Improved analytical tools are urgently required to identify degradation and failure mechanisms in Li-ion batteries. However, understanding and ultimately avoiding these harmful mechanisms requires continuous tracking of complex electrochemical processes in different battery components.
Now a team led by the NanoPhotonics Centre in the Cavendish Laboratory has shown a way to monitor the chemistry of liquid electrolytes during battery cycling by Raman spectroscopy.
They periodically extract tiny liquid electrolyte samples from a working Li:ion battery into an optical fibre with a micro-sized hole down its centre. They then use the fibre’s light confinement to interrogate sub-microlitre samples by sensitive Raman spectroscopy, which measures molecular vibrations.
This approach enables the team to monitor the chemistry of industry-standard carbonate-based liquid electrolytes during electrochemical cycling in Li-ion batteries with a state-of-the-art high-energy-density cathode.
“Similar to a blood test, Raman spectra of battery electrolytes provide unique information on their chemical state-of-health” notes Dr Tijmen Euser
Published in Nature Communications, the team’s spectroscopic measurements reveal significant changes in the carbonate solvents and electrolyte additives during charging and discharging, allowing them to track how lithium-ions repeatably move across the battery.
“Rather than just probing a single material, real-time techniques provide a vital understanding of how these various materials function cooperatively, and crucially within working batteries”, enthuses co-investigator Prof. Dame Clare Grey.
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.
The multidisciplinary work was carried out within the UK-wide Faraday Institution, in close collaboration with the Cambridge Chemistry Department, the Institute of Manufacturing, and the Max Planck Institute for the Science of Light in Erlangen, Germany.
“This is a great way to peer inside the black box, finding out why batteries fail and how to treat them right”, notes lead author Dr Ermanno Miele.
Ermanno Miele et al. ‘Hollow-core optical fibre sensors for operando Raman spectroscopy investigation of Li-ion battery liquid electrolytes’ Nature Commun. https://doi.org/10.1038/s41467-022-29330-4