Na_0.67Co_0.25Mn_0.75−xCr_xO₂ (x = 0, 0.05, 0.10, 0.15) oxides were prepared by a conventional solid-state reaction. The electrochemical properties of P2-type Na–Mn–Co–Cr–O cathodes for sodium-ion batteries have been investigated systematically. X-ray diffractometry and field emission scanning electron microscopy show that Cr ions are successfully incorporated into the lattice of the Na–Co–Mn–O oxide, and a P2-type layered structure with the P6₃/mmc space group remains unchanged after Cr-doping. The electrochemical measurements show that the maximum discharge capacity and the cycling stability of the matrix material is significantly enhanced by Cr-doping, which may be ascribed to the expanded a-axis and lattice volume, and the improvement of the rate capability is attributed to the significant decrease of the charge transfer resistance and the increase of the apparent Na⁺ diffusion coefficient. In the potential region of 2.0–4.0 V at 0.12C, Na_0.67Co_0.25Mn_0.65Cr_0.10O₂ delivers the maximum discharge capacity of 128.1 mA h g⁻¹, which is 10.31% higher than that of the un-doped sample, and the capacity retention of the sample is 66.35% after 100 cycles, which is 39.09% higher than that of the un-doped sample. It is suggested that the optimal Cr content can effectively improve the electrochemical properties of P2-type Na–Mn–Co–O cathodes for sodium ion batteries.

中文翻译：

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钠离子电池用P2-型Na-Mn-Co-Cr-O正极的电化学性能研究

通过常规的固态反应制备Na _0.67 Co _0.25 Mn _{0.75- x} Cr _x O ₂（x = _{0、0.05、0.10、0.15}）氧化物。已对钠离子电池P2型Na–Mn–Co–Cr–O阴极的电化学性能进行了系统研究。X射线衍射和场发射扫描电子显微镜表明，Cr离子已成功地掺入Na-Co-Mn-O氧化物的晶格中，并形成了P2型层状结构，其P 6 ₃ / mmcCr掺杂后，空间群保持不变。电化学测量表明，Cr掺杂显着提高了基体材料的最大放电容量和循环稳定性，这可能归因于扩展的a轴和晶格体积，速率能力的提高归因于电荷转移电阻的显着降低和表观Na ⁺扩散系数的增加。在0.12C的2.0–4.0 V电位区域中，Na _0.67 Co _0.25 Mn _0.65 Cr _0.10 O ₂的最大放电容量为128.1 mA hg ^-1，其比未掺杂样品高10.31％，并且在100次循环后样品的容量保持率为66.35％，比未掺杂样品高39.09％。建议最佳的Cr含量可以有效地改善钠离子电池P2型Na–Mn–Co–O阴极的电化学性能。