Study On The Preparation And Energy Storage Performance Of PEI-Based Films

As one of the indispensable components in energy systems,dielectric capacitors are widely used in the fiels of electronic and electrical engineering.Polymer matrix composites satisfy the development trend of miniaturization,lightweight and highly integrated electronic components due to advantages of high working voltage,excellent flexibility,easy processing and low cost.It has become one of the current research hotspots.However,there are still some drawbacks in the application of polymer-based dielectric composites.For example,the low energy storage density limits the application of high-power devices.The energy storage stability in high temperature environment needs to be improved.In this paper,polyetherimide（PEI）was selected to be polymer matrix.SrTiO₃、TiO₂ and Al₂O₃ were added into the matrix to prepare composite dielectrics.The composites with low volume fraction fillers were prepared by solution casting method to explore the effects of the fillers for dielectric properties and energy storage performances.The main research contents are as follows:（1）Strontium titanate（SrTiO₃）particles were prepared by sol-gel method.The maximum dielectric constant of 7 vol%SrTiO₃/PEI composite was 11.60.The energy storage density of 3vol%SrTiO₃/PEI composite was as high as 11.20 J/cm³ at 25℃under 640 MV/m,which was3.65 times than that of pure PEI film and 2.83 times than that of commercial BOPP.It exhibited an energy storage efficiency of 86%.At 150℃,the breakdown electric field of 3 vol%SrTiO₃/PEI composite reached 530 MV/m and the energy storage density reached 10.30 J/cm³.At 150℃and 500 MV/m,it exhibited high energy storage density of 8.82 J/cm³ and the energy storage efficiency of 80%.After 10⁵ charge-discharge cycles,3 vol%SrTiO₃/PEI composite displayed outstanding stability of energy storage density of 95%at 150℃under 300 MV/m.The dielectric properties of sandwich-structured composite prepared by hot pressing were improved.The breakdown electric field of"0-3-0"was 683 MV/m at 25℃,and the energy storage density and efficiency were 12.17 J/cm³ and 89.25%,respectively.At 150℃,the breakdown electric field of"0-3-0"was 588 MV/m,and the energy storage density and efficiency were 8.05 J/cm³ and 83.85%,respectively.The energy storage performance of sandwich-structured composite was obviously improved compared with that of single-layer dielectric film.（2）TiO₂ particles were prepared by hydrothermal method,and TiO₂/PEI composites were prepared.The dielectric constant of 9 vol%TiO₂/PEI composite reached 5.1,and the dielectric loss at 1 k Hz was only 0.012.The insulating filler TiO₂,inhibited the formation of conductive pathway,which significantly improved the resistance of the composite.Therefore,the energy storage efficiency was greatly improved.The energy storage density of 5 vol%TiO₂/PEI composite at 615 MV/m was 7.10 J/cm³,which was 2.29 times than that of pure PEI film.At150℃,the high breakdown electric field of 474 MV/m and the energy storage density of 5.56J/cm³ were also observed.The energy storage efficiency was maintained at 92%.After 10⁵cycles,5 vol%TiO₂/PEI composite showed the stability of energy storage density and efficiency of 97%and 98%under 300 MV/m.（3）In order to further improve the cyclic stability and temperature stability of the composites dielectrics,low volume fraction Al₂O₃ particles were added into PEI matrix.The dielectric constant of 7 vol%Al₂O₃/PEI composite was 5.25.The leakage current density of 3vol%Al₂O₃/PEI composite was the lowest and it was 10^-7 A/cm².At 25℃,the breakdown electric field of 3 vol%Al₂O₃/PEI composite was 582 MV/m and the energy storage density was 5.56 J/cm³,which was 1.73 times than that of pure PEI film.The energy storage efficiency of 3 vol%Al₂O₃/PEI composite was 87.5%.At 150℃,the breakdown electric field of 3 vol%Al₂O₃/PEI composite was 562 MV/m.The energy storage density and the energy storage efficiency were 4.95 J/cm³ and 85.8%,respectively.Compared with 25℃,the energy storage efficiency of 3 vol%Al₂O₃/PEI composite at 150℃decreased by only 1.7%,indicating that the composite possessed excellent temperature stability.After 10⁵ charge-discharge cycles,the stability of energy storage density and energy storage efficiency remained at 97.50%and98.15%,respectively.