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.
For
the further development of lithium-ion batteries, improvement
of their cyclic performance is crucial. However, the mechanism underlying
the deterioration of the battery cyclic performance is not fully understood.
We investigated the effects of the electronic structure at the electrode/electrolyte
interface on the cyclic performance of the cathode materials via in
situ total-reflection fluorescence X-ray absorption spectroscopy.
In a LiCoO2 thin-film electrode that exhibits gradual deterioration
upon subsequent Li ion extractions and insertions (cycling), the reduction
of Co ions at the electrode/electrolyte interface was observed upon
immersion in an organic electrolyte, with subsequent irreversible
changes after cycling. In contrast, in a LiFePO4 thin-film
electrode, the electronic structure at the electrode/electrolyte interface
was stable and reversible upon electrolyte immersion with subsequent
cycling. The increased stability of the electronic structure at the
LiFePO4/electrolyte interface affects its cycling performance.
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