Study On Preparation And Properties Of Oxide-based Solid State Lithium Ion Batteries

The all solid-state lithium-ion batteries use non-flammable solid electrolytes instead of organic liquid electrolytes to solve the safety problems of lithium-ion batteries from the source.However,the commercialization of solid-state lithium-ion batteries still faces many problems,such as large interfacial impedance between the electrolyte and the electrode,and low room temperature ionic conductivity of the solid electrolyte.The garnet structure of Li_6.75La₃Zr_1.75Ta_0.25O₁₂?LLZTO?material has a room temperature ionic conductivity of 10^-3 S·cm^-1,which is a very promising solid electrolyte material.In this paper,the solid state lithium ion battery was assembled by preparing oxide-polymer composite electrolyte membranes and composite positive and negative electrodes to test and optimize their electrochemical performance.A flexible solid state lithium ion battery was prepared by introducing a buffer layer and its electrochemical performance was tested.The specific research contents of this thesis are as follows:?1?The LLZTO powder was prepared by solid phase synthesis method,and characterized by XRD and SEM.The solid electrolyte was prepared from PVDF,PVDF-HFP,LiTFSI and LLZTO.The ratio of PVDF to PVDF-HFP,the content of LLZTO powder and the effect of temperature on the ionic conductivity of solid electrolyte were investigated.The experimental results show that when the PVDF:PVDF-HFP=5:95?wt%?,LiTFSI:LLZTO=9:3?wt%?,the ionic conductivity of the solid electrolyte is up to 3.29×10^-4 S·cm^-1,and its ionic conductivity increases with increasing temperature.?2?The NCM523 composite positive electrode/organic-inorganic composite solid electrolyte/graphite composite negative electrode all-solid lithium ion battery was prepared and its electrochemical performance was studied.The experimental results showed that the solid lithium ion battery's initial charge-discharge specific capacity is171.53 mA·h/g and 123.76 mA·h/g,respectively.After 20 cycles of 0.05 C charge-discharge cycle,the discharge capacity retention rate is still 94.01%,and the capacity attenuation is small.After optimizing the battery preparation process,the first discharge specific capacity of the battery obtained after optimization of the battery preparation process was 144.1 mAh/g,and the first discharge specific capacity was 96.1%of the gram capacity,and the first coulombic efficiency was 80.8%.?3?The composite positive electrode/flexible solid electrolyte/composite negative electrode all-solid flexible lithium ion battery was prepared.The experiment showed that when the surface of the solid electrolyte was introduced into the PC-PMMA-LiTFSI-LLZTO buffer layer,the first discharge specific capacity of the battery reached 148.4mA·h/g.The battery capacity retention rate reached 94.5%after 30 cycles,and the battery discharge capacity retention rate reached 96.6%after bending 100 times.