Preparation And Electrochemical Properties Of PPC/TiO₂ Based Nanorods Composite Solid Electrolytes

Using solid electrolyte instead of liquid electrolyte is the most effective way to solve the safety problem of lithium-ion battery.However,there are still some problems in the practical application of solid electrolyte,such as low ionic conductivity at room temperature,poor stability to lithium metal,high interface impedance.In this paper,the amorphous structure of poly?propylene carbonate??PPC?and chemically stable TiO₂ nanorods are combined to form organic-inorganic composite solid electrolyte with high stability and ionic conductivity.The main research contents and results are as follows:?1?TiO₂ nanorods were prepared by hydrothermal method,and the surface of TiO₂ nanorods was further treated to obtain surface lithiated TiO₂ nanorods.TiO₂ nanorods were characterized by SEM,TEM,XRD and XPS.The results show that the prepared TiO₂ nanorods have regular morphology,with a length of 2-4?m and a diameter of about 100 nm.The surface of the lithiated TiO₂ nanorods basically maintains the rod shape,but the surface became rougher,mainly due to the formation of Li₄Ti₅O₁₂ particle layer with certain ionic conductivity.This composite structure is applied to solid electrolyte,which helps to improve the packing/polymer interface bonding and Lewis acid-base reaction.?2?The PPC/TiO₂ nanorods composite solid electrolyte?CSE?was prepared by scraping and coating the TiO₂ nanorods and PPC polymer with amorphous structure.The results show that the microstructure of PPC/TiO₂ nanorod composite solid electrolyte film is uniform,the tensile strength is 26.7 Mpa,and the heat-resistant decomposition temperature is over 200?;the room temperature ionic conductivity is 3.8×10^-44 S·cm^-1,and the electrochemical stability window is4.5 V.The assembled NCM622/CSE/Li all solid-state battery can be charged and discharged circularly at 0.3 C.The specific capacity of the first cycle discharge is 157 mAh·g^-1,and the specific capacity above 105 mAh·g^-1 at 300 cycles.The coulombic efficiency is over 95%.Compared with the powder TiO₂ as the filler,the improvement of the electrochemical performance of PPC/TiO₂ nanorods composite electrolyte is attributed to that TiO₂ nanorods provide a more effective lithium ion transport path and promote the ion transport.?3?The composite solid electrolyte of PPC/surface lithiated TiO₂ nanorods was prepared by further compounding the surface lithiated TiO₂ nanorods with PPC.It is found that the lithiated filler has little effect on the mechanical properties and thermal stability of the composite solid electrolyte,but the electrical properties have been greatly improved.Among them,the electrochemical stable voltage can be more than 4.7 V,and the ionic conductivity can be as high as 5.6×10^-44 S·cm^-1.The assembled NCM622/CSE/Li all solid state battery was charged and discharged at 0.3 C.The specific capacity of the first cycle reached 168 mAh·g^-1,and the specific capacity above 116 mAh·g^-1 at 300 cycles.The coulombic efficiency was over 98%.The surface lithiated of TiO₂ nanorods not only provides a continuous ion transport channel,but also promotes the Lewis acid-base reaction at the interface,releases more free lithium ions,and enhances the lithium ion transmission capacity.