An ambiguity of laser-induced degradation in LiFePO4 and advantages of single-particle approach to Raman spectroscopy

Laser-induced degradation is a common issue for the Raman spectroscopy study of lithium battery materials. In this work, the combination of single-particle Raman measurements with scanning electron microscope imaging helped us reveal the variation of the decomposition pathways and products. For the first time, we observed possible laser-induced melting of the LiFePO4 particles and an unidentified decomposition product, an alternative to previously reported alpha-Fe2O3 and gamma-Li3Fe2(PO4)(3). These results and analysis of the time series of Raman measurements raise doubts about laser-induced heating. We suppose non-thermal amorphization and melting processes due to electronic system excitation by intraband transitions with the following covalent bond destabilization. The role of defects in laser-induced decomposition is discussed. We hope that this article could help develop a non-destructive tool for quality control and the study of the electrochemical or thermal degradation of LiFePO4.