Abstract
The real-time interface chemistry between the lithium cobalt oxide (LCO) working electrode and the LiClO4/propylene carbonate (PC) electrolyte is investigated during lithiation/delithiation using dip-and-pull ambient pressure photoelectron spectroscopy (APXPS). The APXPS results appear to exhibit the seldom discussed Co2+ state in the LCO structure, where the operando measurements indicate electron transfer among Co2+, Co3+, and Co4+ states. Specifically, the lithiation of LCO reduces the Co4+ state to both Co3+ and Co2+ states, where, as a function of voltage, reduction to the Co2+ state is initially more pronounced followed by Co3+ formation. In addition, a delay in surface delithiation is observed during the reverse potential steps. This is discussed in terms of overpotential at the interface measurement position as a consequence of the dip-and-pull setup for this experiment. Finally, the shifts in the apparent binding energies of the spectral features corresponding to the electrolyte and LCO at their interface show that the electrochemical potentials at delithiation voltage steps are different from the lithiation steps at the same applied voltages. This further explains the non-responsive delithiation. The BE shift observed from the LCO surface is argued to be dominantly due to the semi-conductive nature of the sample. Overall, this article shows the importance of operando APXPS for probing non-equilibrium states in battery electrodes for understanding electron transfer in the reactions.
| Original language | English |
|---|---|
| Pages (from-to) | 20568-20577 |
| Number of pages | 10 |
| Journal | Journal of Materials Chemistry A |
| Volume | 13 |
| Issue number | 26 |
| DOIs | |
| State | Published - May 21 2025 |
Funding
We thank Swedish research council (2020–04512_VR, 2022–06076_VR, 2018–06465_VR) for funding the presented research. This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. For SEM images we acknowledge Myfab Uppsala for providing facilities and experimental support. Myfab is funded by the Swedish Research Council (2019-00207) as a national research infrastructure. A portion of this work (electrode growth, editing) was supported by the US Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) Vehicle Technologies Office (Tien Duong Program Manager) as part of the US-DE program. This manuscript has been partially authored by UT-Battelle, LLC under Contract no. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doepublic-access-plan ). RT is additionally grateful for funding from Lund University and MAX IV Laboratory. We acknowledge MAX IV Laboratory for preliminary and supporting measurements taken at the HIPPIE beamline50 under proposals 20180403 and 20230036. Research conducted at MAX IV, a Swedish national user facility, is supported by the Swedish Research council under contract 2018–07152, the Swedish Governmental Agency for Innovation Systems under contract 2018-04969, and Formas under contract 2019–02496. We acknowledge Diamond Light Source for the supporting XPS measurement at instrument I09 (proposal SI36581-1).