Preparation And Energy Storage Properties Of Composite Dielectric Films Based On Polyetherimide

Dielectric capacitors have been widely used in microelectronics,power grids,medical equipment and military fields due to their ultra-high power-density and charge-discharge rate.Among the many dielectric materials studied so far,the linear dielectrics have attracted much attention due to their significant advantages in breakdown strength and efficiency.However,the inherent low dielectric constant of linear dielectrics results in low energy storage density,which seriously hinders the practical application of linear dielectrics.Therefore,it is imminent to improve the energy storage density of linear dielectrics and maintain high efficiency.In this paper,the linear dielectric polyetherimide(PEI)was the main research subject,and the inorganic and organic fillers were introduced to prepare polyetherimide-based composites.Through the characterization of their structures and energy storage properties,the mechanism to improve the energy storage was explored.The main research contents and results are as follows:First,the high dielectric constant barium titanate(BTO)nanoparticles were blended with PEI to prepare PEI/BTO composite films by the method of tape-casting.It was found that the dielectric constant of the PEI/BTO composite films raised gradually with the increase of the BTO content,reaching 4.8 when 7 vol.%(volume fraction)BTO was added,but at the same time the breakdown strength of the composite decreased to 354.1 MV/m,indicating that the high dielectric BTO fillers can effectively increase the dielectric constant of the composites,but also lead to a decrease in the breakdown strength.Based on PEI/BTO composite materials,polyimide(PI)was chemically coated to the surface of BTO to obtain core-shell nanoparticles PI@BTO,which were then combined with PEI to prepare PEI/PI@BTO composite films.It was found that the introduction of a PI shell on the surface of BTO can not only effectively improve the dispersion of nanoparticles in the composite films,reducing structural defects,but also form a strong electrostatic interaction with the PEI matrix,promoting the conformation extension and close stacking of the molecular chains,resulting in effectively improved breakdown strength.When 1 vol.%PI@BTO was added,the breakdown strength and dielectric constant of the composite were simultaneously improved,and the final energy density of 6.21 J/cm~3was achieved,which was 49.3%higher than that of the pure PEI film,the efficiency remained above 80%.Aromatic polyurea(Ar PU)with a dielectric constant of 4.99 was synthesized by the addition reaction of diisocyanate and diamine,and it was blended with PEI matrix as an organic filler to prepare the PEI/Ar PU all-organic composite films.It was found that the hydrogen bonds between Ar PU and PEI molecular chains could reduce the average chain spacing and increase the polymer chain packing density.When 1 wt.%(mass fraction)Ar PU was added,the breakdown strength of PEI/Ar PU film increased to 614.2 MV/m,and the final energy density of 5.17 J/cm~3was achieved,which was41.3%higher than that of the pure PEI(3.66 J/cm~3),and the charge-discharge efficiency remained above 95%.