Control over the complex phase evolutions for ultrahigh dielectric energy storage in pure poly(vinylidene fluoride) films

Poly(vinylidene fluoride) (PVDF) is a basic polymer that has been extensively used in flexible electronics, with the properties differing in terms of multiple phases, e.g. α, β, and γ. As generally involved, processing induced phase variations have not yet been identified clearly, which furthermore often embarrasses the attributions and contributions in the properties and mechanisms. To this end, the phase compositions and evolutions in pure PVDF films are systematically tuned and explored by annealing and quenching processing. The annealed PVDF exhibits a predominant γ-phase, while α-phase is dominated in quenched PVDF. Upon the induced different phase compositions, the optimally processed PVDF films similarly exhibit an ultrahigh dielectric energy storage density e.g. 19.66 J cm−3 for annealed and 21.73 J cm−3 for quenched PVDF film, respectively, but only the former maintains a simultaneously high discharge efficiency of 65 %. With showing excellent energy storage performance, the processed especially the annealed PVDF film could compare to many existing high-performance dielectric energy storage systems. This work thus not only uncovers the phase evolutions as well as their impacts on the properties in PVDF system, but also demonstrates firstly a high energy storage performance in pure PVDF.