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Revealing lithium distribution heterogeneities in a commercial 18650 NCA Li-ion battery during early cycling with X-ray diffraction tomography

Lithium-ion batteries (LIBs) have become the preferred energy storage device for a variety of applications, ranging from portable devices to electric vehicles, primarily due to their energy density and extended life-cycle. Structural insights revealed using X-ray techniques can aid in the design of higher performing batteries.

Lithium-ion batteries are complex multicomponent material systems, and their performance directly depends on numerous parameters such as electrochemical stability of the cell components as well as uniform lithium (Li), current and temperature distributions for the desired operating conditions, all of which are interlinked.

The first operando X-ray diffraction computed tomography (XRD-CT) experiment of a cylindrical LIB was performed at beamline ID31 to investigate the device s evolving solid- state chemistry in a spatially resolved manner during electrochemical cycling. Interlaced XRD- CT scans were acquired from a commercially available 18650 NCA LIB, often used in electric vehicle battery packs, using a monochromatic

beam of 95 keV and the PILATUS3 X 2M CdTe area detector. The new ESRF-EBS enabled the fast collection of diffraction patterns with an exposure time of 10 ms, leading to large reconstructed images (ca. 640×640 pixels) with a voxel size of 30 × 30 × 4 μm3.

Multiple chemical heterogeneities related to the Li distribution were observed in both the cathode and the anode from the analysis of the spatially resolved diffraction patterns (see anode results in Figure 136). The unravelling of these heterogeneities is crucial, as non-uniform Li distributions in the cell(s) can have a negative impact on the performance of LIBs and can lead to decreased capacity and power output, local temperature gradients and even to overcharge/overdischarge.

PRINCIPAL PUBLICATION AND AUTHORS

Emerging chemical heterogeneities in a commercial 18650 NCA Li-ion battery during early cycling revealed by synchrotron X-ray diffraction tomography, D. Matras (a,b), T.E. Ashton (c), H. Dong (c), M. Mirolo (d), I. Martens (d), J. Drnec (d), J.A. Darr (c), P.D. Quinn (b), S.D.M. Jacques (e), A.M. Beale (c,e,f), A. Vamvakeros (e), J. Power Sources 539, 231589 (2022); https:/doi.org/10.1016/j.jpowsour.2022.231589 (a) The Faraday Institution, Quad One, Harwell Science and Innovation Campus, Didcot (UK) (b) Diamond Light Source, Harwell Science and Innovation Campus, Didcot (UK) (c) Department of Chemistry, University College London, London (UK) (d) ESRF (e) Finden Limited, Merchant House, Abingdon (UK) (f) Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot (UK)

Fig. 136: Operando LIB XRD-CT experiment at beamline ID31.

Spatial distribution of the anode LixC phases as the cell is charged to

various potentials.