In Situ Phase Transformation of Nanoporous Fe 2 O 3 Dendrite to Fe 2 O 3 /FeS 2 Polycrystalline Texture Achieving Superior Rate Capability and Ultra‐Long Cycling Stability with High Capacity

Structural design combined with crystal engineering is an external and internal modifying strategy for metal oxides and sulfides as anode materials for lithium/sodium-ion batteries (LIBs/SIBs). In this paper, the low-cost iron-based oxide of Fe₂O₃ shaped into dendritic nanostructure is locally in situ phase converted to FeS₂ and form porous Fe₂O₃/FeS₂ polycrystalline texture. The Fe₂O₃/FeS₂ maintains the original porous, cross-linked and low-dimension structural advantages of the Fe₂O₃ precursor for electron transport and ions exchange and alleviating volume expansion. Then, the abundant heterogeneous in the converted Fe₂O₃/FeS₂ dramatically enhances electron diffusion in crystal and the structural stability at phase boundary. The prepared anode achieves superior rate capability and ultra-long cycling stability with high capacity both in LIBs and SIBs. Specially, it shows 1017 and 1016 mAh g^-1 at 10 A g^-1 in LIBs and SIBs, separately. After 3000 cycles, the electrodes maintain 266 mAh g^-1 at 10 A g^-1 in LIBs and 279 mAh g^-1 in SIBs. In addition, the LiFePO₄//Fe₂O₃/FeS₂ and (Na₃V₂(PO₄)₃)//Fe₂O₃/FeS₂ full cells are successfully packaged and also show satisfactory electrochemical performances.