Application Of Dual EELs In Electrode Materials

Acquiring the spatial distribution of Li and the valence state of transition metals?TM?in lithium ion battery?LIB?electrode materials is of critical importance to understand their electrochemical performance.Electron energy loss spectrum?EELS?is an optimal method to analyzing light elements,yet remain some challenges in the quantitative analysis of Li,not only because of the effect of thickness but also the overlap between Li K edge and TM M₂₃3 edge.Besides,the valence map of TM need further.In this thesis,the methods to obtain an accurate Li EELS-mapping of thick sample with complex overlapping edges was studied.The surface chemistry of spinel LiNi_0.5Mn_1.5O₄?LNMO?was studied by Li EELS-mapping and valence map of Ni and Mn.And the mechanism of aqueous zinc ion battery was studied by valence map of Ni and Mn and EDS.Dual EELS is an ideal way to analyze lithium.It can eliminate the effects of energy drift,improving the accuracy of imaging.Besides,it can correct the false caused by thickness variation with zero loss peak?ZLP?.Overlap area calculation is an accurate method to obtain Li EELS-mapping.The as-prepared LNMO particles have a Mn/Ni-enriched and Li-poor surface layer?around 1² nm?,and the valence of Mn gradually changed from+4 in the bulk to+2 in the surface layer.Knowing that the low valent Mn²⁺dissolution is a critical reason for capacity degradation and structure damage for LNMO,our results indicate that rational synthesis of LNMO cathode material with decreased low valence Mn²⁺in the surface could be a previously-neglected approach to enhance their electrochemical performance.During the first discharge,the H⁺prefers reacting with?-MnO₂ along[001]direction,accompanied by the production of zinc sulfate and a trivalent manganese compound.The zinc sulfate disappears after the battery is recharged at the first cycle when Mn²⁺is added into the electrolyte.Besides,K+was observed in the as-prepared?-MnO₂.These discoveries may be the reason for poor cycle performance for aqueous zinc ion.