A first-principles study on the properties of Sn-doped LiCoO₂ for Li-ion batteries

The key for the application of LiCoO₂ as a lithium-ion battery electrode at high voltage is to suppress the irreversible phase transformation from the layered to the spinel/rocksalt structure during cycling. The experimental study (R. Zhao, J. Zhang, G.-H. Lee, K. Zhang, V. W.-H. Lau, J.-J. Lee, I. Moudrakovski, Y.-L. Yang, F. Zou, M. Park, I. M. Hung and Y.-M. Kang, J. Mater. Chem. A, 2020, 8, 12424) demonstrated that Sn doping into LiCoO₂ effectively inhibits the undesired phase transition and ascribed the structural stability to the ability of the Sn dopant to pin the lattice thermal vibration. However, the detailed information on Sn-doped LiCoO₂, such as atomic structures, still remains uncovered. Here, we carried out a comprehensive theoretical study on un-doped and Sn-doped LiCoO₂ with the aid of first-principles calculations. Our study shows that the un-doped and Sn-doped systems investigated in the experiment should contain Co-O vacancies and Sn prefers to be doped at the site that is near to the Co-O vacancies. The study also demonstrates that Sn-doping can significantly decrease the variation in volume and inhibit Co migration during delithiation. Additionally, Sn-doping can reduce the average activation barrier of Li diffusion. The theoretical study gives an insight into the microscopic mechanism of Sn-doping to enhance the performance of LiCoO₂ as a cathode material and is a necessary complement to the experimental study.