Hollow-Core Optical Fibre Sensors for Operando Raman Spectroscopy on Li-Ion Battery Liquid Electrolytes

Liquid-filled hollow-core fibres (HCF) are excellent sample cells in which light propagates in well-defined modes at the centre of a microchannel. The internal sample volumes in HCF can be as small as a few nL per cm interaction length, while long optical paths enable sensitive absorption, fluorescence, and Raman spectroscopy [1,2]. This talk will introduce optofluidic hollow-core fibres and briefly review their applications as microreactors. It will then demonstrate a new operando Raman spectroscopy method that tracks the chemistry of liquid electrolytes during battery cycling. An optofluidic hollow-core fibre is integrated into a working Li-ion cell and used to analyse sub-microlitre electrolyte samples at different stages of the charge-discharge cycle by background-free Raman spectroscopy. The observed changes in electrolyte composition are related to the solid electrolyte interphase (SEI) formation [2]. In addition, Raman measurements over multiple cycles reveal early signs of battery electrolyte degradation and we demonstrate that lost capcity can be recovered by infiltration of fresh electrolyte into a degraded cell. The new methodology contributes to understanding better the limitations of Li-ion batteries and paves the way for studies of degradation mechanisms in different electrochemical energy storage systems.<br/><br/><b>References</b><br/>[1] A. M. Cubillas <i>et al.</i>, Chem. Soc. Rev. <b>42</b>, 8629 (2013). https://doi.org/10.1039/C3CS60128E<br/>[2] <i>Ermanno Miele et al., Nature Commun. </i><b>13</b>, 1651 (2022). https://doi.org/10.1038/s41467-022-29330-4