Substantial Oxygen Loss and Chemical Expansion in Lithium-Rich Layered Oxides at Moderate Delithiation

Diego Rivera^a, Peter Csernica^a, William Chueh^a^,^e, Kit McColl^b, Grace Busse^a, David Shapiro^c, Saiful Islam^d

^aDepartment of Materials Science & Engineering, Stanford University

^bDepartment of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom

^cAdvanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States

^dDepartment of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK

^eStanford Institute of Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA

Proceedings of 24th International Conference on Solid State Ionics (SSI24)

Fundamentals: Experiment and simulation

London, United Kingdom, 2024 July 14th - 19th

Organizers: John Kilner and Stephen Skinner

Poster, Diego Rivera, 556
Publication date: 10th April 2024

Delithiation of layered oxide electrodes triggers irreversible oxygen loss, one of the primary degradation modes in lithium-ion batteries. However, the delithiation-dependent mechanisms of oxygen loss remain poorly understood. Here, we investigate the oxygen nonstoichiometry in Li- and Mn-rich Li1.18-xNi0.21Mn0.53Co0.08O2-δ electrodes as a function of Li content by utilizing cycling protocols with long open-circuit voltage steps at varying states of charge. Surprisingly, we observe significant oxygen loss even at moderate delithiation, corresponding to 2.5, 4.0 and 7.6 mL O2 g-1 after resting at 135, 200, and 265 mAh g-1 (relative to the pristine material) for 100 h. Our observations suggest an intrinsic oxygen instability consistent with predictions of high equilibrium oxygen activity at intermediate potentials. From a mechanistic viewpoint, we show that cation disorder greatly lowers the oxygen vacancy formation energy by decreasing the coordination number of transition metals to certain oxygen ions. In addition, we observe a large chemical expansion coefficient with respect to oxygen nonstoichiometry, which is about three times greater than those of classical oxygen-deficient materials such as fluorite and perovskite oxides. Our work challenges the conventional wisdom that deep delithiation is a necessary condition for oxygen loss in layered oxide electrodes and highlights the importance of calendar aging for investigating oxygen stability.

Acknowledgements:

M.S.I. and K.M. are grateful to the Faraday Institution CATMAT project (EP/S003053/1, FIRG016) for financial support, and to the HEC Materials Chemistry Consortium (EP/R029431/1) for Archer-2 supercomputer facilities. P.M.C. acknowledges support through the Stanford Graduate Fellowship as a Winston and Fu-Mei Chen fellow and through the National Science Foundation Graduate Research Fellowship under Grant no. DGE-1656518. D.F.R. acknowledges support through the National Science Foundation Graduate Research Fellowship under Grant no. DGE-1656518. Use of the SSRL, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. This research used resources of the Advanced Light Source, which is aDOE Office of Science User Facility under contract no. DE-AC02-05CH11231.

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