Preparation Of Garnet-type Solid Electrolyte And Interface Modification Of Solid-state Batteries

As the increasing requirements for safety and energy,traditional organic liquid electrolytes have been unable to meet the development needs of lithium-ion batteries.As a substitute for organic liquid electrolyte,solid-state electrolyte can effectively improve the safety and energy density of the battery,and thus has attracted growing attention.Li₇La₃Zr₂O₁₂（LLZO）has become research hotspot due to its high room-temperature conductivity and excellent air stability.However,the preparation of the garnet-type solid electrolyte is complicated,and its contact with the electrode materials is poor,which limits its application in solid-state lithium ion batteries.This thesis focuses on the preparation and interface modification of garnet-type electrolyte.The results are as follows:Garnet-type LLZO solid electrolytes were prepared by sol-gel method and solid phase method respectively.The effects of precursors,sintering time and doping amount on phase structure were explored.By using solid-state reaction method,a solid electrolyte with chemical formula of Li_6.4La₃Zr_1.4Ta_0.6O₁₂（LLZTO）was finally synthesized.LLZTO powder and electrolyte pellet were synthesized at the temperatures of 950 ⁰C and 1140 ^oC,respectively,and the samples were all of pure cubic phase.The density of LLZTO is 92%,and its room temperature conductivity is 3.2×10^-4 S cm^-1.In order to solve the problem of poor contact with mettalic lithium anode,an ITO modified layer was deposited on the electrolyte pellet by magnetron sputtering.The contact at interface was greatly improved by introducing ITO intermediate layer.The interface impedance between LLZTO and lithium can be greatly reduced from 1192Ωcm² to 32Ωcm².With the aid of ITO,the LLZTO electrolyte pellet prepared by conventional powder tableting exhibited a critical current density of 1.05 mA cm^-2,which was comparable to the critical current density achieved by hot-pressed sintered LLZTO.The ITO-modified LLZTO was applied in a lithium-based symmetric cell.The symmetric cell can be cycled for more than 800 hours at a current density of 0.2 mA cm^-2.Based on the modified LLZTO pellet,the hybrid solid-state battery matched with the LiFePO₄ cathode showed good cycling performance and rate performance.Considering the industrialized ITO film preparation process,this modified layer has great practical application potential.