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Vol. 18 (2026)

Beyond Conversion Chemistry: Unlocking a Cooperative Solid-Solution–Capacitive Sodium-Storage Mechanism in Nickel Phosphide

https://doi.org/10.1007/s40820-026-02076-0
Jiaqin Liu
State Key Laboratory of Chemical Resource Engineering, College of Chemistry, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China
Tongzhen Wang
School of Mechanical Engineering, School of Materials Science and Engineering, Engineering Research Center of Advanced Composite Materials Design & Application of Anhui Province, Hefei University of Technology, Hefei 230009, People’s Republic of China
Jie Yang
School of Mechanical Engineering, School of Materials Science and Engineering, Engineering Research Center of Advanced Composite Materials Design & Application of Anhui Province, Hefei University of Technology, Hefei 230009, People’s Republic of China
Yulei Li
School of Mechanical Engineering, School of Materials Science and Engineering, Engineering Research Center of Advanced Composite Materials Design & Application of Anhui Province, Hefei University of Technology, Hefei 230009, People’s Republic of China
Zhaoqian Li
School of New Energy Engineering, Hefei Institute of Technology, Hefei 238706, People’s Republic of China
Jiewu Cui
School of Mechanical Engineering, School of Materials Science and Engineering, Engineering Research Center of Advanced Composite Materials Design & Application of Anhui Province, Hefei University of Technology, Hefei 230009, People’s Republic of China
Yan Yu
Department of Materials Science and Engineering, CAS Key Laboratory of Materials for Energy Conversion, Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, People’s Republic of China
Yucheng Wu
School of Mechanical Engineering, School of Materials Science and Engineering, Engineering Research Center of Advanced Composite Materials Design & Application of Anhui Province, Hefei University of Technology, Hefei 230009, People’s Republic of China

Corresponding Author: Yucheng Wu

ycwu@hfut.edu.cn

Nano-Micro Letters, Vol. 18 (2026), Article Number: 253

Abstract

Nickel-rich nickel phosphide (Ni2P) has emerged as a promising sodium-ion battery anode owing to its high theoretical capacity and intrinsic electronic conductivity, yet its charge storage chemistry remains controversial and is often oversimplified as a conversion reaction. Herein, we design a freestanding Ni2P composite electrode composed of ultrasmall Ni2P nanocrystals embedded within a phosphorus-doped, graphene-like porous carbon matrix. Comprehensive in-situ and ex-situ analyses unequivocally demonstrate an interstitial solid-solution mechanism, wherein Na+ ions reversibly occupy lattice interstitials via (111)-oriented interplanar channels, inducing reversible lattice breathing without phase transformation. This bulk intercalation process is synergistically coupled with a substantial pseudocapacitive contribution, establishing a cooperative dual-mode storage mechanism. Benefiting from this solid-solution–capacitive chemistry, the electrode delivers a high reversible capacity (≈560 mAh g−1), outstanding rate capability (135 mAh g−1 at 10 A g−1), and exceptional long-term stability (263 mAh g−1 after 2000 cycles). When paired with a Na3V2(PO4)3@C cathode, the full cell achieves a high-energy density of 245 Wh kg−1. This work establishes solid-solution–capacitive coupling as a general paradigm for designing high-rate and durable sodium-ion battery anodes.


Highlights:
1 A cooperative dual-mode sodium-storage mechanism, combining interstitial solid-solution intercalation and surface pseudocapacitance, is identified, diverging from the conventional conversion-dominated chemistry of nickel phosphides.
2 In-situ/ex-situ analyses provide direct evidence of reversible Na+ insertion into lattice interstitials through (111)-oriented interplanar channels, enabling low-strain lattice breathing without phase transformation.
3 The freestanding Ni2P composite electrode achieves exceptional performance, including high reversible capacity (≈560 mAh g−1), remarkable rate capability (135 mAh g−1 at 10 A g−1), and long-term stability over 2000 cycles.

Keywords

Sodium-ion battery Anode Ni2P Solid-solution Pseudocapacitive
Liu, Jiaqin, Tongzhen Wang, Jie Yang, Yulei Li, Zhaoqian Li, Jiewu Cui, Yan Yu, and Yucheng Wu. 2026. “Beyond Conversion Chemistry: Unlocking a Cooperative Solid-Solution–Capacitive Sodium-Storage Mechanism in Nickel Phosphide”. Nano-Micro Letters 18 (February):253. https://doi.org/10.1007/s40820-026-02076-0.
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