All-solid-state lithium metal batteries has great potential for the next generation of energy-storing devices due to its high energy density and power density,broad operating voltage range and high safety.As an important component of the all-solid-state lithium metal battery,solid-state electrolytes(SSEs)directly determines the ionic conduction properties of the battery.Althoughtwo inorganic SSEs of LATP(Li1.3Al0.3Ti1.7(PO3)4)and LLZTO(Li6.5La3Zr1.5Ta0.5O12)have exhibited a wide electrochemical window,high ionic conductivity,and high mechanical strength,these two SSEs still exist some technical bottlenecks,i.e.,the side reactions between SSEs and closely-contacted Li metal anode lead to LATP decomposition and failure;preparation of LLZTO is particularly challenging due to the strong lithium volatilization that occurs during sintering and a lithiophobic impurity phase is formed on the SSEs surface due to its intrinsic environmental sensitivity.To address these issues,in this dissertation,based on the preparation of high ionic conductivity LATP and LLZTO solid electrolytes,two solid electrolytes were mixed and sintered to produce a composite solid electrolyte with improved performance and investigated the interface performance between the composite solid electrolyte and lithium metal anode,constructing the interface between lithium metal anode and solid electrolyte by ultrasonic welding process and investigating the effect of interface on battery performance.The specific achievements that have been achieved are summarized as follows:(1)In view of the low ionic conductivity of LATP and LLZTO and the difficulty of preparing pure phases due to volatilisation of lithium,the optimum conditions for the preparation of the two solid electrolytes were explored by optimising the temperature,ball milling time,doping element ratio,etc.The ionic conductivity of Li1.7Al0.3Ti1.7(PO4)3 electrolyte prepared by the solid phase method was 4.1×10-4 S cm-1 and the densification reached 97.08%;the ionic conductivity of Li6.5La3Zr1.5Ta0.5O12electrolyte prepared by the two-step sintering method with the addition of La2Zr2O7 at a mass fraction of 1%was 9.2×10-4S cm-1 and the density was 94.85%.(2)In view of the interfacial failure induced by the decomposition of LATP at the Li/LATP interface by spontaneous reaction,a route of composite solid electrolytes with LLZTO and LATP was proposed.The phase separation behavior was detected experimentally due to solid solution or reaction between LLZTO and LATP phases at high temperature.The ionic conductivity of the LATP-6 wt.%LLZTO composite electrolyte obtained with the addition of a mass fraction of 6 wt.%LLZTO powder was up to 1.03×10-3 S cm-1,while the electronic conductivity was reduced.Stable cycling of Li||LATP-LLZTO||Li symmetric cells for 200 h at 0.05 m A cm-2,and the composite electrolyte was heated with lithium metal to 300℃ without the onset of thermal runaway.(3)In view of the Li/LLZTO interface poor wettability,poor contact performance,ceramic metallisation combined with room temperature ultrasonic welding process is proposed to solve the issue.Intimate contact between Li and LLZTO can be achieved via room-temperature ultrasonic welding.The anode electrode interface impedance was reduced to 35Ωcm2 from 2200Ωcm2,CCD was increased from 0.2 m A cm-2 to 0.5m A cm-2.Futhermore,the LLZTO ceramics were further metallised using ion sputtering of Au,Ag,Sn and the anode interfacial impedance was reduced to 5Ωcm2 and the CCD raised to 1 m A cm-2 by the ultrasonic welding process.The assembled UW-Li/Au@LLZTO/Li Fe PO4 full cell,after 550 stable cycles at 1 C,had a discharge specific capacity of 120.5 m Ah g-1. |