Preparation,Structure And Electrochemical Performance Of The Solid State Electrolytes With Garnet-like Structre

The liquid electrolyte usually used in the traditional lithium ion battery has many safety problems such as leakage,flammability and explosiveness.The solid state electrolyte has drawn attention due to it can address the safety concerns of the liquid electrolyte.Among the reported solid state electrolyte,the lithium ion conductor with garnet-type structure is a better choice for electrolyte on account of its good electrochemical stability,wide electrochemical window and chemical stability against lithium metal electrode,but its ionic conductivity is low and the cubic phase structure is hard to obtain.In this paper,Cubic phase garnet-type electrolytes with high ionic conductivity were prepared by ion doping and replacement.The electrolyte materials Li7La3Zr2-xGe,O12(x=0-0.4)with garnet-type structure were prepared using the same-valent Ge4+ substitution of Zr4+.Research shows:This materials is a cubic phase garnet-type structure,a small amount of Ge4+ will enter the Li+ site to produce more Li+ vacancies,Substitution of Zr4+ by Ge4+ can promote grain growth and increase the density.The ionic conductivity of Li7La3Zr1.7Ge0.3O12 can reach 4.78x10-4S/cm at room temperature,and the activation energy is 0.29eV at the range of-20? to-60?.The electrolyte of Li7La3Zr1.7Geo.3O12 has a wide electrochemical window,and it is also stable in contact with the lithium metal electrode.The battery using this electrolyte material maintains a discharge capacity of 140.6 mA g-1 after 20 cycles at a current density of 0.1C.The electrolyte materials Li7-xLa3Sn2-xBixO12(x=0-1.0)with garnet-type structure were prepared using the high-valent Bi5+ substitution of Sn4+.Research shows:The Li6.25La3Sn1.25Bi0.75O12 with cubic phase at room temperature can be synthesized through a lower sintering temperature(750?).Increasing the sintering holding time is beneficial to the grain growth,which can obtain the high ion conductivity electrolyte materials.The structure changes from tetragonal phase to cubic phase with the increase of Bi5+concentration,it is a mixed phase of tetragonal phase and cubic phase as x=0.25;it is a pure cubic phase garnet structure when 0.5?x?1.0.When x=0.75,Li6.25La3Sn1.25Bi0.75O12 has a high ionic conductivity and a low activation energy,its ion conductivity can reach 2.25×10-4 S/cm at 60?,and activation energy is 0.55 eV in the range of-20? to 60?.These materials are good ionic conductor with a low electronic conductivity.Li7La3Zr2-xSnxO12(x=0-1.0)ceramic electrolyte materials were synthesized through a high temperature solid state method.Studies show:The sample sintered at 1180? has a high density and a high ionic conductivity.Li7La3Zr2-xSnxO12(x=0-0.5)are cubic phase garnet structure and have a high ionic conductivity with the order of 10-4.The sample with x=1.0 is a mixed phase of tetragonal phase and cubic phase garnet-type structure,and its ionic conductivity is 1.02×10-5 S/cm at room temperature.The grain boundary resistance of the sample is generally greater than the grain resistance,and the grain boundary resistance is the main reason for preventing ion conduction.This material is an ideal ion conductor with a low electronic conductivity,in the meantime,Li7La3ZrSnO12 has a wide electrochemical stability window.