Electrochemical transport across lithium-ion composite electrodes are highly heterogeneous and non-uniform. Origins of such inhomogeneities are both due to intrinsic nature of the electrode active material as well as extrinsic factors such as composition (binder and conductive diluents) and processing conditions. The talk will provide an overview of two decades of work applying conventional as well as micro-Raman spectroscopy to obtain the chemical and morphological information on pristine and cycled lithium-ion battery electrodes^1-2. Topics to be presented include micro-Raman imaging of cycled Li_1-xNi_0.80Co_0.15Al_0.05 (NCA) electrodes highlighting the observation of a phenomenon called “carbon retreat” that eventually leads to capacity loss and degradation.^1-2 Further, based on the metal-oxygen vibrational modes of transition metal oxide cathodes, Raman spectroscopy has been used to measure the spectroscopic state of charge (SOC) of the electrode. The variation of this local spectroscopic SOC is sensitive to local lithium content and defects.^3-4 Using a SOC parameter that is based on both the area and intensity of the cathode Raman bands, we observed SOC gradients within cathode secondary particles on the electrode surfaces.⁴

In situ and ex-situ confocal Raman imaging has been applied to multi-lithium cathode systems Li₂MnO₃⁴ and Li₂Cu_0.5Ni_0.5O₂⁵ to understand formation of secondary phases and structural transitions during delithiation and its correlation with oxidative stability. Finally, the talk will discuss on recent progress in Surface Enhanced Raman (SERS) and Tip Enhanced Raman Spectroscopy (TERS) applied to battery electrolytes and anodes.

Acknowledgement

Research has been supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy.

References

1. J. Lei, F. McLarnen, and R. Kostecki, J. Phys. Chem. B 109, pgs. 952-957 (2005)
2. R. Kostecki, J. Lei, F. McLarnon, J. Shim , K. Striebel , J. Electrochem. Soc. 153 , A669 (2006)
3. Y. Luo, W. B. Cai, X. Xing, D. A. Scherson, Electrochem. Solid-State Lett. 7, E1. (2004).
4. J. Nanda et al. Adv. Func. Mater. 21, 3282 2011
5. R. Ruther et al. J. Phys. Chem. C J. Phys. Chem C 119, (2015)
6. R. Ruther et al. Chem. Mater. 227, 6746, (2015).