Microstructural Characteristics of Hydrothermally Synthesized LiFePO_4 and Relevant Impacts on the Electrochemical Performance

Phospho-olivine LiFePO 4 has been prepared using a facile hydrothermal method by optimizing the reaction temperatures.Structural and morphological properties of the as-prepared LiFePO 4 powders are systematically characterized using X-ray diffraction (XRD),scanning electron microscopy (SEM),transmission electron microscopy (TEM),infrared spectra,UV-vis spectra,and M ssbauer spectroscopy.It is demonstrated that the samples prepared in the temperature range from 160 to 200 ℃ crystallize in a single phase of phospho-olivine structure.All particles are rod-like,showing dimensions of approximately 150～200 nm in width and 500～600 nm in length with a preferential growth direction of [001].Within the lattice of LiFePO 4 rods,Fe 2+ ions partially disorderly occupy the Li + sites,which increases the cell volume.The electrochemical performance of LiFePO 4 is investigated by charge/discharge experiments.It is found that LiFePO 4 rods prepared at 200 ℃ deliver a specific discharge capacity of 147 mAh g-1,which is apparently superior to those prepared at lower reaction temperatures like 160 and 180 ℃.This observation is explained in terms of the thinner surface noncrystalline layer and lower level of Fe 2+ disorderly occupying the Li + sites.     

MFe2O4(M=Co,Zn)中空微球的气泡模板法合成及在锂离子电池中的应用

本文设计并开发了一种气泡模板辅助合成方法,并应用于制备具有中空结构的自组装铁酸盐微球. 采用该方法获得了颗粒尺寸为350nm、颗粒分布均匀的中空微球MFe2O4(M=Co,Zn). 把这两种中空结构材料作为锂电池负极,组装成电池后,在2 Ag-1的电流密度条件下进行充放电测试,发现CoFe2O4的首次放电容量达到1339 mAhg?1,首次充电容量为936 mAhg?1,20次循环后充电容量保持在446 mAhg-1;与之相比,ZnFe2O4的首次放电容量达到1402mAhg?1,首次充电容量为992 mAhg?1,20次循环后充电容量保持在634 mAhg?1. 这两种材料的电化学性能均优于文献报道的同类实心材料的性能,表明自组装中空结构在改善材料锂电性能方面有明显优势.