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Ethan Self1 Gabriel Veith1 Rose Ruther2 Jagjit Nanda1

1, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
2, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States

Development of low-cost cathodes with high energy density and long cycle life is critical to enable advanced Li-ion batteries for transportation applications. Traditional layered LiMO2 (M = Mn, Co, Ni, etc.) cathodes cannot reversibly cycle their entire Li supply (e.g., x ≤ 0.5 in Li1-xCoO2). When charged beyond ~4.3 V vs. Li/Li+, many lithium-transition metal oxides undergo irreversible structural changes with concomitant oxygen gas evolution, resulting in irreversible capacity loss and voltage fade during cycling.[1-3] Understanding and addressing these structural instabilities is necessary to design new cathode materials which can better utilize their Li supply without sacrificing cycle life.

Li2MoO3 has recently received attention as a cathode material due to the unique properties of Mo which can access several oxidation states (e.g., Mo4+ in Li2MoO3 and Mo6+ in MoO3), allowing for the possibility to store multiple Li per transition metal. Our previous work showed that Li2MoO3 also has excellent oxidative stability and thus may be useful to stabilize the oxygen sublattice of conventional cathode materials. This presentation will detail the synthesis and characterization of layered-layered composite Mo-based cathodes with the general formula xLi2MoO3-(1-x)LiMO2 (M = Ni, Mn, and/or Co). Various synthesis routes including solid-state reactions and sol-gel chemistry will be explored to understand the effect of synthesis conditions on the structure and electrochemical properties of these materials. The structural evolution of these cathodes over several charge/discharge cycles will be studied using Raman spectroscopy and X-ray diffraction (XRD). In-situ mass spectrometry will be used to monitor the composition and quantity of gas evolved during battery operation. The effect of fluorine doping on the operating potential and oxidative stability of these materials will also be discussed.

Acknowledgements
Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy.

References
[1] R. E. Ruther, H. Zhou, C. Dhital, K. Saravanan, A. K. Kercher, G. Chen, A. Huq, F. M. Delnick, J. Nanda, Chem. Mater. 2015, 27, 6746-6754.
[2] M. Sathiya, G. Rousse, K. Ramesha, C. P. Laisa, H. Vezin, M. T. Sougrati, M. L. Doublet, D. Foix, D. Gonbeau, W. Walker, A. S. Prakash, M. Ben Hassine, L. Dupont, J. M. Tarascon, Nat Mater 2013, 12, 827-835.
[3] R. E. Ruther, A. S. Pandian, P. Yan, J. N. Weker, C. Wang, J. Nanda, Chem. Mater. 2017, 29, 2997-3005.

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