Structural Characterizations And Electrochemical Investigations Of Electrode Materials In Lithium/Sodium Ion Batteries

Lithium ion batteries play an important role in the field of energy storage.Their advantages include high capacity,high energy density and power density,high energy conversion efficiency,and insignificant memory effect.Considering the following facts that the small reserves of lithium in the earth,people have also turned their attention to other alternative systems,such as sodium ion batteries.With the advent of the 5G era,the functions of portable intelligent devices are becoming more and more powerful,which puts forward higher requirements for the equipped batteries.Therefore,scientific researchers need to seek electrode materials with higher energy density and more stable electrochemical cycle to further improve the performance of lithium and sodium ion batteries.To construct more efficient electrode materials,researchers need to understand the electrochemical process inside the battery.These processes are often nano scale,even atomic and subatomic scale,so advanced characterization methods are particularly important.In addition to the scanning electron microscope which is used to observe the morphology and the X-ray diffraction spectrum which is used to characterize the crystal structure of the material,X-ray absorption spectrum（XAFS）and Raman Scattering Spectroscopy are also powerful tools for unraveling the crystal structure and electronic structure of electrode materials.In this paper,we measure the electrochemical property of MoSe₂@rGO&CNT,Li_xNi_2-4x/3Sb_x/3O₂ and Na₂RuO₃.The change of material structure was also characterized by XRD and XAFS,and the structural changes and charge/discharge mechanism of the materials in the electrochemical process were deeply studied.The specific work is as follows:1.Flower like MoSe₂ nanostructured composites anchored on carbon nanotubes and graphene three-dimensional carbon networks were synthesized by simple hydrothermal method.The first cycle discharge capacity of MoSe₂ increased from 213.8 mAh/g to 717.9 mAh/g.Further analysis shows that the three-dimensional carbon network improves the dispersion of MoSe₂ and provides more active sites,thus improving the performance of the electrode material.2.Li_xNi_2-4x/3Sb_x/3O₂ lithium-rich system was prepared by solid-phase method.The capacity of LNSO-15（136mAh/g）is much higher than that of LNSO-0（45mAh/g）,and the rate capability and cycle stability are also greatly improved.Ex-situ XRD and XAFS characterization showed that LNSO-15 had excellent structural stability during charging and discharging.3.Na₂RuO₃ was prepared by solid-phase method.Taking it as a model,the direct characterization of the local atomic structure of carrier Na in different charge and discharge states by X-ray absorption spectroscopy has been realized.The results show that Na ions at different lattice points in the material exhibit different deblocking paths and induce complex structural phase transitions.4.As a supplement to the methodology,the Raman scattering process is described in detail from both classical and quantum perspectives.The polarized Raman scattering of（001）crystal plane of layered CuTe material is measured.The Raman tensor element ratio of the vibration mode Ag corresponding to the 147.2cm^-1 Raman peak |b/a|=0.32,and the phase difference of the Raman tensor element φ_ba=89.9°。...