Effect of Trap Distribution on Breakdown Probability and Energy Storage Performance of PEI/BNNS Composite Dielectrics
Energy storage equipment tends to be miniaturized and flexible,which puts forward higher requirements for the energy storage performance of dielectric energy storage capacitors.Polyether imide(PEI)has stable chemical properties and high breakdown strength,and is an excellent energy storage polymer dielectric material.However,the key problems that need to be solved are the large dispersion of breakdown field strength and low energy density of dielectric energy storage capacitors.PEI/BNNS nanocomposite dielectrics with PEI as matrix and boron nitride nanosheets(BNNS)as filler are prepared by in-situ polymerization.The chemical groups,micro morphology and electrical properties of the samples are tested.It is found that BNNS is uniformly dispersed in PEI matrix.With the increase of BNNS content,the polarization intensity of PEI/BNNS nanocomposite dielectric gradually increases,the trap energy level increases first and then decreases,the breakdown strength and Weibull distribution shape parameters also increase first and then decrease.Then,the breakdown probability of PEI/BNNS nanocomposite dielectrics is simulated by charge trapping and molecular chain displacement breakdown model.The trap distribution characteristics of nanocomposite dielectrics are obtained by comparing the simulation and experimental results.With the increase of doping content,the expected value of trap energy level increases first and then decreases.The change of trapping effect of traps on carriers causes the breakdown field strength of Weibull characteristic to increase first and then decrease,and the energy storage density shows the same change law,the variance of trap distribution decreases first and then increases,which makes the shape parameters of Weibull distribution increase first and then decrease.The results show that a proper amount of BNNS doping can form a trap with deep energy level and small dispersion,which is the key to improve the breakdown and energy storage performance of the composite dielectric and reduce the breakdown dispersion.
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