Construction And Properties Of Polymer Dielectric Composites Based On Three-dimensional Ceramic Network

As a kind of energy storage material with high power density,polymer dielectric composite finds wide range of applications in communication technology,microelectronic devices,power grid engineering and new energy vehicles.Particularly,the polymer dielectric composite filled with various ceramics has become a hot topic in flexible energy storage devices because it possesses comprehensive characteristics of both high insulation,good flexibility,easy processing of polymers and excellent thermal stability,large dielectric constant of ceramic nanofillers.However,high ceramic loading often leads to the degradation of mechanical properties and breakdown strength of polymer composites,which is difficult to meet the requirements of most engineering applications.Therefore,it is very important to achieve large dielectric constant,high breakdown strength and improved energy storage density with low ceramic content for polymer dielectrics.Focused on the above frontier,we,for the first time,constructed a continuous three-dimensional barium titanate（3DBT）ceramic network by sol-gel method using cleanroom paper as the template.A 3DBT/polymer composite dielectric material was then prepared by reversely introducing polymer into the obtained 3DBT backbone.The effects of different sintering temperatures on the phase transition and 3D network formation of Ba Ti O₃ were systematically investigated,and the influence of the morphology and content of Ba Ti O₃ filler on the electrical properties of 3DBT/polymer composite dielectric was explored in details.Furthermore,graphene oxide（GO）was introduced into the above system,and the synergistic enhancement of GO and 3DBT in the dielectric properties and energy storage performances of the composites were further investigated.Interesting results were obtained and listed as follows.（1）The 3DBT ceramics sintered at 1100 ^oC for 3 h result in the best uniform size（～200nm）and continuous network structure,which maintains the interwoven structure of fibrous cleanroom wiper The large surface area of the obtained 3DBT leads to the good adsorption and coating of polymer chains.（2）The reverse introduction of polyvinylidene fluoride（PVDF）enables continuous embedding and good interfacial compatibility with the 3DBT ceramic network.The dielectric constant of the 3DBT/PVDF composite reaches 25.3（tanδ=0.057,100 Hz）at21.1 wt%of 3DBT ceramic loading,which is 1.4 times higher than that of the 25 wt%nano-BT/PVDF 3DBT/PVDF composite.In addition,it has an energy storage density of 1.6×10^-3J·cm^-3 at 3 k V·mm^-1,4.4 times higher than that of pure PVDF(U_PVDF=0.36×10^-3 J·cm^-3).The continuous polarization induced by the continuous 3DBT network contributes greatly to the improved dielectric and energy storage performances.（3）Reverse introduction of the epoxy resin into the 3DBT network results in similar good adhesion and interfacial interaction.The dielectric constant of the 3DBT/epoxy composite reached 14.3（tanδ=0.019,100Hz）at 20.0 wt%3DBT loading,which was 3.3times higher than that of pure epoxy（ε_r=4.4,tanδ=0.022）and 2.6 times higher than that of 25 wt%nano-BT/epoxy composite（ε_r=6.3,tanδ=0.020）.Meanwhile,the breakdown strength of 3DBT/epoxy composite approached 89.96 k V·mm^-1 and the linear energy storage density reached 0.51 J·cm^-3,which was 1.4 times higher than that of pure epoxy(E_b=140.16k V·mm^-1,U_epoxy=0.38 J·cm^-3).（4）The 3DBT/epoxy-GO ternary composite system was simultaneously prepared by reversely introducing of epoxy-GO（graphene oxide）mixture.Results found that the dielectric constant and breakdown strength were both enhanced.The dielectric constant of the 3DBT/epoxy-GO GO-composite at 100 Hz was 15.6（tanδ=0.021）when the GO and3DBT content were 0.75 wt%and 15.4 wt%,respectively.Meanwhile,the breakdown strength reached as high as 239.84 k V·mm^-1,which is much higher than that of the 15.0 wt%nano-BT/epoxy composite(137.64 k V·mm^-1).What’s more,the 14.5 wt%3DBT/epoxy-0.50 wt%GO system exhibited the best energy storage density of 47×10^-3 J·cm^-3 and efficiency of 49.1%at 40 k V·mm^-1,1.88 times higher than that of pure epoxy.