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Updated: Sep 5, 2026
In Situ Neutron Powder Diffraction Using Custom-made Lithium-ion Batteries
Published on: November 10, 2014
Activating Na4 site via crystalline-phase-engineering enables charge redistribution and stress mitigation in
Linlin Zhou1, Danjing Yang1, Shuting Wen1
1Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, China.
Abstract:
Na4Fe3(PO4)2P2O7 (NFPP) has emerged as a low-cost and durable cathode material for practical sodium-ion batteries. Nevertheless, the intrinsic presence of inactive NaFePO4 (NFP) impurities greatly limits its high-rate capability and long-cycle stability. Herein, we report the synthesis of a high-purity NFPP by customizing the NFP intermediate during synthesis, in which the intermediate with weak crystallinity and low Fe-O coordination enables its complete conversion to NFPP with negligible NFP residue. The high-purity NFPP promotes charge redistribution within Fe-O polyhedra, narrowing the electronic band gap by 15% and lowering the Na4-Na4 migration barrier by 5.5-fold, which facilitates Na4-site utilization at high voltages. Meantime, a 20.8% suppression of lattice distortion is achieved during deep (de)sodiation. Consequently, the high-purity NFPP delivers a near-theoretical charge capacity of 126.6 mAh g-1 at 0.1 C and retains 88.4 mAh g-1 at 50 C in half-cells, while full cells exhibit a 96.9% capacity retention after 3000 cycles at 5 C. This study provides a way to unlock ultrahigh-rate and long-life mixed-polyanion cathodes, accelerating the large-scale applications in grid-scale energy storage.
