Neutron Imaging of Lithium Concentration in LFP Pouch Cell Battery

This paper shows how neutron radiography can be used for in situ quantification of the lithium concentration across battery electrodes, a critical physical system state. The change in lithium concentration between the charged and discharged states of the battery causes a change in number of detected neutrons after passing through the battery. Electrode swelling is also observed during battery charging. The experimental setup and the observations from testing a pouch cell with LFP cathode and graphite anode are reported here. The bulk Li concentration across the electrode and folds of the pouch cell is quantified at various states of charge. To interpret the measurements, the optics of the neutron beam (geometric unsharpness) and detector resolution are considered in order to quantify the lithium concentration from the images due to the thinness of the electrode layers. The experimental methodology provides a basis for comprehensive in situ metrology of bulk lithium concentration.