Kirsanova Maria A, Akmaev Alexey S, Gorbunov Mikhail V, Mikhailova Daria, Abakumov Artem M
Center for Energy Science and Technology, Skolkovo Institute of Science and Technology, Nobel Str. 3, 121205 Moscow, Russia.
Leibniz Institute for Solid State and Materials Research Dresden, Institute for Complex Materials, Helmholtzstraße 20, 1069 Dresden, Germany.
Molecules. 2021 Dec 24;27(1):86. doi: 10.3390/molecules27010086.
NaVO (η-NaVO) has been synthesized via solid-state reaction in an evacuated sealed silica ampoule and tested as electroactive material for Na-ion batteries. According to powder X-ray diffraction, electron diffraction and atomic resolution scanning transmission electron microscopy, NaVO adopts a monoclinic structure consisting of layers of corner- and edge-sharing VO tetragonal pyramids and VO tetrahedra with Na cations positioned between the layers, and can be considered as sodium vanadium(IV,V) oxovanadate NaVO(VO). Behavior of NaVO as a positive and negative electrode in Na half-cells was investigated by galvanostatic cycling against metallic Na, synchrotron powder X-ray diffraction and electron energy loss spectroscopy. Being charged to 4.6 V vs. Na/Na, almost 3 Na can be extracted per NaVO formula, resulting in electrochemical capacity of ~60 mAh g. Upon discharge below 1 V, NaVO uptakes sodium up to Na:V = 1:1 ratio that is accompanied by drastic elongation of the separation between the layers of the VO tetrahedra and VO tetragonal pyramids and volume increase of about 31%. Below 0.25 V, the ordered layered NaVO structure transforms into a rock-salt type disordered structure and ultimately into amorphous products of a conversion reaction at 0.1 V. The discharge capacity of 490 mAh g delivered at first cycle due to the conversion reaction fades with the number of charge-discharge cycles.
偏钒酸钠（η-NaVO）通过在抽真空密封的石英安瓿中进行固态反应合成，并作为钠离子电池的电活性材料进行了测试。根据粉末X射线衍射、电子衍射和原子分辨率扫描透射电子显微镜分析，NaVO具有单斜结构，由角共享和边共享的VO四方金字塔层以及VO四面体层组成，Na阳离子位于层间，可被视为钒（IV，V）氧钒酸钠NaVO(VO)。通过与金属Na进行恒电流循环、同步辐射粉末X射线衍射和电子能量损失谱研究了NaVO在Na半电池中作为正负极的行为。相对于Na/Na+充电至4.6 V时，每个NaVO化学式几乎可以脱出3个Na，电化学容量约为60 mAh g-1。在放电至1 V以下时，NaVO吸收钠直至Na:V = 1:1的比例，同时VO四面体层和VO四方金字塔层之间的间距急剧伸长，体积增加约31%。在0.25 V以下，有序的层状NaVO结构转变为岩盐型无序结构，并最终在0.1 V时转变为转化反应的非晶产物。由于转化反应，首次循环时的放电容量为490 mAh g-1，但随着充放电循环次数的增加而衰减。
