Wang Qin-Chao, Hu Enyuan, Pan Yang, Xiao Na, Hong Fan, Fu Zheng-Wen, Wu Xiao-Jing, Bak Seong-Min, Yang Xiao-Qing, Zhou Yong-Ning
Department of Materials Science Fudan University Shanghai 200433 P. R. China.
Chemistry Division Brookhaven National Laboratory Upton NY 11973 USA.
Adv Sci (Weinh). 2017 Jul 6;4(11):1700219. doi: 10.1002/advs.201700219. eCollection 2017 Nov.
Developing sodium-ion batteries for large-scale energy storage applications is facing big challenges of the lack of high-performance cathode materials. Here, a series of new cathode materials NaCo Mn TiO for sodium-ion batteries are designed and synthesized aiming to reduce transition metal-ion ordering, charge ordering, as well as Na and vacancy ordering. An interesting structure change of NaCo Mn TiO from orthorhombic to hexagonal is revealed when Co content increases from = 0 to 0.33. In particular, NaCoMnTiO with a P2-type layered structure delivers a reversible capacity of 120 mAh g at 0.1 C. When the current density increases to 10 C, a reversible capacity of 63.2 mAh g can still be obtained, indicating a promising rate capability. The low valence Co substitution results in the formation of average Mn valence state in NaCoMnTiO, effectively suppressing the Mn-induced Jahn-Teller distortion, and in turn stabilizing the layered structure. X-ray absorption spectroscopy results suggest that the charge compensation of NaCoMnTiO during charge/discharge is contributed by Co/Co and Mn/Mn redox couples. This is the first time that the highly reversible Co/Co redox couple is observed in P2-layered cathodes for sodium-ion batteries. This finding may open new approaches to design advanced intercalation-type cathode materials.
开发用于大规模储能应用的钠离子电池面临着缺乏高性能阴极材料的重大挑战。在此，设计并合成了一系列用于钠离子电池的新型阴极材料NaCoMnTiO，旨在减少过渡金属离子有序化、电荷有序化以及Na和空位有序化。当Co含量从x = 0增加到0.33时，发现NaCoMnTiO发生了从正交晶系到六方晶系的有趣结构变化。特别是，具有P2型层状结构的NaCoMnTiO在0.1 C下具有120 mAh g的可逆容量。当电流密度增加到10 C时，仍可获得63.2 mAh g的可逆容量，表明其具有良好的倍率性能。低价Co的取代导致NaCoMnTiO中平均Mn价态的形成，有效抑制了Mn诱导的 Jahn-Teller 畸变，进而稳定了层状结构。X射线吸收光谱结果表明，NaCoMnTiO在充放电过程中的电荷补偿由Co/Co和Mn/Mn氧化还原对贡献。这是首次在钠离子电池的P2层状阴极中观察到高度可逆的Co/Co氧化还原对。这一发现可能为设计先进的插层型阴极材料开辟新途径。
