Fabrication And Properties Of LLTO-Based Solid Electrolyte With Perovskite Structure And Its Composite Electrolyte

Traditional lithium-ion batteries have hidden safety hazards such as bulging,electrolyte leakage,and deflagration due to the use of organic liquid electrolytes.In order to solve the above-mentioned problems,solid-state lithium ion electrolytes which have the advantages of stable chemical properties,large electrochemical window,and wide operating temperature range have become one of the current research hotspots.Among them,the perovskite-type ceramic Li_0.33La_0.557TiO₃（LLTO）has attracted much attention because of its high crystalline lithium ion conductivity,but the existence of a lithium ion depletion layer at the grain boundary greatly limits the the ceramic bulk lithium ion conductivity.This article takes LLTO ceramics as the research object,and studies the sintering process and grain boundary modification of ceramics,the mechanical and electrochemical properties of polymer composites electrolytes,and the construction of three-dimensional continuous lithium ion fast transmission channels.The following conclusions are obtained:1.LLTO-xAl₂O₃ ceramics were successfully prepared by introducing the second phase of Al₂O₃ combined Spark Plasma Sintering（SPS）,which lowered the ceramic’s low grain boundary resistance and improved the bulk Lithium ion conductivity.At the LLTO grain boundary,a thin layer of LiAl₅O₈ formed by the reaction of Al₂O₃ with the matrix covers the LLTO grains.LiAl₅O₈ reduces the barrier of Li⁺migration between grains,thereby increasing the grain boundary conductivity of the LLTO.LLTO-0.005Al₂O₃ ceramic achieve the best room temperature grain boundary conductivity of1.44×10^-5 S/cm;the LLTO-0.05Al₂O₃ ceramic achieves the best room temperature crystal conductivity of 1.81×10^-3 S/cm.2.By combining LLTO ceramic particles with polymer electrolyte,a ceramic composite polymer electrolyte with excellent lithium ion conductivity at room temperature was obtained.With the increase of LLTO ceramic content,the lithium ion conductivity of the electrolyte gradually increases.The reason is that the combination of LLTO ceramics not only utilizes the excellent lithium ion conductivity of LLTO itself,but also promotes the amorphousness of the polymer electrolyte.Amorphization creates more effective channels and shortens the transmission path of lithium ions,so the lithium ions conductivity is improved.PVDF-HFP+0.5LiTFSI+0.6LLTO electrolyte membrane has the best room temperature Lithium ion conductivity of 2.59×10^-4 S/cm.3.3D framework ceramics were successfully prepared by electrostatic spinning method.3D framework ceramic composite polymer solid electrolytes was obtained by compounding 3D framework ceramics with PVDF-HFP.The 3D framework ceramics build a 3D continuous Li⁺fast transmission channel in the composite polymer electrolyte,and improve the electrochemical performance of the composite polymer electrolyte.The 3D framework ceramic composite polymer solid electrolytes has a Lithium ion conductivity of more than 1.71×10^-4 S/cm at room temperature.Compared with a pure PVDF-HFP polymer electrolyte without added LLTO ceramic,its Lithium ion conductivity at room temperature is increased by 108.5%;Compared with the polymer electrolyte with similar content of LLTO ceramic particles,the Lithium ion conductivity at room temperature is increased by 23.9%.