To improve the inherent conductivity and extend the cycling durability of Na₃V₂(PO₄)₃ (NVP), this study suggests a technique for synthesis of phenol-formaldehyde (PF) resin-derived lamellar intercalated spherical NVP (PF-NVP/C) structures via solvothermal method. The unique lamellar intercalated sphere structure typically possesses good mechanical toughness, enabling better tolerance to the current impact. Moreover, spherical morphology features a significantly enlarged specific area of 144.32 m² g^-1, facilitating full contact between electrolyte and electrode, and providing additional active sites for Na⁺ storage. Coupled with protective effect of carbon coating layers, the cycling stability is significantly improved. Meanwhile, highly conductive graphitized carbon skeleton from the pyrolysis of PF bonding with the uniform amorphous carbon layers constructs favourable networks for electronic transportation. Notably, the modified PF-NVP/C delivers a capacity of 115.5 mAh g^-1 at 0.1 C. Remarkably, it can maintain a high capacity of 71.1 mAh g^-1 and keeps 50.8 mAh g^-1 even after 16000 cycles at 50 C, exhibiting outstanding cycling stability. Ex-situ XRD indicates the redox reaction of V³⁺/V⁴⁺ is highly reversible. Furthermore, by comparing morphological and electrochemical kinetic characteristics of the PF-NVP/C before and after cycling, further evidence is provided to demonstrate its unique lamellar intercalated spherical morphology and excellent structural stability.

中文翻译：

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层状插层球形 Na3V2（PO4）34，由苯酚-甲醛诱导的表面积扩大，提高了钠离子电池的高容量和长寿命


为了提高 Na ₃ V ₂ （PO） ₃ （NVP ₄ ） 的固有电导率并延长其循环耐久性，本研究提出了一种通过溶剂热法合成酚醛 （PF） 树脂衍生的层状插层球形 NVP （PF-NVP/C） 结构的技术。独特的层状插层球体结构通常具有良好的机械韧性，能够更好地承受电流冲击。此外，球形形态具有显着扩大的 144.32 m ² g ^-1 比面积，促进了电解质和电极之间的完全接触，并为 Na ⁺ 储存提供了额外的活性位点。再加上碳涂层的保护作用，循环稳定性显著提高。同时，PF 键合热解产生的高导电石墨化碳骨架与均匀的非晶碳层构建了有利于电子运输的网络。值得注意的是，改性的 PF-NVP/C 在 0.1 C 下可提供 115.5 mAh g 的 ^-1 容量，值得注意的是，它可以保持 71.1 mAh g ^-1 的高容量，即使在 50 C 下循环 16000 次后也能保持 50.8 mAh g ^-1 ，表现出出色的循环稳定性。非原位 XRD 表明 V ³⁺ /V ⁴⁺ 的氧化还原反应是高度可逆的。此外，通过比较 PF-NVP/C 循环前后的形态和电化学动力学特性，进一步证明了其独特的层状插层球形貌和优异的结构稳定性。