Interaction Parameter (χ) and Ion Dissociation in Lithium and Magnesium Single-Ion-Conducting Block Copolymers Electrolytes

Top: chemical structures of PEO/P[(STFSI)Li] (left) and PEO/P[(STFSI)2Mg] (right). Bottom: (left) Intensity versus magnitude of scattering vector. The lithiated sample (blue curve) is disordered, but the magnesium sample (orange curve) still has structure at elevated temperatures. As a result, the ionic conductivity (right plot) is higher for the lithiated sample (blue triangles) is higher than the magnesium sample (yellow squares)

Scientific Achievement

Ion dissociation and block copolymer thermodynamics are intimately coupled: ion dissociation in lithiated systems suppresses microphase separation.

Significance and Impact

A linear relationship between the charge-concentration-related VTF parameter and the parameter quantifying the enthalpic contribution to χ, indicates ion dissociation and block copolymer thermodynamics are intimately coupled.

Research Details

  • The melt morphology of the single-ion conducting block copolymers is studied using temperature-dependent X-ray scattering and use the mean-field theory of Leibler to extract the effective Flory−Huggins interaction parameter (χ) for PEO/P[(STFSI)Li] and PEO/P[(STFSI)2Mg] from the X-ray scattering data.
  • The temperature dependence of ionic conductivity was measured, and through analysis using the Vogel−Tamman−Fulcher (VTF) relation, demonstrate that ion dissociation is significantly lower for all PEO−P[(STFSI)2Mg] samples when compared to their PEO−P[(STFSI)Li] counterparts.

DOI: 10.1021/acs.macromol.6b01886

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