Doping Modification And Charge-discharge Performance Of High Energy Efficiency BNT-SBT Energy Storage Ceramics

Ceramic dielectric capacitors have attracted extensive attention because of their super-fast charge and discharge rate,high power density and excellent stability.However,compared with traditional energy storage devices such as batteries and electrochemical capacitors,the storage density of ceramic dielectric capacitors is much lower,which limits its further application.Therefore,in the research field of ceramic dielectric capacitor,it is urgent to improve the storage density of capacitor through some optimization strategies.In addition,considering the toxicity of lead and the inherent defects of high energy consumption of antiferroelectric ceramics,lead-free relaxation ferroelectric ceramics are undoubtedly the ideal materials for future commercialization of dielectric ceramics.As a typical representative of lead-free relaxor ferroelectric materials,bismuth sodium titanate(Bi_0.5Na_0.5Ti O₃)based energy storage ceramics are the focus of current research.However,pure Bi_0.5Na_0.5Ti O₃（BNT）ceramics have large grain size,low density,and large ferroelectric domain,leading to high saturation polarization,large coercive field and very low dielectric breakdown strength（E_b）,resulting in low energy storage density.Based on the above problems,this paper designed a series of composition optimization strategies to improve the energy storage performance of BNT based ceramics and made remarkable progress.Firstly,the Sr_0.7Nd_0.2Ti O₃（SNT）component was introduced into BNT matrix.The introduction of SNT reduced the grain size,destroyed the long-range ordered ferroelectric domain and successfully induced the nanodomain,and obtained good relaxation properties while increasing the dielectric breakdown strength.A breakdown electric field of 182 k V/cm and an energy storage density of 3.09 J/cm³ were obtained in the 0.7BNT-0.3SNT component.In addition,it has good frequency and temperature stability in the temperature range of 25-160℃and frequency range of 5-200 Hz,and excellent charge-discharge performance,realizing the optimization of BNT ceramic energy storage performance.Then,in order to obtain high breakdown electric field and excellent relaxation performance,relaxation component Sr_0.7Bi_0.2Ti O₃（SBT）and wide-gap component Ba(Mg_1/3Ta_2/3)O₃（BMT）are introduced into BNT matrix.It is hoped that the storage performance of BNT ceramics can be improved through the dual optimization of domain engineering and band gap engineering.The results show that the introduction of SBT successfully induces the nanodomains,resulting in a fine P-E curve.The further modification of BMT reduces the grain size and widens the band gap,significantly improves the breakdown electric field.Finally,a record-breaking 8.58 J/cm³ energy storage density was achieved at the electric field of 565 k V/cm,with an efficiency of93.5%.At the same time,the material has good stability and excellent discharge performance.Finally,in order to solve the problem that the saturation polarization intensity always decreases significantly when the breakdown electric field is increased,the Ca Hf O₃（～6 e V）component with ultra-wideband gap width is introduced into the 0.7BNT-0.3SNT ceramics.The ionic radius and valence state of Ca Hf O₃（CH）are close to the matrix ions.The crystal structure of the matrix is maintained to the maximum extent,and the dielectric constant decreases slightly,thus maintaining a high saturation polarization strength.At the same time,the introduction of CH reduces the grain size,and due to its inherent high intrinsic breakdown strength,the breakdown electric field in0.7BNT-0.3SNT-0.05CH ceramics reaches 700 k V/cm,and the energy storage density increases to 8.61 J/cm³.Meanwhile,0.7BNT-0.3SNT-0.05CH ceramics also achieved excellent temperature and frequency stability,as well as excellent charge-discharge performance.