Phase behavior of binary and ternary fluoropolymer (PVDF-HFP) solutions for single-ion conductors

Jung Yong Kim

doi:10.1039/d2ra04158h

Phase behavior of binary and ternary fluoropolymer (PVDF-HFP) solutions for single-ion conductors

RSC Adv. 2022 Aug 2;12(33):21160-21171. doi: 10.1039/d2ra04158h. eCollection 2022 Jul 21.

Author

Jung Yong Kim^{1

2}

Affiliations

¹ Department of Materials Science and Engineering, Adama Science and Technology University P. O. Box 1888 Adama Ethiopia.
² Center of Advanced Materials Science and Engineering, Adama Science and Technology University P. O. Box 1888 Adama Ethiopia jungyong.kim@astu.edu.et.

Abstract

A fluoropolymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) has a dielectric constant of ∼11, providing charge screening effects. Hence, this highly polar PVDF-HFP material has been employed as a matrix for solid polymer electrolytes (SPEs). In this study, the phase behavior of binary PVDF-HFP solutions was analyzed using the Flory-Huggins theory, in which ethylene carbonate, propylene carbonate, dimethyl carbonate, γ-butyrolactone, and acetone were employed as model solvents. In particular, for the binary PVDF-HFP/acetone system, the solid-liquid and liquid-liquid phase transitions were qualitatively described. Then, the phase diagram for ternary acetone/PVDF-HFP/polyphenolate systems was constructed, in which the binodal, spinodal, tie-line, and critical point were included. Finally, when a polyelectrolyte lithium polyphenolate was mixed with the PVDF-HFP matrix, it formed a single-ion conductor with a Li⁺ transference number of 0.8 at 23 °C. In the case of ionic conductivity, it was ∼10^-5 S cm^-1 in solid state and ∼10^-4 S cm^-1 in gel state, respectively.