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Vol. 18 (2026)

Tailoring eg Orbital Occupancy of Fe in Ni-Doped Na4.3Fe3(PO4)2P2O7 Cathode for High-Performance Sodium-Ion Batteries

https://doi.org/10.1007/s40820-026-02073-3
Xiaoxue Wang
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China
Yuhui Xu
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China
Jianhua Zhang
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China
Yukun Xi
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China
Ningjing Hou
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China
Yixuan Chen
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China
Dongzhu Liu
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China
Zihao Yang
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China
Haocheng Wen
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China
Jia Kang
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China
Xiaoli Yang
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China
Xuexia Song
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China
Jingjing Wang
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China
Wenbin Li
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China
Jiujun Zhang
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China
Kun Zhang
GEM Co., Ltd., Shenzhen 518101, Guangdong, People′s Republic of China
Xifei Li
Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, People′s Republic of China

Corresponding Author: Xifei Li

xfli@xaut.edu.cn

Nano-Micro Letters, Vol. 18 (2026), Article Number: 237

Abstract

Na4Fe3(PO4)2P2O7 (NFPP) is regarded as a prospective cathode for sodium-ion batteries (SIBs) because of its high structural stability and cost-effectiveness. However, its practical application is hindered by intrinsically low electronic conductivity. Herein, an unconventional electron transfer mechanism from Ni2+ to Fe3+ ions is unveiled in Ni-doped Na4.3Fe3(PO4)2P2O7 (NFPP-Ni) cathode, which facilitates electronic coupling within the Fe−O−Ni coordination unit and thereby effectively boosts electron transport. Moreover, the redox kinetics and reversibility of NFPP materials are predominantly governed by the degree of Fe−O covalency. The intermediate eg occupancy of Fe2+, modulated by the presence of Ni2+, optimizes the overlap between Fe d and O p orbitals. The adjustment of Ni dopant strikes a balance between accelerating Na+ diffusion kinetics and mitigating lattice strain during cycling. As a result, the NFPP-Ni electrode displays impressive rate capacity (121.0 mAh g−1 at 0.1C / 80.9 mAh g−1 at 10C) and stable cyclability (89.1% capacity retention after 1000 cycles). More importantly, the relationship between Fe eg orbital occupancy and Fe−O covalency in NFPP as modulated by various transition metal cations (Ni2+, Mn2+, Zn2+, Co2+ and Cu2+) with different electron configurations are systematically elucidated, thereby providing insights for the commercial development of sodium-ion batteries (SIBs).


Highlights:
1 The Na4.3Fe3(PO4)2P2O7-M cathode constructed by various transition metal cations (M = Ni2+, Mn2+, Zn2+, Co2+ and Cu2+) with different electron configurations for sodium-ion batteries.
2 The Na4.3Fe3(PO4)2P2O7-Ni cathode exhibits superior electronic conductivity, high-rate performance and stable cyclability.
3 A quantitative relationship between the eg occupancy of Fe and the electrochemical activity of The Na4.3Fe3(PO4)2P2O7-M is proposed, serving as an activity descriptor.

Keywords

Na4.3Fe3(PO4)2P2O7 Electronic coupling eg orbital occupancy Descriptor Sodium-ion batteries
Wang, Xiaoxue, Yuhui Xu, Jianhua Zhang, Yukun Xi, Ningjing Hou, Yixuan Chen, Dongzhu Liu, Zihao Yang, Haocheng Wen, Jia Kang, Xiaoli Yang, Xuexia Song, Jingjing Wang, Wenbin Li, Jiujun Zhang, Kun Zhang, and Xifei Li. 2026. “Tailoring Eg Orbital Occupancy of Fe in Ni-Doped Na4.3Fe3(PO4)2P2O7 Cathode for High-Performance Sodium-Ion Batteries”. Nano-Micro Letters 18 (February):237. https://doi.org/10.1007/s40820-026-02073-3.
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