| The requirement for energy is upsurging increasingly,the research on energy storage materials and devices have become a research hotspot.The dielectric ceramic capacitors have become the first choice for power device due to rapid charge-discharge rate.Bismuth sodium titanate ferroelectrics can be used as dielectric materials for ceramic capacitors due to the advantages of high polarization value and temperature stability.However,low breakdown strength and high dielectric loss restrict energy storage and charge-discharge performance.Therefore,in view of the current problems,this thesis uses the means of adjusting the composition of ceramic dielectric materials,optimizing surface electrodes and changing ceramic size parameters to improve energy storage performance.The effects of phase structure and microstructure on ceramic energy storage and charge-discharge performance were systematically studied.The ceramic samples are encapsulated and applied to double voltage circuit to verify its actual performance.The(1-x)Na0.5Bi0.5TiO3-xBa0.85Ca0.15Ti0.85Zr0.1Sn0.05O3(x=0.1-0.7)ceramics were processed by the solid phase method.XRD analysis showed that the doping ions entered Na0.5Bi0.5TiO3 lattice,no heterogeneous phase was generated,and the crystal structure was pseudocubic phase.The XRD diffraction peak shifted to a low angle due to the average ion radius of the ceramics increased after solid solution.The microscopic morphology shows the ceramic grains are significantly refined with the increase of added amount.The ceramic dielectric peak gradually moved to room temperature and widened,and the relaxor characteristic increased significantly.Mainly due to the introduction of non-ferroelectric phase,the original ferroelectric long-range ordered structure is broken,and nanopolar microregions are formed.P-E loop is gradually thinning.The breakdown performance of grain refinement was improved,and the x=0.5 component ceramics reached Wrec of 1.6 J/cm3 and η of 80%at 190 kV/cm.Through the charge-discharge performance test,the ceramic obtained Imax of 42 A and Pmax of 35 MW/cm3 at 120 kV/cm,and the Wdis-max and t0.9 is 0.25 J/cm3 and 63 ns,respectively.At the same time,the Wdis of ceramics showed upward trend at 20120℃,indicating that it has some potential for high-temperature applications.The differences in energy densities obtained by P-E loop and charge-discharge tests were analyzed,which were mainly attributed to the energy loss caused by the flipping of the internal domain structure of ceramics.As a result,the loss of ceramics has increased sharply.The 0.5NBT-0.5BCZTS ceramic were selected to study the effects of electrode preparation process and electrode type on dielectric and chargedischarge properties.Silver electrodes were prepared by magnetron sputtering method(S-Ag)and coating method(C-Ag).The microscopic morphological shows holes in the C-Ag sample and a gap with the ceramic surface,while the S-Ag surface is flat and in close contact with the ceramic.The dielectric constant(970)of S-Ag sample was higher than that of C-Ag sample(926).The DC breakdown electric field was increased from 255 kV/cm to 270 kV/cm.The energy storage density is 2.3 J/cm3 under 220 kV/cm.The charge-discharge test sputtered silver electrode with Imax of 45 A and Wdis-max of 0.37 J/cm3 under 120 kV/cm.This is due to the close contact of the sputtered silver electrode/ceramic,the breakdown performance and the increase in effective capacitance.In addition,sputtering gold(S-Au)sample on the surface of the contrast ceramic showed similar microstructures.The sputtering gold electrode has an energy storage density of 1.9 J/cm3 at 200 kV/cm.Comparing the performance of different electrodes,sputtering silver electrodes have better performance than their electrodes.The 0.5NBT-0.5BCZTS ceramics were selected as the research object to study the effect of shape factor on charge-discharge test.With the increase of electrode area,Imax enhanced from 20 A to 61 A at 100 kV/cm.The power density increased from 12 MW/cm3 to 30 MW/cm3 and the Wdis remained at about 0.2 J/cm3.The t0.9 increased from 25 ns to 140 ns.With the increase of ceramic thickness,the peak underdamping current increased from 50 A to 100 A,the power density increased from 8 MW/cm3 to 17 MW/cm3.After the overdamping circuit test,t0.9 decreased from 190 ns to 60 ns.The t0.9 increased from 60 ns to 420 ns with the value of the overdamping circuit series resistance.In addition,the increasing of the inductance value of the external circuit reduces the underdamp current peak and shift the state from overdamp to underdamp.The samples and circuit parameters have an important impact on the discharge performance of dielectric,indicating that it is not standardized to directly compare the chargedischarge test data in the field of energy storage when the test conditions are not uniform.It is proposed that the ceramic electrode diameter should be set to 0.3 cm,the thickness should be 0.03 cm,the overdamped discharge load should be 100 Ω,and the inductance should be tested under the unified standard of 2 μH.After that,the ceramic sheet is prepared for silver,soldered lead and encapsulated,and the encapsulated capacitor is tested.When an encapsulated ceramic capacitor is applied to a voltage doubler rectifier circuit,the circuit discharge high voltage can break down the air at a distance of 1 mm between the discharge terminals and generate a stable arc. |
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