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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.

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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

Surface modification effects on interfacial reaction for zirconia (ZrO2) coated lithium cobalt oxide (LiCoO2) are studied. ZrO2-coated LiCoO2 thin-film electrodes are prepared by a pulsed laser deposition with different preparation periods. Cyclic voltammetry measurements clearly show that cycle performance and high-potential durability are improved by the ZrO2 coating. AC impedance spectroscopy reveals that there are two types of resistance associated with ZrO2 coating; one is the charge transfer resistance which depends on the Li+-containing electrolyte concentration, and the other is the ZrO2-layer resistance which depends on the deposition periods of ZrO2 coatings. In situ total-reflection fluorescence X-ray absorption spectroscopy for ZrO2-coated LiCoO2 thin-film electrodes reveals that the ZrO2 coating layer suppresses the reduction reaction by electrolyte contact, leading to improving its cycle performance. Depth-resolved X-ray absorption spectroscopy reveals that the ZrO2 coating layer can prevent the increase of local distortion of the LiCoO2 electrode when overcharged, leading to high-potential durability.

We have found that tetrabutylammonium triflate (Bu4NOTf) serves as an effective electrolyte for electrochemical glycosylation using thioglycosides. Based on this method, a one-pot electrochemical glycosylation–Fmoc group deprotection sequence has been developed. This sequence has been successfully applied to the synthesis of a pentasaccharide.

LiCoO 2 thin-films deposited on various platinum substrates, i.e. single crystals of Pt(100), Pt(110) and Pt(111), and polycrystals (Pt-poly), are characterized by cyclic voltammetry (CV), X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) to discuss appropriateness of thin-film modeling of composite electrodes from the electrochemical and spectroscopic viewpoints. Structural characterization indicates (001) orientation of LiCoO 2 /Pt(100) and LiCoO 2 /Pt(111) thin-films, and (104) orientation of LiCoO 2 /Pt(110). LiCoO 2 /Pt-poly thin-film is polycrystalline with a broad distribution of tilt angle of LiCoO 2 c-axis. The LiCoO 2 /Pt(100) and LiCoO 2 /Pt-poly thin-films exhibit reversible CV behavior, while the other two show irreversible behavior. The structural and electrochemical characterization suggests that the c-axis tilt angle is not the predominant factor for reversible electrochemical behavior of the LiCoO 2 electrodes. Instead, polycrystalline structure with weak orientation seems to be preferable for high reversibility. Orientation dependence of XAS also indicates that the LiCoO 2 /Pt-poly thin-film shows similar spectrum to LiCoO 2 powder. Thin-films having strong orientation lead to strong dependence of XAS spectra, and this can result in lack of spectroscopic information. From both the electrochemical and XAS viewpoints, the LiCoO 2 /Pt-poly thin-film having the polycrystalline structure with the broad distribution of the c-axis tilt angle is the most suitable for the thin-film modeling of the composite electrodes.