Li-excess oxides are promising Li-ion battery cathodes, which when charged to high voltages, can display capacities in excess of the theoretical contribution of the redox active transition metal components. This behaviour has previously been attributed to the partial oxidation of the oxygen sublattice upon Li removal, leading to the release of O₂ gas and often accompanied by structural transformations, low coulombic efficiency and poor cycling. Recently, new materials displaying reversible redox behaviour of the oxygen sublattice have been reported, leading to Li-rich cathodes with improved structural stability and alternate charge compensation mechanisms.[1-3]

This study investigates the charge compensation mechanisms and degradation pathways related to oxygen redox activity and oxygen loss in Li-excess cathodes at varying states of delithiation. In order to effectively study the materials in varying states of delithiation, bulk samples free from carbon, binder and electrolyte have been prepared using a range of chemical oxidants and characterised by high-resolution X-ray diffraction, X-ray absorption spectroscopy and electrochemistry techniques.

 [1] Yabuuchi, Naoaki, et al. "High-capacity electrode materials for rechargeable lithium batteries: Li₃NbO₄-based system with cation-disordered rocksalt structure." Proceedings of the National Academy of Sciences 112.25 (2015): 7650-7655.

[2] McCalla, Eric, et al. "Visualization of OO peroxo-like dimers in high-capacity layered oxides for Li-ion batteries." Science 350.6267 (2015): 1516-1521.

[3] Urban, Alexander, and Gerbrand Ceder. "A disordered rock-salt Li-excess cathode material with high capacity and substantial oxygen redox activity: Li_1.25Nb_0.25Mn_0.5O₂." Electrochemistry Communications 60 (2015): 70-73.

Acknowledgment

Support for this work from the Office of Vehicle Technologies of the U.S. Department of Energy, in particular, David Howell and Peter Faguy, is gratefully acknowledged. Sector 20 facilities at the Advanced Photon Source of Argonne National Laboratory, and research at these facilities, are supported by the U.S. DOE, Basic Energy Sciences, and National Sciences and Engineering Research Council of Canada and its founding institutions. The submitted abstract 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.