ACS Appl Mater Interfaces. 2018 Jul 5;10(26):22013-22022. doi: 10.1021/acsami.8b03336. Epub 2018 Jun 22.
The synthesis, structure, and electrochemistry in Na cells of NaFe MO positive electrode materials with M = Ni, CoNi, and Co are reported. In particular, the properties of O3-NaFeO-NaCoNiO solid solutions having compositions NaFe (CoNi)O with 0 ≤ x ≤ 0.5 are explored. It is found that the substitution of Fe in NaNiCoO causes an increase in first cycle energy density from 320 to 440 mWh/g in a 1.5-4.0 V test. However, capacity retention is generally reduced when x is increased for all M = Ni, CoNi, and Co. In general, NaFe MO samples with M = Co had the highest capacity retention for all values of x. Ex situ X-ray diffraction and Mössbauer results of as-prepared and charged materials are directly compared for NaFe (CoNi)O and NaFe CoO ( x = 0.4, 0.5). Iron was found to be in the +3 oxidation state in the as-prepared materials. A significant fraction of Fe is oxidized to Fe in these samples when they are charged to 4.0 V.
本文报道了 NaFeMO（M=Ni、CoNi 和 Co）正极材料在 Na 电池中的合成、结构和电化学性能。特别地，研究了组成式为 NaFe(CoNi)O（0≤x≤0.5）的 O3-NaFeO-NaCoNiO 固溶体的性能。研究发现，在 1.5-4.0 V 测试中，NaNiCoO 中 Fe 的取代会使第一循环能量密度从 320 mWh/g 增加到 440 mWh/g。然而，当 x 增加时，所有 M=Ni、CoNi 和 Co 的容量保持率通常会降低。一般来说，对于所有 x 值，M=Co 的 NaFeMO 样品具有最高的容量保持率。对 NaFe(CoNi)O 和 NaFeCoO（x=0.4，0.5）的制备和充电材料进行了原位 X 射线衍射和穆斯堡尔结果的直接比较。研究发现，在制备材料中 Fe 处于+3 氧化态。当这些样品充电至 4.0 V 时，Fe 中有很大一部分被氧化为 Fe。
