Dielectric Strength Design And Energy Storage Performance Of Flexible Lead Zirconate-Based Composite Films

Dielectric capacitor is a kind of extremely important electric energy storage device,which has the advantages of high power density,fast charge-discharge response,high open-circuit voltage,good safety,etc.,and has many applications in the fields of electromagnetic launch,transmission system,electric vehicle and integrated circuit.Among them,the dielectric energy storage material is the most important part of the capacitor,which directly determines the service performance of the capacitor.Compared with polymer capacitor films,inorganic energy storage dielectrics have higher relative permittivity and energy storage density,but they are usually grown on rigid substrates without flexibility,which limits wider applications.Especially,with the rapid development of flexible electronic technology,higher requirements are placed on the flexibility of embedded dielectric capacitors.At present,the research on inorganic flexible film capacitors is still in its infancy,and the energy storage dielectric still faces many problems,such as low breakdown strength,high energy loss and poor bending resistance.Breaking through the flexible preparation of inorganic energy storage dielectric and developing inorganic energy storage dielectric with excellent energy storage performance and bending fatigue resistance are current research hotspots.Lead zirconate（Pb Zr O₃）is a typical antiferroelectric material,which exhibits excellent energy storage performance due to the field-induced phase transition behavior from antiferroelectric phase to ferroelectric phase.In this thesis,Pb Zr O₃antiferroelectric thin films are taken as the research object,and the flexible preparation of Pb Zr O₃thin films is realized by growing thin films on flexible fluorophlogopite（Mica）substrates.The growth interface layer,element doping and multilayer structure design are used to improve the energy storage performance.The main research contents of this thesis include:The La Ni O₃interface layer is used to improve the crystallinity of flexible Pb Zr O₃film and energy storage performance.The metal Pt is grown on the flexible Mica substrate as the bottom electrode of Pb Zr O₃film.The La Ni O₃interfacial layer is grown between Pt bottom electrode and Pb Zr O₃thin film.The effects of interface layer on microstructure,polarization behavior and energy storage performance of Pb Zr O₃thin films are investigated.The results show that the quality and insulation properties of Pb Zr O₃films can be significantly improved by growing La Ni O₃interfacial layer,and the energy storage density can reach 16.6 J/cm³.Since the La Ni O₃interface layer improves the stability of the antiferroelectric phase of the Pb Zr O₃thin film,the depolarization hysteresis effect of the field-induced phase transition is serious,resulting in a large energy loss.By optimizing the La³⁺doping content and heat treatment temperature,the polarization behavior of the flexible Pb Zr O₃film can be adjusted and energy storage performance can be improved.The effect of La³⁺doping content on the polarization behavior of Pb Zr O₃thin films is studied to determine the optimal doping content.The degree of crystallization of flexible Pb Zr O₃films is controlled by changing the annealing temperature.The results show that the insulation performance of Pb_0.91La_0.06Zr O₃film increases first and then decreases with the increase of La³⁺doping content.The performance of Pb_0.91La_0.06Zr O₃film is the best,and the energy storage density and energy storage efficiency are 34.9 J/cm³and 58.3%,respectively.In order to solve the problem of low charge-discharge efficiency of doped modified films,the crystallization degree of the films is controlled by reducing the annealing temperature.The research results show that when the annealing temperature is550℃,the film exhibits the characteristics of nanocrystalline structure,which reduces the polarization loss caused by the field-induced phase transition,and shows the characteristic of linear polarization.When the nanocrystal structure is induced by appropriate annealing temperature,the film has moderate polarization and high dielectric strength,the energy storage density and energy storage efficiency are 42.0J/cm³and 90.8%,respectively.The flexible antiferroelectric layer-dielectric insulating layer multilayer structure is constructed by introducing Al₂O₃dielectric insulating layer,and the dielectric strength and energy storage performance of the multilayer composite film are improved.The Fermi level difference between Pb Zr O₃and Al₂O₃drives the formation of an interfacial built-in electric field,which induces the transformation of Pb Zr O₃from antiferroelectric phase to ferroelectric phase.When the thickness of the Al₂O₃dielectric insulating layer is 8 nm,the Pb Zr O₃/Al₂O₃/Pb Zr O₃composite film exhibits the characteristics of relaxor ferroelectric.When the Al₂O₃dielectric insulating layer is used as the top/bottom surface layer of the composite film,the interfacial barrier height can be increased,the charge injection can be suppressed,and the conductance loss can be reduced.The energy storage density and energy storage efficiency of the multilayer composite film can reach 35.2 J/cm³and 92.9%,respectively.Using Pb Zr O₃as interfacial barrier to improve high temperature energy storage performance of composite films.The inorganic interfacial barrier layer is grown on the surface of flexible Mica insulating layer to explore the effect and mechanism of interfacial barrier layer structure on dielectric energy storage performance of composite thin films.The results show that the heterostructure Pb Zr O₃/Al₂O₃barrier layer has a built-in electric field at the interface,which inhibits charge injection and transport,and reduces the high temperature leakage current density of the composite film.When the applied electric field intensity is 813.8 MV/m,the energy storage density and efficiency of Pb Zr O₃/Al₂O₃/Pb Zr O₃/Mica/Pb Zr O₃/Al₂O₃/Pb Zr O₃composite films are 40.1 J/cm³and 88.0%at room temperature,and 27.5 J/cm³and87.8%at 200℃,respectively.