Study On Energy Storage Characteristics And Modification Of BST-based Composite Ceramics

Dielectric ceramic capacitors have been widely used in high power systems for consumer,medical,military and industrial applications due to the advantages of high power density,low cost,and good stability.Nevertheless,most ceramic capacitors currently use lead-based materials,and the lead contained in these materials can be hazardous to human health and the environment.Therefore,the green and environmentally friendly lead-free dielectric ceramic capacitors have attracted widespread attention.So far,the energy storage density of lead-free dielectric ceramic capacitors is relatively low compared to that of lead-based dielectric ceramic capacitors,and it is necessary to further improve the energy storage density of lead-free dielectric ceramic capacitors in order to realize their large-scale application in the field of high power energy storage.Barium strontium titanate（（Ba,Sr）TiO₃,BST）-based lead-free dielectric energy storage ceramics are in paraelectric state at room temperature and have good ferroelectric and dielectric properties,which are considered as one of the most suitable lead-free dielectric materials for high-power energy storage applications.However,BST ceramics have low breakdown strength and energy storage density due to defects,which also hinder their promotion in the field of high energy storage density capacitors.In this thesis,the conventional solid-phase reaction method is used to modulate the energy storage behavior by compounding several different dielectrics,and the effects of multiphase compounding on its microstructure as well as electrical properties are characterized.The specific studies and results are as follows:1.The（1-x）Ba_0.6Sr_0.4TiO₃-x Ag Nb O₃ paraelectric-antiferroelectric ceramic system was constructed by compounding Ag Nb O₃（AN）.The results showed that the introduction of AN successfully improves the breakdown strength and relaxation characters of ceramics.When x=0.12,the ceramic obtained a comprehensive performance with a recoverable energy storage density of 2.45 J/cm³ and an energy storage efficiency of 88.87%under the electric field of 310 k V/cm.2.The（1-x）Ba_0.6Sr_0.4TiO₃-x Na Nb O₃ ceramics were prepared,and the resulting samples were found to have an ultra-fine grain size of submicron level and a high relaxationγ.The 0.85BST-0.15NN optimal component ceramic has a high breakdown electric field of 520 k V/cm,and exhibits an ultra-high recoverable energy storage density of 6.10 J/cm³ and a high energy storage efficiency of 87.44%.In addition,the ceramic also has a huge power density of 221.66 MW/cm³,high current density of1231.42 A/cm² and a very short discharge time of 62 ns.This experimental result further validates the feasibility of the paraelectric-antiferroelectric composite strategy.3.Based on the experiment of（1-x）Ba_0.6Sr_0.4TiO₃-x Na Nb O₃ ceramics system,Bi³⁺was further introduced to construct the（1-x）Ba_0.6Sr_0.4TiO₃-x Na_0.7Bi_0.1Nb O₃ ceramic system,which improved the permittivity and saturation polarization strength of ceramics at room temperature.The optimal component x=0.15 sample of this system has a breakdown electric field of 360 k V/cm,and realized a comprehensive performance with a recoverable energy storage density of 3.67 J/cm³ and an energy storage efficiency of 85.95%.4.Based on the experiment of（1-x）Ba_0.6Sr_0.4TiO₃-x Na Nb O₃ ceramics system,the（1-x）Ba_0.6Sr_0.4TiO₃-x Na Nb_0.6Ta_0.4O₃ ceramics system was designed by further introducing Ta⁵⁺.The introduction of Na Nb_0.6Ta_0.4O₃（NNT）has greatly improved the energy storage efficiency of ceramics,and the 0.85BST-0.15NNT optimal component ceramic can maintain an ultra-high energy storage efficiency of 97.77%and a high recoverable energy storage density of 4.42 J/cm³ at a high breakdown electric field of400 k V/cm.In addition,the energy storage efficiency of the ceramic under the electric field of 350 k V/cm varies within 5%with frequency,temperature and number of cycles,which demonstrates its good stability.