Lithium-rich layered oxides (LRLO) have lately emerged as leading candidates for replacing the classical stoichiometric insertion oxides owing to their staggering increase in energy densities provided by the oxygen redox activities.¹ Despite such a positive attribute, LRLO still await commercial success due to practical obstacles that appear during the first cycle and continue upon subsequent cycles (i.e., irreversible structural changes associated with oxygen gas release leading to unfavorable electrochemical properties such as hysteresis and progressive voltage decay).² Though the origin of voltage fade has been discussed from various structural perspectives (i.e., cation capturing through tetrahedral sites, formation of partial dislocations and/or microstructure defects), a consensus has been reached on the strong coupling between structural dynamics and oxygen redox chemistry.^3-6 Nonetheless, establishing an explicit structure-properties scenario has proved challenging due to characterization limitations as well as the inherent complexity of the coupled transition metal and oxygen redox process itself. In this work, we investigated both in-situ and ex-situ the structure evolution of a typical Li-rich material during its initial cycles based on a newly developed oxygen analytical tool, laboratory and synchrotron X-ray diffraction (XRD), coupled with electron microscopic imaging technique. The average and local structure change associated with cation migration, gaseous oxygen loss and solid liquid interfacial reactions will be discussed. Furthermore, a metastable phase transformation pathway induced by the lattice oxygen redox activities will be proposed and its implication for the applicability of such Li-rich oxides will be shared.

References:

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