NASICON Type-Solid Electrolyte Li_1.5Al_0.5Ti_1.5（PO₄）₃ Research On Doping Modification And Interface Modification

Li-ion batteries are widely applied in energy storage devices including the consumer electronics products and electrical vehicles for the merits of high energy density and long cycle life.Compared to the traditional lithium ion batteries based on the organic liquid electrolyte with high activity,volatility,and flammable,Li metal batteries with solid electrolytes demonstrates numerous advantages in terms of safety and energy density.To realize this technique,it is essential to develop the inorganic solid state electrolyte with excellent electrical properties and easily processed procedures.Especially,Li_1.5Al_0.5Ti_1.5（PO₄）₃（LATP）conducting ceramic with Sodium Super ion Conductor（NASICON）crystalline type is considered to one of the most promising solid electrolyte material,which is ascribed to its high grain conductivity and chemical stability to moisture.Nevertheless,LATP solid state electrolyte still undergo the poor total ionic conductivity due to the blocking effect for impeding seriously the Lithium ion mobile of gain boundary.In this paper,sol-gel method with citric acid as complex reagent is used to prepare the LATP precursor powder.The electrochemical impedance spectroscopy result exhibits that the ionic conductivity of the LATP solid electrolyte prepared via the sol-gel method was low(8×10^-5 S cm^-1at 303 K),which is hard to satisfy the practical application for storage devices.In order to ameliorate the ionic conductivity of the LATP conducting ceramic,we incorporated Nb₂O₅ as the doping agent into the LATP solid electrolyte.The influence of the doping levels of Nb₂O₅ on the phase composition,microcosmic morphology,and ionic conductivity of the LATP solid state electrolyte were conducted by the characterization methods of XRD,SEM,and EIS etc.Testing results indicate that the LATP conducting ceramic with an 8-wt%Nb₂O₅doping possessed the highest total ionic conductivity of 3.54×10^-4 S cm^-1 at 303 K,relative density of 91.7%,and lowest activation energy of 0.271 e V.Compared to that of the specimen without Nb₂O₅,the total ionic conductivity of the 8-wt%Nb₂O₅LATP was increased four or five times.In addition,the effects of sintering parameters and chemical stability on the electrical properties of the Nb₂O₅-LATP system were also investigated.Furthermore,the interfacial compatibility between electrolyte and solid electrode would become another vital factor in solid lithium metal battery assembled with LATP conducting ceramic.Generally,the poor contact stability and largely interfacial impedance of electrolyte-electrode interfaces will severely decay the performance of batteries.To apply the as-above LATP ceramic electrolyte with the best property into the solid lithium metal batteries,PEO-LATP-PEO composite electrolyte（PCPCEs）are constructed by the dropping-coating approach.Electrical properties test results show that the composite electrolyte can not only effectively improve the terrible contact between electrode and electrolyte materials,lowering the interfacial impedance of LATP electrolyte and electrode materials,but also prevent the reduction by lithium metal.As a result,the galvanostatic charge-discharge results show that the Li||PCPCEs||Li symmetric cells can stably cycle for 200 h at 0.1 m A cm^-2.Moreover,the Li||PCPCEs||Li Fe PO₄ solid-state lithium metal battery based on the PCPCEs exhibits the good cycle stability at room temperature,delivering the initial discharge specific capacity of 152.5 m Ah g^-1at a rate of 0.1 C.After 50 cycles,the capacity retention rate of the solid-state battery can still maintain above 82%.As-above results further indicate that the construction of PCPCEs can be considered as a general strategy to effectively improve the interfacial stability of inorganic ceramic electrolyte and solid electrode,and thereby broaden its application in solid metal batteries.