Amorphous FePO4 as 3 V cathode material for lithium secondary batteries
Amorphous FePO4 as 3 V cathode material for lithium secondary batteries
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DOI：
10.1039/b200901c
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发表时间：
2002-05
影响因子：
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通讯作者：
Young-Sik Hong;K. Ryu;Y. Park;Min Gyu Kim;J. Lee;S. Chang
中科院分区：
文献类型：
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作者：
Young-Sik Hong;K. Ryu;Y. Park;Min Gyu Kim;J. Lee;S. Chang
采用差热-热重分析（DTA-TGA）、X射线衍射（XRD）、X射线吸收光谱（XAS）、扫描电镜（SEM）、循环伏安（CV）和充放电循环等方法研究了非晶态和六方晶FePO 4·xH 2 O（x = 2，1，0）粉体的结构和电化学性能。在380 °C下，非晶态FePO 4·2 H2O通过非晶态FePO 4·H2O和FePO 4相转变为六方相FePO 4。可逆的锂插入和提取到和从非晶FePO 4发生在2.8和3.2 V相对于Li/Li+，分别，这是低于那些橄榄石结构的LiFePO 4的电位。所有样品在第1次循环时均显示出大的容量损失，但在17 mA g-1的电流密度下，它们的放电容量从65 mA h g-1（第2次循环）逐渐增加到75 mA h g-1（第15次循环），并保持到第50次循环。还研究了非晶FePO 4的放电/充电对电流密度（17、34和85 mA g-1）和工作温度（20、50和80 °C）的依赖性。Fe K边X射线吸收光谱已在非晶LiyFePO 4上进行，以确定在放电过程中的局部电子和几何结构的变化。对于Fe的K-边缘，前边缘和边缘根据LiyFePO 4中的Fe 3 +/Fe 2+氧化还原对的氧化态而移动。
The structural and electrochemical properties of amorphous FePO4·xH2O (x = 2, 1, 0) and hexagonal FePO4 powders have been investigated using differential thermal analysis–thermogravimetry (DTA–TGA), X-ray diffractometry (XRD), X-ray absorption spectroscopy (XAS), scanning electron microscopy (SEM), cyclic voltammetry (CV), and charge/discharge cycling. On heating, amorphous FePO4·2H2O was transformed into hexagonal FePO4 at 380 °C, through amorphous FePO4·H2O and FePO4 phases. Reversible lithium insertion and extraction into and from the amorphous FePO4 occurred at 2.8 and 3.2 V vs. Li/Li+, respectively, which potentials are lower than those of the olivine-structured LiFePO4. All samples show a large capacity loss at the 1st cycle, but their discharge capacities are gradually increased from 65 mA h g−1 (2nd cycle) to 75 mA h g−1 (15th cycle) at a current density of 17 mA g−1 and kept up to the 50th cycle. The discharge/charge dependence on the current densities (17, 34, and 85 mA g−1) and operating temperatures (20, 50, and 80 °C) were also investigated for amorphous FePO4. Fe K-edge X-ray absorption spectroscopy has been performed on amorphous LiyFePO4, to determine the changes in the local electronic and geometric structures during the discharge. For the Fe K-edge, the pre-edge and edge are shifted in accordance with the oxidation state of the Fe3+/Fe2+ redox couple in LiyFePO4.