Preparation And Energy Storage Performance Of Poly(Vinylidene Fluoride) Based Nanocomposite

In recent years,electrical equipment and electrifications have developed rapidly owing to the proposals of green and renewable energy,meanwhile,these power equipment are advancing toward the direction of greater power,faster speed,and smaller size,and these new developments have spawned an urgent demand for dielectric capacitors with high energy storage performance.Nevertheless,compared with batteries and electrochemical capacitors,the low energy density of dielectric capacitors hinders their practical application range.Hence,the preparation of dielectric capacitors with high energy storage performance has become a pivotal issue to be solved.In this,polyvinylidene fluoride(PVDF)polymer with larger dielectric constant and better processability has attracted extensive attention in the preparation of dielectric capacitors,and has gradually become a research hotspot of dielectric materials.To solve this problem,PVDF and its blends are used as the matrix in this paper.The dielectric capacitors with outstanding energy storage property are obtained by synchronously enhancing the dielectric constant and breakdown strength of dielectric capacitors through introducing surface-modified Ba Zr0.2Ti0.8O3(BZT)nanofibers with the large aspect ratio.The main findings are as follows:(1)Preparation,structure and energy storage performance of BZT/PVDF nanocomposites.Novel nanocomposites with PVDF as matrix and BZT nanofibers as fillers was fabricated.To strengthen the dispersion of the BZT nanofibers and improve the compatibility between the fibers and the matrix,the nanofibers were coated with polydopamine.The values of Young’s modulus and DC resistivity of BZT/PVDF nanocomposites firstly raise and then reduce as the increase of volume percentage content of BZT nanofibers,from which the maximum values of Young’s modulus and DC resistivity were obtained at 5 vol.% of BZT nanofibers content.Simulation is used to show the electric field distribution for different volume fraction of BZT/PVDF nanocomposites.Both experimental and theoretical results corroborate that the moderate addition of BZT nanofibers into the PVDF matrix can lead to an improvement of breakdown strength of the nanocomposites.Strikingly,the optimal discharged energy density of the BZT/PVDF composite is 13.0 J/cm3 with 5 vol.% BZT fillers at 5219 k V/cm,quite larger than that of PVDF(energy density≈6.6 J/cm3 and breakdown strength≈4447 k V/cm).Meanwhile,the sample exhibits an ultra-fast discharge time of 0.14 μs under load resistor of 2000 Ω.It provides a feasible avenue to obtain good energy density of the nanocomposites under low filler loading,which will yield good application prospect to next generation of electrical mini capacitors.(2)Preparation,structure and energy storage performance of BZT/PVDF-PMMA nanocomposites.PVDF is used as the main matrix,and polymethyl methacrylate(PMMA)is added to it to enhance its breakdown performance.As the content of PMMA reached 15 wt%,the breakdown strength of the dielectric material increases from 4447 k V/cm of pure PVDF to 5400 k V/cm,meanwhile,the energy density augmentes to 9 J/cm3 and the discharge efficiency also enhances to 74.3%.Subsequently,a small amount of BZT nanofibers were introduced into the PVDF-PMMA dielectric material to improve the dielectric constant,thereby increasing the energy storage property.The breakdown strength of BZT/PVDF-PMMA nanocomposites firstly increase and then decrease with the increase of the mass percentage content of BZT nanofibers.Using simulation,it proves from a theoretical point of view that a reasonable selection of the content of BZT fibers can form a shielding layer in the region of the nanofiber tip in the nanocomposite,thereby effectively uniformizing the local electric field distribution and increasing the breakdown strength.The introduction of excess nanofillers will cause the exorbitant electric field concentration in the area near the nanofiber and make the electric field concentrated,thereby reducing the breakdown performance.It is worth mentioning that the energy density of 1 wt% BZT/PVDF-PMMA nanocomposite reaches 15.3 J/cm~3 at 6612 k V/cm,with the discharge efficiency of 67.2%.In addition,the nanocomposite keeps stable performance after 105 charge-discharge cycles.This study provides valuable insights into the development of high energy storage performance polymer-based nanocomposites with low filling content.