Probing Electrochemically Induced Structural Evolution and Oxygen Redox Reactions in Layered Lithium Iridate
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Northwestern Univ., Evanston, IL (United States)
- Univ. of Illinois, Chicago, IL (United States)
- Canadian Light Source, Saskatchewan (Canada)
- National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
In order to exploit electrochemical capacity beyond the traditionally-utilized transition metal redox reactions in lithium-metal-oxide cathode materials, it is necessary to understand the role that oxygen ions play in the charge compensation mech-anisms, i.e., to know the conditions triggering electron transfer on the oxygen ions and whether this transfer is correlated with battery capacity. Theoretical and experimental investigations of a model cathode material, Li-rich layered Li2IrO3, have been performed to study the structural and electronic changes induced by electrochemical delithiation in a lithium-ion cell. First-principles density functional theory (DFT) calculations were used to compute the voltage profile of a Li/Li2-xIrO3 cell at various states of charge, and the results were in good agreement with electrochemical data. Electron energy loss spectroscopy (EELS), X-ray absorption near-edge spectroscopy (XANES), resonant/non-resonant X-ray emission spectroscopy (XES), and first principles core-level spectra simulations using the Bethe Salpeter Equation (BSE) approach were used to probe the change in oxygen electronic states over the $$x$$ = 0 to 1.5 range. The correlated Ir M3-edge XANES and O K-edge XANES data provided evidence that oxygen hole states form during the early stage of delithiation at ~3.5 V due to the interaction between O $$p$$ and Ir $$d$$ states, with Ir oxidation being the dominant source of electrochemical capacity. At higher potentials, the charge capacity was predominantly attributed to oxidation of the O2- ions. It is argued that the emergence of oxygen holes alone is not necessarily indicative of electrochemical capacity beyond transition metal oxidation, since oxygen hole states can appear as a result of enhanced mixing of O $$p$$ and Ir $$d$$ states. Prevailing mechanisms accounting for the oxygen redox mechanism in Li-rich materials were examined by theoretical and experimental X-ray spectroscopy; however, no unambiguous spectroscopic signatures of oxygen dimer interaction or non-bonding oxygen states were identified.
- Research Organization:
- Energy Frontier Research Centers (EFRC) (United States). Center for Electrical Energy Storage (CEES); Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)
- Grant/Contract Number:
- AC02-06CH11357; AC02-05CH11231; ACI-1053575
- OSTI ID:
- 1542596
- Journal Information:
- Chemistry of Materials, Vol. 31, Issue 12; ISSN 0897-4756
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
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