Sodium polyanionic compounds with transition metals are of considerable research interest for the search of new cathode materials for sodium-ion batteries. In this work, we employed ab initio calculations to evaluate three key battery properties: phase stability, diffusion barriers and redox voltage of low-symmetry molybdates NaMFe(MoO₄)₃ (M = Mg, Ni) with α- and β-NaFe₂(MoO₄)₃ structures. First, we showed that the Hubbard Ucorrection within the GGA + Uapproach is necessary to correctly refer these molybdates to semiconductors. The sodium diffusion along various pathways was thoroughly examined, which allowed us to establish the most probable pathways with the lowest migration barriers. These compounds have different directions of sodium diffusion with twice different barriers that was associated to the peculiarities of their crystal structure. The high potentials and structural stability during sodium extraction, along with low-diffusion barriers predicted for NaMFe(MoO₄)₃ (M = Mg, Ni) indicate that these molybdates may be promising high-voltage cathode materials for sodium-ion batteries.

中文翻译：

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低对称性 NaMFe(MoO4)3 (M = Mg, Ni) 的电子结构、钠扩散和氧化还原电位

具有过渡金属的钠聚阴离子化合物对于寻找用于钠离子电池的新型正极材料具有相当大的研究兴趣。在这项工作中，我们采用从头算计算来评估三个关键电池特性：具有 α- 和 β- 的低对称钼酸盐 Na M Fe(MoO ₄ ) ₃ ( M  = Mg, Ni) 的相稳定性、扩散势垒和氧化还原电压NaFe ₂ (MoO ₄ ) ₃结构。首先，我们展示了 GGA + U内的 Hubbard U校正 正确地将这些钼酸盐用于半导体是必要的。彻底检查了沿各种途径的钠扩散，这使我们能够建立具有最低迁移障碍的最可能的途径。这些化合物具有不同的钠扩散方向，具有与其晶体结构特性相关的两倍不同的屏障。Na M Fe(MoO ₄ ) ₃ ( M = Mg, Ni)在钠提取过程中的高电位和结构稳定性以及预测的低扩散势垒 表明，这些钼酸盐可能是用于钠离子电池的有前途的高压正极材料.