Compositional dependence of free volume in PAN/LiCF3SO3 polymer-in-salt electrolytes and the effect on ionic conductivity

✍ Scribed by M. Forsyth; Jiazeng Sun; D. R. Macfarlane; A. J. Hill

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 214 KB
• Volume: 38
• Category: Article
• ISSN: 0887-6266
• DOI: 10.1002/(sici)1099-0488(20000115)38:2<341::aid-polb6>3.0.co;2-s

✦ Synopsis

The free volume behaviour of the polyacrylonitrile/lithium triflate system is investigated over the composition range 0 -75 wt % salt. The addition of salt, up to 45 wt %, to the PAN polymer substantially increases the free volume as measured by the orthopositronium pickoff lifetime, 3 . Beyond this salt concentration (i.e., 45-70 wt %) the free volume remains approximately constant. This constant free volume region corresponds to a region of high ionic conductivity in the glassy state, making these materials polymer-based fast ion conductors, that is, having a decoupling ratio R ӷ1. The high salt content in these fast ion conductors results in a high susceptibility to polar solvents such as water. For all compositions, water absorption results in a free volume increase attributed to plasticization; however, in the fast ion conducting region, a significantly larger free volume response due to plasticization is measured and may be connected to a percolation morphology in these samples. Salt addition is shown to lower the T g , as measured by positron annihilation lifetime spectroscopy (PALS). T g is 115°C for PAN and 85°C for 66 wt % lithium triflate.