Preparation Of Li₇La₃Zr_1.7Ti_0.3O₁₂ And Li_1.3Al_0.3Ti_1.7?PO₄?₃ Solid Electrolytes And Study In Lithium Batteries

Lithium metal is used as an ideal anode material for lithium secondary battery because of its high theoretical specific capacity(3860 mAhg^-1),and it has been applied to lithium metal secondary battery,Li-S battery system and so on.However,there are many unsolved problems in lithium batteries in practical applications,such as the growth of lithium dendrites that will reduce battery cycle life and coulombic efficiency,"shuttle effect" in Li-S battery system and“self-discharge”.Solid electrolyte Li₇La₃Zr_2-xTi_xO₁₂?LLZTO?with garnet-type and Lithium ion conductor Li_1+xAl_xTi_2-x?PO₄?₃?LATP?with NASICON structure were chosen which have high application value.Solid electrolyte is expected to modify lithium dendrites and shuttle effect,optimize the interface between electrodes and electrolytes,and improve the long-term cycling stability of batteries.LLZTO and LATP solid electrolyte materials were prepared and their properties were studied by phase characterization and electrochemical characterization including the XRD analysis of the material precursor powder,the sintering curve analysis,the SEM of the pressed powder after sintering,and the impedance test at different sintering temperatures.The calculated electrical conductivity of LLZTO was 1.18×10^-5S cm^-1,while LATP showed higher conductivity of 4.46×10^-4S cm^-1at room temperature.LLZTO powder and the selected polymer electrolyte were uniformly mixed in a ratio of 1:1.Obtaining a composite solid electrolyte membrane with uniform solid electrolyte particle distribution and good mechanical strength.After phase characterization and line-scan voltammograms analysis,it was found that the LLZTO particles can reduced interfacial resistance of polymer electrolyte membrane and metal.Composite solid electrolyte membranes were used in Li-Li?Li-Cu and Li-LiFePO₄ batteries,respectively,to verify their advantages such as the inhibition of the growth of Li anode dendrites and the promotion of lithium ion conduction.Li-Li battery with PVDF-HFP:5%LLZTO electrolyte membrane protected can be continuously charged and discharged for 200 h to maintain good stability.For Li-Cu batteries,the cyclic Coulomb efficiency quickly becomes stable and remains around 90%during the cycle.;By analyzing the change of battery impedance during the charge-discharge cycle,it is concluded that the battery cycle stability is good under different systems.The Li-LiFePO₄ battery has the first discharge specific capacity of 149.6 mAh g^-1and 95%charge and discharge efficiency at a current density of 0.75 mA cm^-2,and the discharge specific capacity can still reach 144.5 mAh g^-1after the rate tests at different current densities with good cycle stability.NASICON solid electrolyte having two layers was designed and prepared.LATP powder and selected organic pore forming material were mixed together in definite propertions to find the most suitable mixture ratio to get porosity after sintering and porous layer with appropriate mechanical strength.Slurry with different mixing proportions was coated by spin-coating.A dense film with appropriate density and thickness can be obtained when the ratio of LATP to binder is 5:5.NASICON solid electrolyte having two layers was applied in Li-S batteries,and the batteries were tested by line-scan voltammograms analysis,and the reaction of the cathode active substance in the charge and discharge process were analyzed.The long-term charge and discharge cycle test.The cyclic discharge specific capacity remains around 75 mAh g^-1for 100 cycles,and the cyclic Coulomb efficiency remains at around 80%.A rate performance test was performed.After returning to the initial current density,a discharge specific capacity of 76.1 mAh g^-1was still obtained,indicating a good charge-discharge stability.