Yuan Ding D, Wang Yan X, Cao Yu L, Ai Xin P, Yang Han X
College of Chemistry and Molecular Science, Wuhan University, Wuhan 430072, China.
ACS Appl Mater Interfaces. 2015 Apr 29;7(16):8585-91. doi: 10.1021/acsami.5b00594. Epub 2015 Apr 15.
A series of O3-phase NaFe(x)(Ni0.5Mn0.5)(1-x)O2 (x = 0, 0.1, 0.2, 0.3, 0.4, and 1) samples with different Fe contents was prepared and investigated as high-capacity cathodic hosts of Na-ion batteries. The partial substitution of Ni and Mn with Fe in the O3-phase lattice can greatly improve the electrochemical performance and the structural stability. A NaFe0.2Mn0.4Ni0.4O2 cathode with an optimized Fe content of x = 0.2 can deliver an initial reversible capacity of 131 mAh g(-1), a reversible capacity greater than 95% over 30 cycles, and a high rate capacity of 86 mAh g(-1) at 10 C in a voltage range of 2.0-4.0 V. The structural characterizations reveal that pristine NaMn0.5Ni0.5O2 and Fe-substituted NaFe0.2Mn0.4Ni0.4O2 lattices underwent different phase transformations from P3 to P3″ and from P3 to OP2 phases, respectively, at high voltage interval. The as-resulted OP2 phase by Fe substitution has smaller interslab distance (5.13 Å) than the P3″ phase (5.72 Å), which suppresses the co-insertion of the solvent molecules, the electrolyte anions, or both and therefore enhances the cycling stability in the high voltage charge. This finding suggests a new strategy for creating cycle-stable transition-metal oxide cathodes for high-performance Na-ion batteries.
制备了一系列具有不同铁含量的O3相NaFe(x)(Ni0.5Mn0.5)(1 - x)O2（x = 0、0.1、0.2、0.3、0.4和1）样品，并将其作为钠离子电池的高容量阴极主体进行研究。在O3相晶格中用铁部分替代镍和锰可以极大地改善电化学性能和结构稳定性。具有优化铁含量x = 0.2的NaFe0.2Mn0.4Ni0.4O2阴极在2.0 - 4.0 V电压范围内，初始可逆容量为131 mAh g(-1)，在30次循环中可逆容量大于95%，在10 C时高倍率容量为86 mAh g(-1)。结构表征表明，原始的NaMn0.5Ni0.5O2和铁取代的NaFe0.2Mn0.4Ni0.4O2晶格在高电压区间分别经历了从P3到P3″和从P3到OP2相的不同相变。铁取代后形成的OP2相的层间距离（5.13 Å）比P3″相（5.72 Å）小，这抑制了溶剂分子、电解质阴离子或两者的共嵌入，因此提高了高电压充电时的循环稳定性。这一发现为高性能钠离子电池制造循环稳定的过渡金属氧化物阴极提出了一种新策略。
