Battery Compound Analysis Using Raman and FTIR Spectroscopy

Raman and FTIR instruments In situ and Ex situ analysis

Thermo Scientific Raman and FTIR instruments can be used for both in situ and ex situ analysis. The term in situ is used to describe experiments in which the battery components are studied in an assembled cell under operating conditions. For example, in situ analysis can reveal chemical reactions that take place during charge and discharge cycles.

In situ analysis is generally used to research and develop new battery materials. Once a formulation is designed and a candidate battery is piloted and produced, researchers turn their attention to failure modes and performance differences. For example, what makes one production run work better than another? Why did one battery fail yet others from the same batch work fine?

To answer these questions, researchers carefully disassemble a battery cell to examine the individual components. This is called ex situ analysis because the battery components are removed from the operating battery cell. The disassembly and analysis must be carried out in an inert environment such as an argon-filled glove box to protect the battery components from moisture and oxidation. For example, the anode-separator-cathode sandwich must be carefully separated and rinsed to remove excess electrolytes.

Compact spectrometers such as Thermo Scientific Nicolet Summit FTIR instruments can be installed inside the glove box to analyze the samples. Otherwise, the sample must be removed from the glove box and transferred in a sealed transfer cell (available from Thermo Fisher Scientific) to an external instrument for analysis. 

Unlike other lithium-ion battery testing techniques, Raman spectroscopy can often identify battery materials within seconds with minimal or no sample preparation. With today’s Thermo Scientific Raman instrumentation and software, these tools can now be operated by users of all levels, including those with limited scientific expertise.

Raman spectroscopy is used to identify the chemical properties of raw materials for cathodes, anodes, and electrolytes used in lithium-ion batteries. It is also used to ensure that the final battery includes the specific composition of materials required for top performance.

Ex situ Raman analysis of anode SEI layer

One important focus of Li-ion battery research is understanding why performance degrades over time. Research indicates that the solid electrolyte interphase (SEI) layer formed on the surface of the electrode is key to performance. The SEI layer, which is formed by the deposition of organic and inorganic compounds during the first several charge/discharge cycles, stabilizes the electrode from further decomposition and promotes reversible capacity. Because the SEI layer is complex, many analytical techniques can contribute to understanding its formation and behavior.

The figure shows a micrograph of the anode cross‐section after extraction from a used battery in an argon-filled glove box, with the copper current collector in the center and anode material coated on both surfaces. Superimposed is the color-coded Raman image created on a Thermo Scientific DXR3xi Raman Imaging Microscope from the spectral differences shown by the inset Raman spectra. The Raman image clearly shows that the coating on one side of the copper current collector is dominated by carbon black (labeled red) while the other side has a much greater density of the active graphite phase (labeled blue).  

This example demonstrates the advantage of Raman imaging over traditional single-point measurements. The major differences in the two coatings could easily have been missed by single-point measurements depending on where the points were measured.

Ex situ Raman analysis of an anode SEI. Micrograph shows a cross-section of a Li-ion battery anode. Raman image indicates a dramatic difference in the anode coating on each side of the copper current conductor, contrasting carbon black (red) on one side vs the active graphite phase (blue) on the other. Colors were assigned by multivariate curve resolution (MCR) analysis. Inset shows Raman spectra, color-coded to the areas in the Raman image. Samples were extracted in an argon-filled glove box and sealed in a Thermo Scientific transfer cell for analysis on a predecessor of the DXR3xi Raman Microscope.

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