Gao He, Zhang Sen, Deng Chao
Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, Heilongjiang, China.
Dalton Trans. 2015 Jan 7;44(1):138-45. doi: 10.1039/c4dt02498b.
An iron-based mixed-polyanion compound, Li9Fe3(P2O7)3(PO4)2, is introduced as a possible cathode material for Li-ion batteries. Phase-pure Li9Fe3(P2O7)3(PO4)2 is successfully prepared by a sol-gel method, and its physicochemical properties are investigated in detail. Special attention is paid on making clear the variation of the phase composition with the annealing temperature and the effect of carbon coating on the electrochemical performance. Apparently phase-pure Li9Fe3(P2O7)3(PO4)2 can only be obtained in a narrow temperature range, either higher or lower annealing temperature outside this temperature range always leads to the impurity phase. The pristine Li9Fe3(P2O7)3(PO4)2 is suffering from its low electronic conductivity (10(-9) S cm(-1)) and theoretical capacity (85 mA h g(-1)), it has a first discharge capacity of only 36 mA h g(-1). Carbon coating is employed to improve the electrochemical performance. When the carbon content is 10 wt%, the discharge capacity of Li9Fe3(P2O7)3(PO4)2/C reaches the maximum value of 60 mA h g(-1). The electronic conductivity of the composite, the exact discharge capacity of Li9Fe3(P2O7)3(PO4)2 in the composite and the capacity retention of the composite after 30 cycles vary in the same fashion with an increase in carbon content, i.e. first quickly increase and then stabilize.
一种铁基混合聚阴离子化合物Li9Fe3(P2O7)3(PO4)2被作为锂离子电池的一种可能的正极材料引入。通过溶胶-凝胶法成功制备了纯相的Li9Fe3(P2O7)3(PO4)2，并对其物理化学性质进行了详细研究。特别关注了明确相组成随退火温度的变化以及碳包覆对电化学性能的影响。显然，只有在较窄的温度范围内才能获得纯相的Li9Fe3(P2O7)3(PO4)2，在此温度范围之外，较高或较低的退火温度总会导致杂质相。原始的Li9Fe3(P2O7)3(PO4)2由于其低电子电导率（10(-9) S cm(-1)）和理论容量（85 mA h g(-1)）而存在不足，其首次放电容量仅为36 mA h g(-1)。采用碳包覆来改善电化学性能。当碳含量为10 wt%时，Li9Fe3(P2O7)3(PO4)2/C的放电容量达到最大值60 mA h g(-1)。复合材料的电子电导率、复合材料中Li9Fe3(P2O7)3(PO4)2的准确放电容量以及复合材料在30次循环后的容量保持率随碳含量的增加以相同的方式变化，即先快速增加然后稳定。
