磷酸钒锂正极材料的合成与性能研究

Synthesis and Electrochemical Characteristics of Cathode Materials Li_3V_2(PO_4)_3

本文以LiOH·H2O，NH4VO3，NH4H2PO4和柠檬酸等为原料采用流变相法成功地合成了磷酸钒锂化合物。利用XRD，TEM等手段对目标产物的结构和形貌进行了表征，结果表明：在800℃煅烧的样品具有单一纯相的单斜晶体结构。晶体颗粒分布在200—500nm范围，而且在颗粒表面包覆了一层碳，有利于材料的导电率的改善。对该材料的电化学性质进行了测试，实验发现：800℃煅烧的样品在0．1C和1C倍率电流条件下，首次放电比容量分别高达122．8和107mAh·g^-1，经过30次循环后容量衰减很少。交流阻抗谱证实了800℃煅烧的样品具有较高的电导率。本文对800℃煅烧的样品具有较好电化学性能的原因进行了初步讨论。

A novel rheological phase method was used to synthesize nanocrystalline Li3V2（PO4）3 compound. In this route, LiOH ·H2O, NH4VO3, NH4H2PO4 and citric acid were selected as starting materials to prepare precursor, and the Li3V2（PO4）3 was obtained by sintering precursor at different temperature for 8 h in flowing argon. The Li3V2（PO4）3 has been characterized by XRD and TEM techniques, the compound synthesized at 800 ℃ take on pure monoclinic crystal structure, the particle size of the samples are ranged from 200-500 nm and there is a layer of carbon particles on the surface of Li3V2（PO4）3 particles, which is available for enhancing the conductivity of LiaV2（PO4）3. The influence of sinterirlg temperatures on electrochemical properties of Li3V2（PO4）3 has been investigated also, the results showed that the Li3VE（PO4）3 synthesized at 800 ℃ exhibited the highest initial discharge capacity （122 mAh·g^-1 at 0.1C and 107 mAh·g^-1 at 1C, respectively） and good capacity retention in the voltage range of 3.0 -4.3 V. The electrochemical impedance spectroscopy （EIS） showed that the sample synthesized at 800 ℃ behaved the higher conductivity. The reasons for the excellent electrochemical performance of the carbon coated Li3V2（PO4）3 calcined at 800 ℃cathode material were presented also.