Preparation And Interfacial Modification Of Li_1.3Al_0.3Ti_1.7（PO₄）₃ Solid Electrolytes For Solid State Lithium Battery

With the advantages of high energy density,high safety and long cycle life,solid-state batteries can replace liquid lithium-ion batteries as a new type of battery.However,the development of solid-state batteries depends on the solid electrolyte.Solid electrolytes suitable for solid-state batteries should have high lithium-ion conductivity and wide electrochemical window,and NASICON-type solid electrolyte Li_1.3Al_0.3Ti_1.7（PO₄）₃（LATP）has these characteristics.However,LATP has limited its practical application due to high grain boundary impedance and severe side reactions with lithium metal.Based on these problems,this thesis investigates the effect of particle size on the performance of LATP solid electrolytes,obtains high-performance LATP ceramic electrolytes,and uses polyethylene oxide（PEO）solid electrolyte films for interfacial modification to prepare high-performance all-solid-state lithium-ion batteries.The main studies are as follows:（1）Li_1.3Al_0.3Ti_1.7（PO₄）₃ precursors were prepared using the solid-phase method to investigate the effect of particle size on the performance of LATP ceramic electrolytes.When the initial particle size was 2μm,the densities of LATP ceramic electrolytes were>97%and the conductivities were up to 6.7×10^–4 S cm^–1.The powder phases as well as the microstructures were analyzed by SEM,XRD and Rietveld refinement.The grain evolution of ceramics sintered at different particle sizes was observed to infer the sintering mechanism of LATP.The ceramic electrolytes of LATP sintered with medium particle size were operated stably for 1000h at a current density of 0.05 m A cm^–2 with a critical current density of 0.855 m A cm^–2.The assembled Li Fe PO₄ batteries had an initial discharge specific capacity of 157m Ah g^–1 at 0.1 C,which remained 140 m Ah g^–1 after 60 cycles,with a coulomb efficiency close to 100%.（2）A PEO polymer electrolyte film was modified on the LATP ceramic surface to hinder the interfacial reaction between LATP and lithium metal.The results show that when the LATP surface is modified with PEO solid electrolyte（PEO@LATP）,its interfacial impedance is reduced from 5000Ωto 2000Ω,and it can operate stably for400 h at a current density of 0.2 m A cm^–2.The effect of the PEO solid electrolyte film in hindering the interfacial reaction is demonstrated using XPS.The LFP cells of PEO@LATP at 0.1 C released a high specific capacity of 160 m Ah g^–1 and still had96 m Ah g^–1 at 1 C.Its initial discharge specific capacity at 0.2 C was 153.4 m Ah g^–1and after 120 cycles,the discharge specific capacity remained at 147.2 m Ah g^–1 with a capacity retention of up to 96%and the Coulomb efficiency of the cell were maintained at～100%.This work provides an effective strategy for the practical application of LATP solid electrolytes.There are 38 figures,4 tables and 130 references in this thesis.