Enhanced performance of all-organic sandwich structured dielectrics with linear dielectric and ferroelectric polymers

Abstract

Dielectric polymer materials have received increasing attention in the electronic and electrical industries, however, the miniaturization and intelligent applications of polymer capacitors are limited due to their low energy density. Recently, the construction of sandwich structured films provides a good pathway to improve the energy storage performance of dielectric polymers. In this research, all-organic sandwich structured dielectric polymer films consisting of linear dielectric and ferroelectric polymers are proposed and successfully made by simple layer-by-layer solution casting. Theoretically, the ferroelectric poly(vinylidene fluoride–trifluoroethylene–chlorotrifluoroethylene) (PVTC) layer can enhance the dielectric displacement because of high dielectric constant, while the polyetherimide (PEI) layers can raise the operating temperature, owing to the high glass transition temperature, and increase the breakdown strength (E_b) and reduce the loss due to their linear characteristic. Therefore, a series of positive-sandwich structured films (with the central PVTC layer and the outer PEI layers), reverse-sandwich structured films and single-layered blend films are fabricated for optimization and comparison. The influence of the linear/ferroelectric volume ratio and the polymer film structure on the energy storage performance has been thoroughly researched. Experimental results showed that the all-organic positive-sandwich structured film with an optimized low content ratio of PVTC can endure a highest E_b of 530 kV mm⁻¹ and exhibits a maximum discharge energy density of 8.0 J cm⁻³, which was more than two times that of the pure PEI film. Furthermore, the efficiency was up to 81%. More importantly, it possesses excellent temperature stability of the dielectric and energy storage properties from 25 °C to 100 °C. This work provides theoretical analysis and experimental guidance for the fabrication of all-organic sandwich structured films with high energy storage performance, which promotes the development and application of flexible polymer high temperature dielectric capacitors.