Promoted liquid-liquid phase separation of PEO/PS blends with very low LiTFSI fraction

Studies on phase behavior of polymer blends with lithium salts can provide a theoretical basis for developing solid polymer electrolytes in lithium-ion battery. In this paper, the liquid-liquid phase separation of PEO/PS/LiTFSI system is characterized by small angle neutron scattering (SANS) and small angle laser light scattering (SALLS). A combination of the Debye-Bueche equation and Ornstein-Zernike scattering function is employed to fit the SANS data in the homogeneous state. The thermodynamic parameters, including the forward scattering intensity I0, correlation length ξ, spinodal temperature Ts, effective interaction parameter χeff and cloud point boundaries, are obtained. The cloud point temperatures increase with LiTFSI concentration, especially at the low PEO fractions. We conclude that even a small amount of lithium salt enhances the liquid-liquid phase separation of PEO/PS blends significantly, and the effect of electrostatic interaction increases with temperature.