NYU Chemistry Professor Alexej Jerschow and postdoctoral fellow Konstantin Romanenko published their findings in an article called "Distortion-free inside-out imaging for rapid diagnostics of rechargeable Li-ion cells" in PNAS.
Abstract: Safety risks associated with modern high energy-dense rechargeable cells highlight the need for advanced battery screening technologies. A common rechargeable cell exposed to a uniform magnetic field creates a characteristic field perturbation due to the inherent magnetism of electrochemical materials. The perturbation pattern depends on the design, state of charge, accumulated mechanical defects, and manufacturing flaws of the device. The quantification of the induced magnetic field with MRI provides a basis for noninvasive battery diagnostics. MRI distortions and rapid signal decay are the main challenges associated with strongly magnetic components present in most commercial cells. These can be avoided by using Single-Point Ramped Imaging with T1 enhancement (SPRITE). The method is immune to image artifacts arising from strong background gradients and eddy currents. Due to its superior image quality, SPRITE is highly sensitive to defects and the state of charge distribution in commercial Li-ion cells.
The wide use of portable electronics and rapidly expanding market for electric vehicles have driven the demand for high capacity and safe rechargeable batteries. Challenges arise due to the presence of flammable materials in cells and their high energy densities. Noninvasive means of diagnostics can facilitate understanding of battery failure modes (1⇓⇓–4). MRI is a powerful tool for studying chemical, biological, and solid-state phenomena (5⇓⇓–8). Recently, in situ MRI of model electrochemical devices shed light on underlying physical and mechanistic processes (9⇓⇓⇓⇓⇓⇓–16). These techniques however could not be used to study commercial cells due to the conductive casings and small distances between electrodes, which hamper radiofrequency (RF) penetration. An inside-out MRI (ioMRI) approach that overcomes these limitations has been recently introduced (1). A magnetic field (MF) perturbation created by a cell depends on the magnetic susceptibility and morphology of its constituents. For example, the source of a strong induced magnetization in lithium-ion cells is often a lithium-intercalation compound. The magnetic susceptibility changes as a function of the amount of inserted lithium. Therefore Li intercalation and its state of charge (SOC) could be assessed in cells nondestructively and rapidly by ioMRI. Cells can also exhibit unique MF features characteristic of their defects.
Industrial-scale applications of such battery diagnostics could also employ rapid MRI methods (e.g., Fast Low Angle Shot – FLASH) (17). These techniques rely on either long evolution times and echo trains, frequency encoding, or slice-selective RF pulses. Conductive and magnetic materials are known to induce severe MRI artifacts (18⇓–20). Several complications arise: a) The signals in the vicinity of such features can decay rapidly due to destructive interferences within voxels, and b) strong background gradients lead to image misregistration. These problems are resolved with fully phase-encoded MRI. Single-point ramped imaging with T1 enhancement, SPRITE (21⇓⇓–24), has been successfully employed for imaging of challenging systems (14, 25⇓⇓–28) and is highly suitable for MF visualization in regions with strong local magnetism. This aspect is particularly important as incorporation of ferromagnetic materials into commercial batteries is a common practice.
This research was funded by the National Science Foundation and by Mercedes-Benz Research & Development North America.