3D Correlative Imaging of Lithium Ion Concentration in a Vertically Oriented Electrode Microstructure with a Density Gradient

Abstract

The performance of Li + ion batteries (LIBs) is hindered by steep Li + ion concentration gradients in the electrodes. Although thick electrodes (≥300 μm) have the potential for reducing the proportion of inactive components inside LIBs and increasing battery energy density, the Li + ion concentration gradient problem is exacerbated. Most understanding of Li + ion diffusion in the electrodes is based on computational modeling because of the low atomic number (Z) of Li. There are few experimental methods to visualize Li + ion concentration distribution of the electrode within a battery of typical configurations, for example, coin cells with stainless steel casing. Here, for the first time, an interrupted in situ correlative imaging technique is developed, combining novel, full-field X-ray Compton scattering imaging with X-ray computed tomography that allows 3D pixel-by-pixel mapping of both Li + stoichiometry and electrode microstructure of a LiNi 0.8 Mn 0.1 Co 0.1 O 2 cathode to correlate the chemical and physical properties of the electrode inside a working coin cell battery. An electrode microstructure containing vertically oriented pore arrays and a density gradient is fabricated. It is shown how the designed electrode microstructure improves Li + ion diffusivity, homogenizes Li + ion concentration through the ultra-thick electrode (1 mm), and improves utilization of electrode active materials.

Mapping of lithium ion concentrations in 3D structures through development of in situ correlative imaging of X-ray Compton scattering-computed tomography

“…3(b) shows the overall energy spectrum obtained by summing all pixels in the masked XCS image in the top region of the cathode at the fully charged state. The dominant peak (the Compton peak) occurs at 94 keV which is defined by the inelastically scattered photon energy from the incident photons (Huang et al, 2022). There is a cluster of peaks at 50-90 keV which belongs to the characteristic X-rays from the tungsten pinhole and lead shielding around the detector, and escape peaks associated with the self-fluorescence of the cadmium and tellurium in the detector material (Thompson & Vaughan, 2001).…”

“…The valence electrons are those that are transferred between the lithium atom and the cathode material compound for redox reactions during battery charging and discharging; equation ( 3) is used to calculate electron momentum factor (EMF) which is the ratio of the areas under the Compton profile between the low and high electron momentum. Previous results show that the lithium-ion concentration is directly proportional to the EMF, and the EMF can be used to calibrate the lithium-ion concentration in the cathode materials (Huang et al, 2022),…”

“…In our study, full-field X-ray Compton scattering (XCS) imaging is realized through direct imaging of the sample by collecting the Compton scattering signals perpendicular to the sample along the plane of the incident X-ray beam. XCS can detect lithium at the battery cell level as XCS measures the energy of incoherently scattered photons that have interacted with the valence electrons, including those in the electrode materials (Huang et al, 2022;Suzuki et al, 2017). The valence electrons are of interest because they react with lithium ions during battery charging and discharging redox reactions, hence, XCS can quantify the number of lithium ions moving into and being removed from the electrodes.…”

Realising higher capacity and stability for disordered rocksalt oxyfluoride cathode materials for Li ion batteries

“… 2 Two prevalent cathode materials, LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) 3 and LiNi x Mn y Co z O 2 (NMC), 4 adopt a layered crystal structure that has an ordered arrangement of Li and transition metal (TM) atoms where Li + ions diffuse in the alkali layer with a 2D pathway upon battery (dis)charge. 5 Another widely used cathode material LiFePO 4 (LFP) has an olivine crystal structure that still exhibits a clear 1D Li + diffusion pathway. 6 For decades, cation disordering, i.e., mixing of the Li and transition metals (TMs) atoms in the lattice sites, has been considered to limit Li + ion diffusion.…”

Diagnosis of Current Flow Patterns Inside Fault‐Simulated Li‐Ion Batteries via Non‐Invasive, In Operando Magnetic Field Imaging

“…Postmortem and in situ/operando analytical techniques using advanced imaging tools have been developed to unveil failure mechanisms at the material level of batteries, identifying physicochemical defects of active materials, [9][10][11][12][13] electrolyte degradation, [14][15][16] and structural damage in inactive components (e.g., separators, current collectors, tabs). [17][18][19][20] However, correlating material-level defects with cell-level failure scenarios is challenging because these defects randomly occur within complex cell structures.…”