Study On Microwave Sintering And Doping Modification Of Solid Electroiyte Li₇La₃Zr₂O₁₂

All-solid-state lithium-ion batteries have good safety and high energy density.The use of solid electrolytes to replace the organic electrolyte and diaphragm in traditional lithium-ion batteries can greatly increase the energy density of traditional lithium-ion batteries and effectively solve the problem of flammable,explosive,and corrosive Safety issues have become one of the development directions of lithium-ion batteries in recent years.The core of the all-solid-state battery is the solid electrolyte.Among them,the garnet-type Li₇La₃Zr₂O₁₂（LLZO）solid electrolyte with excellent stability and high ionic conductivity is the most promising.LLZO has two crystal phase structures:tetragonal phase（t-LLZO）and cubic phase（c-LLZO）.Compared with the tetragonal phase,the room temperature ionic conductivity of the cubic phase is about 2 orders of magnitude higher,but the cubic phase is unstable at room temperature.The stable cubic phase is the prerequisite for studying the solid electrolyte LLZO.On the other hand,LLZO solid electrolytes are currently mostly prepared by the traditional high-temperature solid-phase sintering method,which has simple process,convenient operation,controllable crystal phase and low raw material cost.However,the high sintering temperature and long sintering time result in excessive crystal grains.Microwave sintering is an overall heating,with low sintering temperature,short sintering time,high efficiency,no pollution,and uniform material microstructure.It is a novel sintering method that can replace traditional sintering.Therefore,in this paper,two sintering methods of traditional sintering and microwave sintering are used to prepare LLZO solid electrolyte.On this basis,LLZO is doped and modified with Al³⁺ instead of Li⁺,and X-ray diffraction,SEM,EDS and electrochemical performance tests are used.Research on the structure and performance of the prepared solid electrolyte by other means.Li₇La₃Zr₂O₁₂ was prepared by high-temperature solid-phase method.First,the precursor powder was pre-fired at 900℃ for 6 hours,and then the effects of the sintering temperature and holding time of the two sintering methods on the phase,morphology and electrochemical performance of the sample were explored.Studies have found that traditional sintering at 1100℃ for 12 hours produces a tetragonal-cubic transition phase structure LLZO,with tighter inter-grain bonding,a bulk density of 3.91 g/cm³,and a room temperature ion conductivity of 5.89×10^-6 S/cm;while microwave sintering at 1000℃ for 20 minutes to prepare a pure cubic LLZO solid electrolyte,but the bulk density is low,only 3.21 g/cm³,room temperature ion conductivity is 1.01×10^-5 S/cm.On this basis,Li_7-3xAl_xLa₃Zr₂O₁₂ solid electrolyte was prepared by replacing Li⁺with Al³⁺,and the influence of doping amount,sintering temperature and holding time on the microscopic morphology,phase composition and performance of the sample was explored.The results show that when the doping amount is 0.2mol,the traditional sintering process is kept at 1100℃ for 12h to prepare pure cubic phase structure Li_6.4Al_0.2La₃Zr₂O₁₂.The sample has high crystallinity,tight inter-grain bonding,bulk density and room temperature ion conductivity.The rates were 4.37 g/cm³ and 1.21×10^-4 S/cm;microwave sintering was also prepared at 1000℃ for 20 minutes to obtain a pure cubic structure of Li_6.4Al_0.2La₃Zr₂O₁₂.The bulk density and room temperature ionic conductivity were 4.58 g/cm³ and 8.28×10^-5 S/cm.