Design on polarization distribution in all-organic polymer hybrids for high density energy storage

Polymer-based dielectric capacitors have attracted increasing attention in advanced electronics and pulsed power systems due to their high power density and ultrafast charge–discharge speed. However, most of recent achievements focus on polymer-based nanocomposites employing high-k inorganic nanofillers, generating mismatched filler/matrix interfaces that need careful modification. Herein, all-organic hybrid polymers have been explored to achieve ultrahigh energy storage density. Ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) with large polarization was introduced into poly(vinylidene fluoride) (PVDF) with smaller polarization forming blend films, and next sandwich structures constructed by PVDF and P(VDF-TrFE)/PVDF blend films were elaborately designed. A high discharge energy density (Ue) of 23.6 J/cm3 at 636 MV/m has been achieved in 30/70 (volume ratio) P(VDF-TrFE)/PVDF blend film, which is 55% and 130% higher than that of PVDF and P(VDF-TrFE), respectively. Further, by designing sandwich structured all-organic films with 50/50 (volume ratio) P(VDF-TrFE)/PVDF blend film as middle layer to provide high electric displacement and PVDF as two outer layers to withstand high electric field, high Ue = 20–24 J/cm3 and charge–discharge efficiency (>65%) have been achieved. In-depth understanding on the microscopic mechanism for achieving high Ue is gained via finite element analysis showing that the volume fraction of ferroelectric phase in the hybrid system and the mesoscopic layer/layer interfaces are crucial. This work thus provides a promising alternative strategy for high-density energy storage via all-organic films design.