Following lithium ion flow in batteries to design better charging methods

Charging lithium-ion batteries today is quicker than several years ago, but it is still not fast enough in applications such as renewable energy for electric cars. Fast charging involves balancing the need for speed with considerations for battery health and safety. It relies on delivering higher currents to the battery, but this can generate heat, potentially shortening the battery's lifespan.

Now scientists led by the Université de Quebec and McGill University (Canada), in collaboration with the ESRF, have developed a new technique to combine X-ray diffraction and X-ray fluorescence to characterize the solid and the liquid part of the battery. The new technique, called «LIME» for Lithium Inventory Mapping in Electrodes has been used on beamline ID31.

“What is innovative is that we managed to observe the movement of ions in the solid parts (the electrodes) and the liquid part (the electrolyte) of the battery at the same time, thus obtaining insight into what is happening”, explains Steen B. Schougaard, professor at the University of Quebec and corresponding author of the paper. He adds: “It all takes place in real time and with high time and high spatial resolution.”

The technique of X-ray fluorescence provides information on the electrolyte, and the X-ray diffraction can track the lithium content in the electrodes. “We work at a lower energy than we would normally have, 40 keV instead of 70keV, so we have a higher signal for spectroscopy and can carry out the study of the whole battery during charge and discharge”, explains Marta Mirolo, junior scientist at the ESRF and part of the team. The researchers also tweaked the composition of the liquid electrolyte, substituting the commonly found phosphorous with arsenic, as only the latter is detected by X-ray fluorescence.

The team found that, in the studied system, one of the electrodes is not fast enough in delivering the lithium ions. “We tested different protocols to see what happens if you fast-charge the battery and realised that with a specific protocol, based on pulses, you can overcome the mass transport limitations”, says Mirolo. The results could lead to design better electrodes and charging protocols.

This technique will be useful for testing existing lithium-ion batteries on the market and new models that will be developed in the coming years, as well as other electromechanical system. “The ultimate goal is to design a battery that rivals the 'recharge' speed of petrol-powered cars, eliminating or alleviating one of the biggest frustrations with renewable energy in transportation: waiting time to recharge a battery,” concludes Schougaard.

Reference

Daukins, J.I.G, et al, Joule, 28 November 2023. https://doi.org/10.1016/j.joule.2023.11.003

Text by Montserrat Capellas Espuny