by Marian Cabañero, CICenergigune
Raman spectroscopy is a vibrational characterization technique that provides unique structural information at atomic scale. It provides a structural fingerprint that allows the identification of organic and inorganic compounds [1].
The phenomenon of Raman scattering was discovered in 1928 by Chandrasekhara Venkata Raman. After discovering the nature of light scattering that caused the blue colour of water in 1923, this Indian physicist was honored for his discovery with the 1930 Physics Nobel Prize. But the first prototype of a commercial instrument was developed in 1974. More information about the historical evolution of Raman spectroscopy can be found in [1].
Raman spectroscopy works by the excitation of the sample with a monochromatic light source (usually a laser) and detecting the scattered light [2]. The main advantages are: it allows easy interpretation and identification of molecules, it is a non-destructive technique (under certain excitation conditions) and it presents high spatial resolution (up to 1 micrometer). The main disadvantages are the fluorescence background [3], poor sensitivity or reproducibility [1].
Raman spectroscopy is a standard technique for the study of lithium ion batteries (see a review of its application in this field [2]), especially for graphite (negative electrode in Li-ion batteries) as it is one of the most sensitive tools for studying the structural properties of carbonaceous materials [2][4].
Why is Raman spectroscopy useful for the CoFBAT project?
Raman spectroscopy is employed at CICenergigune in order to better understand the modifications that occur in the active materials during battery cycling so as to identify degradation phenomena occurring when the materials that are being developed within the project are combined and integrated in full cells. This technique has been also employed to detect the formation of impurities during the up-scaling of the synthesis processes.
As an example, the figure below shows the Raman spectrum of the silicon-graphite right after its production (material to be used in new batteries). The following bands (fingerprints) can be identified:
· Crystalline Silicon: 287, 515 and 937 cm-1
· Graphite: 1340 and 1608 cm-1
As not further bands were detected, this means that the material produced by IFE does not contain impurities, which could be detrimental for the performance and the life expectancy.
This characterized pristine material is used in CoFBAT as a reference when post-mortem analysis are performed to aged batteries. Raman spectroscopy allows to study the crystallinity lost from silicon particles, the apearance of new bands from the SEI, disordering of the graphite (ratio between G and D bands at 1340 and 1680 cm-1), etc.
[1] Stancovski, V., Badilescu, S. In situ Raman spectroscopic–electrochemical studies of lithium-ion battery materials: a historical overview. J Appl Electrochem 44, 23–43 (2014). https://doi.org/10.1007/s10800-013-0628-0
[2] Baddour-Hadjea, R., Pereira-Ramos J-P, Chem. Rev. 2010, 110, 3, 1278–1319. https://doi.org/10.1021/cr800344k
[3] Dong Wei, Shuo Chen & Quan Liu (2015) Review of Fluorescence Suppression Techniques in Raman Spectroscopy, Applied Spectroscopy Reviews, 50:5, 387-406. https://doi.org/10.1080/05704928.2014.999936
[4] M.A. Cabañero, M Hagen, E. Quiroga-González, Electrochimica Acta, Volume 374,2021,https://doi.org/10.1016/j.electacta.2020.137487.
