Layered oxides are the widely investigated cathodes for sodium-ion batteries (SIBs), especially their pure phases (e.g., P2, O3). In this work, we report a series of Mn-Ni-Fe based cathode materials with P2/O3 bi-phase, which possesses advantages of both P2 and O3 structures. At first, the manuscript shows a synthesis phase diagram of NaMnNiFeO to pre-screen and select the P2/O3 bi-phase material NaMnNiFeO. Then, it is found that the cationic ratio has a significant impact on the phase formation. The structure of the materials gradually changes with the various of the Mn/Ni ratio. When the Mn/Ni ratio reaches 3/2, P2/O3 bi-phase is formed. Moreover, Fe content will influence the P2/O3 ratio in the bi-phase material. In particular, the synthesized bi-phase NaMnNiFeO has a P2/O3 ratio of 71/29 wt%. It delivers a high specific capacity of 136.6 mA h g (at current density 20 mA g) between 2.0 and 4.0 V and 94.8% retention (at current density 100 mA g) after 100 cycles. In addition, an 85.6 mA h g discharge capacity can be maintained at a superior high current density of 2000 mA g. The work offers critical guidance to the rational design of the bi-phase layered cathode materials.

中文翻译：

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钠离子电池用阳离子比例调节高性能P2/O3双相层状氧化物材料的合理设计

层状氧化物是广泛研究的钠离子电池（SIB）阴极，尤其是其纯相（例如P2、O3）。在这项工作中，我们报道了一系列具有P2/O3双相的Mn-Ni-Fe基正极材料，其同时具有P2和O3结构的优点。首先，手稿展示了NaMnNiFeO的合成相图，以预筛选并选择P2/O3双相材料NaMnNiFeO。然后，发现阳离子比例对相形成有显着影响。材料的结构随着Mn/Ni比例的变化而逐渐变化。当Mn/Ni比达到3/2时，形成P2/O3双相。此外，Fe含量会影响双相材料中的P2/O3比。特别地，合成的双相NaMnNiFeO的P2/O3比率为71/29wt%。它在 2.0 至 4.0 V 之间提供 136.6 mAh g（电流密度 20 mA g）的高比容量，100 个循环后保留率为 94.8%（电流密度 100 mA g）。此外，在2000 mA g-1的优越高电流密度下仍可保持85.6 mA h g的放电容量。该工作为双相层状正极材料的合理设计提供了重要指导。