Study On Composition Design And Performance Regulation Mechanism Of BNBST-NN Energy Storage Ceramics

With the rapid development of energy storage technology,electronic components are developing in the direction of miniaturization and high efficiency,and dielectric capacitor materials with fast charging and discharging speed and high power density have been widely studied.In this paper,Na Nb O₃（NN）antiferroelectric ceramics and0.5Bi_0.5Na_0.5Ti O₃-0.5Ba_0.3Sr_0.7Ti O₃（BNBST）relaxation ferroelectric ceramics are studied to improve their energy storage performance through composition design.The specific research work is done as follows:（1）NN is an antiferroelectric ceramic that has been widely studied in recent years.However,NN ceramics undergo an irreversible antiferroelectric-ferroelectric（AFE-FE）phase transition under the applied electric field and exhibit a square polarization-electric field（P-E）hysteresis loop with larger P_r,which limit the further development in the direction of energy storage.In this paper,a novel lead-free relaxor ferroelectric ceramic,（1-x）Na Nb O₃-x(0.5Bi_0.5Na_0.5Ti O₃-0.5Ba_0.3Sr_0.7Ti O₃)[（1-x）NN-x BNBST,x=0,0.10,0.15,0.20,0.25,0.30],was designed and prepared via a local random field relaxation strategy.The dielectric test results showed that the addition of BNBST significantly improved the relaxation behavior of NN,and the energy storage density(W_rec)and energy storage efficiency（η）of NN-based ceramics were effectively improved.When x=0.2,the ceramic obtains a high recoverable energy storage density(W_rec=2.024 J/cm3)and energy storage efficiency（?=63%）at a low electric field of 130 k V/cm.Meanwhile,the P-E loops and charge-discharge results of the sample with x=0.2 at different temperatures and frequencies show that it is a prospective material for pulsed energy storage capacitors.（2）From the study in the previous chapter,it is clear that BNBST ceramics are a better relaxation component,but they themselves have two phase structures due to the presence of a polar tripartite phase（R3c）and a weakly polar tetragonal phase（P4bm）.In the presence of an applied electric field,the polar tripartite phase R3c transforms into a long-range ordered ferroelectric structure,resulting in a large P_r,which limits its application in energy storage.In this chapter,the phase composition is regulated by adding NN to BNBST ceramics to induce the transformation of the polar phase R3c phase to the weakly polar phase P4bm phase to reduce P_rand improve the energy storageperformance.The（1-x）(0.5Bi_0.5Na_0.5Ti O₃-0.5Ba_0.3Sr_0.7Ti O₃)-x Na Nb O₃[（1-x）BNBST-x NN,x=0、0.05、0.10、0.15、0.20、0.25]series ceramics were designed and prepared.The ferroelectric test results showed that the ceramic sample with x=0.1 achieves a high effective energy storage density(W_rec=2.58 J/cm³)and energy storage efficiency（?=91%）at 140 k V/cm.The results of pulsed charge-discharge tests in the temperature range of 40 to 140℃show that the ceramic samples with x=0.1 have high and stable discharge energy density（W_d≥1.11 J/cm³）and ultra-fast charge-discharge rates(t_0.9≤0.05μs).（3）The previous chapter found that although the 0.9BNBST-0.1NN ceramic sample exhibited good energy storage characteristics,it was still some distance from the practical application.In this chapter,the composition structure of0.9BNBST-0.1NN ceramic sample is further optimized by doping with rare earth ions toimproveitsenergystoragecharacteristics.The0.9(0.5Bi_0.5Na_0.5Ti O₃-0.5Ba_0.3Sr_0.7Ti O₃)-0.1Na Nb O₃+x wt%Gd₂O₃（abbreviated as0.9BNBST-0.1NN+x Gd,x=0,0.5,1,2.5,3）series ceramics were prepared.The ferroelectric test results showed that the ceramic sample with x=2.5 among them obtained a high energy storage density of W_rec=4.86 J/cm³and a high energy storage efficiency ofη=85.5%at 250 k V/cm.Further impedance test results indicate that the mechanism is mainly due to the introduction of appropriate Gd³⁺,which reduces the oxygen vacancy concentration,increases the activation energy,and the insulation is enhanced,leading to a higher resistance to breakdown.The results of the pulse charge-discharge tests showed that the introduction of Gd₂O₃did not change the discharge energy density and discharge rate of the 0.9BNBST-0.1NN ceramics.The x=2.5 ceramic samples exhibited stable discharge density（W_d≥1.11 J/cm³）and ultrafast discharge rate(t_0.9≤0.05μs)in the temperature range of 140 k V/cm,40～140℃.Figure:[114]Table:[2]Reference:[131]...