Chemical Sciences and Engineering Division, Argonne National Laboratory , 9700 South Cass Avenue, Argonne, Illinois 60439, United States.
National High Magnetic Field Laboratory , 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States.
ACS Appl Mater Interfaces. 2017 Dec 20;9(50):43632-43639. doi: 10.1021/acsami.7b13018. Epub 2017 Dec 6.
The development of highly reversible multielectron reaction per redox center in sodium super ionic conductor-structured cathode materials is desired to improve the energy density of sodium-ion batteries. Here, we investigated more than one-electron storage of Na in NaVCr(PO). Combining a series of advanced characterization techniques such as ex situ V solid-state nuclear magnetic resonance, X-ray absorption near-edge structure, and in situ X-ray diffraction, we reveal that V/V and V/V redox couples in the materials can be accessed, leading to a 1.5-electron reaction. It is also found that a light change on the local electronic and structural states or phase change could be observed after the first cycle, resulting in the fast capacity fade at room temperature. We also showed that the irreversibility of the phase changes could be largely suppressed at low temperature, thus leading to a much improved electrochemical performance.
在钠离子超离子导体结构阴极材料中，每个氧化还原中心都具有高度可逆的多电子反应，这是提高钠离子电池能量密度的理想选择。在此，我们研究了在 NaVCr(PO) 中超过一电子存储的 Na。通过结合一系列先进的表征技术，如原位 V 固体核磁共振、X 射线吸收近边结构和原位 X 射线衍射，我们揭示了材料中 V/V 和 V/V 氧化还原对可以被访问，从而导致 1.5 电子反应。我们还发现，在第一次循环后，局部电子和结构状态或相变化的轻微变化可以被观察到，从而导致在室温下快速的容量衰减。我们还表明，在低温下可以大大抑制相变化的不可逆性，从而导致电化学性能得到很大改善。
