多钒氧酸盐K₉PV₁₄O₄₂的合成及其储锌性能的研究

Synthesis of Polyoxovanadate K₉PV₁₄O₄₂ and Its Zinc Storage Performance

摘要: 水系锌离子电池(AZIBs)正极材料受限于Zn²⁺扩散动力学缓慢和循环稳定性差，开发新型高性能正极材料是推动AZIBs走向实用的核心任务。本研究以Keggin型多钒氧酸盐K₉PV₁₄O₄₂为研究对象，利用团簇间丰富的通道和空隙实现Zn²⁺的传输与存储，并通过K⁺作为抗衡阳离子在充放电过程中的部分离子交换，起到稳定结构和辅助电导的作用。XRD和FTIR证实材料成功合成，TG显示其热稳定性良好，SEM表明其形貌可为Zn²⁺的嵌入提供丰富的活性位点。电化学测试表明，K₉PV₁₄O₄₂具有良好的比容量和循环稳定性：在0.1 mV∙s⁻¹扫描速率下，前四圈CV曲线逐步趋于重合，显示良好的可逆性；在0.1 A∙g⁻¹电流密度下循环100圈时比容量为162.5 mAh∙g⁻¹，在1 A∙g⁻¹下循环400圈仍保持101.7 mAh∙g⁻¹，库伦效率始终接近100%；不同电流密度下的倍率测试及前三圈GCD结果均与CV结论一致。本工作为构建高容量、结构稳定的钒基正极材料提供了新思路，丰富了多钒氧酸盐在AZIBs领域的应用研究。

Abstract: Cathode materials for aqueous zinc-ion batteries (AZIBs) are severely constrained by sluggish Zn²⁺ diffusion kinetics and poor cycling stability, which arise from the strong electrostatic interactions between the divalent Zn²⁺ ions and the anionic frameworks of host materials. Developing novel high-performance cathode materials with open frameworks and robust structural stability is therefore a core task for promoting the practical application of AZIBs. Polyoxovanadates (POVs), as a subclass of polyoxometalates, feature well-defined cluster structures, tunable compositions, and abundant inter-cluster voids, making them promising candidates for multivalent ion storage. In this study, the Keggin-type polyoxovanadate K₉PV₁₄O₄₂ is investigated as a cathode material for AZIBs, aiming to achieve high reversible capacity and long-term cycling stability through its unique structural advantages. The K₉PV₁₄O₄₂ material was synthesized via a straightforward aqueous solution method. Structural characterization confirmed the successful synthesis of phase-pure K₉PV₁₄O₄₂ with a well-defined Keggin-type architecture. XRD patterns showed sharp and distinct diffraction peaks matching the standard PDF card, with no detectable impurity peaks, indicating high crystallinity and long-range structural order. FTIR spectra revealed characteristic absorption bands at 950 cm⁻¹ (terminal V=O stretching), 850 and 790 cm⁻¹ (asymmetric V-O-V or V-O-P bridging vibrations), and 1050 cm⁻¹ (P-O vibration of the central PO₄ tetrahedron), which are consistent with the typical features of Keggin-type polyoxovanadates. TGA demonstrated a mass loss of approximately 15.22% below 300˚C, attributable to the removal of adsorbed and crystalline water, with negligible mass loss above 300˚C, confirming good thermal stability under operating conditions. SEM images revealed square block-shaped crystalline particles with a uniform size distribution of approximately 20 μm, providing abundant active sites for Zn²⁺ intercalation. Electrochemically, CV curves showed two reduction peaks at 0.57 V and 0.99 V, corresponding to the V⁵⁺/V⁴⁺ redox couple and Zn²⁺ intercalation, respectively, and two oxidation peaks at 0.74 V and 1.05 V for the reverse processes. The CV curves gradually overlapped from the third cycle onward, indicating excellent electrochemical reversibility. EIS analysis yielded a charge-transfer resistance of approximately 110 Ω and a steep Warburg-type tail in the low-frequency region, suggesting favorable ion diffusion kinetics. In GCD tests, the K₉PV₁₄O₄₂ electrode delivers a specific capacity of 162.5 mAh∙g⁻¹ after 100 cycles at 0.1 A∙g⁻¹, and maintained 101. 7 mAh∙g⁻¹ after 400 cycles at 1 A∙g⁻¹; with Coulombic efficiency approaching 100% throughout. Rate performance tests further demonstrated that the material can readily recover its capacity upon returning to low current densities, with no irreversible degradation observed. The GCD curves for the first three cycles showed good overlap from the second cycle onward, consistent with the CV results and further confirming the structural stability and reaction reversibility of the material. In summary, this work not only enriches the application of polyoxovanadate-based materials in the field of AZIBs but also provides new insights for the rational design of high-performance vanadium-based cathode materials with high reversible capacity and robust structural stability.