Co-induced local structure-defect regulation for fast and stable Fe₂O₃/ZnFe₂O₄-based anodes

In this work, Co-doped Fe₂O₃/ZnFe₂O₄ multiphase composites embedded in an N-doped carbon matrix were prepared to investigate the effect of Co incorporation on phase evolution and lithium-storage behavior. Co addition altered the relative fractions of ZnFe₂O₄ and Fe₂O₃ and induced a slight contraction of the spinel lattice. Rietveld refinement suggests that Co partially substitutes for Zn at Zn-related sites in the spinel phase. Among the investigated samples, N-C/Co-FO/ZFO-10 exhibited the highest spinel-phase fraction and a more balanced local structural state. EPR and O 1 s XPS analyses revealed stronger oxygen-defect-related signals for N-C/Co-FO/ZFO-10, indicating that the local oxygen coordination environment changed along with Co-induced cation redistribution. The optimized electrode delivered an initial discharge capacity of 1395.2 mAh g⁻¹ at 100 mA g⁻¹ and retained 938.6 mAh g⁻¹ after 100 cycles. Compared with the undoped electrode, it showed lower polarization, more favorable apparent Li⁺ diffusion, and a slightly higher surface-controlled contribution. In situ EIS and DRT analyses further showed weaker charge-transfer and slow-relaxation responses during lithiation, suggesting that the optimized sample experienced less kinetic hindrance during the conversion/alloying process. The improved electrochemical performance is mainly associated with the Co-dependent regulation of phase composition and local cation-oxygen coordination. The defect-related signals are considered accompanying features of this structural change. The N-doped carbon matrix provides conductive support and helps maintain particle contact during repeated lithiation/delithiation. This work clarifies the role of Co incorporation in regulating the reaction kinetics and cycling stability of Fe₂O₃/ZnFe₂O₄-based anodes.