Preparation And Electrochemical Performance Of LI7LA3ZR2012 Based Lithium Ion Solid Electrolyte

All solid-state lithium batteries are one of the most promising energy storage systems for electric vehicles,owing to their high energy densities,wide operation temperatures,compact structures,adjustable scales,large design flexibility and high safety.Garnet-type Li7La3Zr2O12(LLZO)solid electrolyte has high conductivity(10-4-10-3 S cm-1),wide electrochemical window(about 6V)and high stability against the lithium metal,which demonstrates the promising application in the field of electric vehicles.In this work,LLZO solid electrolyte materials were successfully prepared using high-temperature solid-state method.The effects of sintering time and temperature on the synthesis of LLZO materials were systematically investigated.The results show that the as-prepared LLZO solid electrolyte material,sintered at 1220? for 36 hours,has high relative density and ionic conductivity(about 1.54×10-4 S cm-1).The structure of garnet LLZO is pure cubic phase,confirmed by XRD characterization.The effects of Al3+-and Nb5+-doping in LLZO are further examined.The results show that the dense Al-doped LLZO solid electrolyte can be obtained by sintering at 1150? for 18 hours,which shows the conductivity at room temperature of 1.84X 10-5S cm-1.The phase of Al-doped LLZO is mainly cubic garnet with some impurity phases of Li2ZrO3 and La2Zr2O7.The Nb-doped LLZO is sintered at 1180? for 12 hours,which does not show a cubic phase and only delivers a conductivity of 1.31×10-5Scm-1.After sintering at 1220? for 36 hours,a dense Gd-doped LLZO solid electrolyte can be obtained.When the content of Gd is 20%,the conductivity of Li7.2La3Zr1.8Gd0.2O12(LLZG20)reaches the maximum value of 2.3×10-4 S cm-1 among all the Gd-doped LLZO electrolytes.The symmetrical cell using LLZG20 electrolyte is evaluated by cyclic voltammetry and AC impedance measurements.The results show that the cell has a high performance for lithium de-solution and deposition reaction.Gd-doped LLZO with high lithium ion conductivity and chemical stability,can be a promising solid electrolyte material for all solid-state lithium batteries.