Chemical speciation and mapping of the Si in Si doped LFP ingot with synchrotron radiation technique

Development of LiFePO4 cathode material with high cycle life through Si doping (substituting Si at P sites of LiFePO4) has shown that small changes to the structure of LiFePO4 can significantly affect the performance of Li ion batteries. However, determining the nature of elemental doping and their effects on the electronic and atomic structure of LiFePO4 remains challenging. Here we present x-ray absorption spectroscopy and x-ray fluorescence mapping as ideal characterization methods for understanding the effect of Si doped LiFePO4 prepared using a melt-synthesis process. x-ray absorption spectra of silicon doped LiFePO4 indicate subtle changes in the local structure surrounding the dopants compared to SiO2 and amorphous glass phases formed as impurities in Si containing undoped samples. The study of Fe and P K-edges x-ray absorption spectra illustrates the effect of Si in the LiFePO4 structure in doped and impurity containing samples. Utilizing x-ray absorption spectroscopy, in conjunction with x-ray fluorescence mapping, has enabled a better overview of the non-uniform nature of prepared ingot samples. These results highlight the power of x-ray absorption spectroscopy as a tool for better understanding the structure of modified LiFePO4 and subsequently designing materials for Li ion batteries.