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How do lithium batteries age?

With a doctoral thesis on monitoring the state of lithium batteries, Innovation & Research is helping prepare SNCF to benefit from this promising and rapidly developing energy storage method.

With the SIGALi project, hybrid train development, and other work, lithium batteries have been an important focus of research at SNCF for about three years. “A working group has been formed by SNCF Réseau, SNCF Mobilité, Gares & Connexions, and Innovation & Research to investigate this technology of the future, facilitate the sharing of findings, and thus enable SNCF to maintain its lead at this stage of research”, says Bogdan Vulturescu, project leader in the Energy Group of the Rail Physics department of SNCF Innovation & Research.

Filling the gaps in knowledge

Though promising, lithium batteries are not without their drawbacks. The first is their high acquisition cost, which can only be justified if their service life can be optimised by scheduling maintenance operations or replacing them at exactly the right time. “On this particular point, we have to admit that knowledge is still lacking”, says Vulturescu. “For while all lithium batteries have sensors to monitor their state of health at any given moment, we are still unable to model their aging over time, which would allow us to plan ahead and optimise investments.”

Developing an algorithm to monitor batteries

It was this need that prompted the research of Maxime Juston, who joined the Energy Group last February to do an internship at the end of his engineering studies. (This autumn he will be starting work on a CIFRE thesis jointly supervised with the Université Technologique de Compiègne.) Juston’s research will focus precisely on the “monitoring of the aging of on-board lithium batteries for railway applications”. After reviewing the state of the art of lithium battery modelling, he will do an inventory of the current and possible future uses of these batteries at SNCF. In a second phase of research, he will focus on modelling the aging process and then develop an algorithm to monitor battery state of  health. “In parallel to his research, he will begin battery aging tests in the laboratory in 2018. The objective will be to accelerate the natural process, without degrading the battery so as to better understand the aging mechanisms and to have benchmark batteries for the modelling work”, says Vulturescu.