First Principles Investigation of Li/Fe-Oxide as a High Energy Material for Hybrid All-in-One Li-ion/Li-O$_{2}$ Batteries

We recently introduced a vision for high energy all-in-one electrode/electrocatalyst materials that can be used in hybrid Li-ion/Li-O$_{2}$ (Li-air) cells [1]. Recent experiments using Li$_{5}$FeO$_{4}$ demonstrated substantially smaller voltage polarizations and hence higher energy efficiency compared to standard Li-O$_{2}$ cells forming Li$_{2}$O$_{2}$ [2]. The mechanism by which the charge process activates the Li$_{5}$FeO$_{4}$, however, is not well understood. Here, we present first principles density functional theory (DFT) calculations to establish the thermodynamic conditions for the extraction of Li/Li$+$O from Li$_{5}$FeO$_{4}$. A step-by-step, history-dependent, removal process has been followed and the stability of the Li and Li$+$O deficient samples is investigated on the basis of the energies of the extraction reactions. Various stages of Li/Li$+$O removal are identified, and structural changes and electronic structure evolution, as well as computed XRD, XANES, and PDF characterizations are reported. \\[4pt] [1] M. M. Thackeray, M. K. Y. Chan, L. Trahey, S. Kirklin, and C. Wolverton, Journal of Physical Chemistry Letters, 4, 3607 (2013).\\[0pt] [2] L. Trahey, C. S. Johnson, J. T. Vaughey, S.-H. Kang, L. J. Hardwick, S. A. Freunberger, P. G. Bruce, M. M. Thackeray, Electrochemical and Solid-State Letters, 14, A64 (2011).