Study On Preparation And Energy Storage Properties Of Ceramic Polymer Multilayer Dielectric Composites

Polymer-based dielectric materials have been widely studied in many dielectric materials,not only because of their high external breakdown electric field,low dielectric loss and ultra-high power density,but also because of their excellent mechanical properties and flexibility.Therefore,polymer matrix composites have a good development prospect in the military and civil fields.At present,a large number of researchers improved the dielectric properties by designing the interface of inorganic-organic composites phases,and adjusted the interlayer interface by changing the composite ratio and chemical composition,so as to improve the energy density of the composites.Barium strontium titanate(Ba_1-xSr_xTi O₃)is a kind of ceramic material with excellent properties,which not only has high dielectric constant and low dielectric loss,but also has good dielectric frequency stability.Barium strontium titanate is a solid solution of strontium titanate and barium titanate.Barium strontium titanate materials with different structures can be obtained by adjusting the molar ratio of titanium to strontium.Polyvinylidene fluoride（PVDF）is a kind of high molecular polymer material with excellent insulation,which is polymerized by monomer and free radical,and its monomer is vinylidene fluoride（-CH₂CF₂-）.The C atoms in the PVDF molecular chain will form different shape and structure distribution under different crystallization conditions,which makes PVDF have many different crystal phases.Therefore,this topic mainly focuses on the interlayer structure design of ceramic polymer-based multilayer composite films around BST and PVDF.（1）Firstly,four kinds of micron barium strontium titanate powders Ba_1-xSr_xTi O₃（x=0.5,0.4,0.3,0.2）with different titanium-strontium ratio were prepared by two-step solid-state sintering method using strontium titanate（Sr Ti O₃,ST）and barium titanate（Ba Ti O₃,BT）.By observing the XRD diffraction pattern of the powder,it was found that the pure barium strontium titanate phase was successfully sintered.And at room temperature,barium strontium titanate begins to transform from tetragonal phase to cubic phase with the increase of x content,and the diffraction peak gradually shifts to a high angle,and the lattice plane spacing decreases gradually.By observing the SEM images of barium strontium titanate powder,it is found that with the increase of Sr content,the grain size gradually becomes uniform,and the coexistence of large and small grains is improved to some extent.And at the same sintering temperature,the higher the content of Sr,the more favorable for the preparation of BST with high density.Therefore,in the end,Ba_0.7Sr_0.3Ti O₃（B₇S₃T）powder was introduced into PVDF polymer as ceramic filler to prepare composite films.（2）Secondly,x%B₇S₃T/PVDF single-layer and three-layer composite films with different B₇S₃T ceramic filling ratios were prepared by solution spin coating method,and the structural morphology,dielectric properties and energy storage of the two films were characterized.The results show that the polymer matrix in the composites with lower filling ratio can better cover the ceramic fillers and thus have better dielectric properties,and the single-layer and three-layer composites with different filling ratios get the highest dielectric constant at 10%and 5%,respectively.The highest energy storage density of 10%B₇S₃T/PVDF single-layer composite film is about 0.3J/cm³under the electric field close to 950k V/cm,while that of 15%B₇S₃T/PVDF three-layer composite film is about 0.098J/cm³ under the electric field of 250k V/cm.Because the composite films with low filling ratio have higher inorganic-organic interface and lower porosity,the 0.5%B₇S₃T/PVDF three-layer composite films also obtain a higher energy storage density of about 0.096J/cm³ under the electric field of 250k V/cm.（3）Finally,the solution spin coating method was used to prepare and characterize two kinds of three-layer thin films with different spatial structures,x%B₇S₃T/PVDF-PVDF-x%B₇S₃T/PVDF（x-0-x）and PVDF-x%B₇S₃T/PVDF-PVDF（0-x-0）.The results show that the potential barrier is increased due to the weakening of the outer electric field,which suppresses the charge input of the electrode under the high external electric field and increases the breakdown electric field of the composite.The experimental results show that 20%of the x-0-x composites have the energy storage density of 0.156J/cm³,while 20%of the 0-x-0 composites have the energy storage density of 0.19J/cm³.