CNRS, Université de Bordeaux, ICMCB, 87 avenue du Dr. A. Schweitzer, 33608 F-Pessac, France.
Nat Mater. 2011 Jan;10(1):74-80. doi: 10.1038/nmat2920.
Sodium layered oxides NaxCoO2 form one of the most fascinating low-dimensional and strongly correlated systems; in particular P2–NaxCoO2 exhibits various single-phase domains with different Na+/vacancy patterns depending on the sodium concentration. Here we used sodium batteries to clearly depict the P2–NaxCoO2 phase diagram for x≥0.50. By coupling the electrochemical process with an in situ X-ray diffraction experiment, we identified the succession of single-phase or two-phase domains appearing on sodium intercalation with a rather good accuracy compared with previous studies. We reported new single-phase domains and we underlined the thermal instability of some ordered phases from an electrochemical study at various temperatures. As each phase is characterized by the position of its Fermi level versus the Na+/Na couple, we showed that the synthesis of each material, even in large amounts, can be carried out electrochemically. The physical properties of the as-prepared Na1/2CoO2 and Na2/3CoO2 ordered phases were characterized and compared. Electrochemical processes are confirmed to be an accurate route to precisely investigate in a continuous way such a complex system and provide a new way to synthesize materials with a very narrow existence range.
钠离子层状氧化物 NaxCoO2 形成了最引人入胜的低维强关联体系之一；特别是 P2–NaxCoO2 表现出不同的单相区域，其钠离子和空位的分布随钠离子浓度的变化而变化。在这里，我们使用钠离子电池清楚地描绘了 P2–NaxCoO2 的相图，其中 x≥0.50。通过将电化学过程与原位 X 射线衍射实验相结合，我们确定了在钠离子嵌入过程中单相或两相区域的顺序，与之前的研究相比，其准确性相当高。我们报道了新的单相区域，并强调了一些有序相在不同温度下的电化学研究中的热不稳定性。由于每个相的费米能级相对于 Na+/Na 对的位置都可以表征，因此我们表明，即使是大量合成每个材料，也可以通过电化学方法进行。我们对制备的 Na1/2CoO2 和 Na2/3CoO2 有序相的物理性质进行了表征和比较。电化学过程被证实是一种精确的连续研究方法，可以为这种复杂的体系提供新的研究途径，并为具有非常狭窄的存在范围的材料合成提供新的方法。
