A facile method for pre-insertion of cations and structural water in preparing durable zinc storage vanadate cathodes

Abstract

For improving the overall energy storage performance of aqueous zinc-ion battery (ZIB) systems, it is important to identify new cathode materials with superior characteristics. Along these lines, in this work, Na, K, and structural water were pre-inserted in vanadium oxide via a simple solution reaction method at room temperature. More specifically, Na₂V₆O₁₆·1.96H₂O (NVO) and K₂V₆O₁₆·2.13H₂O (KVO) nanorods were successfully prepared using CH₃COONa and CH₃COOK, respectively, and commercial V₂O₅ powder as starting materials. The NVO and KVO nanorods exhibited high Zn²⁺ storage ability; while the specific capacity of the NVO cathode reached 366.8 mAh g⁻¹ at 0.3 A g⁻¹, its capacity retention was 86.6% after 1000 consecutive cycles at 3 A g⁻¹, and the KVO cathode also showed impressive performance. NaV₃O₈ and KV₃O₈ were prepared for comparison by annealing NVO and KVO at high temperatures. The comparison of their cycling stability, Zn²⁺ diffusivity coefficients, and electronic conductivity with the same characteristics of both NVO and KVO cathodes demonstrated that the presence of structural water had a positive impact on the electrochemical performance of the prepared materials. The high performance of NVO and KVO is mainly attributed to the synergistic effect between structural water and metal ions.