Abstract O3-type Na[Ni1/3Fe1/3Mn1/3]O2 (NaNFM) is considered as a promising cathode material for sodium-ion batteries; however, its poor cycling stability is still a concern. In this study, we discuss the structural, surface and electrochemical properties of Mg-doped NaMgx[Ni1/3Fe1/3Mn1/3]1–xO2 materials and their enhanced cycling performance. The variations of the lattice parameters by substitution of Mg ion and its uniform distribution on the particles are confirmed using X-ray diffraction and transmission electron microscopy. The optimized NaMg0.05[Ni1/3Fe1/3Mn1/3]0.95O2 delivers a discharge capacity of ~120 mAh g−1 and has a diffusion coefficient of Na ranging from 6.5 × 10−13 to 2.7 × 10−10 cm2 s−1. In particular, it shows a relatively high discharge capacity of 42 mAh g−1 even at a high current density of 1200 mA g−1 and exhibits considerably enhanced cycling stability (77% capacity retention after 50 cycles), compared with that of the undoped NaNFM (40%). Based on structural and electrochemical analyses, it is suggested that Mg doping can effectively suppress the irreversible structural degradation and induce more reversible phase transitions; this results in a more stable cycling performance of the Mg-doped NaNFM than that of undoped NaNFM.

中文翻译：

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具有增强循环稳定性的镁掺杂 Na[Ni1/3Fe1/3Mn1/3]O2 作为钠离子电池的正极材料

摘要 O3型Na[Ni1/3Fe1/3Mn1/3]O2（NaNFM）被认为是一种很有前景的钠离子电池正极材料。然而，其较差的循环稳定性仍然是一个问题。在本研究中，我们讨论了掺杂 Mg 的 NaMgx[Ni1/3Fe1/3Mn1/3]1-xO2 材料的结构、表面和电化学性能及其增强的循环性能。使用 X 射线衍射和透射电子显微镜证实了由 Mg 离子取代引起的晶格参数的变化及其在颗粒上的均匀分布。优化后的 NaMg0.05[Ni1/3Fe1/3Mn1/3]0.95O2 的放电容量约为 120 mAh g-1，Na 的扩散系数范围为 6.5 × 10-13 至 2.7 × 10-10 cm2 s- 1. 特别是，即使在 1200 mA g-1 的高电流密度下，它也显示出 42 mAh g-1 的相对高放电容量，并且与未掺杂的 NaNFM（40 %）。基于结构和电化学分析，表明Mg掺杂可以有效抑制不可逆结构退化并诱导更多可逆相变；这导致 Mg 掺杂的 NaNFM 的循环性能比未掺杂的 NaNFM 更稳定。