Kerr gated Raman Spectroscopy

Jelly-fish glow in the dark and so do lithium-ion batteries

Fluorescent species are formed during cycling of lithium-ion batteries because of electrolyte decomposition due to the instability of the non-aqueous electrolytes and side reactions that occur at the electrode surface. The increase in the background fluorescence due to the presence of these components makes it harder to analyse data due to the spectroscopic overlap of Raman scattering and fluorescence.

Our group uses a technique called Kerr Schegated Raman spectroscopy to overcome this challenge and have been able to study a range of cycled battery electrolytes and electrodes. An in-house operando cell has been developed to study interfacial processes under potential control.

Kerr gated Raman is based on the different time-dependence of fluorescence and Raman scattering signals upon short-pulse optical excitation. While fluorescence has a finite lifetime in the order of hundreds of picoseconds (ps) to nanoseconds (ns), Raman scattering is instantaneous and follows in time the initiating laser pulse within picoseconds (ps) or femtoseconds (fs). Such distinct time-domains for these two processes creates a technical opportunity for separating them, provided an ultra-fast gating mechanism of the optical signal is coupled with the excitation pulse. Kerr gated consists of a non-linear medium carbon disulphide (CS₂), which acts as a half-wave plate due to a transient anisotropy induced in the medium by a high-energy gating laser pulse (λ = 800 nm, 1 ps). When gating laser pulse and excitation laser are timed appropriately, the polarisation of the Raman signal is rotated by 90° vs. the slower fluorescence emission signal, resulting in an effective transmission of the Raman scattering by the two crossed polarisers, while the fluorescence is mostly blocked (Scheme 1). Our group collaborates with the Central Laser Facilities Team in Ultra, at the Rutherford Appleton Laboratory, UK to access this instrument.

Scheme 1 Schematic representation of Kerr gated Raman spectroscopy setup (adapted from Central Laser Facilities website Kerr-gated Raman Spectroscopy article).

Publications on Kerr Gated Raman Spectroscopy

• Simultaneous Surface-Enhanced Raman Scattering with a Kerr Gate for Fluorescence Suppression
  G. Cabello, I.V. Sazanovich, I. Siachos, M. Bilton, B.L. Mehdi, A.R. Neale, L.J. Hardwick. J.
  Phys. Chem. Lett. (2024) Read the full article.
• Lithium Insertion into Graphitic Carbon Observed via Operando Kerr-Gated Raman Spectroscopy Enables High State of Charge Diagnostics
  A.R. Neale, D. Costa-Milan, F. Braga, I.V. Sazanovich, L.J. Hardwick.
  ACS Energy Letts. 7 (2022) 2611 Read the full article.
• Kerr gated Raman spectroscopy of LiPF₆ salt and LiPF₆-based organic carbonate electrolyte for Li-ion batteries
  L. Cabo-Fernandez, A. R. Neale, F. Braga, I. V. Sazanovich, R. Kostecki and L. J. Hardwick
  Phys. Chem. Chem. Phys., 21 (2019), 23833 Read the full article.

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