Neutron Imaging for In Situ Metrology of Li Concentratin in LFP Li Ion Batteries

Jason B. Siegel, Xinfan Lin, and Anna G. Stefanopoulou (PI), University of Michigan

Neutron radiography offers a unique opportunity to measure in situ the spatial distribution of lithium concentration across the electrode active material at the 10 micron length scale. These measurements can be used for the parameterization and validation of necessary physics based mathematical models of Li-ion cells. The measurements can also be used to observe the manufacturing defects and degradation of energy storage material, by the changes (or non-uniformity) in local lithium concentration distributions during normal operation of the battery. The movement of lithium ions between the anode and cathode active material has been successfully observed in the radiographic neutron images. 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. A methodology for quantifying the change in lithium concentration in situ is based on the Lambert-Beer law. 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. Swelling and contraction of the unconstrained active material during lithium intercalation (cycling of the battery) is also observed in the images. These observations point to the internal stress in the battery, which may contribute to the degradation of the energy storage materials. Further research is ongoing to utilize this measurement for calibration of a physics based battery model.

More details can be found in the following publication

Neutron Imaging of Lithium Concentration in LFP Pouch Cell Battery

Jason B. Siegel, Xinfan Lin, Anna G. Stefanopoulou, Daniel S. Hussey, David L. Jacobson, and David Gorsich, J. Electrochem. Soc. 158, A523 (2011),

Experiments were performed at the NIST Center for Neutron Research

http://physics.nist.gov/MajResFac/NIF/

The authors would like to acknowledge the help of the instrument scientists at NIST, Dr. David L. Jacobson and Dr. Daniel S. Hussey. The authors would also like to thank Dr. David Gorsich of United States Army Tank Automotive Research, Development and Engineering Center (TARDEC).

Funding for this research is provided by the Automotive Research Center (ARC).