Neutron Imaging of Lithium Concentration in Battery Pouch Cells
Daniel S. Hussey, David L. Jacobson, Jason B. Siegel, C. D. Stefan, Xinfan Lin, David Gorsich
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 measurements are taken at steady-state conditions (after a long relaxation time or small load). To interpret the measurements, the expected neutron attenuation through the different layers of a battery pouch cell is modeled using the known material densities and dimensions. The optics of the neutron beam (geometric unsharpness) and detector resolution need to be 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 lithium concentration. The measurements can be used to validate an electrochemical model for the purpose of battery management.