Abstract
Time-of-flight secondary ion mass spectrometry (TOF-SIMS) using a focused ion-beam scanning electron microscope (FIB-SEM) is a promising and economical technique for lithium detection and quantification in battery materials because it overcomes the limitations with detecting low Li content by energy dispersive spectroscopy (EDS). In this work, an experimental calibration curve was produced, which to our best knowledge allowed for the first time, the quantification of lithium in standard nickel manganese cobalt oxide (NMC-532) cathodes using 20 nm resolution. The technique overcomes matrix effects and edges effects that makes quantification complex. This work shows the high potential of TOF-SIMS tool for analytical characterization of battery materials, and demonstrates its tremendous capabilities towards identification of various chemical or electrochemical phenomena in the cathodes via high-resolution ion distributions. Various phenomena in the ion distributions are also assessed, such as edge effects or measurement artifacts from real signal variations.
Highlights
Scanning electron microscopes (SEM) are essential tools for microstructure characterization and microanalysis of new materials, and their ease of use has made them one of the most widespread tools for analysis of structures down to the nanometer scale[1]
Under similar bombardment conditions and ion dose, our experiments show that Li intensity is 1.76 times higher in the compound that in the pure material
A TOF-Secondary ion mass spectrometry (SIMS) detector mounted on a focused ion-beam scanning electron microscope (FIB-SEM) platform was used to detect lithium in standard NMC cathodes with different state-of-charge, and this technique is proposed as a solution to the detection limitation of energy-dispersive x-ray spectrometer (EDS) for lithium
Summary
Scanning electron microscopes (SEM) are essential tools for microstructure characterization and microanalysis of new materials, and their ease of use has made them one of the most widespread tools for analysis of structures down to the nanometer scale[1]. Solution to the detection limits of EDS, since being a physical sputtering technique, it relies on collision cascades created by energetic ions rather than electronic transitions following excitation of an atom by a primary beam electron It allows high surface sensitivity, as well as full coverage of the elements, including lithium. Edge effects can lead to misinterpretation of the content of an element in a sample by showing regions with higher intensities that are artifacts related to the increased sputtering In semiconductor materials, these edges effects are mainly seen at the edges of the crater formed during SIMS analysis. Considering that (a) battery materials are inhomogeneous and (b) the cycling process creates defects in the particles (cracks, pores, etc...), identifying the edge effect is made more complex and this gating technique cannot be applied
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