Preparation And Electrochemical Properties Of Na₂Ti₃O₇ For Sodium Ion Batteries

Sodium-ion batteries?SIBs?has renewed interest in researchers in recent years rely on their low cost.Layered sodium titanate?Na₂Ti₃O₇?is considered to be one of the most promising SIB electrode materials due to its low voltage and excellent rate performance;solid-state battery was regarded the research direction of the next generation of batteries battery due to its more excellent in safety and more free design concept.;In this thesis,Na₂Ti₃O₇ was obtained by different preparation schemes,and it was prepared and assembled into sodium ion liquid battery,solid state battery,and flexible electrode.The phase structure,composition and morphology were investigated by means of XRD,XPS,SEM,TEM and other characterization methods.The electrochemical behaviors were studied by electrochemical methods such as constant current charge and discharge,AC impedance and cyclic voltammetry.Firstly,the effect of the doping amount of fluorine?F?on the morphology and electrochemical properties of Na₂Ti₃O₇ was studied.SEM indicated that F doping favored the morphology of Na₂Ti₃O₇ tending to rod-like structure;cyclic voltammetry results show that F-doping increases the diffusion coefficient of sodium ions by an order of magnitude of 1.7×10^-8 cm² s^-1.The results of constant current charge and discharge confirm that the specific capacity of F-doped Na₂Ti₃O₇ increases by 30%and exceeds 800 cycles.Better coulombic efficiency and excellent cycle performance are shown in the secondary cycle.Secondly,Na₂Ti₃O₇ was synthesized by high temperature hydrothermal method.The results showed that the phase was pure and the crystallinity was high by XRD and XPS.The results of SEM and TEM showed that the prepared Na₂Ti₃O₇ was a 10nm diameter tubular structure.The results of constant current charge and discharge showed that maintains a specific capacity of 109.9 mAh g^-1 after 2000 cycles,and the cycle performance is excellent;when the material is applied in a solid-state battery,a specific capacity reached to 101.2 mAh g^-1 after 200 cycles at room temperature.Finally,Na₂Ti₃O₇ was synthesized by hydrothermal method using tetrabutyl titanate.The XRD results showed that a mixture of foamed nickel and Na₂Ti₃O₇ was obtained.The SEM results confirmed that Na₂Ti₃O₇ was grown in situ in a foamed nickel sheet with a nanosheet thickness of about 5 nm.As a non-adhesive,non-conductive agent electrode,the AC impedance indicates that the impedance is smaller than that prepared by the conventional scheme;the constant current charge and discharge results show that the specific capacity of 77.6 mAh g^-1 is 8% higher than that of the conventionally prepared Na₂Ti₃O₇ electrode.