In this work, the authors explore the sodium salt of the 14‐vanado(V)phosphate, Na₇[H₂PV₁₄O₄₂], as a potential anode material for sodium‐ion batteries (NIBs). The multi‐electron redox activity of the polyoxovanadate [H₂PV₁₄O₄₂]^7‐leads to high capacity. This polyanion is synthesized by a simple aqueous solution procedure and isolate as a sodium salt with different numbers of crystal waters, Na₇[H₂PV₁₄O₄₂]·nH₂O (n = 15–24). Na₇[H₂PV₁₄O₄₂] as anode in NIBs exhibits a high and reversible capacity of 322 mA h g⁻¹ at 25 mA g⁻¹ with a high cycling stability (with capacity retention of 87% after 120 cycles). Some of the V⁵⁺ ions in [H₂PV₁₄O₄₂]^7‐ can be reduced to V³⁺ after being discharged to 0.01 V versus Na/Na⁺, resulting in an average oxidation state of V^3.7+, as based on ex situ X‐ray photoelectron spectroscopy and in situ synchrotron X‐ray absorption near edge structure studies. The crystalline material becomes amorphous during the charge/discharge processes, which can be observed by in situ synchrotron X‐ray diffraction, indicating that functionality does not require crystallinity. The authors propose that the charge storage mechanism of Na₇[H₂PV₁₄O₄₂] anodes mainly involves redox reactions of V accompanied by insertion/extraction of Na ions in‐between polyoxo‐14‐vanadate ions and adsorption/desorption of Na ions on the surface of the vanadate material.

中文翻译：

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Na7 [H2PV14O42]钠离子电池阳极中钠离子的存储机理

在这项工作中，作者探索了14-vanado（V）磷酸盐的钠盐Na ₇ [H ₂ PV ₁₄ O ₄₂ ]，作为钠离子电池（NIB）的潜在阳极材料。聚氧钒酸盐[H ₂ PV ₁₄ O ₄₂ ] ^7-的多电子氧化还原活性导致高容量。该聚阴离子是通过简单的水溶液法合成的，并作为钠盐与不同数量的结晶水Na ₇ [H ₂ PV ₁₄ O ₄₂ ]·nH ₂ O（n = 15-24）分离。Na ₇ [H ₂ PV ₁₄O ₄₂ ]作为NIB中的阳极，在25 mA g ^-1时具有322 mA hg ^-1的高且可逆容量，并具有高循环稳定性（120个循环后容量保持率达87％）。[H ₂ PV ₁₄ O ₄₂ ] ^7‐中的一些V ⁵⁺离子在放电至相对于Na / Na ^+的0.01 V电压后可以还原为V ³⁺，导致平均氧化态为V ^3.7+，基于异位X射线光电子能谱和边缘结构附近的原位同步加速器X射线吸收研究。晶体材料在充电/放电过程中变为非晶态，这可以通过原位同步加速器X射线衍射观察到，表明功能不需要结晶性。作者认为，Na ₇ [H ₂ PV ₁₄ O ₄₂ ]阳极的电荷存储机理主要涉及V的氧化还原反应，伴随着Nax在多氧-14-钒酸盐离子之间的插入/抽出以及Na离子的吸附/解吸。在钒酸盐材料的表面上。