Failure mechanism of LiCoO2/graphite pouch cell at high temperature

Lithium cobalt oxide (LiCoO2) and graphite are considered the optimal cathode and anode, respectively, for lithium-ion batteries (LIBs) in digital 3C products, including computers, communication devices, and consumer electronics. The underlying failure mechanism of commercial LiCoO2/graphite LIBs at high temperatures has been elucidated through non-destructive and disassembling characterizations. The findings demonstrate that the capacity retention at 1 C following 800 cycles declines from 92% to 82%, and the associated interface film thickens by approximately 25% as the temperature rises from 25 degrees C to 45 degrees C. The Al2O3 coating layer is initially compromised, resulting in the formation of a spinel phase on the surface of LiCoO2 and the dissolution of Co ions. The diffusion of Co ions and their deposition on graphite serve to accelerate the decomposition of the electrolyte. Following the disassembly of the LiCoO2/graphite cell and the reassembly of half cells, it is observed that the capacity of LiCoO2 can not be recovered, and the graphite exhibits a significant amount of electrolyte decomposition. However, following the removal of the interface films of LiCoO2 and graphite and subsequent reassembly of half cells, it is observed that the capacity of LiCoO2 remains unresponsive, whereas the capacity of graphite is recoverable. This indicates that both surface structural damage to the LiCoO2 electrode and the thickening of the interface films on the graphite anode contribute to a deterioration in the electrochemical performance.