Preparation And Properties Of Chitin/Copper Calcium Titanate Dielectric Energy Storage Composite Films

With the ever-increasing demand for electronic devices in the rapid development of modern technology,film capacitors,especially polymer-based capacitors have drawn much attention recently owing to the great mechanical properties,good processability and much higher power density.However,the mainstream polymer dielectric materials are mostly based on the traditional polymers derived from fossil energy sources,such as poly（vinylidene fluoride）（PVDF）,polyimide（PI）,biaxial tensile polypropylene（BOPP）,polyetherimide（PEI）and so on,which were not renewable.Therefore,it is of great significance to develop more renewable,biodegradable and environmentally friendly biomass-based dielectric materials.Chitin is the abundant biomass resource in nature with excellent mechanical properties,which is very suitable for the application in the flexible electronic field.However,there are few researches on chitin-based composite dielectrics.In this paper,chitin was used as the matrix,and calcium copper titanate（CCTO）with high dielectric constant was selected as the core filler to prepare chitin based composite dielectric materials with excellent dielectric properties.The main research contents and results are as follows:（1）Copper calcium titanate nanoparticles（CCTO NPs）and nanofibers（CCTO NFs）were prepared by molten salt method and electrostatic spinning method,and the RCH-CCTO NPs and RCH-CCTO NFs film were obtained by combining with chitin.The FTIR spectra and XRD diffraction of the composite films showed that the chitin used in the experiment isαcrystal,and the introduction of filler has no effect on the structure of the matrix material.The dielectric properties measurements indicated that the introduction of CCTO greatly improves the dielectric constant,and the appropriate amount of CCTO can also reduce the dielectric loss and improve the breakdown strength of the composite films.In addition,the chitin-based composite films with CCTO NFs loading showed better dielectric properties compared with RCH-CCTO NPs films.When CCTO NFs content was 3 wt.%,the composite film obtained the discharge energy density of 6.14 J cm^-3 at 410 MV m^-1,and the charge-discharge efficiency was 78%.（2）The CCTO NFs were coated with a thin layer of SiO₂ through nucleation method in solution thus creating a core-shell structure CCTO@SiO₂ to prepare the RCH-CCTO@SiO₂films by compounding with chitin.The XRD spectra showed that SiO₂ in the shell is amorphous,and the TEM and FTIR characterization results fully prove the successful preparation of CCTO@SiO₂ core-shell structure.The results of dielectric test showed that the introduction of SiO₂ reduces the dielectric constant of composite films,but also greatly reduces the dielectric loss and improves the breakdown strength of composite films,so that the energy density and charge and discharge efficiency of composite films have been significantly improved.Finally,the RCH-3CCTO@SiO₂ composite film obtained a discharge energy density of 7.78 J cm^-3,which is 1.3 times of RCH-3CCTO composite film,while the charge-discharge efficiency of the composite film still remains at 81.8%.（3）The chitin-based sandwich-structure composite films with boron nitride nanosheets（BNNS）distributed in the outer layer and CCTO distributed in the middle layer was prepared.The cross-section SEM figure of the composite film showed that the layers of the trilayered composite film are closely fitted without gaps.The results of dielectric properties test showed that CCTO can improve the dielectric constant and the high insulating BNNS layer can greatly improve the breakdown strength.Under the synergistic effect of dielectric constant and breakdown strength,the sandwich structure composite film obtained the optimal dielectric properties when CCTO content in the middle layer was 5 wt.%,that is,the discharge energy density of10.8 J cm^-3 and the high charge-discharge efficiency of 79.2%was obtained under the electric field of 500 MV m^-1,which are better than the monolayer ternary composite film with the same filler content(9.26 J cm^-3 at 440 MV m^-1).