The power of vibrational spectroscopy

Lithium-ion batteries are now virtually ubiquitous, powering everything from cell phones and laptops to vacuum cleaners and electric vehicles.

This has led to a constant demand for higher capacity energy storage in ever-smaller formats, driving the development of new materials that can bolster device performance. However, any tweaks to electrode composition must be thoroughly characterised and tested under operating conditions before they can be cleared for use in commercial products, which can be both time consuming and expensive. Additionally, many of the analytical technologies traditionally used in this process require highly skilled personnel to interpret the results, limiting the pool of qualified operators and slowing the rate at which novel battery components can be developed and cleared for manufacture. Fortunately, modern vibrational spectroscopy solutions — such as Raman and Fourier transform infrared (FTIR) instruments — are becoming increasingly intuitive, allowing a greater number of individuals to quickly become proficient in their operation. This can help to lighten the workload for more experienced team members, as well as speed up analyses for increased plant throughput.

What is Raman?

Raman spectroscopy is a non-destructive technique that relies on the inelastic scattering of incident photons, from ultraviolet through to visible and near-infrared, to determine a sample’s spectral fingerprint. In battery development, it can be used to identify compound constituents, characterise molecular structures, evaluate morphologies, and monitor dynamic processes in cathodes, anodes and electrolytes. Raman imaging takes this concept a step further, allowing users to make thousands of spectral measurements over an area of interest in quick succession to create a 2D snapshot of a surface, rather than just capturing data from a single point.

In situ inspection

Whether used for single- or multi-point analysis, Raman technologies play an important role in battery R&D, especially for in situ and operando applications, where battery components are studied within an assembled cell under a variety of operating conditions. This allows their performance to be evaluated over entire charge and discharge cycles — assessing everything from ionic dispersion to electrolyte degradation — giving researchers added confidence that their novel designs will stand up to the rigours of everyday use. In situ measurements are particularly helpful in the investigation of lithiation and delithiation, two opposing processes that describe the movement of lithium ions within the battery during charging and discharging cycles. Raman spectral data is also proving invaluable in the search for alternative carbon allotropes that can be substituted for graphite, helping researchers to determine everything from the number of sheets in a graphene stack to the diameters of single-wall nanotubes, as well as providing vital information about structural defects or disorders. Furthermore, it can be used to study the degree of association of electrolyte ions in solutions and polymers, a factor that directly affects battery performance.

Vibrational versatility

In addition to excelling in the measurement of solids and solutions, Raman is also capable of monitoring gaseous emissions during in situ battery tests, providing an early warning of cell damage prior to any visible signs appearing. This can help to establish a battery’s susceptibility to overheating, overvoltage and mechanical stresses, informing the development of safer, more resilient products. Thanks to the versatility of Raman techniques, they are not limited solely to product development applications, and can also be used to determine the purity of raw materials used in the manufacturing process. Many state-of-the-art instruments feature their own material libraries that facilitate the detection of contaminants, bolstering production QC by minimising the chances of downstream defects.

Infrared insights

A complementary technology often employed alongside Raman in many battery R&D and manufacturing applications is FTIR spectroscopy. Like Raman, FTIR is also a non-destructive technique, making it ideal for examining the behaviour of various regions of battery cells while in situ, aiding the rapid identification of changes that could affect product lifespan and safety. It can also be applied during raw material QC to assess incoming goods, and is widely used for ex situ characterisation of lithium salts, electrolyte formulations and catalytic systems. FTIR again comes into play during final product QC, helping to confirm that regulatory and stakeholder specifications have been met.

Keeping pace

QC in battery applications is becoming more important than ever, as manufacturers look to squeeze every last drop of efficiency out of existing energy storage solutions, as well as looking ahead to emerging technologies. This has led to vibrational spectroscopy becoming a mainstay of development and production lines around the globe, offering unparalleled insights into the characteristics of novel materials, while also enabling the early detection of impurities and defects during the manufacturing process. With production pressures only likely to increase as time goes by, lithium-ion battery manufacturers must be sure to include Raman and FTIR technologies in their arsenals if they are to produce high-quality products in the vast quantities needed to keep pace with market demands.

Top image credit: iStock.com/KanawatTH