Spatial Resolution of Micro-Raman Spectroscopy for Particulate Lithium Iron Phosphate (LiFePO₄)

The fast-growing lithium battery industry needs quality control tools. Micro-Raman spectroscopy is a popular technique for structural characterization and can be used for impurity revealing. The problem is that the method resolution can be appropriately quantified for a sample with a simple planar geometry, like a single crystal. Much less studied are powders consisting of particles of irregular shape and sizes close to the wavelengths of the probing laser irradiation. In this work, we have examined a series of single particles of transparent lithium iron phosphate (LiFePO₄) on a Si substrate. This model experiment revealed the significant spread of local optical properties, blocking properties of pores, and abnormal enhancement of Raman response from a bottom Si layer under some of particles. As the result, we can conclude that vertical resolution of micro-Raman spectroscopy for particulate systems with inhomogeneity of shape and structure should be described not quantitative, but qualitative, and the Raman probing of powder samples can be both multilayer and superficial.