Raman and FTIR spectroscopy for battery components
Raman spectroscopy uses the interactions of light and molecular vibrations to produce spectra that are used to identify materials, characterize molecular structure, evaluate morphology, and monitor dynamic processes. Raman microscopy applies Raman analysis to small sample domains, allowing visualization and mapping of components and structural differences.
Thermo Scientific Raman instruments are invaluable tools across a range of battery applications. Raman technology is fast, non-destructive, requires minimal sample preparation, and can be used in situ or ex situ.
Like Raman, Fourier transform infrared (FTIR) spectroscopy provides molecular information about a sample. Its information is complementary in nature to Raman. Thermo Fisher Scientific offers a range of Thermo Scientific Nicolet FTIR spectrometers for use in battery research, development, and production. With advantages in compactness, multiplexing, throughput, and precision, FTIR has become a technique of choice for compound identification in many labs.
Battery research and development using Raman and FTIR spectroscopy
Raman microscopy is primarily used in battery research and development for characterizing new battery materials and components, investigating changes that occur during charge and discharge cycles, and analyzing failures of battery components. Raman spectroscopy is used to analyze various components of batteries, including cathode, anode and electrolyte. Cathode (such as LiMnO4) and anode (graphite) materials in batteries fade over time, and Raman spectroscopy is used to analyze the molecular structures of such components to understand rate of degradation. This helps further research and understand ways for slowing down the degradation process.
Raman spectroscopy can also assess the degree of association for electrolyte ions in solutions as well as polymeric materials, which has a direct correlation to battery performance. The method can also provide insight into the polymer matrix and how additives can affect its crystallinity, which also impacts performance.
In battery materials research, FTIR can be used to identify lithium species and provide highly precise information about samples’ chemical bonding, functional groups, and changes during chemical reactions. This makes FTIR a powerful technique for both reaction monitoring and finished product quality assurance.
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.
Raman and FTIR sample data for battery components
Rapid battery materials analysis with minimal sample preparation using Raman spectroscopy
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.
Raman spectra of battery-grade lithium hydroxide batches
Four batches of battery-grade lithium hydroxide salts were analyzed on the Thermo Scientific DXR3 SmartRaman Spectrometer to check for contaminants. The Raman spectrum in red (bottom) shows no contaminants, while the spectra in violet, green, and blue all indicate the presence of carbonate contaminants (regions below 200 cm-1).
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.
Lithium salts characterization with FTIR analysis
FTIR spectroscopy is widely used to characterize materials across many applications. Lithium and other salts used in batteries, however, are extremely reactive and must be analyzed in an inert environment like an argon-filled glove box.
The compact size and high sensitivity of the Nicolet Summit X FTIR Spectrometer enable it to measure attenuated total reflection (ATR) spectra within an argon-purged glove box using remote control. The intuitive Thermo Scientific OMNIC Paradigm Software (included) can be used to obtain spectra as the sample degrades or to compare spectra from good vs failed samples.
The figure shows a time series of lithium hexafluorophosphate spectra, analyzed overnight at half-hour intervals, charting its degradation over time. FTIR analysis can also be used to verify specific lithium salts and their structure, detect contamination, and study reaction rates in different environments.
FTIR time study showing degradation of lithium salts over time. A several-year-old sample of lithium hexafluorophosphate was analyzed on a predecessor of the Nicolet Summit X FTIR Spectrometer with an attenuated total reflection (ATR) accessory in an argon-filled glove box. In a series of spectra acquired every half hour overnight, the shoulder near 820 cm-1 (corresponding to the hexafluorophosphate) decreased, suggesting further decomposition of the sample over time.
Raman and FTIR instruments use cases in battery research and manufacturing
Selected Raman and FTIR spectroscopy use cases for battery technology
| Challenge | Technologies | Solution | Resources |
| Profile battery components ex situ without missing variability across an area | Raman | Raman microscopy can consolidate measurements of a component area or cross-section | App note: Ex situ Raman analysis of Li-ion batteries |
| Identify phases and determine structures in anodes and cathodes | Raman | Raman microscopy can visually show the spatial distribution of different phases of the same material with different performance characteristics | App note: Raman analysis of lithium-ion batteries – Part I: Cathodes |
| App note: Raman analysis of lithium-ion batteries – Part II: Anodes | |||
| Trace and map anode composition across charge and discharge cycles | Raman | Raman microscopy can be used for in situ monitoring of changes on electrode surfaces during charge/discharge cycles | App note: In situ Raman analysis of Li-ion batteries |
| Confirm the presence of specific carbon allotropes as anode components and in hybrid materials | Raman | Raman spectroscopy is particularly adept at the analysis of allotropes of carbon, including carbon in hybrid materials | App note: Raman analysis of lithium-ion batteries – Part II: Anodes |
| Understand the association of ionic species and distribution of components in solid polymer electrolytes (SPEs) | Raman | Raman microscopy can be used to visualize the spatial distribution of components in SPEs and indicate ionic associations | App note: Raman analysis of lithium-ion batteries – Part III: Electrolytes |
| Rapidly characterize lithium, metal oxide, and lithium compounds | Raman | Thermo Scientific Raman instruments can analyze these compounds quickly with minimal sample preparation | Blog post: Using Raman spectroscopy during lithium-ion battery manufacturing |
| Differentiate carbon allotropes, reveal anode material structure, and track changes during usage | Raman | Raman spectroscopy is particularly useful for distinguishing between different allotropes of carbon and evaluating the structural quality of these materials | App note: Raman analysis of lithium-ion batteries – Part II: Anodes |
| Map degradation of the anode SEI layer | Raman | Raman microscopy can be used for visualizing changes to electrode materials and component distributions after a cell has been used | App note: Ex situ Raman analysis of Li-ion batteries |
| Characterize lithium and other highly reactive salts | FTIR | Compact Thermo Scientific FTIR instruments can measure sample spectra within an argon-purged glove box using remote control | App note: FTIR characterization of lithium salts in an inert atmosphere |
| Monitor battery off-gassing or chemicals released during a fire, short circuit, or other hazardous conditions | FTIR | Thermo Scientific Antaris IGS system with Heated Valve Drawer can quantify release of HF and other fluorinated gasses under overtaxed conditions like a vehicle crash | Tech note: Gas-phase FTIR for smoke toxicity measurements |
Abbreviations: FTIR = Fourier transform infrared spectroscopy; SEI = solid electrolyte interface; SPE = Solid polymer electrolytes.
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