Polyvinylidene fluoride (PVDF)-based fluoropolymers have generated interest in electrical energy storage due to their high dielectric constant. The dielectric properties of these fluoropolymers can be significantly improved by uniaxial/biaxial orientation, a common practice adopted in industrial manufacturing, but the underlying molecular origins still remain unclear. In this paper, we explore a series of stretched poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) and investigate the stretching-induced structure development and its correlation with dielectric properties. With increasing strain, P(VDF-HFP) exhibits the expected paraelectric to ferroelectric transition. Increased crystal orientation and reduced crystallite size facilitate dipole orientation, resulting in elevated polarization. Breakdown strength is improved with stretching because of enhanced barrier effects, and recoverable energy density is also improved arising from the formation of reversible ferroelectric nanodomains. Contrary to expectations, the β-phase is not unfavorable for energy storage under DC conditions. The energy density of stretched P(VDF-HFP) can reach ∼20 J/cm³, indicating the great potential of optimizing the crystalline morphology of ferroelectric polymers for high-energy storage applications.

中文翻译：

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定向聚偏二氟乙烯-共-六氟丙烯的高场介电性能：结构-介电性能关系及其在储能应用中的意义

基于聚偏二氟乙烯（PVDF）的含氟聚合物由于其高介电常数而引起了对电能存储的关注。这些含氟聚合物的介电性能可通过单轴/双轴取向得到显着改善，这是工业生产中的一种常见做法，但潜在的分子起源仍然不清楚。在本文中，我们探索出一系列拉伸聚（偏氟的合作-六氟丙烯）（P（VDF-HFP）），并研究拉伸诱导的结构发展及其与介电性能的关系。随着应变的增加，P（VDF-HFP）表现出预期的顺电向铁电转变。增大的晶体取向和减小的微晶尺寸有助于偶极子取向，从而导致极化升高。由于增强的势垒效应，通过拉伸提高了击穿强度，并且由于形成可逆的铁电纳米域而提高了可回收的能量密度。与预期相反，在直流条件下，β相并非不利于能量存储。拉伸P（VDF-HFP）的能量密度可以达到约20 J / cm ³，表明在高能量存储应用中优化铁电聚合物晶体形态的巨大潜力。