Preparation And Energy Storage Properties Of BNT-based Lead-free Ceramics

Sodium bismuth titanate(Bi_0.5Na_0.5Ti O₃,abbreviation BNT)based ceramics are lead-free relaxation ferroelectric materials,which are widely used in functional devices devices because of their excellent dielectric and piezoelectric properties.In the past ten years,researchers have carried out a research hotspot on BNT-based energy storage ceramics.Pure BNT ceramics,due to the own properties,are limited in the field of energy storage and charge-discharge performances.In this paper,BNT ceramics were selected as the matrix material,and the perovskite-like structural components were used as modifier.BNT-based energy storage ceramics were prepared by the traditional ceramic preparation process,the dielectric relaxation of the matrix ceramics was enhanced,and the breakdown electric field was improved,thus the energy storage and charge-discharge performances of the material were improved.The main research contents are listed below:The structure and energy storage properties of two binary ceramics(Bi_0.5Na_0.47Li_0.03)Ti O₃-Sr Ti O₃（BNLT-ST）and(Bi_0.5Na_0.47Li_0.03)Ti O₃-Na Nb O₃were systematically studied.The analysis of the results showed that:all ceramics formed the perovskite structure in which rhombohedral-tetragonal phases coexisted.The doping of ST and NN both enhanced the relaxation of the BNLT matrix material,and the hysteresis loops showed slimmer shape.By optimizing the doping content,it was found that the ceramics with composition of 0.7BNLT-0.3NN in two systems exhibited the best excellent energy storage performance:Under an AC electric field of 190k V/cm,the recoverable energy density(W_rec)and efficiency（h）values of the ceramic were 1.90J/cm³ and 85.59%respectively.In addition,at the DC breakdown strength（E_b）of 180k V/cm,the discharge energy density（W_D）was～1.44J/cm³,the discharge time(t_0.9)～0.090μs.The structure and energy storage properties of ternary ceramics(Bi_0.5Na_0.47Li_0.03)Ti O₃-Sr Ti O₃-Ba(Zr_0.3Ti_0.7)O₃（BNLT-ST-BZT）and(Bi_0.5Na_0.5)Ti O₃-Ba Ti O₃-Ba(Zr_0.3Ti_0.7)O₃（BNT-BT-BZT）were systematically studied.After solid solution of BZT,the ternary ceramics both presented a pseudo-cubic perovskite structure without impurity phase.The introduction of BZT weakened the ferroelectricity of the matrix ceramics and increases E_b,which was conducive to the improvement of energy storage performance.It was found that BNT-BT-0.4BZT ceramics showed the best energy storage characteristics,and the W_rec and h values were 1.90J/cm³ and 85.53%respectively.0.7（0.7BNLT-0.3ST）-0.3BZT ceramics had excellent charge and discharge performance,power density（P_D）and current density（C_D）were 64.82MW/cm³,864.21A/cm²,and both have fast discharge time,t_0.9～0.071μs.In order to further optimize the performance,Mn was added ternary system ceramics for optimization and improvement.The doping of Mn was beneficial to reduced leakage current and loss,and effectively improved the energy storage performance of the ceramics.0.1wt%Mn-BNT-BT-0.4BZT ceramics showed the best energy storage performance,under the electric field of 220k V/cm,W_rec～2.11J/cm³,the energy storage performance has increased by 11%.And the ceramic had a higher discharge density,W_D～1.57J/cm³,and the discharge performance was improved by 70%.By comparing the gold and silver polarized electrodes,the gold electrode effectively improves the interface between the ceramic and electrode,the performance of energy storage and charge-discharge has been improved.