Origin of capacity retention in Ti-doped LiCoO2: An AIMD study of Ti segregation effects on antisite defects, oxygen vacancies, and Li-ion charge transfer at the LiCoO2/EC interface

Titanium dopants are known to strongly segregate to the (104) surface of LiCoO2, as demonstrated in both experimental and computational studies. However, their impact on surface stability remains largely unexplored. In this study, DFT-PBE+U and AIMD simulations are used to investigate Ti effect on surface defect energetics and Li-ion interfacial migration and transfer in the presence of explicit/implicit ethylene carbonate solvent. The results reveal that Ti segregation inhibits O vacancy formation in the delithiated state, promotes antisite defects, lowers Li vacancy formation energies, and slightly increases Li-ion migration barriers. These effects contribute to stabilizing the surface structure under high-voltage operation, which should decrease interfacial resistance, despite a minor negative impact of Ti on Li-ion subsurface migration. To explore the role of electrolyte conditions, implicit and explicit solvent models are compared. While implicit solvent models provide a computationally efficient approach for capturing surface defect energetics, explicit solvent models are essential for accurately describing adsorption phenomena. These findings underscore the critical role of Ti in mitigating detrimental surface reconstruction, providing insights into the Li-ion interfacial charge transfer, and elucidating the origin of capacity retention in Ti-doped cathodes, offering valuable guidance for the design of robust, high-performance cathode materials for next-generation Li-ion batteries.