Electrochemically grown nanocrystalline V ₂ O ₅ as high-performance cathode for sodium-ion batteries

Abstract Nanocrystalline V ₂ O ₅ with a bilayer structure is directly grown on a steel substrate electrochemically in VOSO ₄ -based solution as a cathode for sodium-ion batteries. No complicated slurry preparation procedure, involving polymer binder and conducting agent additions, is needed for this electrode synthesis. The incorporation of NaCH ₃ COO in the VOSO ₄ solution promotes oxide growth and improves oxide film uniformity. The interlayer distance between two-dimensional V ₂ O ₅ stacks in the structure is as large as ∼11.6 Å, which is favorable for accommodating Na ⁺ ions. The growth potential is critical to determine the oxide architectures and thus the corresponding Na ⁺ storage properties (in terms of capacity, high-rate capability, and cycling stability). An optimal charge-discharge capacity of 220 mAh g ^-1 is achieved for V ₂ O ₅ grown in an activation-controlled potential region (i.e., 0.8 V vs. an Ag/AgCl reference electrode). This V ₂ O ₅ electrode shows only 8% capacity decay after 500 cycles.