Preparation And Dielectric Properties Of CNTs/Inorganic Nanowires/PVDF Three-Phase Composite

As the developing of science and technology,high energy storage density and processing performance material is required.Fiml capacitor has the advantages of low density,light weight has attracted extensive attention.Currently,there are two primary approaches of polymer-based dielectrics:The first method involves incorporation of high-k ceramic ferroelectric materials,such as CCTO,BaTiO₃,etc.which is high dielectric constant,but the main shortfall of method is high filling amount required for ceramic fillers(>50 wt%),this will greatly reduce the flexibility and processability of the polymer matrix.The second method involves incorporation of conductive fillers,such as CNTs,C,graphene and other conductive fillers,the main shortfall of method is the mutual contact between the conductive fillers,a conductive path is formed,which will significant increase of the dielectric loss.The biggest challenge is to achieve high dielectric properties and low dielectric loss.Therefore,some studies have proposed to a hybrid structure of cinductive fillers and ceramic fillers,by taking the advantages of individual fillers and their synergistic effect.In summary,we choose filler of CNTs and MnO₂nanowires or BaTiO₃nanowires,and the polymer matrix of PVDF.Firstly,we prepare CNTs/PVDF and CNTs-COOH/PVDF composite materials.The results show that the percolation threshold of CNTs/PVDF is about 4 wt%,while the percolation threshold of CNTs-COOH/PVDF composite is about 5 wt%,indicating that the carboxylation of CNTs surface effectively improves the dispersion of CNTs in PVDF matrix.As the amount of CNTs increases,the breakdown strength of CNTs/PVDF composites decreases.Secondly,we prepare CNTs/MnO₂NWs/PVDF composite materials successfully.The results show that the best hydrothermal reaction temperature is 140°C,the aspect ratio of MnO₂nanowires is the highest,about 20.The dielectric constant of 3 wt%CNTs/9wt%MnO₂NWs/PVDF three-phase composite at 10³Hz is 21 and the dielectric loss is 0.08,Compared with 3 wt%CNTs/PVDF two-phase composite,the dielectric constant has increased by 52%,compared with 9 wt%MnO₂NWs/PVDF two-phase composite material,the dielectric constant has increased by 23%.And when the CNTs reached the percolation threshold of 4 wt%,the filling amount of MnO₂nanowires was 8 wt%and 12 wt%,the three-phase composite showed the characteristics of an insulator.Compared with the CNTs/PVDF two-phase composite,the CNTs/MnO₂NWs/PVDF three-phase composite has an higher breakdown strength.Thirdly,we prepare CNTs/BTNWs/PVDF three-phase composite materials successfully.The results show that the best temperature of first step hydrothermal reaction is 240?,the best temperature of second step hydrothermal reaction is 95?,the highest ratio of BaTiO₃nanowires is about 40.The dielectric constant of 5 wt%CNTs/15 wt%BTNWs/PVDF three-phase composite is 25 at frequency of 10³Hz,and the dielectric loss is about 0.13,compared with two-phase composite material 5 wt%CNTs/PVDF reduces the dielectric loss by 96%.Compared with the 15 wt%BTNWs/PVDF two-phase composite material,the dielectric constant has increased by 78%,and the filling amount of CNTs reaches the percolation threshold of 4 wt%and 5 wt%,composite materials still have insulator characteristics.Compared with the two-phase composite CNTs/PVDF,the breakdown strength of CNTs/BTNWs/PVDF three-phase composite has improved.Finally,we successfully prepare the CNTs-COOH/BTNWs/PVDF three-phase composite material.The results show that the dielectric constant of the 5wt%CNTs-COOH/15 wt%BTNWs/PVDF composite material reaches 26 at 10³Hz,and the dielectric loss is 0.075,compared with 5 wt%CNTs-COOH/PVDFP composite material,the dielectric loss has gone down 50%,compared with the 15 wt%BTNWs/PVDF composite material,the dielectric constant rose by 25%,and when the CNTs-COOH reaches the percolation threshold of 5 wt%,the composite material is insulator features,compared with the CNTs-COOH/PVDF composite,the breakdown strength of CNTs-COOH/BTNWs/PVDF has improved.Finally realized the complementary advantages of two fillers.