A technology to “see” in commercial batteries

Batteries offer the ability to store energy in chemical form: during charging, the current forces chemical reactions and the energy is stored, then during discharge a spontaneous electrochemical reaction generates the inverse movement of electrons in the system. Energy is released to create an electric current.

Controlling and studying the chemistry of a battery is therefore crucial to understanding its operation, but also to improving its design. If the exercise is easy in the laboratory, it is much less so when it is integrated into a system. But a multidisciplinary research team led by scientists from the Chemistry of Solids and Energy laboratory (CNRS/Collège de France/Sorbonne University) has just developed a method to follow the evolution of the chemistry of a commercial battery. , live, during its charging or discharging.

The technology, presented in an article published in Nature, is based on the transport of infrared light in chalcogenide glass optical fibers placed through a battery. The interaction of this light with the constituents of the battery makes it possible to identify and follow the chemical molecules present around the fibre.

The researchers were thus able to observe the evolution of electrolytes as well as the insertion/extraction of sodium-lithium ions in the electrodes as a function of the charge. And this while it was in use, a first! With this system, the scientists were also able to study the interface between the electrolyte and the negative electrode material called Solid electrolyte interphase (UTE). This layer, which both conducts ions and insulates electrons, determines the longevity of batteries. In particular, the team was able to follow in situ the nature of the chemical species involved in the nucleation and growth of the SEI which is set up during the very first charge of a battery.

From a practical point of view, these results open the way to easier and improved battery design. Currently, the optimization of electrolytes and load test protocols takes a long time to find the best option for an ideal SEI, and thus improve the longevity of a battery. With this new and unprecedented method, it is possible to quickly and precisely see how each element of the recipe evolves, interacts with the others and influences the performance of the battery. The research team continues its work focusing on the SEI and hopes to reveal all its secrets.

Diagram of the propagation of infrared light through the core of a glass optical fiber of composition: Te2As3Se5 (TAS). On the surface of the fiber, an evanescent wave is created which can interact with the surrounding molecules. The TAS fiber is passed through a vacuum in the center of an 18650 type battery. The chemical bonds corresponding to the electrolyte can thus be observed during its use.
© Gervillié-Mouravieff et al./Collège de France
Battery traversed by a chalcogenide glass optical fiber to transport light in the infrared range. The interaction of this light with the constituents of the battery makes it possible to identify and follow the chemical molecules present around the fibre.
© Frédérique PLAS / CSE / CNRS Photo library

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