Ultrahigh discharge efficiency and excellent energy density in oriented core-shell nanofiber-polyetherimide composites

A new energy storage dielectric system-polyetherimide (PEI) based composite was developed and investigated intensively. The system possesses the advantages of excellent energy storage efficiency along with energy storage density. A comprehensive energy storage performance with ultrahigh efficiency of 90% and outstanding density of 11.3 J/cm(3) is simultaneously achieved in PEI/BaTiO3 nanofiber coated by thick SiO2 layer (PEI/BT@T-SiO2) composites. The optimized energy storage efficiency is ascribed to the lower intrinsic dielectric loss of PEI matrix, insulted SiO2 shell outside the BaTiO3 nanofibers, and the oriented arrangement (parallel to the composite surface) of above "core-shell" structured fillers. In addition, three types of "core-shell" structured fillers ((BaSr) TiO3@SiO2, BT@SiO2 and BT@T-SiO2) were fabricated. The effects of dielectric constant for "core" and thickness for "shell" in the "core-shell" structured fillers on the dielectric and energy storage performance of composites were also investigated. The combination of experimental and simulated results indicates that larger dielectric constant of "core" doesn't mean the high polarization it can provide, and thickness of "shell" can influence the electric field distribution on "core". This work not only provides a new choice for matrix selection, but also points out a design route for the "core-shell" structured fillers used in the polymer based dielectric composites.