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Exploring Oxygen Activity in the High Energy P2-Type Na0.78Ni0.23Mn0.69O2 Cathode Material for Na-Ion Batteries
Journal of the American Chemical Society ( IF 15.0 ) Pub Date : 2017-03-22 , DOI: 10.1021/jacs.7b00164
Chuze Ma 1 , Judith Alvarado 1 , Jing Xu 2, 3 , Raphaële J. Clément 4, 5 , Moses Kodur 1 , Wei Tong 2 , Clare P. Grey 4 , Ying Shirley Meng 1
Affiliation  

Large-scale electric energy storage is fundamental to the use of renewable energy. Recently, research and development efforts on room-temperature sodium-ion batteries (NIBs) have been revitalized, as NIBs are considered promising, low-cost alternatives to the current Li-ion battery technology for large-scale applications. Herein, we introduce a novel layered oxide cathode material, Na0.78Ni0.23Mn0.69O2. This new compound provides a high reversible capacity of 138 mAh g-1 and an average potential of 3.25 V vs Na+/Na with a single smooth voltage profile. Its remarkable rate and cycling performances are attributed to the elimination of the P2-O2 phase transition upon cycling to 4.5 V. The first charge process yields an abnormally excess capacity, which has yet to be observed in other P2 layered oxides. Metal K-edge XANES results show that the major charge compensation at the metal site during Na-ion deintercalation is achieved via the oxidation of nickel (Ni2+) ions, whereas, to a large extent, manganese (Mn) ions remain in their Mn4+ state. Interestingly, electron energy loss spectroscopy (EELS) and soft X-ray absorption spectroscopy (sXAS) results reveal differences in electronic structures in the bulk and at the surface of electrochemically cycled particles. At the surface, transition metal ions (TM ions) are in a lower valence state than in the bulk, and the O K-edge prepeak disappears. On the basis of previous reports on related Li-excess LIB cathodes, it is proposed that part of the charge compensation mechanism during the first cycle takes place at the lattice oxygen site, resulting in a surface to bulk transition metal gradient. We believe that by optimizing and controlling oxygen activity, Na layered oxide materials with higher capacities can be designed.

中文翻译:

探索用于钠离子电池的高能 P2 型 Na0.78Ni0.23Mn0.69O2 正极材料中的氧活性

大规模电能储存是可再生能源利用的基础。最近,室温钠离子电池 (NIB) 的研发工作重新焕发了活力,因为 NIB 被认为是当前锂离子电池技术的大规模应用的有前途的低成本替代品。在此,我们介绍了一种新型层状氧化物正极材料 Na0.78Ni0.23Mn0.69O2。这种新化合物具有 138 mAh g-1 的高可逆容量和 3.25 V vs Na+/Na 的平均电位,具有单一的平滑电压曲线。其卓越的倍率和循环性能归因于在循环至 4.5 V 时消除了 P2-O2 相变。第一次充电过程产生了异常过剩的容量,这在其他 P2 层状氧化物中尚未观察到。金属 K-edge XANES 结果表明,在 Na 离子脱嵌过程中金属位点的主要电荷补偿是通过镍 (Ni2+) 离子的氧化实现的,而在很大程度上,锰 (Mn) 离子保持其 Mn4+ 状态. 有趣的是,电子能量损失光谱 (EELS) 和软 X 射线吸收光谱 (sXAS) 结果揭示了电化学循环颗粒的本体和表面电子结构的差异。在表面,过渡金属离子 (TM 离子) 处于比本体低的价态,并且 O K 边缘预峰消失。根据之前有关锂过量 LIB 正极的报道,有人提出第一次循环期间的部分电荷补偿机制发生在晶格氧位点,导致表面到体相过渡金属梯度。
更新日期:2017-03-22
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