Sythesis Of Zr Site Doped Li₇La₃Zr₂O₁₂ Solid-State Electrolyte By Sol-Gel Method And Their Ionic Conducting Properties

With the rapid development of the social economy, lithium-ion batteries have been widely used in many aspects. During the process of heavily used lithium ion batteries, the safety hazards of the flammable and explosive problem caused by the liquid electrolyte is an urgent one to be solved. The concept of all solid state lithium ion batteries is put forward in view of the security problem. Solid electrolyte is one of the important components of all-solid-state batteries. At present, the high lithium ion conductivity, good chemical and electrochemical stability, environmental benignity, low cost and ease of preparation of Li7La3Zr2O12 suggest that it is a promising solid state electrolyte for all-solid-state lithium ion rechargeable batteries.Mn4+ and Mo6+doped Li7La3Zr2O12 have been prepared by sol-gel method, respectively. X-ray diffraction(XRD) analysis, Archimedes method, scanning electron microscope(SEM), and AC impedance spectroscopy(EIS) have been used to characterialzed the structure and peoperties of as prepared ionic conductor.Oxides with composition of Li7La3Zr2-xMnxO12(0≤x≤0.07) were synthesized by sol-gel method at temperature 900℃ for 6h. Ceramic samples were sintered at 1115℃ for 3h. XRD result showed that the all samples were mixed of cubic and tetragonal phase. The sample of Li7La3Zr1.97Mn0.03O12 has the highest relative density(94%). The composition with x=0.03 exhibits the highest total conductivity(9.71×10-5S/cm), and the lowest activation energy(0.33eV).Lithium ion solid-state electrolyte with the formula Li7-2xLa3Zr2-xMoxO12(0≤x≤0.30) have been synthesized by sol-gel method at temperature at 750℃ for 6h. Ceramic were sintered at 1100℃ for 3h. In the Li7-2xLa3Zr2-xMoxO12 powders, it is found that the cubic phase can be obtained at 750℃ for 6 h when 0.1≤x≤0.30. After final sintering at 1100℃ for 3h, XRD results showed that the undoped sample of LLZO is mixture of cubic and tetragonal phase. When x increased to 0.05, a mixtures changes to cubic one. Doping by small amount of Mo can greatly accelerates densification. For the sample with x=0.20, the relative densities is up to 92.8%. Results show that composition with x=0.20 exhibits the highest total conductivity(5.09×10-4S/cm), and the lowest activation energy(0.29eV). Compared to solid-state synthesis method,the sol-gel synthesis method is benefit for stabilizing the high conductive cubic structure at lower sintering temperatures and improving its ionic conductivity of ceramic.