Preparation Of MoS₂ And CaTi₂O₄（OH）₂ Nanosheets And Their Applications In Dielectric Composites

This thesis focuses on the preparation and enchances energy storage density of polyvinylidene fluoride(PVDF)and polyether imide(PEI)based on dielectric composites at room and high temperature were studied.As fillers,MoS2 NSs and CaTi2O4(OH)2 NSs were prepared to form three kinds of dielectric composites,MoS2 NSs/PVDF,CaTi2O4(OH)2 NSs/PVDF and CaTi2O4(OH)2 NSs/PEI.The effects of fillers contents on the dielectric constant,breakdown strength and energy storage density of the composites were studied.The internal electric field distribution of the dielectric composite was simulated by finite element method in order to obtain the dielectric composite with high temperature resistance and high energy storage.MoS2 NSs powder was prepared by liquid-phase stripping with a transverse size of about 200-300 nm and a thickness of about 5 nm.The effect of MoS2 NSs contents on the properties of MoS2 NSs/PVDF dielectric composites was investigated at room temperature.The results show that when the MoS2 NSs content is 3 wt%,the dielectric constant of the composite is 10.04,the breakdown strength reached 533 kV/mm,and the energy storage density is 12.67 J/cm3.The breakdown strength and energy storage density of the composite are 18%and 50%higher than pure PVDF material.CaTi2O4(OH)2 NSs powders with a length of about 400 nm,a width of about 200 nm and a thickness of about 20 nm were synthesized using tetra-butyl titanate as the titanium source and anhydrous calcium chloride as the calcium source under hydrothermal conditions of 180℃ for 36 h.The effects of CaTi2O4(OH)2 NSs addition on the properties of CaTi2O4(OH)2 NSs/PVDF dielectric composites were investigated at room temperature.The results show that when the addition amount is 3 wt%,the dielectric constant of CaTi2O4(OH)2 NSs/PVDF composite is 11.2,the breakdown strength is 568 kV/mm,the energy storage density is reach to 15.53 J/cm3,which is 1.76 times that of pure PVDF matrix.The internal electric fields of CaTi2O4(OH)2 NSs/PVDF and MoS2 NSs/PVDF were simulated by finite element method.The results show that CaTi2O4(OH)2 NSs with high band gap can improve the breakdown performance of composite materials more effectively,thus improving the energy storage density.The effects of CaTi2O4(OH)2 NSs content on the dielectric properties of CaTi2O4(OH)2 NSs/PEI composites at room temperature and high temperature were investigated.When CaTi2O4(OH)2 NSs content is 3 wt%,the breakdown strength of the dielectric composite is 623 kV/mm,which is higher than that of the pure PEI matrix at room temperature.The results indicate that CaTi2O4(OH)2 NSs with lamellar structure can improve the breakdown field strength of PEI matrix,and-OH on CaTi2O4(OH)2 can form hydrogen bond with O atom on PEI,which improves the interface compatibility of them,which is conducive to the increase of the breakdown field strength.At 150 ℃,When CaTi2O4(OH)2 NSs content is 3 wt%,the breakdown strength reaches 527 kV/mm,and the energy storage density is 5.35 J/cm3,which is 65%higher than that of the pure PEI matrix.The thermal analysis results can explain the thermal stability of the material,and CaTi2O4(OH)2 NSs/PEI composites have good thermal stability.This thesis chooses two kinds of nanosheets to improve the dielectric breakdown strength and the energy storage density of composite materials,mainly because they have the lamellar structure,in the polymer matrix they are almost perpendicular to the direction of the electric field distribution,electronic insulating barrier effect,makes the breakdown path more twists and turns,to improve the breakdown voltage and dielectric composite energy storage density effect.