Studies of fast-ion conducting Li₃V₂(PO₄)₃ coated LiFePO₄ via sol-gel method

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• 作者：Xiaoping Zhang ; Huajun Guo ; ^{hjguo_csu@163.com} ; Xinhai Li ; Zhixing Wang ; Ling Wu
• 关键词：Lithium-ion battery ; Lithium iron phosphate ; Lithium vanadium phosphate ; Fast ion conductor ; Coating
• 刊名：Solid State Ionics
• 出版年：2012
• 期刊代码：96_01672738
• 类别：ch
• 出版时间：29 March, 2012
• 卷：212
• 期：Complete
• 页码：106-111
• 文件大小：1108 K

摘要

To improve the electrochemical performance and energy density, LiFePO₄ powders are firstly coated with the fast-ion conducting Li₃V₂(PO₄)₃ using a sol-gel process. X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS) and electrochemical measurements are used to study the structure and properties of the materials. The results show that a uniform coating layer of Li₃V₂(PO₄)₃/C exists on the surface of LiFePO₄/C particles. The modified sample contains olivine LiFePO₄ and monoclinic Li₃V₂(PO₄)₃ phases. Some V^3 + and Fe^2 + ions are doped into the lattices of LiFePO₄ and Li₃V₂(PO₄)₃ separately, resulting in the lattice contraction and the formation of lattice defects. Compared with the commercial LiFePO₄, the diffusion coefficient of lithium ion and exchange current density of modified LiFePO₄ is both improved by one order of magnitude. Electrochemical measurements indicate that the rate capability and cycle performance of LiFePO₄ are significantly enhanced by coating with Li₃V₂(PO₄)₃, especially at high current rates. At 5 掳C and 10 掳C rates, the modified LiFePO₄ exhibits the initial discharge capacities of 134.85 and 104.99 mAh g^鈭?#xA0;1 and capacity retentions of 93.79%and 94.53%after 190 cycles, respectively, whereas the commercial LiFePO₄ shows much lower capacities of 100.61 and 40.58 mAh g^鈭?#xA0;1 at the same current rates.