Degradation Characterization in Batteries Using Simultaneous Neutron and X-Ray Tomography

Abstract

Minimizing capacity fade and ensuring safety, especially during rapid charging, is critical to the widespread adoption of lithium-ion batteries in the transportation sector. In situ diagnostic tools are essential to track the evolution of chemical and physical changes in a cycled battery so that proper electrochemical and thermal conditions are maintained. Neutrons and X-rays offer complementary, penetrating probes for electrochemical systems. Neutrons are highly sensitive to the lithium content of batteries and the hydrogen content in the electrolytes, binders, and separators. X-rays of sufficient energy to penetrate commercial batteries lack the sensitivity to lithium, but excel at identifying higher density materials such as the transition metals typically used on the cathode of lithium-ion batteries. Combining the two modalities together provides the location of lithium and structural changes such as cracking and deformation as a function of the state of charge.The NIST-NeXT system provides the capability to perform simultaneous neutron and X-ray tomography so that both modalities can be correlated in samples evolving with time. An X-ray generator is oriented perpendicular to a reactor sourced neutron beam so that the sample can be viewed simultaneously. NIST offers a bivariate histogram segmentation program that leverages the complementarity of the two modalities for facile segmentation of samples of interest as shown in Figure 1. This talk will discuss new tools that are currently being developed to aid in the tracking of deformation and inactive lithium as a function of cycle number. Batteries with engineered defects are being developed to provide verification of detection limits for the method.Figure 1: (A) Bivariate histogram segmentation tool showing polygons drawn on histogram to identify various materials in a commercial 10180 battery, (B) 3D visualization of segmentation results from (A) for 10180 battery, the case is shown in gray, the copper current collector foil and NMC cathode layers are shown in magenta, and the graphite and electrolyte are shown in orange, (C) and (D) show the evolution of deformation during discharge for a AA lithium iron disulfide battery from (C) fully charged to (D) fully discharged with neutron tomography. Figure 1