The hydrated iron fluoride (Fe₃F₈·2H₂O) with mixed valence cations is successfully synthesized through a rapid electrolytic synthesis route for the first time using low-concentration HF solution as fluorine source and cheap carbon steel as iron source. By controlling the value of current density, submicron structured hydrated iron fluoride with different grain sizes is obtained. The thermal behavior of Fe₃F₈·2H₂O under air atmosphere is studied. The product cooling to room temperature after heat treatment is FeF_2.2(OH)_0.8·0.33H₂O, which is determined by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), Fourier transform infrared spectrometer (FT-IR), and thermogravimetry/differential scanning calorimetry (TG/DSC). The evaluation of the electrochemical performance of FeF_2.2(OH)_0.8·0.33H₂O as a cathode for lithium batteries shows that it has an initial discharge capacity as high as 580 mAh g⁻¹ in a wide voltage range of 1.0–4.5 V at a current density of 20 mA g⁻¹, but the cycle performance is not very satisfactory, only 170 mAh g⁻¹ after 50 cycles.

Graphical abstract

中文翻译：

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电解合成铁基氟化物锂离子电池正极材料

以低浓度HF溶液为氟源，廉价碳钢为铁源，首次通过快速电解合成路线成功合成了混合价阳离子水合氟化铁（Fe ₃ F ₈ ·2H _{2 O）。}通过控制电流密度的大小，得到不同晶粒尺寸的亚微米结构水合氟化铁。研究了Fe ₃ F ₈ ·2H ₂ O在空气气氛下的热行为。热处理后冷却至室温的产物为FeF _2.2 (OH) _0.8 ·0.33H ₂ O，经X射线衍射(XRD)、X射线光电子能谱(XPS)、傅里叶变换红外光谱仪(FT- IR）和热重分析/差示扫描量热分析（TG/DSC）。_{对FeF 2.2} (OH) _0.8 ·0.33H ₂ O作为锂电池正极的电化学性能评估表明，其在1.0~4.5 V的宽电压范围内首次放电容量高达580 mAh g ^-1在电流密度为20 mA g ^-1时，但循环性能不是很理想，50次循环后只有170 mAh g ^-1。

图形概要