Glass transition and free volume behaviour of poly(acrylonitrile)/LiCF3so3 polymer-in-salt electrolytes compared to poly(ether urethane)/LiClO4 solid polymer electrolytes

M. Forsyth, D. R. MacFarlane, A. J. Hill

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Abstract

Measurements of the glass transition temperature (Tg) and free volume behaviour of poly(acrylonitrile) (PAN) and PAN/lithium triflate (LiTf), with varying salt composition from 10 to 66 wt% LiTf, were made by positron annihilation lifetime spectroscopy (PALS). Addition of salt from 10 to 45 wt% LiTf resulted in an increase in the mean free volume cavity size at room temperature (r.t.) as measured by the orthoPositronium (oPs) pickoff lifetime, τ3, with little change in relative concentration of free volume sites as measured by oPs pickoff intensity, 73. The region from 45 to 66 wt% salt displayed no variation in relative free volume cavity size and concentration. This salt concentration range (45 wt% < [LiTf] < 66 wt%) corresponds to a region of high ionic conductivity of order 10-5 to 10-6 S cm-1 at Tg as measured by PALS. A percolation phenomenon is postulated to describe conduction in this composition region. Salt addition was shown to lower the Tg as measured by PALS; Tg was 115°C for PAN and 85°C for PAN/66 wt% LiTf. The Tg and free volume behaviour of this polymer-in-salt electrolyte (PISE) was compared to a poly(ether urethane)/LiClO4 where the polymer is the major component, i.e. traditional solid polymer electrolyte (SPE). In contrast to the PISE, the Tg of the SPE was shown to increase with increasing salt concentration from 5.3 to 15.9 wt%. The relative free volume cavity size and concentration at r.t. were shown to decrease with increasing salt concentration. Ionic conductivity in this SPE was of order 10-5 S cm-1 at r.t., which is over 60°C above Tg, 10-8 S cm-1 at 25°C above Tg, and conductivity was not measurable at Tg.

Original languageEnglish
Title of host publicationProceedings
Pages1243-1247
Number of pages5
Volume45
Edition8-9
DOIs
Publication statusPublished - 3 Jan 2000
EventProceedings of the 1998 6th International Symposium on Polymer Electrolytes (ISPE-6) - Hayama, Kanagawa, Japan
Duration: 1 Nov 19986 Nov 1998

Publication series

NameElectrochimica Acta
PublisherElsevier
ISSN (Print)0013-4686

Conference

ConferenceProceedings of the 1998 6th International Symposium on Polymer Electrolytes (ISPE-6)
CountryJapan
CityHayama, Kanagawa
Period1/11/986/11/98

Keywords

  • Glass transition
  • LiCFSO
  • Poly(acrylonitrile)
  • Polymer-in-salt electrolytes
  • Positron annihilation lifetime spectroscopy

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