Charging-induced defect formation in Li x CoO2 battery cathodes studied by positron annihilation spectroscopy

Charging-induced formation of vacancy-type defects in LixCoO2 battery cathodes was studied by the defect-specific techniques of positron lifetime spectroscopy and Doppler broadening of positron–electron annihilation radiation. The regime of reversible charging is dominated by vacancy-type defects on the Li+-sublattice the size of which increases with increasing Li+-extraction. Indication is found that Li+-reordering which occurs at the limit of reversible Li+-extraction (x = 0.55) causes a transition from two-dimensional agglomerates into one-dimensional vacancy chains. Degradation upon further Li+-extraction is accompanied by the formation of vacancy complexes on the Co- and anion sublattice.