Oberflächenanalyse: Mittels In‐situ‐Totalreflexions‐Röntgenfluoreszenz‐Absorptionsspektroskopie wurde gefunden, dass Cobalt an der Oberfläche einer LiCoO2‐Elektrode vom flüssigen Elektrolyten reduziert wird. Ein irreversibles Verhalten wurde an der LiCoO2‐Oberfläche während des ersten Lade‐/Entladeprozesses beobachtet, wohingegen das Bulk‐Material ein reversibles Verhalten zeigte. Die Cobalt‐Reduktion ist Auslöser für den Abbau der Elektrode.
Lifetimes of lithium-ion batteries are often affected by deterioration of positive electrodes. It is well-known that the deterioration of the positive electrodes can be reduced by using electrolyte additives; however, the mechanism underlying this cyclability improvement needs to be clarified. In this study, we investigate electronic structure at the electrode/electrolyte interface using in situ total-reflection fluorescence X-ray absorption spectroscopy to elucidate the mechanism underlying the cyclability improvement of a LiCoO 2 electrode upon addition of vinylene carbonate (VC) to the electrolyte. The results indicate that the reduction of cobalt ions at the surface of the LiCoO 2 electrode, which occurs upon soaking in the electrolyte in the absence of VC, is suppressed by the presence of the VC additive. The VC additive also suppresses irreversible change in the electronic structure of the cobalt ions at the LiCoO 2 surface during successive charge/discharge processes. The effects of the VC additive can be attributed to the formation of a layer of decomposed VC molecules at the LiCoO 2 /electrolyte interface, which plays an important role in the suppression of the irreversibility at the LiCoO 2 surface during the charge/discharge processes. 24
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