Aluminum ion doped vanadium oxides as highly stable cathodes for aqueous zinc ion batteries

In this work, Al³⁺- doped nanosized layered vanadium oxides (Al_xV₂O₅) with different Al:V ratios have been synthesized by hydrothermal method. The morphology and structure of the obtained compounds were characterized by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Thin layers of Al-doped vanadium oxide agglomerated in the form of “nanoflowers”. The presence of Al³⁺ in the layered structure of the vanadium oxide Al_xV₂O₅ with expanded interlayer distance was confirmed. The electrochemical properties of the obtained cathode materials were investigated in coin-type zinc-ion battery cells with a zinc anode in an aqueous solution of 3 M ZnSO₄ by cyclic voltammetry and galvanostatic charge/discharge. The initial capacity of the cathodes depended on the aluminum content (x-values). The highest initial capacity of 383 mAh·g⁻¹ at a current density of 1.0 A·g⁻¹ was observed for Al_0.060V₂O₅, which degraded faster due to the lower content of Al³⁺ ions, and the capacity retention was 89 % of the initial value. Al_0.072V₂O₅ had the lowest initial discharge capacity (196 mAh·g⁻¹), but was the most stable with a capacity retention of 98 % (192 mAh·g⁻¹ after 100 cycles) and 96 % (189 mAh·g⁻¹ after 300 cycles). Except for the first cycle, the coulombic efficiency of all cathodes is close to 100 %, confirming the perfect reversibility of the charge/discharge process.