Atomic-scale insight into the lattice volume plunge of LixCoO2 upon deep delithiation

The practical capacity utilization of LiCoO2 is limited to 50-70% due to the dramatic volume shrinkage induced cracks and subsequent interface parasitic reactions at high voltage. However, the fundamental understanding of the dramatic lattice volume shrinkage remains unclear. In this work, we discover that the delithiation paths have an impact on the lattice volume turning point of LixCoO2, where the corresponding capacity utilization can be as low as 62.5% or as high as 75% consequently. In addition, the O <-> O interlayer distance across the Li layer (O-(d3)) mainly contributes to the volume increase before 62.5-75% delithiation, and the O <-> O interlayer distance across the Co layer (O-(d2)) is the dominant factor for the dramatic volume decrease after the volume turning point. The electron localization function (ELF) around O keeps increasing during delithiation and it increases significantly after more than 62.5% delithiation, indicating that the lattice oxygen participates in charge compensation during the whole delithiation process and it becomes the main contributor to the charge compensation at a high delithiated state compared with Co. This work unravels the fundamental reason for the dramatic volume shrinkage of LixCoO2 at high voltage. It claims that the antisite defects (Co-Li) of LiCoO2 should be designed carefully owing to the weaker Co-O bond strength and further oxygen release, which accelerate the degradation of LiCoO2, although it can increase the voltage of LiCoO2. More importantly, LiCoO2 material design with elemental doping, oxygen defects (V-O), Li defects (V-Li), and Co defects (V-Co) will contribute to the capacity utilization of LiCoO2.

Automated summary

In this study, the impact of delithiation paths on the lattice volume turning point and capacity utilization of LixCoO2 was investigated. The results showed that the interlayer distances between oxygen atoms played a significant role in volume increase and decrease. Moreover, the study revealed the involvement of lattice oxygen in charge compensation during the delithiation process, emphasizing the importance of careful design to avoid Co-Li antisite defects and oxygen release for better LiCoO2 performance. Furthermore, it proposed the use of elemental doping and defects control to enhance the capacity utilization of LiCoO2.