A Simple and Low‐Cost Method to Synthesize Cr‐Doped α‐Fe2O3 Electrode Materials for Lithium‐Ion Batteries

Chromium‐doped α‐Fe2O3 samples are successfully synthesized by using a ball‐milling‐assisted rheological phase method combined with heat treatment. The electronic properties of undoped α‐Fe2O3 and 4.0 at % Cr‐doped α‐Fe2O3 are investigated by first‐principles calculations. The calculation results show that Cr doping can reduce the band gap and impurity levels that appear in the band gap. The structure and morphology of the samples are evaluated by X‐ray diffraction, field‐emission scanning electron microscopy, and high‐resolution transmission electron microscopy. The Cr‐doped α‐Fe2O3 electrode delivers a higher reversible capacity and outstanding rate capability as the anode of a lithium‐ion battery compared with the undoped α‐Fe2O3 electrode. The initial discharge/charge capacities of the 4.0 at % Cr‐doped α‐Fe2O3 electrode can reach 1624/1065.9 mAh g−1, respectively, and exhibit an excellent reversible capacity of 971.3 mAh g−1 after 150 cycles at a current density of 0.1 A g−1. Even after 200 cycles, the capacity can remain as high as 758.1 mAh g−1 at a current density of 0.5 A g−1, far beyond than that of the undoped α‐Fe2O3 electrode (376.5 mAh g−1). The forbidden fruit: For Cr‐doped α‐Fe2O3 and undoped α‐Fe2O3, the calculated band gap is 1.82 and 1.90 eV, respectively. The appearance of impurity levels in the forbidden band can be observed, which can convert photons into electron‐hole pairs below the band gap energy. The decrease in the band gap and the appearance of impurity levels in the band gap indicate that the increase in conductivity is an important factor in improving the cycle stability of the Cr‐doped α‐Fe2O3 electrodes.