Study On Energy Storage Properties And Mechanism Of Cerium Doped Strontium Titanate Based Composites

Dielectric film capacitors are widely used in fields such as new energy electric vehicles and pulsed power systems due to their advantages of high power density and fast charging and discharging speeds.Capacitors are composed of upper and lower plates and dielectric materials in the middle.Generally speaking,the dielectric is required to have the advantages of good processability,high breakdown strength and good dielectric properties.Polymer materials have good breakdown properties and are easy to process,but their dielectric properties are poor.Ceramic materials have excellent dielectric properties but their processability and breakdown properties are poor.Therefore,combining the two to prepare polymer-based nanocomposites is expected to obtain energy storage materials with improved performance.In this paper,polyvinylidene fluoride(PVDF)with a relatively high dielectric constant is selected as the substrate,and cerium(Ce)doped with strontium titanate(Sr Ti O₃)is used as the nano-filler to carry out the research.The following work has been done systematically:(1)For the different valence states of cerium,Sr_1-xCe_xTi O₃nanoparticles with+3valence and+4 valence Ce elements doped were synthesized by the sol-gel-hydrothermal method,and mixed with PVDF to prepare composite films.The effect of Ce doping ratio on the energy storage performance of composite materials was studied.The results show that after Ce doping,the dielectric properties and ferroelectric properties of the composite material are improved.Among them,the doping of+3 valence Ce is beneficial to increase the polarization strength.When the doping ratio is 0.1,it has a medium dielectric constant and the highest polarization strength,making its energy storage performance the best.After+4 valence Ce doping,the particle unit cell volume is reduced,and the breakdown resistance of the material is improved.When the doping ratio is 0.1,it has the highest breakdown field strength,and the corresponding discharging energy density is 4.2J/cm³.Compared with the undoped situation,it has been greatly improved.(2)On the basis of the previous research,the optimal doping ratio of Ce element with positive tetravalent Sr_0.9Ce_0.1Ti O₃particles were selected as fillers to study the effect of nanoparticles addition on energy storage performance.Studies have shown that as the content of nanoparticles increases,the dielectric constant and dielectric loss of composite materials increase,but the energy storage effect will first increase and then decrease.When the content of Sr_0.9Ce_0.1Ti O₃particles is 20%,the composite material has the best energy storage effect.In order to further improve the energy storage performance of the composite materials,the sandwich membrane structure filled with PVDF is also designed.The introduction of the PVDF layer significantly improves the breakdown strength of the composite material,which in turn stimulates greater polarization,20-0-20 structure due to the high breakdown field strength and polarization displacement,the energy storage density is the highest,which is increased by 254%compared to the single-layer film with the same doping amount.(3)Based on COMSOL and MATLAB software,the electrical properties and breakdown process of composite materials are analyzed.The results show that the particle size has an effect on the distribution of electric potential,and the electric field distribution and the polarization ability are mutually restrictive.Appropriately reducing the particle volume is beneficial to improve the electric field distribution,but the polarization ability will be weakened.Compared with round particles,fillers with large length-to-diameter ratios such as rectangles and ellipses can easily guide the breakdown path to propagate along the fillers,dissipate more energy,and improve the breakdown performance of the material.