Preparation And Properties Of Li₇La₃Zr₂O₁₂ Composite Solid Electrolyte By Fast Hot-press Sintering

With the development and innovation of science and technology,all-solid state lithium battery as a new form of lithium battery is gradually developed and applied.Garnet Li₇La₃Zr₂O₁₂（LLZO）solid electrolyte is one of the most promising candidates for inorganic solid electrolytes because of its wide potential window,good compatibility and high safety.As well known,the traditional pressureless preparation method requires high temperatures and generates a large amount of energy consumption.Hence,in order to obtain solid-state electrolyte materials with better performance and less preparation costs,fast hot pressing sintering method has attracted the attention of many researchers.Rapid densification of samples can be achieved at low temperature by using new field-assisted rapid sintering techniques such as spark plasma sintering and flash sintering.This article explores the effects of different fast hot pressing sintering techniques and material doping modifications on the phase structure,phase stability,microstructure and electrochemical properties of lithium lanthanum zirconium oxide composite oxide solid electrolyte.The main research contents are as follows:（1）Preparation of LLZO solid electrolyte by spark plasma sintering.The influence of key process parameters such as sintering temperature,heating rate,and holding time on the microstructure,phase structure,density,and electrochemical performance of sintered products are investigated using spark plasma sintering process under pure DC current.The experimental results show that a relatively stable cubic phase LLZO solid electrolyte was successfully prepared by heating at a rate of 60℃/min to 850℃and holding for 15 min.The grain size and distribution were relatively uniform,with a maximum relative density of 92.6%and the optimal room temperature ionic conductivity of 1.14×10^-4 S·cm^-1.（2）Preparation of LLZO solid electrolyte by flash sintering.By using the flash sintering process,the required LLZO electrolyte grain size is changed and controlled by adjusting the initial field strength,limit current density,and holding time,and optimizing its performance.The results show that the cubic phase LLZO solid electrolyte is successfully prepared by applying a 70 V/cm electric field at 800℃,with an ultimate current density of 360 m A/mm²,and being energized for 15 min.The highest relative density reached 93.6%,and the optimal room temperature conductivity value is 1.9×10^-4 S·cm^-1.（3）Preparation of Ta doped LLZO solid electrolyte by flash sintering.Introducing an appropriate amount of high-valence element Ta into the Zr site of LLZO,the cubic phase LLZTO was sintered and densified using flash sintering technology at 700℃within 15 min.The effects of different Ta⁵⁺doping contents on the phase structure and electrochemical properties of LLZO solid electrolyte are investigated.The results show that when the Ta⁵⁺doping content x=0.6,the solid electrolyte has a stable pure cubic phase structure,and the optimal room temperature ionic conductivity is 9.9×10^-4 S·cm^-1,relative density 94.72%.When the doping content is further increased,the mixed phase structure is formed.（4）Preparation of Cu,Ta_0.6 co-doped LLZO solid electrolyte by flash sintering.In order to further improve the electrochemical performance of LLZO electrolyte,based on Ta_0.6 doping at the Zr site,Cu elements with different contents are introduced at the Li site.The cubic phase LCLZTO was sintered and densified using flash sintering technology at 600℃for 20 s.The sintering behavior of copper oxide with different doping contents is studied,and the optimal doping content of copper oxide is determined to be x=0.35.At this time,Cu/Ta_0.6-LLZO has the highest relative density of 96.6%,and the optimal room temperature ionic conductivity is 2.3×10^-3 S·cm^-1.