title: High energy density and breakdown strength from β and γ phases in poly(vinylidene fluoride-co-bromotrifluoroethylene) copolymers.
abstract: Poly(vinylidene fluoride) PVDF-based copolymers represent the state of the art dielectric polymers for high energy density capacitors. Past work on these copolymers has been done with limited emphasis on the effects of copolymer composition and with a limited range of defect monomers, focusing primarily on the commercially available poly(vinylidene fluoride-co-chlorotrifluoroethylene), P(VDF-CTFE), and poly(vinylidene fluoride-co-hexafluoropropylene), P(VDF-HFP), and the processing thereof. To expand on this area of research, copolymers of VDF and bromotrifluoroethylene (BTFE) were synthesized examining the composition range where uniaxial stretching was possible. It is found that P(VDF-BTFE) copolymers with small BTFE contents (< 2 mol %) stabilize the γ phase, compared to P(VDF-CTFE)s and P(VDF-HFP)s that are largely α phase in composition. Furthermore, different from P(VDF-CTFE)s and P(VDF-HFP)s, whose energy storage capabilities depend on the reversibility of the α to β phases transformation, high discharged energy densities (i.e., 20.8 J/cm(3) at 716 MV/m) are also achievable through the β and γ phases in P(VDF-BTFE)s without significantly reducing crystallinity and breakdown strength. This study demonstrates new avenues to the development of high energy density ferroelectric copolymers via manipulation of the γ phase through variation of the structure and content of comonomers.
authors.affiliation: Department of Materials Science and Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Gadinski
authors.forename: Kuo
authors.initials: K
authors.lastname: Han
authors.forename: Qi
authors.initials: Q
authors.lastname: Li
authors.forename: Guangzu
authors.initials: G
authors.lastname: Zhang
authors.forename: Wuttiichai
authors.initials: W
authors.lastname: Reainthippayasakul
authors.forename: Qing
authors.initials: Q
authors.lastname: Wang
keywords: capacitors; dielectric properties; energy storage; ferroelectric polymers; poly(vinylidene fluoride)