Properties Of Doped-Li₇La₃Zr₂O₁₂Solid State Electrolyte And Design Of The Interface Of Electrode/Electrolyte

Organic liquid electrolytes in traditional lithium-ion batteries have potential safety hazards such as leakage or firing.Solid-state lithium-ion batteries have attacted more and more attention due to the possibility of overcoming the defects of organic liquid electrolytes.The garnet-type Li₇La₃Zr₂O₁₂?LLZO?is gaining focued by virtue of its high ionic conductivity at room temperature,good mechanical properties,high electrochemical stability,and wide electrochemical window,among many types of solid electrolytes.However,problems such aslarge interface resistances of LLZO/metal-lithium-anode and LLZO/layered-oxide-cathode severely limit its commercialization.This article focused on overconing above problems,the main contents and results are as follows:?1?Ta-doping can change the ion conductivity and relative density of LLZO solid electrolyte.When x=0.3,the ion conductivity is up to 3.7×10^-4S/cm,and the relative density is 97%.Ta-doping?x=0.1?0.5?will not change the cubic crystal structure of garnet.Fe-doping can maitain the garnet-type solid electrolyte structure of cubic crystal system,and lithium ion conductivity can reach 6.8×10^-5 S/cm at room temperature.Moreover,the ceramic sheet of Fe-doped LLZO exhibited the highest relative density?97%?.Al-doping can also influence the lithium ion conductivity and relative density of the garnet-type solid electrolyte.When the amount of Al is increased,the density and lithium ion conductivity of the garnet-type solid electrolyte increase.When the amount of Al doping exceeds 0.3,a cubic garnet-type solid electrolyte cannot be obtained,and the zirconia phase is found,indicating a large amount of zirconia have not yet participated in the reaction,so the density is not high.?2?In order to improve the wettability of Li metal on LLZTO electrolyte and reduce the interface resistance of Li/LLZTO,a new Li-ZnO negative electrode material was constructed by a simple method,in which zinc oxide was added to the melting lithium metal.The Li-ZnO negative electrode can be evenly spread on the surface of LLZTO,the interface impedance is reduced from 2350?·cm²?pure Li metal anode?to35?·cm².The high surface roughness of Li-ZnO negative electrode increases the contact between the negative electrode and the solid electrolyte..The adding of zinc oxide can alleviate the lithium penetration to the LLZTO electrolyte during charge and discharge,and assymetamic cell assembled by two Li-?ZnO?_0.2 electrodes has no lithium penetration at a current density of 0.2 mA/cm².The main reason is that lithium oxide and metal zinc,which are generated by the reaction of zinc oxide and metal lithium,improve the dispersion of metal lithium,reduce the effective current density of metal lithium,and weaken the producing conditions of lithium dendrites.?3?An all-solid battery(LFP/LLZTO/Li-?ZnO?_0.2)was constructed usinglithium iron phosphate?LFP?as the positive electrode,Li-?ZnO?_0.2 as the negative electrode,and Li_6.7La₃Zr_1.7Ta_0.3O₁₂ as the electrolyte.,was,and Thebuffer layer between the positive electrode and LLZTO electrolyte was the mixture of PEO+LITFSI+?LLZTO?_x.Electrochemical resultsshows that the solid-state battery assembled by this method can be normally charged and discharged at 60?.The solid-state battery with PEO+LITFSI buffer layer has a discharge capacity of 136 mAh/g and the Coulomb efficiency is above 95%.The composition of the buffer layer is more,the battery capacity reaches the maximum value need more time.When 30%LLZTO is added to the buffer layer,the solid-state battery can be charged and discharged at room temperature,but more LLZTO makes the buffer layer uneven and poor contact,therefore increases the battery impedance.