Unlocking Iron Redox Depth for High-Energy Layered Sodium Oxide Cathodes

Abstract

High-capacity O3-type layered NiFeMn-based oxides are promising cathodes for sodium-ion batteries, though their practical deployment is constrained by the inherent limitations of Fe redox chemistry. Traditional designs generally enforcing stoichiometric symmetry (Ni ═ Mn) yield low Fe redox activity. Herein, we propose a valence engineering strategy that breaks conventional Ni/Mn stoichiometry to reconfigure Fe's local chemical environment and unlock unprecedented redox depth. Density functional theory (DFT) calculations reveal that the designed NaNi_0.35Fe_0.225Mn_0.425O₂ cathode exhibits a reduced Bader charge on Fe (1.598 vs. 1.638 in NaNi_1/3Fe_1/3Mn_1/3O₂) and elevated Fe 3d orbital energy, signifying enhanced Fe redox activity. This configuration enables an exceptional Fe^2.60+/Fe^3.88+ redox (1.28 e⁻ per Fe), delivering a reversible capacity of 184.3 mAh g⁻¹ within 2–4.2 V at 0.2 C, markedly exceeding the benchmark NaNi_1/3Fe_1/3Mn_1/3O₂ (161.3 mAh g⁻¹) with low reaction depth of Fe^3.01+/Fe^3.61+. The intensified cationic redox reaction enables an ultrahigh energy density of 596 Wh kg⁻¹. The NaNi_0.35Fe_0.225Mn_0.425O₂ cathode demonstrates robust performance over a broad temperature range from −15°C to 60°C. In situ and ex situ characterizations unveil a reversible O3 ↔ P3 ↔ OP2 phase transition with minimal volume change (1.88%) that circumvents detrimental deleterious O′3 intermediates and intragranular cracking. This work establishes valence engineering as a paradigm to consolidate cationic redox reaction in high-energy layered sodium oxide cathodes.

Keywords

layered oxide cathodes / phase transition / redox depth / sodium-ion battery / valence engineering

References

[1] H. Yang, D. Wang, Y. Liu, et al., “Improvement of Cycle Life for Layered Oxide Cathodes in Sodium-Ion Batteries,” Energy & Environmental Science 17, no. 5 (2024): 1756–1780.

[2] Y. Li, G. Liu, J. Che, et al., “Review on Layered Oxide Cathodes for Sodium-Ion Batteries: Degradation Mechanisms, Modification Strategies, and Applications,” Interdisciplinary Materials 4, no. 1 (2025): 24–51.

[3] J. Wang, Y.-F. Zhu, Y. Su, et al., “Routes to High-Performance Layered Oxide Cathodes for Sodium-Ion Batteries,” Chemical Society Reviews 53, no. 8 (2024): 4230–4301.

[4] Y. Wang, Z. Sun, J. Jin, et al., “In Situ Bulk Oxygen Vacancy Manufacturing and Surface Spinel Layer Coating Enable High-Performance Na-Ion Layered Fe–Mn Based Cathodes,” Advanced Functional Materials 35, no. 38 (2025): 2504354.

[5] D. Yang, X.-W. Gao, G. Gao, et al., “Local Electronic Structure Constructing of Layer-Structured Oxide Cathode Material for High-Voltage Sodium-Ion Batteries,” Carbon Energy 6, no. 10 (2024): e574.

[6] S. Zhao, Q. Shi, W. Feng, et al., “Suppression of Multistep Phase Transitions of O3-Type Cathode for Sodium-Ion Batteries,” Chinese Chemical Letters 35, no. 5 (2024): 108606.

[7] S. Zhao, Q. Shi, W. Feng, et al., “Research Progresses in O3-Type Ni/Fe/Mn Based Layered Cathode Materials for Sodium Ion Batteries,” Carbon Neutrality 2, no. 1 (2023): 13.

[8] V. A. Shevchenko, I. S. Glazkova, D. A. Novichkov, et al., “Competition Between the Ni and Fe Redox in the O3-NaNi_1/3Fe_1/3Mn_1/3O₂ Cathode Material for Na-Ion Batteries,” Chemistry of Materials 35, no. 10 (2023): 4015–4025.

[9] H.-R. Yao, W.-J. Lv, Y.-X. Yin, et al., “Suppression of Monoclinic Phase Transitions of O3-Type Cathodes Based on Electronic Delocalization for Na-Ion Batteries,” ACS Applied Materials & Interfaces 11, no. 25 (2019): 22067–22073.

[10] J. Lamb, L. Stokes, and A. Manthiram, “Delineating the Capacity Fading Mechanisms of Na(Ni_0.3Fe_0.4Mn_0.3)O₂ at Higher Operating Voltages in Sodium-Ion Cells,” Chemistry of Materials 32, no. 17 (2020): 7389–7396.

[11] M. Jeong, H. Lee, J. Yoon, and W.-S. Yoon, “O3-Type NaNi_1/3Fe_1/3Mn_1/3O₂ Layered Cathode for Na-Ion Batteries: Structural Evolution and Redox Mechanism Upon Na (De) Intercalation,” Journal of Power Sources 439 (2019): 227064.

[12] C. Deng, E. Gabriel, P. Skinner, et al., “Origins of Irreversibility in Layered NaNi_xFe_yMn_zO₂ Cathode Materials for Sodium Ion Batteries,” ACS Applied Materials & Interfaces 12, no. 46 (2020): 51397–51408.

[13] D. D. Yuan, Y. X. Wang, Y. L. Cao, X. P. Ai, and H. X. Yang, “Improved Electrochemical Performance of Fe-Substituted NaNi_0.5Mn_0.5O₂ Cathode Materials for Sodium-Ion Batteries,” ACS Applied Materials & Interfaces 7, no. 16 (2015): 8585–8591.

[14] J.-Y. Hwang, S.-T. Myung, D. Aurbach, and Y.-K. Sun, “Effect of Nickel and Iron on Structural and Electrochemical Properties of O3 Type Layer Cathode Materials for Sodium-Ion Batteries,” Journal of Power Sources 324 (2016): 106–112.

[15] S. Huang, Y. Sun, T. Yuan, et al., “Mitigating Voltage Decay of O3-NaNi_1/3Fe_1/3Mn_1/3O₂ Layered Oxide Cathode for Sodium-Ion Batteries by Incorporation of 5d Metal Tantalum,” Carbon Neutralization 3, no. 4 (2024): 584–596.

[16] X.-Y. Liu, S. Li, Y.-F. Zhu, et al., “Promoting Layered Oxide Cathodes Based on Structural Reconstruction for Sodium-Ion Batteries: Reversible Phase Transition, Stable Interface Regulation, and Multifunctional Intergrowth Structure,” Advanced Functional Materials 35, no. 4 (2025): 2414130.

[17] H. Wang, Y. Xu, Y. Tong, et al., “Annealing Modulation Defect Chemistry Toward High-Performance Sodium-Layered Cathodes,” Journal of Physical Chemistry Letters 15, no. 26 (2024): 6743–6749.

[18] X. Zhao, L. Zhang, X. Wang, et al., “Deciphering Cycling Voltage-Dependent Failures of O3-Layered Cathode for Sodium Ion Battery,” Journal of Materials Chemistry A 12, no. 19 (2024): 11681–11690.

[19] C. Zheng, S. He, J. Gan, et al., “Scientific Challenges Faced by Mn-Based Layered Oxide Cathodes With Anionic Redox for Sodium-Ion Batteries,” Carbon Energy 7, no. 1 (2025): e605.

[20] S.-B. Wei, Y.-J. He, Y. Tang, et al., “A Ca-Substituted Air-Stable Layered Oxide Cathode Material With Facilitated Phase Transitions for High-Performance Na-Ion Batteries,” Rare Metals 43, no. 11 (2024): 5701–5711.

[21] G. S. Henderson, F. M. F. de Groot, and B. J. A. Moulton, “X-Ray Absorption Near-Edge Structure (XANES) Spectroscopy,” Reviews in Mineralogy and Geochemistry 78, no. 1 (2014): 75–138.

[22] Y. Yu, D. Ning, Q. Li, et al., “Revealing the Anionic Redox Chemistry in O3-Type Layered Oxide Cathode for Sodium-Ion Batteries,” Energy Storage Materials 38 (2021): 130–140.

[23] S. Zhang, X. Li, Y. Su, et al., “Four-in-One Strategy to Boost the Performance of Na_x[Ni,Mn]O₂,” Advanced Functional Materials 33, no. 36 (2023): 2301568.

[24] S. Li, W. Zhou, F. Liu, et al., “Mitigating Long Range Jahn-Teller Ordering to Stabilize Mn Redox Reaction in Biphasic Layered Sodium Oxide,” Advanced Energy Materials 15, no. 10 (2025): 2403955.

[25] H. Guo, M. Avdeev, K. Sun, et al., “Pentanary Transition-Metals Na-Ion Layered Oxide Cathode With Highly Reversible O3–P3 Phase Transition,” Chemical Engineering Journal 412 (2021): 128704.

[26] Z. Zeng, A. Abulikemu, J. Zhang, et al., “High-Entropy O3-Type Cathode Enabling Low-Temperature Performance for Sodium-Ion Batteries,” Nano Energy 128 (2024): 109813.

[27] T. Zhang, M. Ren, Y. Huang, et al., “Negative Lattice Expansion in an O3-Type Transition-Metal Oxide Cathode for Highly Stable Sodium-Ion Batteries,” Angewandte Chemie International Edition 63, no. 8 (2024): e202316949.

[28] X.-Z. Wang, Y. Zuo, Y. Qin, et al., “Fast Na+ Kinetics and Suppressed Voltage Hysteresis Enabled by a High-Entropy Strategy for Sodium Oxide Cathodes,” Advanced Materials 36, no. 24 (2024): 2312300.

[29] S. Feng, C. Zheng, Z. Song, et al., “Boosting Fast Ionic Transport and Stability of O3-NaNi_1/3Fe_1/3Mn_1/3O₂ Cathode via Al/Cu Synergistically Modulating Microstructure for High-Rate Sodium-Ion Batteries,” Chemical Engineering Journal 475 (2023): 146090.

[30] W. Dong, L. Wu, B. Liu, et al., “Fast-Charging High-Entropy O3-Type Layered Cathodes for Sodium-Ion Batteries,” Chemical Engineering Journal 504 (2025): 158997.

[31] B. Peng, Z. Zhou, J. Shi, et al., “A Customized Strategy Realizes Stable Cycle of Large-Capacity and High-Voltage Layered Cathode for Sodium-Ion Batteries,” Angewandte Chemie International Edition 63, no. 50 (2024): e202411618.

[32] Y. Wu, Y. Li, Y. Lu, et al., “Enhanced Cyclability of O3-NaNi_0.33Fe_0.31Mn_0.36O₂ by Mg and Cu Synergistic Doping With Strengthened MnO Bonds,” Journal of Energy Storage 102 (2024): 114046.

[33] X. Wang, H. Li, Z. Dai, et al., “Consolidating Cationic and Anionic Redox by All-in-One Approach for Air-Stable Layered Sodium-Ion Oxide Cathodes,” Energy Storage Materials 79 (2025): 104345.

[34] M. Liu, Z. Cheng, X. Zhu, et al., “Biphase-to-Monophase Structure Evolution of Na_0.766+xLi_xNi_0.33−xMn_0.5Fe_0.1Ti_0.07O₂ Toward Ultradurable Na-Ion Batteries,” Carbon Energy 6, no. 9 (2024): e565.

[35] M. Jia, Y. Qiao, X. Li, et al., “Identifying Anionic Redox Activity Within the Related O3- and P2-Type Cathodes for Sodium-Ion Battery,” ACS Applied Materials & Interfaces 12, no. 1 (2020): 851–857.

[36] H. Ren, Y. Li, Q. Ni, Y. Bai, H. Zhao, and C. Wu, “Unraveling Anionic Redox for Sodium Layered Oxide Cathodes: Breakthroughs and Perspectives,” Advanced Materials 34, no. 8 (2022): 2106171.

[37] Y. Wang, X. Zhao, J. Jin, et al., “Boosting the Reversibility and Kinetics of Anionic Redox Chemistry in Sodium-Ion Oxide Cathodes via Reductive Coupling Mechanism,” Journal of the American Chemical Society 145, no. 41 (2023): 22708–22719.

[38] X. Gao, L. Fang, H. Wang, et al., “Origin of Fast Capacity Decay in Fe–Mn Based Sodium Layered Oxides,” Advanced Functional Materials 33, no. 10 (2023): 2212685.

[39] T.-Y. Yu, J. Kim, J.-Y. Hwang, et al., “High-Energy O3-Na_1−2xCa_x[Ni_0.5Mn_0.5]O₂ Cathodes for Long-Life Sodium-Ion Batteries,” Journal of Materials Chemistry A 8, no. 27 (2020): 13776–13786.

[40] S. Lee, S. W. Doo, M. S. Jung, S. G. Lim, K. Kim, and K. T. Lee, “Direct Observation of the In-Plane Crackformation of O3-Na_0.8Mg_0.2Fe_0.4Mn_0.4O₂ due to Oxygen Gas Evolution for Na-Ion Batteries,” Journal of Materials Chemistry A 9, no. 24 (2021): 14074–14084.

[41] H. Li, J. Wang, S. Xu, et al., “Universal Design Strategy for Air-Stable Layered Na-Ion Cathodes Toward Sustainable Energy Storage,” Advanced Materials 36, no. 27 (2024): 2403073.

[42] K. Zhang, Z. Xu, G. Li, et al., “Regulating Phase Transition and Oxygen Redox to Achieve Stable High-Voltage O3-Type Cathode Materials for Sodium-Ion Batteries,” Advanced Energy Materials 13, no. 45 (2023): 2302793.

[43] T. Yuan, P. Li, Y. Sun, et al., “Refining O3-Type Ni/Mn-Based Sodium-Ion Battery Cathodes via ‘Atomic Knife’ Achieving High Capacity and Stability,” Advanced Functional Materials 35, no. 5 (2025): 2414627.

[44] B. Peng, Y. Chen, F. Wang, et al., “Unusual Site-Selective Doping in Layered Cathode Strengthens Electrostatic Cohesion of Alkali-Metal Layer for Practicable Sodium-Ion Full Cell,” Advanced Materials 34, no. 6 (2022): 2103210.

[45] F. Ding, C. Zhao, D. Zhou, et al., “A Novel Ni-Rich O3-Na[Ni_0.60Fe_0.25Mn_0.15]O₂ Cathode for Na-Ion Batteries,” Energy Storage Materials 30 (2020): 420–430.

[46] L. Yu, Y.-X. Chang, M. Liu, et al., “O3-Type Na_0.95Ni_0.40Fe_0.15Mn_0.3Ti_0.15O₂ Cathode Materials With Enhanced Storage Stability for High-Energy Na-Ion Batteries,” ACS Applied Materials & Interfaces 15, no. 19 (2023): 23236–23245.

[47] H. Wang, X. Gao, S. Zhang, et al., “High-Entropy Na-Deficient Layered Oxides for Sodium-Ion Batteries,” ACS Nano 17, no. 13 (2023): 12530–12543.

RIGHTS & PERMISSIONS

2025 The Author(s). Carbon Energy published by Wenzhou University and John Wiley & Sons Australia, Ltd.