Influence of Helium on Microstructure and Electrochemical Properties of LiFePO4 Thin Films Electrodes

摘要:

提出利用氦渗透法优化LiFePO4材料的结晶生长过程，达到提高材料电化学性能的目的。采用磁控溅射法制备含氦LiFePO4薄膜电极，利用扫描电镜观察样品的微观形貌，发现样品表面与截面皆呈现多孔结构。用X射线衍射仪分析含氦LiFePO4薄膜电极的晶体结构。结果表明，氦渗入薄膜后显著增强了材料在29.81o的衍射峰强度，而此处正对应了锂离子在LiFePO4材料中的扩散路径（[010] 方向）。这表明含氦LiFePO4薄膜中存在有利于材料脱锂/嵌锂的结晶择优生长取向，会导致薄膜电极电化学性能的提高。

Abstract:

The changes of the crystal orientation and lattice defects have a considerable impact on the electrochemical performances of lithium ion electrodes. Here, a new method of controlling the crystal growth of the LiFePO4 films by helium permeation was developed. The helium-permeated LiFePO4 thin film cathodes were prepared by radio frequency (RF) magnetron sputtering deposition. The morphologies of the helium-permeated LiFePO4 samples characterized by scanning electron microscope (SEM) presented pore structure. The X-ray diffraction (XRD) results of the LiFePO4 thin film cathodes indicate that the permeation of helium results in a noticeable increase of peak intensity at the 29.81o, which is normal to the pathway for lithium ion conduction (the [010] direction). It is concluded that there exists a preferential crystal growth orientation of (010) face which is in favor for the reversible insertion/de-insertion of Li ions, and therefore leading to the improvement in electrochemical performance of LiFePO4 samples.