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

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 29.81°, 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.