Enhancement Of The Dielectric Energy Storage Performance Of PVDF-TrFE Composite Film Via Core-shell Structured BZT-xBCT@TiO₂

With the acceleration of climate change and industrialization,improving energy storage and energy efficiency have become the focus of research.The ultra-high power density（up to～10⁸W/kg）and long service life of dielectric capacitors make them critical to high power/pulsed power technologies.Polyvinylidene fluoride trifluoroethylene copolymer（PVDF-Tr FE）polymer-based dielectric energy storage materials have become a research hotspot in recent years due to their excellent breakdown strength and power density.However,the power density of PVDF-Tr FE is relative lower owning to its low dielectric constant.The feasible strategy is to introduce piezoelectric ceramic with high dielectric constant accompanying with dielectric transition layer to compensate the dielectric gap between them,further improving the electric breakdown strength.In this paper,PVDF-Tr FE composite films were fabricated via core-shell structured（1-x）Ba(Ti_0.8Zr_0.2)O₃-x(Ba_0.7Ca_0.3)Ti O₃@Ti O₂（BZT-xBCT@T）to enhance their dielectric energy storage performance.The main work and innovative achievements of the paper were as follows:1.The energy density was elevated by optimizing the composition and content of BZT-xBCT,while the thickness of Ti O₂transition layer with moderate dielectric constant was adopted to enhance the breakdown strength of the composite films.The phase and microstructure were analyzed by XRD,FTIR,SEM and TEM.The experimental results exhibited that when the composition is BZT-0.6BCT,the content is 3wt%,and the film is kept at 200℃for 60min,it is most beneficial to promote the crystallization ofβ-phase andγ-phase in PVDF-Tr FE,and the crystallinity is 41.24%and 44.89%,respectively.2.The energy storage properties of the composite films were comprehensively characterized by ACS4200 semiconductor parameter analyzer,ferroelectric tester and electric breakdown tester.The results show that the composite film（P-3%0.6 BCT-1）achieves excellent energy storage performance,the maximum breakdown field strength can reach to327k V/mm（β～12.9）,and the maximum U_ecan reach to 14.22J/cm³with a large energy storage efficiency of 67.38%.3.Under the optimal fiber composition,loading and hot-pressing preparation process conditions,Ti O₂transition shell structures with different thicknesses were prepared by hydrothermal method.Conbined with the microscopic phase analysis,the energy storage properties of the composite films were comprehensively characterized by the test methods such as dielectric spectrum,electric breakdown strength and ferroelectric test,and the influence of Ti O₂transition shell thicknesses on the energy storage performance of the composite films was studied.It was found that with the increase of Ti O₂shell thickness,the energy storage performance increased first and then decreased.When the shell thickness is about 75 nm,the composite film has the best energy storage performance.Specifically,the composite exhibits a Weber-distributed breakdown field strength（E_b）of 365 k V/mm and a discharge energy density（U_e）of 18.71 J/cm³（η～60.03%）,which is almost 3.5 times higher than that of the pure PVDF-Tr FE film with the energy storage efficiency.The work in this paper opens up new avenues for the selection and optimization of polymer-based dielectric nanocomposites.