest that the larger and more irregularly shaped anions disrupt the potential around the Li+ ions, thus enhancing the ionic conductivity in a manner somewhat analogous to the AgBr(1-x)I(x) ionic conductors. The demonstration that doping strategies can enhance the conductivity of crystalline polymer electrolytes represents a significant advance towards the technological exploitation of such materials.
authors.affiliation: School of Chemistry, University of St Andrews, St Andrews KY16 9ST, UK.
authors.forename: Alasdair M
authors.initials: AM
authors.lastname: Christie
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Lilley
authors.forename: Edward
authors.initials: E
authors.lastname: Staunton
authors.forename: Yuri G
authors.initials: YG
authors.lastname: Andreev
authors.forename: Peter G
authors.initials: PG
authors.lastname: Bruce