| Among the inorganic lithium ion solid electrolytes,garnet-type Li7La3Zr2O12(LLZO)has become a promising solid electrolyte due to its high electrical conductivity and excellent electrochemical stability.However,LLZO still has many aspects to be improved,such as stabilizing its cubic phase structure,improving room temperature ionic conductivity and sintering properties of the material.This paper addresses the above issues,Li7-3xAlxLa3Zr2O12,Li6.4+yAl0.2La3Zr2-yBiyO12powders were prepared by solid state method,and then sintered at 1150? for 8 h to obtain Li7-3xAlxLa3Zr2O12?Li6.4+yAl0.2La3Zr2-yBiyO12solid electrolytes.XRD,SEM,EDS,EIS and other test and characterization methods were used to analyze and characterize the microscopic morphology and electrical conductivity of LLZO,the main results are as follows:Li7-3xAlxLa3Zr2O12(x=0,0.1,0.2,0.3)powders were prepared by solid phase method,and sintered at 1100?,1150?,1200? for 8 h to obtain Li7-3xAlxLa3Zr2O12solid electrolytes.XRD test results show that LLZO solid electrolyte with cubic phase structure can be prepared when the sintering temperature is higher than 1150?.When the doping amount of Al element is 0.2,Li6.4Al0.2La3Zr2O12solid electrolyte can form a cubic phase structure.SEM test results show that the cross-section of the Li6.7Al0.1La3Zr2O12sample has only a few micron-level pores,and no crystal grains or grain boundaries can be distinguished.The grains of the Li6.4Al0.2La3Zr2O12and Li6.1Al0.3La3Zr2O12samples present irregular polygons,and the grains and grain boundaries can be clearly distinguished.The density calculation results show that the sintered density of Li7-3xAlxLa3Zr2O12increases with the increase of Al doping.The AC impedance test results show that the doping amount corresponding to the highest conductivity value under the above process is x=0.2,and the room temperature ion conductivity reaches 1.86×10-4S·cm-1.Compared with the non-doped LLZO sample,the total conductivity is improved by an order of magnitude.The effects of three sintering atmospheres of argon,air and oxygen on the conductivity of Li6.4Al0.2La3Zr2O12were studied.The Li6.4Al0.2La3Zr2O12solid electrolyte powder was prepared by high temperature solid phase method,and then sintered at 1150? for 8 h in argon,air and oxygen atmospheres to obtain Li6.4Al0.2La3Zr2O12(Ar),Li6.4Al0.2La3Zr2O12(Air),Li6.4Al0.2La3Zr2O12(O2)samples.XRD results show that all samples only contain the characteristic peaks of cubic LLZO.SEM results show that the grains of the Li6.4Al0.2La3Zr2O12(Ar)and Li6.4Al0.2La3Zr2O12(Air)samples present irregular polygons,and some porosity can be observed between the grains.There is no clear grain boundary in the Li6.4Al0.2La3Zr2O12(O2)sintered in oxygen.The density calculation results show that the density of the Li6.4Al0.2La3Zr2O12(Ar)sample is only 88.5%,and the Li6.4Al0.2La3Zr2O12(O2)has the highest density(98.6%).The result of AC impedance spectroscopy shows that the order of ion conductivity is:Li6.4Al0.2La3Zr2O12(Ar)<Li6.4Al0.2La3Zr2O12(Air)<Li6.4Al0.2La3Zr2O12(O2),the Li6.4Al0.2La3Zr2O12(O2)sample sintered in oxygen has a total conductivity of 5.55×10-4S·cm-1at 30?.In order to further improve the ionic conductivity of the LLZO solid electrolyte,the effect of double doping of Al and Bi elements on the performance of the LLZO solid electrolyte was explored.Li6.4+yAl0.2La3Zr2-yBiyO12(y=0,0.05,0.1,0.15)powders co-doped with Al and Bi elements were prepared by high temperature solid phase method.After sintering in oxygen at 1150?,the Li6.4+yAl0.2La3Zr2-yBiyO12(O2)samples were obtained.The Li6.4+yAl0.2La3Zr2-yBiyO12(O2)samples all have a cubic crystal structure.Li6.4+yAl0.2La3Zr2-yBiyO12(O2)have uniform composition,no clear grain boundaries and grains were observed in all samples,and the density of all samples has reached more than 97%.As the doping content of Bi element increases,the ion conductivity increases,The doping content reaches the maximum at 0.1.At30?,the Li6.45Al0.2La3Zr1.9BiyO12(O2)has the highest lithium ion conductivity,reaching 6.89×10-4S·cm-1. |
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