Time-of-flight neutron imaging (ToF-NI) has the unique capability of being able to map real-time changes to, for example, hydrogen-containing materials such as a battery electrolyte inside metallic casings such as battery packs. This enables investigation of the battery materials while in operation, without dismantling the cell.
In their study, published in Materials Today Energy, a group of researchers from PSI and ISIS used diffraction contrast neutron imaging, known as Bragg edge imaging, on the IMAT instrument to study a commercial-size battery cell.
As a battery charges, the lithium ions intercalate into the graphite anode, changing the crystal structure and leading to shifts in the positions of the Bragg edges within the spectrum. By measuring these shifts, the team was able to determine the stages of Li+ intercalation as a function of the state-of-charge of the battery. By applying Bragg edge imaging, they create a two-dimensional map of the state of charge across the battery cell and find out if there was consistency across it.
They found that the intercalation, and therefore the charging, was inhomogeneous throughout the cycling process, with faster intercalation occurring close to the electrode tabs. During long term use, such an effect can be detrimental to the battery. This is because constant cycling will cause localised stress and fatigue. Different degrees of lithiation will also make the different parts of the cell age differently.
By doing studies like these, it's possible to identify defects in the electrodes that could contribute to the degradation of a battery's performance. This can help to understand premature battery cell aging or sudden “death."
“The spatially resolved and non-destructive nature of ToF-NI is an ideal diagnostic tool for investigating electrochemical systems such as fuel cells and batteries and can be used for lots of conventional battery systems including cylindrical and coin cells," explains Ricardo Carreón Ruiz, from PSI.
https://doi.org/10.1016/j.mtener.2024.101710
