Dielectric And Energy Storage Properties Of Polythiourea Based Composites

In the past decade,biaxially oriented polypropylene（BOPP）,a nonpolar polymer,has been widely used in power storage due to its high breakdown strength（600 k V/mm）and low loss（0.0002）.However,the dielectric constant of BOPP is only 2.2（1 k Hz）,resulting in a low overall energy storage（2.5 J/cc）.In contrast,strong dipole linear polymers,such as aromatic polythiourea（ArPTU）,have attracted widespread attention due to their high dielectric constant.In addition,its loss is much lower than that of traditional ferroelectric polymers.In this paper,the linear strong dipole moment polymer ArPTU is used as the matrix.Ba Ti O₃（BT）nanoparticles（NPs）,BT nanowires（NWs）,and cyanoethyl cellulose（CNEC）were incorporated into ArPTU to obtain composite films of inorganic/organic and all-organic systems.Finally,the microstructure and electrical properties of the composite film were tested.The specific research work and conclusions are listed as follows:（1）Dopamine（Dopa）-modified BT nanoparticles were introduced into the high dipole moment linear polymer ArPTU.Thus,the combination of high dielectric constant and high charge-discharge efficiency is realized.The effects of the interface on the dielectric response and breakdown strength of the nanocomposite were analyzed by finite element simulation.The surface of inorganic nanoparticles was modified according to the structure and function of inorganic/polymer nanocomposites.The experimental results show that the BT nanoparticles modified by Dopa can be uniformly dispersed in ArPTU,and the local electric field and dielectric behavior of the interface area have been effectively adjusted.As a result,the dielectric properties of the nanocomposite are enhanced.In particular,when Dopa@BT NPs of 1 wt.%are filled,the energy storage of the composite film can reach 5 J/cc while maintaining high charge-discharge efficiency.It can be seen that the energy storage density of Dopa@BT NPS/ARPTU composite is almost twice that of traditional linear polymer BOPP.（2）BT nanowires are prepared by a two-step hydrothermal method.Then the Dopa-modified BT nanowires were introduced into ArPTU.As we all know,1 D nanofillers have lower surface energy to avoid agglomeration compared with 0 D nanofillers.The interfacial polarization is more easily generated when nanowires are recombined with ArPTU,which ultimately leads to an increase in dielectric constant.At the same time,the dielectric loss of BT nanowires composites can be effectively reduced by modifying with Dopa.And the energy storage stability of the composite material is realized.In particular,when Dopa@BT NWs of 3 wt.%is filled,the energy storage of the composite film can reach 7.5 J/cc while maintaining an energy storage efficiency of more than 90%.Compared with traditional BOPP,the energy storage density is increased by several orders of magnitude,which provides an effective solution for the preparation of high energy density energy storage dielectric films.（3）Two strong dipole moment polymers Cyanethylcellulose（CNEC）and ArPTU are blended.ArPTU will suppress the early polarization saturation of CNEC,resulting in composite materials with higher breakdown strength while maintaining lower loss.Research shows that CNEC/ArPTU composite film has higher charge-discharge efficiency and breakdown electric field.At the same time,its dielectric constant remains at a high level.Compared with Dopa@BT inorganic fillers with higher specific surface energy,the specific surface energy difference between CNEC and ArPTU is smaller,so that agglomeration can be effectively avoided.Finally,the breakdown strength is further improved,and the loss is kept at a low level.In particular,the energy storage density of CNNEC/ARPTU（95/5）composite film can reach 26 J/cc under the electric field of686k V/mm,which is several orders of magnitude higher than that of Dopa@BT NWS/ARPTU composite film.And its charge and discharge efficiency is maintained at more than 90%.In addition,a laminated capacitor was prepared using CNEC/ArPTU（95/5）composite film by hot pressing method,which finally improved the capacitance and energy storage.