Design And Performance Study Of Energy Storage Polymer Membranes Based On MMA Copolymer

With the rapid development of the electronics industry and electronic information technology,traditional capacitor materials are facing enormous challenges.Polymers have become potential candidate materials for electrostatic capacitors due to their high breakdown strength,high charge discharge efficiency,and low dielectric loss.Ferroelectric polymers such as poly(vinylidene fluoride)(PVDF)and their copolymers have high dielectric constants,but their high residual polarization and energy loss limit their further applications.The performance of PVDF based energy storage films can be improved by adding linear dielectric materials such as polymethyl methacrylate(PMMA)to design fully organic blend films and organic multilayer structures.However,there is still a lot of room for further improvement in the energy density of the blending strategy.The cracks and voids between the interfaces of multi-layer dielectric films have adverse effects on the stability and breakdown strength of the films,making it difficult to achieve large-scale production and industrial applications.Therefore,it is of great significance to prepare all organic electromechanical dielectric films with high breakdown strength and energy density,while maintaining low dielectric loss and low residual polarization.The matrix material studied in this paper is a linear methyl methacrylate and glycidyl methacrylate copolymer(MMA-co-GMA,abbreviated as MG),where the content of GMA is 8 wt%..It has a higher dielectric constant,breakdown strength,and energy density than PMMA.By selecting PVDF with high dielectric constant and excellent compatibility with MG as an organic filler,an all organic composite material is prepared to further improve its energy storage performance.The main content is as follows:(1)MG/PVDF fully electromechanical dielectric thin films with high breakdown strength and energy density were prepared by solution blending method,which were regulated by PVDF.Compared with PMMA homopolymer,MG copolymer has a higher energy density(5.6 J/cm~3),due to the higher polarity of the epoxy group on GMA and its ability to trap charge carriers as deep traps to improve breakdown strength.The introduction of PVDF in MG further improves the dielectric constant,breakdown strength and energy storage properties by optimizing the percentage of PVDF in MG.Meanwhile,the introduction of PVDF overcomes the brittleness of MG.The hydrogen bonding effect between PVDF and MG can be used as a deep trap for carriers to further improve the breakdown strength of MG by density functional theory(DFT),and the optimal energy storage performance is achieved by optimizing the percentage of PVDF in MG.When the PVDF content is 30wt%,the discharged energy density of PVDF/MG film at 600MV/m is10.8 J/cm~3with a 78.7%discharge efficiency,which is 2.5 times that of pure PVDF(4.3J/cm~3at 320 MV/m)and 1.9 times that of pure MG(5.6 J/cm~3at 460 MV/m).The improvement in energy storage performance might be ascribed to the excellent thermodynamic miscibility and hydrogen bond interaction between the linear MG copolymer and the ferroelectric PVDF.(2)Based on the research of MG/PVDF composite membranes,polyether amine(PEA)was added as a crosslinking agent to initiate ring opening reactions between epoxy groups and amino groups on MG.At the same time,the molecular chains of PVDF were bound in the crosslinking network of MG,achieving the goal of further improving breakdown strength,reducing dielectric loss,and increasing energy density.Through the thermal stimulated depolarization current(TSDC)and density functional theory theory(DFT),it is proved that the cross-linking point can be used as a deep trap for carriers,which leads to further improvement of the breakdown strength.At the same time,the brittleness of MG is improved by using PVDF and polyether amine with freely rotatable ether bonds as crosslinking agents.The presence of PVDF can appropriately compensate for the low polarization strength caused by cross-linked MG.When the content of PVDF reaches 30%,the fully organic cross-linked dielectric film achieves ultra-high breakdown strength(800MV/m)and 77.4%charge discharge efficiency.The maximum discharge energy density of PEA/MG-30%PVDF composite film reaches 12.1 J/cm~3,which is nearly 120%higher than that of pure MG film(5.6 J/cm~3).The improvement in energy storage performance is attributed to the good thermodynamic compatibility between PVDF and MG,the hydrogen bonding interaction between linear MG copolymer and ferroelectric PVDF,and the capture of free electrons by crosslinking points.