Glass transition and free volume behaviour of poly(arcylonitrile)/LiCF{sub}3SO{sub}3 polymer-in-slat electrolytes compared to poly(ether urethane)/LiClO{sub}4 solid polymer electrolytes

摘要

Measurements of the glass transition temperature (T{sub}g) 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, τ{sub}3, with little change in relative concentration of free volume sites as measured by oPs pickoff intensity, I{sub}3. 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{sup}(-5) to 10{sup}(-6) S cm{sup}(-1) at T{sub}g as measured by PALS. A percolation phenomenon is postulated to describe conduction in this composition region. Salt addition was shown to lower the T{sub}g as measured by PALS; T{sub}g was 115℃ for PAN and 85℃ for PAN/66 wt% LiTf. The T{sub}g and free volume behaviour of this polymer-in-salt electrolyte (PISE) was compared to a poly(ether urethane)/LiClO{sub}4 where the polymer is the major component, i.e. traditional solid polymer electrolyte (SPE). In contrast to the PISE, the T{sub}g 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{sup}(-5) S cm{sup}(-1) at r.t., which is over 60℃ above T{sub}g, 10{sup}(-8) S cm{sup}(-1) at 25℃ above T{sub}g, and conductivity was not measurable at T{sub}g.