Issue

Vol. 19 (2027)

Defect-to-Phase Transduction and Interface Reconstruction Enable Regeneration of Spent LiFePO4 Cathodes

https://doi.org/10.1007/s40820-026-02451-x
Liwei Chen
Xinjiang Key Laboratory of New Energy and Energy Storage Technology, Xinjiang Institute of Technology, Aksu 843100, Xinjiang, People’s Republic of China
Zhiheng Wu
Xinjiang Key Laboratory of New Energy and Energy Storage Technology, Xinjiang Institute of Technology, Aksu 843100, Xinjiang, People’s Republic of China
Shouyu Qu
School of Materials Science and Engineering, Hunan Provincial Key Laboratory of Electronic Packaging and Advanced Functional Materials, Central South University, Changsha 410083, People’s Republic of China
Siyu Zhang
School of Materials Science and Engineering, Hunan Provincial Key Laboratory of Electronic Packaging and Advanced Functional Materials, Central South University, Changsha 410083, People’s Republic of China
Magdi E. A. Zaki
Department of Chemistry, Faculty of Science, Imam Mohammad Ibn Saud Islamic University (IMSIU), 11623 Riyadh, Saudi Arabia
Mohamed H. Helal
Center for Scientific Research and Entrepreneurship, Northern Border University, 73213 Arar, Saudi Arabia
Yangyang Liu
School of Instrument Science and Technology, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China
Guanhua Jin
Xinjiang Key Laboratory of New Energy and Energy Storage Technology, Xinjiang Institute of Technology, Aksu 843100, Xinjiang, People’s Republic of China
Jiang Zhou
Xinjiang Key Laboratory of New Energy and Energy Storage Technology, Xinjiang Institute of Technology, Aksu 843100, Xinjiang, People’s Republic of China

Corresponding Author: Jiang Zhou

zhou_jiang@csu.edu.cn

Nano-Micro Letters, Vol. 19 (2027), Article Number: 125

Abstract

Retired lithium-ion batteries are becoming an important material resource, yet recovering cathode value without dissolution and resynthesis remains challenging. Direct regeneration of spent LiFePO4 is hindered by Li vacancies, Li-Fe anti-site defects, and heterogeneous Fe valences trapped within the olivine lattice. Here we examine defect-to-phase transduction together with carbon-interface reconstruction to address this constraint. Controlled oxidation converts the detectable olivine phase into intermediates containing Li3Fe2(PO4)3 and Fe2O3, removing the inherited olivine site topology. Lithiation and reduction subsequently reconstruct LiFePO4 from these intermediates. Rietveld refinement estimates a decrease in Fe-on-Li site occupancy from 5.72% to 0.68%, with a further estimated decrease to 0.35% in the guanidine-assisted sample and a narrower measured electrochemical response. The regenerated cathode delivers 167 mAh g-1 at 0.1 C and 123 mAh g-1 at 5 C, retaining 99.2% capacity after 500 cycles at 1 C. Process analysis estimates a profit of US$2.28 kg-1 of spent cell recycled with lower energy use and greenhouse gas emissions than hydrometallurgical recycling. These results link phase reconstruction and carbon-interface regulation with structural recovery and improved electrode response in spent LiFePO4.


Highlights:
1 Defect-to-phase transduction describes oxidative conversion of the degraded olivine lattice into intermediates from which LiFePO4 is reconstructed.
2 Guanidine hydrochloride supplies nitrogen during carbon formation, constructing an N-doped carbon interface associated with improved electrochemical response and lower refined Fe-on-Li site occupancy.
3 This coupled lattice-interface reconstruction yields low refined Fe-on-Li site occupancy, high-rate performance and durable cycling in regenerated spent LiFePO4 cathodes.

Keywords

Spent LiFePO4 cathodes Direct regeneration Defect-to-phase transduction Lattice reconstruction Anti-site defects
Chen, Liwei, Zhiheng Wu, Shouyu Qu, Siyu Zhang, Magdi E. A. Zaki, Mohamed H. Helal, Yangyang Liu, Guanhua Jin, and Jiang Zhou. 2026. “Defect-to-Phase Transduction and Interface Reconstruction Enable Regeneration of Spent LiFePO4 Cathodes”. Nano-Micro Letters 19 (November):125. https://doi.org/10.1007/s40820-026-02451-x.
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