The structure of a novel compound, LiFeV₂O₇, has been determined from single-crystal X-ray diffraction data. The phase crystallizes in the non-centrosymmetric monoclinic Cc space group. The structure can be described as a layered type compound alternating (Li,Fe)–O sheets and V–O chains that are perpendicular to the [101] direction. Within the (Li,Fe)–O sheets, “hexagonal” holes are formed and assembled into tunnels running parallel to the [201] direction and hosting the vanadium atoms. Original (V₄O₁₄)^8– strings are observed within the structure in association with well-known (V₂O₇)^4– pyrovanadate units. Both units alternate parallel to the [−101] direction. LiFeV₂O₇ displays a reversible insertion–deinsertion mechanism for Li⁺ ions. The theoretical capacity for the insertion of one Li⁺ into LiFeV₂O₇ reaches 97 mAh/g. When the compound is cycled between 3.50 and 2.35 V versus Li⁺/Li, the electrochemical curve displays an initial capacity of 100 mAh/g, with 85% of this capacity retained after 60 cycles. No evidence of the formation of Fe⁴⁺ upon oxidation to a high voltage was observed. LiFeV₂O₇ represents the first reported phase in the Li₂O–Fe₂O₃–V₂O₅ ternary diagram with electrochemical activities.

中文翻译：

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LiFeV ₂ O _7的合成，结构及电化学性质

已经从单晶X射线衍射数据确定了新型化合物LiFeV ₂ O ₇的结构。该相在非中心对称单斜Cc空间群中结晶。该结构可以描述为垂直于[101]方向的交替（Li，Fe）–O薄片和V–O链的层状复合化合物。在（Li，Fe）–O片中，形成“六角”孔并将其组装成平行于[201]方向延伸并包含钒原子的隧道。在结构中观察到原始的（V ₄ O ₁₄）^8–弦与已知的（V ₂ O ₇）^4–弦相关丙酮酸单位。两个单元都平行于[-101]方向交替排列。LiFeV ₂ O ₇显示了Li ⁺离子的可逆插入-去插入机制。将1个Li ⁺插入LiFeV ₂ O ₇的理论容量达到97 mAh / g。当化合物在相对于Li ⁺ / Li的3.50和2.35 V之间循环时，电化学曲线显示出100 mAh / g的初始容量，在60个循环后保留了该容量的85％。没有观察到氧化为高电压时形成Fe ^4+的证据。LiFeV ₂ O ₇代表Li _2中的第一个报告相具有电化学活性的O–Fe ₂ O ₃ –V ₂ O ₅三元图。