A formal FeIII/V redox couple in an intercalation electrode

Hari Ramachandran; Edward W. Mu; Eder G. Lomeli; Augustin Braun; Masato Goto; Kuan H. Hsu; Jue Liu; Zhelong Jiang; Kipil Lim; Grace M. Busse; Brian Moritz; Joshua J. Kas; John Vinson; John J. Rehr; Jungjin Park; Iwnetim I. Abate; Yuichi Shimakawa; Edward I. Solomon; Wanli Yang; William E. Gent; Thomas P. Devereaux; William C. Chueh

doi:10.1038/s41563-025-02356-x

A formal Fe^III/V redox couple in an intercalation electrode

Hari Ramachandran
, Edward W. Mu
, Eder G. Lomeli
, Augustin Braun
, Masato Goto
, Kuan H. Hsu
, Jue Liu
, Zhelong Jiang
, Kipil Lim
, Grace M. Busse
, Brian Moritz
, Joshua J. Kas
, John Vinson
, John J. Rehr
, Jungjin Park
, Iwnetim I. Abate
, Yuichi Shimakawa
, Edward I. Solomon
, Wanli Yang
, William E. Gent

Thomas P. Devereaux, William C. Chueh

Powder Diffraction

Research output: Contribution to journal › Article › peer-review

Abstract

Iron redox cycling between low-valent oxidation states of Fe^II and Fe^III drives crucial processes in nature. The Fe^II/III redox couple charge compensates the cycling of lithium iron phosphate, a positive electrode (cathode) for lithium-ion batteries. High-valent iron redox couples, involving formal oxidation higher than Fe^III, could deliver higher electrochemical potentials and energy densities. However, because of the instability of high-valent Fe electrodes, they have proven difficult to probe and exploit in intercalation systems. Here we report and characterize a formal Fe^III/V redox couple by revisiting the charge compensation mechanism of (de)lithiation in Li₄FeSbO₆. Valence-sensitive experimental and computational core-level spectroscopy reveal a direct transition from Fe^III (3d⁵) to a negative-charge-transfer Fe^V (3d⁵L²) ground state on delithiation, without forming Fe^IV, or oxygen dimers. We identify that the cation ordering in Li₄FeSbO₆ drives a templated phase transition to stabilize the unique Fe^V species and demonstrate that disrupting cation ordering suppresses the Fe^III/V redox couple. Exhibiting resistance to calendar aging, high operating potential and low voltage hysteresis, the Fe^III/V redox couple in Li₄FeSbO₆ provides a framework for developing sustainable, Fe-based intercalation cathodes for high-voltage applications.

Original language	English
Pages (from-to)	91-99
Number of pages	9
Journal	Nature Materials
Volume	25
Issue number	1
DOIs	https://doi.org/10.1038/s41563-025-02356-x
State	Published - Jan 2026

Funding

Certain commercial equipment, instruments or materials are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose. This work was partially supported by the US Department of Energy (DOE), Office of Basic Energy Sciences, Division of Materials Sciences and Engineering (contract DE-AC02-76SF00515). H.R. was supported by the Stanford Knight-Hennessy Scholarship program. E.W.M. was supported by a National Science Foundation Graduate Research Fellowship under grant number 1656518. A part of the work by M.G. and Y.S. was supported by Grants-in-Aid for Scientific Research (numbers 20H00397, 23H05457 and 23K13814) from MEXT and by AdCORP (JPMJKB2304) and ASPIRE (JPMJAP2314) programs from JST, Japan. This research used resources of the Advanced Light Source, which is a DOE, Office of Science User Facility, under contract number DE-AC02-05CH11231. Use of the SSRL, SLAC National Accelerator Laboratory, is supported by the US DOE, Office of Science, Office of Basic Energy Sciences, under contract number DE-AC02-76SF00515. This research also used resources of the Advanced Photon Source, a US DOE, Office of Science User Facility, operated for the DOE, Office of Science, by the Argonne National Laboratory under contract number DE-AC02-06CH11357. Part of this work was performed at the Stanford Nano Shared Facilities (SNSF), supported by the National Science Foundation under award number ECCS-2026822. Neutron diffraction and neutron pair distribution function were conducted at the NOMAD beamline at ORNL’s Spallation Neutron Source, which was sponsored by the US DOE, Scientific User Facilities Division, Office of Basic Sciences. Computational work was performed on the Sherlock cluster at Stanford University and on resources of the National Energy Research Scientific Computing Center (NERSC), a DOE, Office of Science User Facility, using NERSC award number BES-ERCAP0027203. We thank G. Lee for experimental XAS/RIXS support at Advanced Light Source beamline 8.0.1.1; A. Yao for help in developing the electrode slurry coating method; J. Lee for assistance with the XRD capillary sample preparation and pouch cell preparation; S. Narasimhan, N. Liang and E. Kaeli for help in optimizing the pouch cell electrochemistry; M. Preefer and K. Stone for assistance with experiments at SSRL BL 11-3; N. Strange, K. Stone, Y. Wu, C. Troxel, Jr., and Z. Liang for assistance with experiments at SSRL BL 2-1; and A. Marks, A. Geslin, D. Rivera, D. Eum, D. Edelman, E. Choy, K. Harmon, N. Siemons, N. Liang, S. Wang, W. Thompson, X. Cui, F. Zhang, D. R. Black and J. L. Weaver for proofreading and suggestions on the paper.

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Ramachandran, H., Mu, E. W., Lomeli, E. G., Braun, A., Goto, M., Hsu, K. H., Liu, J., Jiang, Z., Lim, K., Busse, G. M., Moritz, B., Kas, J. J., Vinson, J., Rehr, J. J., Park, J., Abate, I. I., Shimakawa, Y., Solomon, E. I., Yang, W., ... Chueh, W. C. (2026). A formal Fe^III/V redox couple in an intercalation electrode. Nature Materials, 25(1), 91-99. https://doi.org/10.1038/s41563-025-02356-x

@article{efc561a2833b4e5dac47d8257ce6e9ec,

title = "A formal FeIII/V redox couple in an intercalation electrode",

abstract = "Iron redox cycling between low-valent oxidation states of FeII and FeIII drives crucial processes in nature. The FeII/III redox couple charge compensates the cycling of lithium iron phosphate, a positive electrode (cathode) for lithium-ion batteries. High-valent iron redox couples, involving formal oxidation higher than FeIII, could deliver higher electrochemical potentials and energy densities. However, because of the instability of high-valent Fe electrodes, they have proven difficult to probe and exploit in intercalation systems. Here we report and characterize a formal FeIII/V redox couple by revisiting the charge compensation mechanism of (de)lithiation in Li4FeSbO6. Valence-sensitive experimental and computational core-level spectroscopy reveal a direct transition from FeIII (3d5) to a negative-charge-transfer FeV (3d5L2) ground state on delithiation, without forming FeIV, or oxygen dimers. We identify that the cation ordering in Li4FeSbO6 drives a templated phase transition to stabilize the unique FeV species and demonstrate that disrupting cation ordering suppresses the FeIII/V redox couple. Exhibiting resistance to calendar aging, high operating potential and low voltage hysteresis, the FeIII/V redox couple in Li4FeSbO6 provides a framework for developing sustainable, Fe-based intercalation cathodes for high-voltage applications.",

author = "Hari Ramachandran and Mu, \{Edward W.\} and Lomeli, \{Eder G.\} and Augustin Braun and Masato Goto and Hsu, \{Kuan H.\} and Jue Liu and Zhelong Jiang and Kipil Lim and Busse, \{Grace M.\} and Brian Moritz and Kas, \{Joshua J.\} and John Vinson and Rehr, \{John J.\} and Jungjin Park and Abate, \{Iwnetim I.\} and Yuichi Shimakawa and Solomon, \{Edward I.\} and Wanli Yang and Gent, \{William E.\} and Devereaux, \{Thomas P.\} and Chueh, \{William C.\}",

note = "Publisher Copyright: {\textcopyright} The Author(s), under exclusive licence to Springer Nature Limited 2025.",

year = "2026",

month = jan,

doi = "10.1038/s41563-025-02356-x",

language = "English",

volume = "25",

pages = "91--99",

journal = "Nature Materials",

issn = "1476-1122",

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Ramachandran, H, Mu, EW, Lomeli, EG, Braun, A, Goto, M, Hsu, KH, Liu, J, Jiang, Z, Lim, K, Busse, GM, Moritz, B, Kas, JJ, Vinson, J, Rehr, JJ, Park, J, Abate, II, Shimakawa, Y, Solomon, EI, Yang, W, Gent, WE, Devereaux, TP & Chueh, WC 2026, 'A formal Fe^III/V redox couple in an intercalation electrode', Nature Materials, vol. 25, no. 1, pp. 91-99. https://doi.org/10.1038/s41563-025-02356-x

TY - JOUR

T1 - A formal FeIII/V redox couple in an intercalation electrode

AU - Ramachandran, Hari

AU - Mu, Edward W.

AU - Lomeli, Eder G.

AU - Braun, Augustin

AU - Goto, Masato

AU - Hsu, Kuan H.

AU - Liu, Jue

AU - Jiang, Zhelong

AU - Lim, Kipil

AU - Busse, Grace M.

AU - Moritz, Brian

AU - Kas, Joshua J.

AU - Vinson, John

AU - Rehr, John J.

AU - Park, Jungjin

AU - Abate, Iwnetim I.

AU - Shimakawa, Yuichi

AU - Solomon, Edward I.

AU - Yang, Wanli

AU - Gent, William E.

AU - Devereaux, Thomas P.

AU - Chueh, William C.

PY - 2026/1

Y1 - 2026/1

N2 - Iron redox cycling between low-valent oxidation states of FeII and FeIII drives crucial processes in nature. The FeII/III redox couple charge compensates the cycling of lithium iron phosphate, a positive electrode (cathode) for lithium-ion batteries. High-valent iron redox couples, involving formal oxidation higher than FeIII, could deliver higher electrochemical potentials and energy densities. However, because of the instability of high-valent Fe electrodes, they have proven difficult to probe and exploit in intercalation systems. Here we report and characterize a formal FeIII/V redox couple by revisiting the charge compensation mechanism of (de)lithiation in Li4FeSbO6. Valence-sensitive experimental and computational core-level spectroscopy reveal a direct transition from FeIII (3d5) to a negative-charge-transfer FeV (3d5L2) ground state on delithiation, without forming FeIV, or oxygen dimers. We identify that the cation ordering in Li4FeSbO6 drives a templated phase transition to stabilize the unique FeV species and demonstrate that disrupting cation ordering suppresses the FeIII/V redox couple. Exhibiting resistance to calendar aging, high operating potential and low voltage hysteresis, the FeIII/V redox couple in Li4FeSbO6 provides a framework for developing sustainable, Fe-based intercalation cathodes for high-voltage applications.

AB - Iron redox cycling between low-valent oxidation states of FeII and FeIII drives crucial processes in nature. The FeII/III redox couple charge compensates the cycling of lithium iron phosphate, a positive electrode (cathode) for lithium-ion batteries. High-valent iron redox couples, involving formal oxidation higher than FeIII, could deliver higher electrochemical potentials and energy densities. However, because of the instability of high-valent Fe electrodes, they have proven difficult to probe and exploit in intercalation systems. Here we report and characterize a formal FeIII/V redox couple by revisiting the charge compensation mechanism of (de)lithiation in Li4FeSbO6. Valence-sensitive experimental and computational core-level spectroscopy reveal a direct transition from FeIII (3d5) to a negative-charge-transfer FeV (3d5L2) ground state on delithiation, without forming FeIV, or oxygen dimers. We identify that the cation ordering in Li4FeSbO6 drives a templated phase transition to stabilize the unique FeV species and demonstrate that disrupting cation ordering suppresses the FeIII/V redox couple. Exhibiting resistance to calendar aging, high operating potential and low voltage hysteresis, the FeIII/V redox couple in Li4FeSbO6 provides a framework for developing sustainable, Fe-based intercalation cathodes for high-voltage applications.

UR - https://www.scopus.com/pages/publications/105018839023

U2 - 10.1038/s41563-025-02356-x

DO - 10.1038/s41563-025-02356-x

M3 - Article

AN - SCOPUS:105018839023

SN - 1476-1122

VL - 25

SP - 91

EP - 99

JO - Nature Materials

JF - Nature Materials

IS - 1

ER -

A formal Fe^III/V redox couple in an intercalation electrode

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