Cobalt doped ovoid magnetite (Fe3O4) nanocomposites incrusted on sheets of reduced graphene oxide as anode for sodium-ion batteries

Fe3O4 could be a better choice as anode for sodium-ion batteries (NIBs) due to high sodium ion storage capability and abundant resource. Yet, the low conductivity and severe volume expansion during cycling have fetched large defies towards practicality. In this work, an ovoid Fe3O4/rGO and (5%, 10%) cobalt doped Fe3O4/rGO nanocomposites were synthesized through one-step hydrothermal route. Structural, morphological chemical, vibrational, and compositional analysis have been employed using X-ray diffraction, Scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The results indicate the successful substitution of cationic Co2+ ions in Fe3O4 lattice. Hence, integration of optimal cobalt doping in Fe3O4 lattice can alter the charge/discharge specific capacity as compared to undoped Fe3O4-rGO anode. Due to sufficient production of oxygen vacancies in the structure 5% Co- Fe3O4/rGO reveals the highest initial charge capacity of 434 mAh g−1 at 0.05 C and exhibits stable prolonged cycling and delivers upto 303 mAh g−1 of charge capacity during 100 cycles (with 100% of CE and 72% of remaining capacity retention)as compared to 10% Co- Fe3O4/rGO (414 mAh g−1) and Fe3O4/rGO (357 mAh g−1) nanocomposite. Moreover, the Nyquist plot reveals the rapid transfer of charge for 5% Co- Fe3O4/rGO anode due to lowest charge transfer impedance of 56.5 Ω as compared to 10% Co- Fe3O4/rGO (114.3 Ω) and pristine Fe3O4/rGO (177.8 Ω). Therefore, the presence of rGO layers and the optimum doping of Co atoms in Fe3O4 crystal can curtail volume expansion, generate more contact sites for electrode/electrolyte, deep penetration of electrolyte into the electrode and can yield superior electrochemical performance via fast Na-ion diffusion rate. Sodium-ion batteries are a promising technology for electric vehicles, the energy grid and other applications.