Synthesis And Lonic Conducting Properties Of Doped Li₇La₃Zr₃O₁₂Solid-state Electrolyte

Lithium-ion battery has drawn great attention due to its high voltage, small volume,low weight, high energy density, non-memory effect, low self-discharge, and long cyclelife. Liquid electrolytes used in present lithium ion battery have severe safty problems.Solid-state electrolyte with high reliability, high security is expected to replace thecurrently-used liquid electrolyte. In recent years, a novel class of inorganic ceramic solidelectrolyte with garnet structure has been developed. It has several advantages, such ashigher conductivity, high chemical, electrochemical stability. However, total conductivityof this solid electrolyte is lower than liquid electrolyte. It is important for practicalapplication to enhance its conductivity.Sb-Ba codoped and Al doped Li7La3Zr2O12have been prepared by solid state andsol-gel methods, respectively. X-ray diffraction (XRD), Archimedes method, scanningelectron microscope (SEM), and AC impedance spectroscopy (EIS) have been used tocharacterialzed the structure and properties of as preprared ionic conductor.Lithium electrolyte of the formula Li6.925+xLa3-xBaxZr1.925Sb0.075O12(0≤x≤0.08) havebeen synthesized by solid-state at temperature at900℃for6h. Ceramic were sintered at1180℃for6h. Doping by small amount of Ba and Sb can greatly accelerate densification.For the sample of x=0.02, the relative densities is up to95%. An amorphous film wasintroduced on grain boundaries of x=0.02ceramic. This special microstructure effectivelyreduced grain boundary resistance, which enhance the ionic conductivity. Results showedthat composition with x=0.02showed the highest grain boundary (9.8710-4S/cm) andtotal conductivity (1.7710-4S/cm), and the lowest activation energy (0.25eV).Oxides with composition of Li7-3xAlxLa3Zr2O12(0≤x≤0.15) were synthesized by sol-gelmethod at temperature900℃for6h. Compared with solid-state method, particles of LLZOby sol-gel method were small. The dense ceramic samples of Li7-3xAlxLa3Zr2O12(0≤x≤0.15)were sintered at1135℃for3h. XRD result showed that the undoped sample of undopedwas tetragonal LLZO. Doping suppressed the grain growth. When x increased to0.05,tetragonal phase changed to cubic one. Moreover, the grains become slightly smaller and more uniform. The result showed that composition with x=0.10exhibited the highest bulk(2.01×10-4S/cm), grain boundary (4.90×10-4S/cm) and total conductivity (1.43×10-4S/cm),and the lowest activation energy (0.29eV).