(565e) Polymer Nanocomposites: Advanced Polymer Electrolyte Materials for Li Ion Batteries

The high degree of poly(ethylene oxide) (PEO) crystallinity (leading to low ionic conductivity) at ambient temperature is unfavorable and excludes many practical applications of PEO as electrolyte in lithium ion batteries. Moreover, in presence of high Li+ ion concentration ( optimally [Li+]/[O-] ~ 0.04), PEO degrades fast which in turn reduces the battery lifetime. We have developed carbon nanotubes reinforced PEO nanocomposites as an alternative polymer electrolyte. The successful dispersion of single walled carbon nanotubes in poly(ethylene oxide) using an anionic surfactant (lithium dodecyl sulfate) as compatibilizer is reported here. The geometrical percolation threshold of nanotubes, as revealed by melt state rheological measurements, is found to be at ~ 0.09 vol % loading which corresponds to effective tube anisotropy ~ 650. Significant change in melting and crystallization behavior of poly(ethylene oxide) along with a decrease in fractional crystallinity has been observed in these nanocomposites. Incorporation of nanotubes acts as solid confinements to the PEO chains which not only make the chains stiffer but also provide steric hindrance to the chain transport. This effect coupled with high crystallization activation energy barrier leads to dramatic slowing down in PEO growth kinetics and makes the system more amorphous. The observed changes in the SWNTs based nanocomposites far exceed those observed for equivalent Li+ ion concentration (in this nanocomposites [Li+]/[O-] ~ 0.001) mixture and indicate that the SWNTs and LDS synergistically affect the crystallization of PEO. Finally, nanotubes are successfully aligned (to break their electrical conductivity) to develop this polymer nanocomposite as an alternative polymer electrolyte for Li ion batteries.