Dresden 2009 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 20: Poster Session I

MM 20.4: Poster

Dienstag, 24. März 2009, 14:45–16:30, P4

Investigation of point defects in the cathode material LiCoO₂: first-principles calculations — •Melanie Gröting¹, Peter C. Schmidt², and Karsten Albe¹ — ¹Materialwissenschaft, TU Darmstadt, Germany — ²Physikalische Chemie, TU Darmstadt, Germany

Li_xCoO₂ has been widely used in rechargeable lithium ion batteries for decades. Still, there exists no comprehensive understanding of the mechanisms that contribute to degradation in these batteries. However, in the commercially applied concentration range 1.0>x>0.5 microstructural changes, redox and intercalation reactions with the electrolyte, and particularly point defects in the active material are believed to play an important role in the degradation process. Knowledge of the energetics of different point defects are therefore mandatory in order to understand this material more properly.

In this study we use density-functional theory calculations (DFT) to investigate the thermodynamic stability of Li_xCoO₂ with lithium contents x=1.0, 0.5 and 0.0 with respect to the competing metal oxides. Moreover, the formation energies of several charged point defects in these compounds using the supercell approach are calculated. We take lithium and cobalt vacancies into account, as well as oxygen vacancies and interstitials. Especially the oxygen related defects play an important role, which is also evidenced experimentally by performance improvement on coating of the active material e.g. with alumina. Besides the thermodynamic behavior of the defects also the electronic structures and density of states are examined in order to compare them with XPS data.