Investigating the Electrochemical Performance of MnFe₂O₄@xC Nanocomposites as Anode Materials for Sodium-Ion...

Transition metal oxides (TMOs) are important anode materials in sodium-ion batteries (SIBs) due to their high theoretical capacities, abundant resources, and cost-effectiveness. However, issues such as the low conductivity and large volume variation of TMO bulk materials during the cycling process result in poor electrochemical performance. Nanosizing and compositing with carbon materials are two effective strategies to overcome these issues. In this study, spherical MnFe₂O₄@xC nanocomposites composed of MnFe₂O₄ inner cores and tunable carbon shell thicknesses were successfully prepared and utilized as anode materials for SIBs. It was found that the property of the carbon shell plays a crucial role in tuning the electrochemical performance of MnFe₂O₄@xC nanocomposites and an appropriate carbon shell thickness (content) leads to the optimal battery performance. Thus, compared to MnFe₂O₄@1C and MnFe₂O₄@8C, MnFe₂O₄@4C nanocomposite exhibits optimal electrochemical performance by releasing a reversible specific capacity of around 308 mAh·g^-1 at 0.1 A·g^-1 with 93% capacity retention after 100 cycles, 250 mAh·g^-1 at 1.0 A g^-1 with 73% capacity retention after 300 cycles in a half cell, and around 111 mAh·g^-1 at 1.0 C when coupled with a Na₃V₂(PO₄)₃ (NVP) cathode in a full SIB cell.