Cobalt dissolution in LiCoO2-based non-aqueous rechargeable batteries

Rechargeable lithium batteries using a variety of differently prepared LiCoO2 samples were cycled to 4.5 V versus Li and the negative electrode was investigated for Co deposits after the cell was cycled over 25 times. Qualitative analysis revealed evidence of cobalt dissolution for samples showing high capacity loss with cycle number. A direct correlation between the percentage capacity loss and percentage cobalt loss was established. Cycling LiCoO2-based cells to voltages ranging from 4.1 to 4.5 was found to result in an increase in the capacity fade for voltages greater than 4.2 V, consistent with the traditional limit of reversibility of 4.2 V for LiCoO2. For voltages greater than 4.2 V, the capacity fading scaled with the measured amount of cobalt dissolution which was found to correlate with structural changes observed by in-situ X-ray diffraction.