The capacity decay mechanism of the 100% SOC LiCoO2/graphite battery after high-temperature storage

LiCoO2||graphite full cells are one of the most promising commercial lithium-ion batteries, which are widely used in portable devices. However, they still suffer from serious capacity degradation after long-time high-temperature storage, thus it is of great significance to study the decay mechanism of LiCoO2||graphite full cell. In this work, the commercial 63 mAh LiCoO2||graphite battery was employed to reveal the capacity decay mechanism during the storage process at a high temperature of 65 °C. It was found that after storing at 65 °C under 100% state-of-charge (SOC) for 1 month, 2 months, 3 months, and 6 months, the discharge capacity of the battery decreases by 27%, 36%, 43%, and 66% respectively, compared to that of the fresh battery. Moreover, the corresponding restored capacity is 14%, 18%, 23%, and 35%, respectively, where the irreversible capacity loss is 13%, 18%, 20%, and 31%. After characterizing the stored electrodes at 65 °C, the quantitative analysis results illustrated that the capacity decay is related to the formation of dead lithium on graphite electrode and the shuttle effect of Co3+ after a long storage time.