Preparation And Research Of Energy Storage Properties Of Na_0.5Bi_0.5TiO₃/PVDF Composite Films

In the wake of developments in science and technology,consumer electronics are moving towards miniaturization,low cost,high performance and high reliability.The high integration of the circuit components is the essential prerequisite for the development of consumer electronics.For capacitance to realize large scale integration,researchers need to develop new materials of high energy storage performance.In generally,energy storage materials mainly include ferroelectric ceramic materials and polymer materials.The major advantages of ferroelectric ceramic materials are high dielectric constant,and it also has some disadvantages of low breakdown strength and high sintering temperature.The advantages of polymer materials are high breakdown voltage and good mechanical performance but low dielectric constant.Therefore,composite flms represent a promising approach,which has the potential of combining the high breakdown strength of the polymer matrix with the high dielectric constant of the ceramic fllers to realize high energy density.In this paper,Na_0.5Bi_0.5TiO₃?NBT?ceramics with high electric displacement can be expected to be an excellent candidate as the fllers in high energy density composite flms.PVDF is chosen as the polymer.We hope to develop of a new type of polymer composite films with high energy density.NBT ceramic powders,prepared by environmentally friendly and simple solid state method,are selected as the fller and introduced into the PVDF matrix to form composite films.NBT-NPs/PVDF composite films are manufactured by tape-casting.The sample with 1 vol%NBT-NPs/PVDF composite film exhibits the highest breakdown strength?380 kV/mm?,and thus a high energy density of9.16 J/cm³ is achieved in the composition,which is 1.5 times higher than that of pure PVDF.The improved breakdown strength is attributed to the reduced mobility of polymer chains induced by the NBT-NPs powders.The value of energy density is much higher than other polymer-based composite films.In addition,the NBT-NPs/PVDF composite films have the outstanding transmittance and flexibility.The three-layers composite flms comprised of two outer layers of NBT-NPs dispersed in a PVDF matrix to provide high dielectric constant and a middle layer of pure PVDF to offer high breakdown strength are prepared by a solution casting layer-by-layer process.Experimental results indicate that the breakdown strength and energy density of three-layers composite flms are improved significantly via tailoring the contents of NBT-NPs fillers.The three-layers composite flms with optimized filler content result in enhanced breakdown strength of 410 kV/mm,and thus an impressive energy density of 12.49 J/cm³ is obtained.Moreover,compared with single-layer composite flms,three-layers composite flms exhibit the higher breakdown strength and energy density.It can be explained that three-layers composite flms prevent the development of electrical trees during breakdown process due to the strong barrier interfaces attributed by the electric field gradient between adjacent layers.The three-layers flexible composite flms comprised of two outer layers of Na_0.5Bi_0.5TiO₃ nanofibers?NBT-NFs?dispersed in PVDF matrix to provide high dielectric constant and the middle layer of pure PVDF to offer high breakdown strength are prepared by tape-casting layer-by-layer process.The dielectric constant of composite flms filled by NBT-NFs is larger than that filled by NBT-NPs at same content due to stronger interfacial polarization.Thus,a large energy density 11.69 J/cm³ is achieved at the relatively lower electric field?350kV/mm?for the composite flms with 1%volume fraction of NBT-NFs in the outer layers,which is higher than that of the composite flms filled by NBT-NPs and the reported PVDF-based composite flms at the same electric field.The stronger interfacial polarization of composite flms filled by NBT-NFs is proved via calculating the activation energy of conductivity and electric modulus.In addition,the composite flms filled by NBT-NFs have outstanding winding and bending stability.