Preparation And Properties Of Novel Bi₂O₃ Medium And Low Temperature Solid Electrolyte Materials

High-temperature sintering is the main method for preparing high-density electrolyte materials.Under high-temperature conditions,interfacial reactions between electrode materials and connecting materials will occur,forming shear stress,resulting in deterioration of material properties,and co-sintering between electrolyte materials and electrode materials is difficult.Therefore,it is of great significance to study electrolyte materials with high electrical conductivity,high stability and low cost under medium and low temperature conditions.People have focused their attention on oxide electrolyte materials with a fluorite-type structure,which rely on oxygen ion conduction to conduct electricity,have an open structure,and have voids,which are conducive to the diffusion and migration of oxygen ions,and have good electrical conductivity.Among the many electrolytes relying on oxygen ion conduction,the cubicδ-Bi₂O₃crystal type has the best conductivity,is highly disordered,oxygen defects account for a quarter,and bismuth ions have strong polarizability.Cation doping or compounding can increase the oxygen vacancy concentration,improve the electrical conductivity,and stabilize theδ-Bi₂O₃crystal form,which has become the main research object for the development of medium and low temperature solid electrolyte materials.Based on this,a ternary doped bismuth oxide-based system was designed in this paper.By co-doping various rare earth metal oxides and compounding with cerium oxide-based electrolyte materials,the study of different doping elements under the same doping ratio And the influence of the same element on the phase structure,density and conductivity of solid electrolyte under different doping amounts,explore the optimal doping amount and other process parameters,and further improve its stability and conductivity through compounding.The research results show that the ternary doped bismuth oxide-based system has high ionic conductivity,and the cubic fluorite structureδ-Bi₂O₃crystal form can exist stably at medium and low temperatures,with good electrical conductivity and high density.The composite electrolyte material has stable performance and excellent electrical conductivity.The main contents are as follows:Gd,Er,Sm ternary doped bismuth oxide-based BEGS electrolyte materials were prepared by sol-gel method.XRD phase analysis shows that theδ-Bi₂O₃phase can be stabilized between room temperature and 800℃;when Er,Gd and Sm are co-doped,the relative doping amount of Sm and the sintering temperature have a great influence on the density of the electrolyte material.Quantity x=0.04,the sintered density at 800℃is the highest,reaching 97.6%,which is 12%higher than that of undoped Sm;under the condition of medium and low temperature,it has good electrical conductivity,and its conductivity reaches 0.2092S·cm^-1at 800℃,which is Compared with undoped Sm,the ionic conductivity is increased by 2.12 times,and the activation energy is decreased by 1.2%.By comparing the ternary doped bismuth oxide-based systems of BEGD,BEGY and BEGS,the research shows that theδ-Bi₂O₃crystal structure can be stabilized when Sm,Y,Dy are co-doped with Er respectively.The density of BEGS is better than that of BEGY and BEGD.The maximum relative density of BEGD is96.2%,and the maximum relative density of BEGY is 96.5%.Electrochemical analysis of the three electrolytes shows that proper doping improves the electrical conductivity at medium and low temperature and reduces the activation energy of the electrolyte material.At 800°C,the highest conductivity of BEGD/BEGY is0.2002S·cm^-1and 0.1984S·cm^-1It can be lower than the undoped electrolyte,and its power density is improved.At 750°C,the corresponding power densities of single cells based on 4BEGD and 6BEGY are 0.582W·cm^-2and 0.7933W·cm^-2,respectively,compared with undoped ones.there was a marked improvement.After the preparation of 4BEGS-SDC composite electrolyte by solid-phase synthesis and sol-gel method,the ionic conductivity of the ternary doped bismuth oxide-based system was further increased and the activation energy was reduced.The region activation energy is lower,the electrical conductivity is better,the power density is higher,the density is higher,and theδ-Bi₂O₃crystal form can be stabilized.The total conductivity reaches 0.2964S·cm^-1,which is 12.1% higher than that of 4BEGS.1.123W·cm^-2.