Energy Storage Properties Of Sandwich-Structured Composite Dielectric With Boron Nitride Barrier Layers

Polymer dielectrics are widely used in the field of power electronics and pulsed power,generally have excellent storage capacity at room temperature,but the thermal stability of the polymer is poor,and the next generation of polymer dielectric capacitors needs to meet the increasing requirements of energy storage and power regulation under extreme conditions.Therefore,the performance degradation at high temperature is unable to meet the demand.In view of this,this thesis adopted high-temperature resistant linear dielectric PEI as the intermediate layer,high insulation and wide band gap BN as the surface barrier layer to construct BN-PEI/PEI/BN-PEI sandwich polymer matrix composite dielectric.The experimental variables were BN particle size and BN volume fraction in BN-PEI layer.In order to improve the dielectric properties and insulation of PEI,room temperature and high temperature energy storage characteristics of BN-PEI/PEI/BN-PEI were studied,and finally preferable room temperature and high temperature energy storage characteristics were obtained.Firstly,pure PEI dielectric was prepared by high-speed directional spinning combined with hot pressing,and the optimum hot pressing temperature of PEI was explored.The hot pressing temperatures were 180℃,190℃and 200℃,and PEI-190℃films had the best performance.The dielectric constant was 3.1 at 10 Hz,the breakdown strength(E_b)was 482 k V/mm,the discharge energy density(U_e)was 4J/cm~3 and the discharge efficiency(η)was 96%,so the hot pressing temperature of this experiment was set to 190℃.On this basis,BN-PEI/PEI/BN-PEI sandwich composite dielectric films were prepared by layer-by-layer high-speed directional spinning method,and then hot pressed at 190℃to form dense films.BN-PEI/PEI/BN-PEI(BN-2μm)composite dielectric(referred to as BPB-2)had the best performance when BN volume fraction in the BN-PEI barrier layer was5 vol.%:At room temperature,5 vol.%BPB-2 composite dielectric E_b was 520.9k V/mm U_e was 5.38 J/cm~3,andηcould be maintained at 96%.At 100℃,5 vol.%BPB-2 composite dielectric E_b was 443 k V/mm,U_e was 3.42 J/cm~3,andηwas 90%.At 150℃,5 vol.%BPB-2 composite dielectric E_b was 333.8 k V/mm,U_e was 2.23J/cm~3,andηwas 93%.The BN-PEI layer of BN-PEI/PEI/BN-PEI(BN-200 nm)composite dielectric(referred to as BPB-2)had smaller BN particle size,less BN agglomeration,5 vol.%BPB-200 composite dielectric obtained better energy storage characteristics at room temperature and high temperatures:At room temperature,5 vol.%BPB-200composite dielectric E_b was 584.4 k V/mm,U_e was 5.65 J/cm~3,andηwas 96%.At100℃,5 vol.%BPB-200 composite dielectric E_b was 458.4 k V/mm,U_e was 3.63J/cm~3,andηwas 93%.At 150℃,5 vol.%BPB-200 composite dielectric E_b was361.6 k V/mm,U_e was 2.52 J/cm~3,andηwas 95%.The BN-PEI/PEI/BN-PEI sandwich structure designed in this thesis uses the broadband gap of BN to improve the height of carrier barrier and inhibit carrier injection,finally effectively improves the insulation of PEI at room temperature and high temperature,and achieves relatively excellent high temperature energy storage performance.