Heo Jongwook W, Bu Hyeri, Hyoung Jooeun, Hong Seung-Tae
Department of Energy Science and Engineering, DGIST (Daegu Gyeongbuk Institute of Science and Technology), Daegu 42988, Republic of Korea.
Inorg Chem. 2020 Apr 6;59(7):4320-4327. doi: 10.1021/acs.inorgchem.9b03160. Epub 2020 Mar 13.
A new type of ammonium vanadium bronze, (NH)VO, was synthesized by the hydrothermal method. The triclinic crystal structure (1̅) is successfully identified by the single-crystal X-ray diffraction method. The layered structure is similar to that of other vanadium bronzes but with an unprecedented stoichiometry and crystal structure. The structure is composed of a stack of VO layers along the axis, and two NH ions occupy the interlayer space per formula unit. Each ammonium ion is hydrogen-bonded to four lattice oxygen atoms, resulting in a stable structure with a large interlayer space, thus enabling the intercalation of various guest ions. Lithium ions are electrochemically intercalated into (NH)VO, with an initial discharge capacity of 232 mAh g and an average discharge voltage of 2 V (vs Li/Li). Upon the first discharge, lithium ions are inserted, whereas ammonium ions are extracted. Upon charging, a reverse reaction takes place. However, only a fraction of the extracted ammonium ions are reaccommodated. Despite the small quantity, the reinsertion of ammonium ions contributes crucially to the structural stability, improving the electrochemical performance. These results could provide a general understanding of the intercalation mechanism of host materials containing ammonium ions. In addition, (NH)VO intercalates Na ions reversibly, implying a potential capability as a host material for other guest ions.
通过水热法合成了一种新型铵钒青铜(NH)VO。采用单晶X射线衍射法成功确定了其三斜晶体结构(1̅)。该层状结构与其他钒青铜类似，但具有前所未有的化学计量比和晶体结构。结构由沿轴堆叠的VO层组成，每个化学式单元有两个NH离子占据层间空间。每个铵离子通过氢键与四个晶格氧原子相连，形成具有大层间空间的稳定结构，从而能够嵌入各种客体离子。锂离子通过电化学方式嵌入(NH)VO中，初始放电容量为232 mAh g，平均放电电压为2 V(相对于Li/Li)。首次放电时，锂离子插入，铵离子被提取。充电时，发生逆反应。然而，只有一小部分被提取的铵离子重新容纳。尽管数量少，但铵离子的重新插入对结构稳定性至关重要，提高了电化学性能。这些结果可以提供对含铵离子主体材料嵌入机制的一般理解。此外，(NH)VO可逆地嵌入Na离子，这意味着它有作为其他客体离子主体材料的潜在能力。
