Garnet Type LLZO Solid State Electrolyte Preparation And Doping Studies

With the increasing demand for electric vehicles and grid energy storage applications,high-capacity cathodes and anodes are required in the energy storage field to provide high power density.However,the current application of electrode materials has serious safety issues and poor cycle stability.All-Solid-State Lithium Battery（ASSLB）is a new type of battery.It has the advantages of high energy density,simple packaging,and wide operating temperature range,so it is considered as a potential choice for electrochemical energy storage devices.Solid state electrolyte（SSE）,as a key component in solid-state batteries,has largely led its future development.To date,a great deal of research work has been done to find suitable solid electrolytes.The garnet-type solid electrolyte LLZO has good chemical stability to lithium metal.However,garnet-like solid electrolytes still face some key issues.For example,the ionic conductivity of garnet-type electrolytes and the interface between electrodes and electrolytes still have a lot of room for development.In this thesis,the doping research on improving the ionic conductivity of LLZO electrolyte is carried out,aiming at improving the ion transport ability of garnet solid electrolyte to promote its practical application in solid state batteries.This thesis discusses how to fabricate LLZO solid-state electrolytes by a high-temperature solid-state method,and uses two different doping methods:single-element doping and dual-element mixed doping.By doping metal ions,we were able to effectively stabilize the cubic phase structure and improve the conductivity of LLZO.The specific research contents are as follows:（1）Research on the preparation process of LLZO solid electrolyte.Firstly,the effects of pre-sintering temperature and time on the preparation of precursor powders were studied,and it was found that the LLZO powders obtained by pre-sintering at900°C for 6 hours had better phase purity and morphology.Then,the electrolyte sheets sintered at different temperatures and lithium excess levels were analyzed,and it was found that the electrolyte sheets sintered at 1150°C and 20%lithium excess had the best electrical conductivity.（2）Doping modification of LLZO solid electrolyte.Li-site doping with Al elements,and Zr-site doping with Ta and W elements were carried out respectively.It is found that Al doping in LLZO can stabilize the cubic phase and adjust the concentration of lithium vacancies by replacing Li⁺ions in the lattice with Al³⁺ions.When the Al³⁺doping amount in LLZAO is 0.3mol,it has a higher room temperature ionic conductivity.is 1.05×10^-5S·cm^-1.The supervalent doping of Ta⁵⁺ions in LLZO to replace Zr⁴⁺ions can also increase the concentration of lithium vacancies.When the Ta⁵⁺doping amount is 0.6mol,the room temperature ionic conductivity reaches the highest of 1.11×10^-4S·cm^-1.When the doping amount of W⁶⁺in LLZWO is 0.3mol,the highest room temperature ionic conductivity is 1.34×10^-4S·cm^-1.（3）On the basis of Li_6.4La₃Zr₂Al_0.2O₁₂,Zr-site Ta and W element double-doping studies were carried out,and a small amount of Al doping stabilized the cubic phase with high conductivity,and metal ion doping was carried out at the same time to further control the concentration of lithium vacancies.It was found that when the Ta⁵⁺doping amount in LLZATO was 0.6mol,the room temperature ionic conductivity of the LLZTAO electrolyte sheet was further improved compared with the single-doped LLZTO electrolyte sheet,which was 1.30×10^-4S·cm^-1.When the W⁶⁺doping amount in LLZAWO is 0.3mol,the room temperature ionic conductivity of LLZAWO electrolyte sheet is as high as 2.75×10^-4S·cm^-1.