Regulation of energy storage capacitance and efficiency in semi-crystalline vinylidene fluoride copolymers through cross-linking method

The increasing demands for compact and low-cost electrical power systems lead to developing high-energy-density dielectric materials. We carry out systematic investigation on the regulation of the semi-crystalline structure in the polymers and their related energy storage/release behavior through the cross-linking method. With respect to poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)], the cross-linked system exhibits a higher energy density and charged-discharged efficiency, as well as lower dielectric loss. In contrast, cross-linked poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] has a lower energy density/charged-discharged efficiency and higher dielectric loss than the pristine polymer. The somewhat contradicted results for these two polymers are closely related to the semi-crystalline structure controlled by cross-linking. The cross-linking mainly take place in the crystalline phase for P(VDF-HFP), while in both the crystalline phase and amorphous matrix for P(VDF-TrFE-CFE). Besides, crystal structures keep intact when setting up cross-linking networks in the polymers. Our approach provides a facile and straightforward way to tailoring PVDF-based polymers for high-energy-density capacitors.