Synthesis and performance of Mg-doped non-stoichiometric lithium iron phosphate

doi:10.16085/j.issn.1000-6613.2017-0623

Abstract

Abstract: LiFe_0.94Mg_0.04PO₄/C, LiFe_0.96Mg_0.02PO₄/C and LiFe_0.96Mg_0.04PO₄/C have been synthesized by a solid-state reaction using Li₂CO₃,FeC₂O₄·2H₂O,MgO,and NH₄H₂PO₄ as starting materials and C₆H₆O₆ as carbon source. X-ray diffraction(XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy(SEM),transmission electron microscopy(TEM)and Fourier transform infrared spectroscopy(FTIR)were used to investigate the effect of Fe²⁺ or Mg²⁺ on the morphology and structure of the prepared materials. The electrochemical performances of different samples were characterized by galvanostatic charge/discharge test and electrochemical impedance spectroscopy(EIS). The results indicated that the crystal lattice parameters and the Li-Fe anti-site defects were reduced, whereas the content of conductive Fe₂P in non-stoichiometric lithium iron phosphate increased when Mg was doped, and LiFe_0.94Mg_0.04PO₄/C exhibited the highest discharge performance, rate capability and excellent cycle performance,whose initial capacities were 161.2mAh/g at 0.1C,and 74.7mAh/g at 20C and the retention rate was 97.3% at 20C after 500 cycles.

Key words: lithium iron phosphate, non-stoichiometric, electrochemistry, nanomaterials, synthesis, optimization

摘要： 以Li₂CO₃、FeC₂O₄·2H₂O、MgO、NH₄H₂PO₄为原料，无水葡萄糖为碳源，采用高温固相合成法制备获得4% Mg²⁺掺杂的LiFe_0.96Mg_0.04PO₄/C，并通过分别减少2% Mg²⁺和2% Fe²⁺合成了非化学计量比的LiFe_0.96Mg_0.02PO₄/C和LiFe_0.94Mg_0.04PO₄/C材料。利用X射线衍射（XRD）、X射线光电子能谱（XPS）、红外光谱分析（FTIR）、扫描电镜（SEM）、透射电镜（TEM）表征了Fe²⁺和Mg²⁺含量的变化对材料的物质构成、形貌及结构的影响。通过交流阻抗（EIS）及恒流充放电循环测试对材料的电化学性能进行表征。研究结果表明Mg²⁺均匀地掺入LiFePO₄的晶格中，非化学计量比的LiFe_0.96Mg_0.02PO₄/C和LiFe_0.94Mg_0.04PO₄/C材料的晶胞体积减小，导电性杂质Fe₂P的含量升高，Li-Fe错位现象减少；其中，LiFe_0.94Mg_0.04PO₄/C表现出最优的充放电容量、倍率性能以及循环性能，0.1C、20C倍率下的放电比容量分别为161.2mAh/g、74.7mAh/g，500次循环后20C的容量保持率达到97.3%。

关键词: 磷酸铁锂, 非化学计量比, 电化学, 纳米材料, 合成, 优化

CLC Number:

TM912.9

FENG Ying, LIU Kai, HUO Taotao, ZHANG Minqing, ANJUM Abdul Waqas. Synthesis and performance of Mg-doped non-stoichiometric lithium iron phosphate[J]. Chemical Industry and Engineering Progress, 2017, 36(08): 3006-3012.

冯颖, 刘凯, 霍涛涛, 张敏卿, Abdul Waqas ANJUM. 镁掺杂的非化学计量比磷酸铁锂的制备及性能[J]. 化工进展, 2017, 36(08): 3006-3012.

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