145 / 2018-08-25 14:19:00

Study on the Energy Storage Perfomance of Amorphous-Al2O3 / PVDF Nanocomposite Film Based on Sol Blending Doping Strategy

PVDF, microstructure, polarization, energy storage performance.

With the rapid development of modern science and technology, flexible polymer materials with moderate dielectric constant and low dielectric loss have received great attention due to their excellent electrical properties, especially in energy storage and conversion. Generally, although polymer materials have excellent flexibility and high breakdown strength, their application is still limited due to their low dielectric constant. The introduction of inorganic fillers with high dielectric constant into a polymer matrix to form a polymer composite materials is one of the effective methods for improving the dielectric properties of capacitive energy storage media. The high dielectric constant inorganic nano-filled phase often requires a high filler loading content, causing a large amount of agglomeration of the packed phase, resulting in deterioration of the flexibility of the polymer material and a decrease in breakdown strength. Based on the above mentioned, a doping strategy of directly blending inorganic sol with organosol has been proposed for solving the bottleneck problem caused by uneven distribution of inorganic filled phase in the matrix. In this study, inorganic alumina (Al2O3) sol and polyvinylidene fluoride (PVDF) sol were solution-solved by sol-gel method, and then flexible amorphous-Al2O3/PVDF nanocomposite film was prepared by solution casting process. The crystal structure and microstructure of the composite film were characterized by X-ray diffraction and scanning electron microscopy. The dielectric properties and polarization behavior of the film were tested by broadband dielectric spectrometer and ferroelectric comprehensive tester, the energy storage performance of composite materials was also analyzed.
It can be found that the dielectric constant of Al2O3/PVDF nanocomposite film (the dielectric constant of the nanocomposite film is 20 when the mass fraction of Al2O3 is 7.5 wt.%) is higher than that of pure PVDF composite film (~11). At the same time, the discharge energy density of the Al2O3/PVDF nanocomposite film also shows improvement with the increase of the mass fraction. For example, when the mass fraction of Al2O3 is 7.5wt.%, the discharge energy density of the nanocomposite film is up to 14 J/cm3 at an electric field strength of 470 kV/mm, which is higher than that of a pure PVDF nanocomposite film (the maximum energy density is 10 J/cm3 at an electric field strength of 340 kV/mm).
For the Al2O3/PVDF nanocomposite film, the homodisperse of fillers in the PVDF matrix can be induced by the direct mixing of the Al2O3 inorganic sol with the polyvinylidene fluoride (PVDF) , and the higher quality of interfacial fusion between the filler and the matrix can be achieved. The increase of dielectric constant of Al2O3/PVDF is attributed to interficial polarization effect caused by doping Al2O3 fillers. Meanwhile, the doping strategy of inorganic and organosol blending induces the uniform dispersion of amorphous Al2O3, which reduces the interface defects and structural defects in the polymer matrix, leading to the improvement of the film quality and the breakdown strength of the composite film, the excellent energy storage performance has been obtained in the Al2O3/PVDF composite film. The results in this study indicate that the sol blending doping strategy may be expected to an effective way for improving the structural characteristics and electrical performances of the polymer-based energy storage dielectrics.