Preparation And Characterization Of Garnet Solid Electrolyte Li₇La₃Zr_2-xSi_xO₁₂

All-solid-state lithium-ion battery has become a hot topic because of its high energy density,simple structure and good safety performance.As the decisive material in all-solid-state lithium battery,the performance of solid-state electrolyte will largely determine the electrochemical performance and practical application of all-solid-state lithium battery.In this paper,the preparation technology of garnet solid electrolyte Li₇La₃Zr₂O₁₂（LLZO）was investigated,and on this basis,Si-doped LLZO（Si-LLZO）was prepared,which decreased the sintering temperature and increased the ionic conductivity.At the same time,the prepared Li₇La₃Zr_1.76Si_0.24O₁₂（0.24Si-LLZO）and polyethylene oxide（PEO）were compounded to prepare 0.24Si-LLZO/PEO-based composite solid electrolyte,and the effects of various inorganic fillers on the properties of PEO composite membrane were compared and analyzed.The specific research contents are as follows:（1）Garnet solid state electrolyte LLZO was prepared by high temperature solid state method,and the effect of Si doping on the sintering system of LLZO was investigated.In this paper,the effects of Si doping amount,sintering time and sintering temperature on the phase composition,microstructure,relative density and ionic conductivity of Si-LLZO were investigated systematically.The results show that when the sintering temperature is 1150℃and the holding time is 7 h,the prepared LLZO has cubic phase structure,uniform grain growth and the highest ionic conductivity of 2.76×10^-4 S cm^-1.When the doping amount of Si is 0.24,the sintering temperature is 1050℃and the holding time is 10 h,the prepared 0.24Si-LLZO has a cubic phase structure,the grain size is uniform,the size is in the range of 2-3μm,the relative density is increased by 5.9%,the ionic conductivity is 4.86×10^-4 S cm^-1,and the conductivity activation energy is 0.32 e V.Compared with the LLZO without Si element,the sintering temperature is reduced by 100℃and the ionic conductivity is increased by 0.76times.（2）The 0.24Si-LLZO/PEO-based composite solid electrolyte was prepared by casting method,and the film forming process was explored,and the ionic conductivity,phase composition,thermal stability and electrochemical properties of the PEO membrane with0.24Si-LLZO,LLZO,LLTO and Al₂O₃were compared,and the PEO membrane with only lithium salt was used as the blank group.The results showed that the PEO composite membrane was successfully prepared when the molar ratio of EO:Li was 8:1,and the ionic conductivity was 1.57×10^-6 S cm^-1.With the decrease of lithium salt content,the ionic conductivity of the composite membrane decreased significantly.From the phase composition of the composite membrane,it can be concluded that the addition of inorganic fillers can reduce the crystallinity of PEO,and then the decrease of melting point of the composite membrane is related to it.The electrochemical tests of five groups of PEO-based composite membrane electrolytes showed that the capacity retention rate of 0.24Si-LLZO/PEO composite membrane was 98.13%after 100 cycles at 50℃,and the initial discharge capacity was 134.2 m Ah g^-1,which was the highest among the five,and its rate performance is also better than the other four composite electrolytes.