The cathode material Na₄Fe₃(PO₄)₂P₂O₇ (NFPP) has shown great potential for sodium-ion batteries (SIBs) due to its cost-effectiveness, prolonged cycle life, and high theoretical capacity. However, the practical large-scale production of NFPP is hindered by its poor intrinsic electron conductivity and the presence of a NaFePO₄ impurity. In this study, we propose a mutually reinforcing approach involving Ti doping, mechanical nano treatment, and in situ carbon coating to produce Ti-NFPP via the solid-state methods of synthesis. Ti doping strengthens the covalent Fe–O interaction, hence accelerating the electron transfer and the redox reactions Fe²⁺/Fe³⁺. In situ carbon coating improves electrical conductivity and allows for accommodating the volumetric variation. Nanosized treatment promotes the uniform progression of solid-state reactions. The synthesized Na₄Fe_2.98Ti_0.01(PO₄)₂P₂O₇ material (Ti-NFPP) exhibits promising electrochemical properties with an initial discharge specific capacity of 112.5 mA h g^–1 at 0.1 C. A volumetric change of only 2.98% was observed during the de/sodiation process, indicating an enhanced reversibility of the crystal lattice. Moreover, it demonstrates exceptional cycling stability with a capacity retention rate of 97.2 mA h g^–1 at 10 C over 5000 cycles. These findings offer a promising pathway for the large-scale production of Ti-NFPP in SIBs.

中文翻译：

---

Ti掺杂固态合成Na4Fe3(PO4)2P2O7/C，促进长循环钠离子电池的结构可逆性


正极材料Na ₄ Fe ₃ (PO ₄ ) ₂ P ₂ O ₇ 杂质的存在阻碍了NFPP的实际大规模生产。在这项研究中，我们提出了一种相辅相成的方法，包括钛掺杂、机械纳米处理和原位碳涂层，通过固态合成方法生产 Ti-NFPP。 Ti 掺杂增强了 Fe-O 共价相互作用，从而加速了电子转移和氧化还原反应 Fe ²⁺ /Fe ³⁺ 。原位碳涂层提高了导电性并允许适应体积变化。纳米处理促进固态反应的均匀进行。合成的Na ₄ Fe _2.98 Ti _0.01 (PO ₄ ) ₂ P ₂ O ₇ 材料 (Ti-NFPP) 表现出良好的电化学性能，在 0.1 C 下的初始放电比容量为 112.5 mAh g ^–1 。在放电过程中观察到体积变化仅为 2.98%脱/钠化过程，表明晶格的可逆性增强。此外，它还表现出出色的循环稳定性，在 10 C 下经过 5000 次循环后容量保持率为 97.2 mAh g ^–1 。这些发现为在 SIB 中大规模生产 Ti-NFPP 提供了一条有前途的途径。