Lithium metal oxides with high Li₂O contents, such as Li₆MnO₄, Li₆CoO₄ and Li₅FeO₄, are of particular interest as novel, high capacity hybrid cathode materials due to their potential dual Li-ion/Li-O₂ activity [1, 2]. Previous experiments on the charge process of Li₅FeO₄ have demonstrated a significant electrochemical capacity of 475 mAh/g in a Li-O₂ cell[3]. However, the geometrical and electronic structure changes during the charge process remain elusive, and whether and how oxygen is evolved is uncertain.

In this study, we employed first-principles density functional theory (DFT) to monitor the structural and energetic changes of hybrid batteries along various delithiation routes. Two delithiation routes of Li₆MnO₄, Li₆CoO₄ and Li₅FeO₄ systems, namely Li removal and 2Li+O concerted removal, are investigated by DFT calculations. Step-by-step removals have been carried out and the stabilities of the Li and Li/O deficient systems are investigated based on DFT energies of each extraction step. The energetic competition between Li and oxygen removal is determined as a function of Li content and compared among the three systems. Bader charge analysis is used to compare charge compensation tendencies, upon delithiation, among Fe, Co and Mn. The implications of these results for other hybrid battery systems will be discussed.

Acknowledgements

This work was supported as a part of the Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under award number DE-AC02–06CH11. Use of the Advanced Photon Source, a US DOE Office of Science User Facility operated by Argonne National Laboratory, was supported by DOE under Contract No. DE-AC02-06CH11357. Use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

Reference:

1. M. M. Thackeray, M. K. Y. Chan, L. Trahey, S. Kirklin, and C. Wolverton, “Vision for Designing High-Energy, Hybrid Li Ion/Li-O₂ Cells,” Journal of Physical Chemistry Letters 4, 3607 (2013).
2. S. Kirklin, M. K. Y. Chan, L. Trahey, M. M. Thackeray, and C. Wolverton, “High-throughput screening of high-capacity electrodes for hybrid Li-ion/Li-O2 cells,” Physical Chemistry Chemical Physics 16, 22073 (2014).
3. L. Trahey, C. S. Johnson, J. T. Vaughey, S.-H. Kang, L. J. Hardwick, S. A. Freunberger, P. G. Bruce, and M. M. Thackeray, “Activated Lithium-Metal-Oxides as Catalytic Electrodes for Li–O₂ Cells,” Electrochemical and Solid-State Letters 14, A64-A66 (2011).

The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.