Influence of accidental overcharging on the performance and degradation mechanisms of LiCoO2/mesocarbon microbead battery

Abstract

The accidental overcharging is emulated in fully charged LiCoO2/mesocarbon microbeads (MCMB) batteries through initial one-off overcharging and successive long-term normal cycling. The aging mechanism and effect of accidental overcharging on the performance of LiCoO2/MCMB battery is studied by the electrochemical tests and physical characterizations. The result clearly shows that not all accidentally overcharged batteries should be discarded and the extent of the degradation is highly dependent on the overcharging cutoff voltages. Compared with the blank batteries, low overcharging cutoff voltages have almost no influence on the performance degradation during successive long-term normal cycling. Under this condition, the aging is primarily due to the consumption of active lithium. However, high overcharging cutoff voltages, even just one time, decay the battery. Furthermore, further cycling accelerates the aging and changes the aging mechanism of battery under normal operation condition. Under this condition, the surface structure destruction of the LiCoO2 is revealed as the primary contributor to battery degradation, which is related to the dissolution and reduction of cobalt ions after overcharging at high cutoff voltages and successive long-term normal cycling.