Enhanced energy storage performance of poly(vinylidene fluoride) by water-environmental annealing induced smaller crystallite size

Poly(vinylidene fluoride) (PVDF) based dielectric capacitors with low dielectric loss, high charge-discharge efficiency and excellent energy storage density are very important for their application. The energy storage performances of PVDF have a close relationship with its crystallization characters, such as crystalline polymorphism, crystallite size, crystal confinement, and orientation. Here, the non-polar α-form crystal PVDF films with different crystallite sizes were prepared by the water-environmental treatment method with varying temperatures. When the water-environmental aging temperature was 80 ℃, the PVDF film showed the smallest crystallite size of 20.9 nm. The smaller crystallite size of the annealed PVDF film decreased its dielectric loss, furthermore, the ferroelectric domain coupling was weakened by the confinement effect in the smaller nanoscale crystallites. Therefore, the PVDF film prepared by the water-environmental treatment method at 80 ℃ improved the discharge energy density and charge-discharge efficiency by more than 128% and 82.5% than the normal PVDF film with a larger crystallite size. The present research provides a facile and useful strategy to achieve the optimum crystalline morphology of PVDF for its application in the energy storage field.