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Cr/Br Doping Induced Electron Delocalization Tuning D-Band Center Upshift in Na4Fe3(PO4)2P2O7 Cathode for Unlocking Electron/Ion Transport
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DOI：10.1002/aenm.71298.png)
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Abstract
En 中文
The electron localization around Fe, caused by strong covalent bonds with the polyanions, has been identified as the primary reason for poor electron-transfer capability and slow ion diffusion kinetics of Na4Fe3(PO4)2P2O7 (NFPP) cathodes, which limits its high-rate performance in sodium-ion batteries (SIBs). Herein, an electron delocalization strategy is proposed to overcome this challenge. Specifically, the 3d3 (t2g3 eg0) electronic configuration of Cr3+ and the 4p orbital effects of Br− reduce the electron density around oxygen, driving orbital overlap between Fe 3d and O 2p and facilitating the delocalization of electrons in Fe 3d orbitals. This promotes the Fe d-band center toward Fermi level, thereby enhancing the electron transport rate and decreasing the diffusion energy barrier of Na+ ions. Additionally, stronger Cr─O bonds serve as structural backbones to strengthen structural stability, while gradient-distributed Br− ions alleviate surface degradation. Therefore, the obtained NFPP-Cr-Br cathode exhibits surprising capacity (120.5 mAh g−1 at 0.1C) and long-term cycle stability at high rate (86.2% after 2000 cycles at 10C). It also demonstrates good compatibility with different hard carbon anodes, including in pouch cells (80.6% after 500 cycles at 1C). This work provides new perspective to design efficient polyanionic cathode through electronic structure modulation strategy for SIBs.
Keywords:
cathode material
Cr/Br co-doping
Fe-based mixed phosphate compound
sodium-ion batteries
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