单向拉伸对P(VDF-HFP)膜结晶相、介电和储能特性的影响

Uniaxial-stretching induced crystal phase transition and its effect on dielectric and energy storage properties of the P(VDF-HFP) copolymer films

铁电聚合物的结晶区相变对其介电和储能性能有显著的影响。本文利用溶液流延法制得厚度为20μm的P(VDF-HFP)厚膜,并通过单向拉伸工艺改变样品结晶性能。然后采用X射线衍射仪(XRD)和差热分析仪(DSC)研究了拉伸处理对P(VDF-HFP)结晶相结构的影响,利用阻抗分析仪和铁电测试仪分别比较了拉伸前后介电、聚合物能量存储和释放性能的变化。结果表明,不同HFP摩尔含量的P(VDF-HFP)厚膜拉伸后,不仅非晶区分子链趋于有序,聚合物膜缺陷减少,而且晶区发生了从非极性的α相到高极性的β相的转变,使介电响应降低,耐电强度增强。拉伸后的P(VDF-HFP)95.5/4.5mol%厚膜耐击穿电压高达900 MV·m^(-1),该电场下放电能量密度高达27.7J·cm^(-3)。经放电脉冲测试,P(VDF-HFP)95.5/4.5mol%拉伸膜在500MV·m^(-1)电场下循环持续放电次数超过1 000次,放电能量密度接近10J·cm^(-3)。P(VDF-HFP)优异的能量存储和放电特性使其在高储能密度电容器领域有广阔的应用前景。

The crystal phase transition of a ferroelectric polymer has a significant effect on the dielectric and energy storage performances.In this paper,the P（VDF-HFP）thick films with the thickness of 20μm are obtained by the solution casting method,with their crystal structures further fabricated by an uniaxial-stretching processing.The X-ray diffraction（XRD）and differential scanning calorimeter（DSC）are performed to express the changes of crystal phase structures of stretched films,with an impedance analyzer and ferroelectric testing system used to indicate the dependence of dielectric and energy storage performance of the crystal properties of the various samples.The results show that the amorphous of the polymer films is well aligned and that the crystal region has a phase transition from non-polarαto all transβphase in stretched P（VDF-HFP）.Interestingly,it has a higher discharge energy density of 27.7 J·cm^（-3） under 900 MV·m^（-1） and a favorable discharging energy density near 10 J·cm^（-3） for thousands of times at 500 MV·m^（-1） is achieved in stretched P（VDF-HFP）95.5/4.5 mol% film,respectively.Consequently,the excellent charging-discharging properties of P（VDF-HFP）provide a prospect of application in the field of high energy storage density capacitors.