Preparation And Electrochemical Properties Of Garnet-type Solid Electrolyte

Lithium-ion batteries use flammable liquid electrolytes,which results in low safety performance.Therefore,all-solid-state batteries with solid electrolytes have attracted attention due to their high energy density,high safety,and high stability.Among them,garnet-structured solid electrolyte Li₇La₃Zr₂O₁₂ has high ionic conductivity and good electrochemical performance,and is an ideal solid electrolyte material.In this paper,the sol-gel method is used to prepare Li₇La₃Zr₂O₁₂.The preparation process of Li₇La₃Zr₂O₁₂ is explored first,and then the effect of double doping on Li₇La₃Zr₂O₁₂ is studied.The conductivity and electrochemical performance of the modified materials are discussed.This article takes garnet structure solid electrolyte Li₇La₃Zr₂O₁₂ as the research object,and explores the preparation process of synthetic Li₇La₃Zr₂O₁₂ and the effect of different Al doping amount on the structure and conductivity of synthetic Li₇La₃Zr₂O₁₂.The results show that the synthesized LLZO exhibited a cubic garnet structure at 900?for 6 h.An excess of10%lithium can compensate lithium volatilization in the material during high temperature sintering.Cubic LLZO is synthesized with no impurities.The material has the best ionic conductivity and high density when the tablet pressure is 12 M Pa.The doping of Al can change the LLZO from a tetragonal phase to a cubic phase.When the amount is x=0.25,the ionic conductivity is 4×10^-5S/cm,and the density is 83.7%,which shows good electrical conductivity.In terms of the best process synthesis parameters,the amount of Mo doping,the sintering temperature,and sintering time have an impact on the solid electrolyte Li_6.25-2xAl_0.25La₃Zr_2-xMo_xO₁₂?x=0-0.4?co-doped with Al and Mo.Among them,the solid electrolyte having a sintering temperature of 1120?,a sintering time of 6 hours,and a doping amount of Mo of x=0.3 has the highest ionic conductivity,which is 2.12×10^-4S/cm and the density is 91.2%.Too high sintering temperature and long sintering time will lead to serious lithium volatilization and low conductivity of the material.The co-doping of Al and Mo can promote the formation of cubic LLZO,and can improve the conductivity and density of the solid electrolyte.All-solid-state battery Li/Li_5.65Al_0.25La₃Zr_1.7Mo_0.3O₁₂/Li Fe PO₄ is assembled.At a current density of 10?A/cm²,the first discharge capacity of the cell is 100.1 m Ah/g.After 20cycles,the discharge capacity is 90.1 m Ah/g and corresponding capacity retention rate is 90%.On the best process synthesis parameters,a solid electrolyte Li_6.25Al_0.25La₃Zr_2-xTi_xO₁₂?x=0-0.375?was prepared by sol-gel method,and the effect of doping amount of Ti,different temperatures and different times on materials was investigated.The results show that the undoped particles are relatively coarse and the pores are large.After doping,the density of the material is increased,and the garnet structure solid electrolyte can be combined above 1100?.The material has a high ionic conductivity and a high density at 1160?for 9 h and the doping amount of Ti is x=0.25.The ionic conductivity is 1.53×10^-4S/cm and the density is 89.3%.All-solid-state battery Li/Li_6.25Al_0.25La₃Zr_1.75Ti_0.25O₁₂/Li Fe PO₄is assembled.The first charge and discharge capacity of the cell is 116.1 m Ah/g and 96.1 m Ah/g,the first coulomb efficiency is 82.7%.After 20 cycles,the discharge capacity is 93.0 m Ah/g and the retention rate reached96.8%.