Battery quality inspection of lithium ion batteries
As manufacturers and regulators pivot towards vehicle electrification (1), lithium-ion batteries (LIBs) remain the most widely adopted, safe, and relatively inexpensive energy storage technology (2). The quick ramp-up in demand for electric vehicles (3) greatly expanded the scope of battery research and quality assurance (4). As batteries are highly structured and multiscale devices, inspecting components at several length scales can assure a certain level of performance and reliability (5).
Challenges in lithium detection with SEM and advances in 3D elemental mapping
Already, one can match the image from an SEM with a rasterized chemical map using energy dispersive X-ray spectroscopy (EDS). This technology relies on characteristic X-ray peaks that are emitted from the imaging process, yet the method struggles to measure lithium due to the low energy of characteristic X-rays emitted (9). Other spectroscopy techniques extend the useful range of detection to include lithium and other light elements but are typically for bulk sample analysis or for 2D maps only. Thermo Fisher Scientific recently partnered with TOFWERK to provide an add-on for SEMs that allows elemental mapping of lithium at the nanoscale in 3D in materials such as LIB cathodes (10,11).
Utilizing ToF-SIMS and FIB-SEM for 3D nanoscale mapping of lithium for battery quality inspection
A trusted spectroscopic technique is employed: time-of-flight secondary ion mass spectrometry (ToF-SIMS) (12). This method collects and separates isotopes according to their mass-to-charge ratio (m/z), and samples can be collected from a variety of methods such as by sputtering of material from the SEM imaging process. The sputtered ions are available as a side-effect of the milling process in focused ion beam SEM (FIB-SEM) (13). Here, an ion beam (e.g., gallium) is drawn across the surface of a sample to incrementally cut and reveal successive layers for serial 3D imaging. Compared to standalone ToF-SIMS, milling the surface increases the spectral depth profile and permits precise ion milling with a smaller ion beam spot size. By milling the sample and performing 2D imaging layer after layer, the 3D distribution of light isotopes such as lithium is revealed at the nanoscale in a way not possible with EDS (14).
To illustrate this capability, scientists at Thermo Fisher Scientific produced a 3D map of 7Li+ within NMC811 (lithium nickel manganese cobalt oxide) cathode particles using ToF-SIMS and FIB cross-sectioning (11). To avoid Ga+ ion chemical interaction with the sample, a Xe+ ion beam plasma FIB was employed. Sequential milling of the sample surface with the plasma FIB permitted imaging of the ion-induced secondary electrons and secondary ions in spatial context. In other words, a topological map is made from the electrons and a chemical map is made from the ions as detected by the ToF-SIMS instrument.
Automated 3D imaging and lithium mapping in NMC811 using ToF-SIMS and FIB-SEM
The high ionization yield of 7Li+ allowed quick data acquisition in the FIB-SEM compared to EDS acquisition (9). Thermo Scientific™ Auto Slice and View™ 5 Software automated the ion milling, rocking polish, imaging, and communication with the ToF-SIMS for correlated imaging of a consistently smooth imaging surface. Automated data acquisition took place over 23 hours. Ion-induced secondary electron images and rasterized ToF-SIMS maps were then aligned and jointly viewed in Thermo Scientific Avizo™ Software (15). The ToF-SIMS maps represent a depth profile deeper than the FIB-milled cut. This is useful to characterize uneven surfaces like cathode batteries. These spectral depth maps are directly read by Avizo Software and reconstructed into a 3D volume. By using the secondary electrons created by the Xe+ plasma FIB, the two images are easily correlated for downstream analysis. These 3D data revealed visible defects and internal cracks within the NMC811 secondary particles (Figure 1).Viewed with 2D cross-sections or with 3D rendering, ToF-SIMS imaging revealed a heterogenous and unequal distribution of 7Li+ within the NMC811 secondary particles (Figure 2).
Advancing nanoscale lithium detection in LIBs with integrated FIB-SEM and ToF-SIMS for improved battery performance
Ultimately, the combination of FIB-SEM and ToF-SIMS successfully illustrates how light particles, such as lithium ions, can be seen at the nanoscale resolution at which LIB chemistry occurs. Uniquely, by pairing FIB-SEM with ToF-SIMS, the lithium distribution in LIB components can be mapped at high resolution and in 3D with relative ease (9,11,14). For 3D visualization and analysis, Avizo Software paired these two sources of data for a correlated look at the NMC811 cathode particles. Finding cracks, secondary particle agglomeration, dendritic growth, and other defects via FIB-SEM can inform battery researchers aiming to make LIBs safer and higher performing.
Learn more: How to automate battery quality inspection with image interpretation >>
References and further reading
- Bohnsack, R., Pinkse, J. & Kolk, A. Business models for sustainable technologies: Exploring business model evolution in the case of electric vehicles. Research Policy, 43(2), 284–300 (2014).
- Goodenough, J. B. & Park, K. S. The Li-ion rechargeable battery: A perspective. Journal of the American Chemical Society, 135(4), 1167–1176 (2013).
- Ziegler, M. S. & Trancik, J. E. Re-examining rates of lithium-ion battery technology improvement and cost decline. Energy & Environmental Science, 14(4), 1635–1651 (2021).
- Whittingham, M. S. History, evolution, and future status of energy storage. Proceedings of the IEEE, 100, (Special Centennial Issue), 1518–1534 (2012).
- Liu, X., et al. Bridging multiscale characterization technologies and digital modeling to evaluate lithium battery full lifecycle. Advanced Energy Materials, 2200889 (2022)
- Dahn, J. R., & Ehrlich, G. M. Lithium-ion batteries: Advanced materials and technologies. In: Linden’s Handbook of Batteries. 4th ed. New York: McGraw-Hill (2011).
- Liu, H., et al. Three-dimensional investigation of cycling-induced microstructural changes in lithium-ion battery cathodes using focused ion beam/scanning electron microscopy. Journal of Power Sources, 306, 300–308 (2016).
- Hall, A. S., Lavery, L. L. & Doux, P. Effective multi-modal multi-scale analytical and imaging correlation. IEEE Sensors Letters, 3, 1 (2018).
- Hovington, P., et al. Can we detect Li K X-ray in lithium compounds using energy dispersive spectroscopy? Scanning, 38, 571–578 (2016).
- Jiao, C., Pillatsch, L., Mulders, J. & Wall, D. Three-dimensional time-of-flight secondary ion mass spectrometry and DualBeam FIB/SEM imaging of lithium-ion battery cathode. Microscopy and Microanalysis, 25(S2), 876–877 (2019).
- Jiao, C., Pacura, D., Priecel, P. & Barthelemy, P. 3D ToF-SIMS detection of 7Li+ in NMC811 via automated FIB cross-sectioning. The 65th Battery Symposium in Japan (2024)
- Shen, Y., L. Howard & Yu, X.-Y. Secondary ion mass spectral imaging of metals and alloys. Materials, 17, 528 (2024).
- Pillatsch, L., Östlund, F. & Michler, J. FIBSIMS: A review of secondary ion mass spectrometry for analytical dual beam focused ion beam instruments. Progress in Crystal Growth and Characterization of Materials, 65, 1–19 (2019).
- Priebe, A. & Michler, J. Review of recent advances in gas-assisted focused ion beam time-of-flight secondary ion mass spectrometry (FIB-TOF-SIMS). Materials, 16, 2090 (2023).
- Avizo Software for battery and energy materials characterization
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