Effects of surface modification on degradation suppression of lithium cobalt oxide thin-film electrodes

Lithium cobalt oxide (LiCoO2) is one of the positive electrode materials most widely used in lithium ion batteries. Although the theoretical capacity of LiCoO2 (0surface modification of LiCoO2 by MgO, ZrO2, diamond-like carbon, etc. could suppress the capacity fading [1-2]. However, the detailed mechanism of the degradation suppression has not been clearly understood. In this work, we prepared surface-modified LiCoO2 thin-films as model electrodes, and investigated their surface upon electrochemical insertion and extraction of lithium-ion. LiCoO2 thin-films were prepared by pulsed laser deposition (PLD). After depositing LiCoO2 thin-films on Pt, various kinds of compounds including Al2O3 were successively deposited by PLD. Electrochemical behaviours of the thin film electrodes were examined by cyclic voltammetry. Compared to a bare LiCoO2 electrode, Al2O3modified LiCoO2 electrode showed excellent capacity retention. The surface structure of the electrodes was studied by Raman spectroscopy. Two main peaks at around 596 and 486 cm -1 , which are assigned to A1g and Eg mode frequencies, respectively, remained unchanged for the Al2O3-modified LiCoO2 electrode even after repeated potential cycling. These results suggest that the surface structure of LiCoO2 electrodes could be stabilized by surface modification. The surface-modified LiCoO2 electrodes were investigated by X-ray photoelectron spectroscopy. Based on these results, the mechanism of the degradation suppression by surface modification will be discussed. Acknowledgment This work was financially supported by “Research & Development Initiative for Scientific Innovation of New Generation Batteries (RISING) project” from New Energy and Industrial Technology Development Organization (NEDO). Reference