ICYS Annual Report 2023

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ICYS Annual Report 2023The drive toward a low-carbon, sustainable future has spurred the advancement of next-generation battery technologies. Lithium (Li) metal anodes are considered the “holy grail” for high-energy-density batteries due to their exceptional theoretical specific capacity (3860 mAh/g vs. 372 mAh/g for graphite) and low redox potential (–3.04 V vs. standard hydrogen electrode).1-2 However, commercialization remains challenging due to low Coulombic efficiency, limited cycle life, and safety issues. A fundamental barrier to addressing these challenges is the limited understanding of (3D) microstructure of electrodeposited Li. The heterogeneous deposition behaviours and complex phase composition of Li metal require high-resolution, large-scale 3D analysis, which remains challenging when using existing 3D characterization technologies. To address this, we employ Xenon plasma focused ion beam scanning electron microscopy (Xe/PFIB) for the high-resolution, large-volume 3D reconstructions of electrodeposited Li. As shown in Figure 1, the electrodeposited metallic Li, individual Li grains and pores phase are successfully visualized at a large volume (dimensions of 200 µm), enabling a comprehensive statistical analysis of their distribution, volume, number, and shape. When analyzing the deposited Li at different current densities, we found that the obtained Li grains decreased in number and increased in volume with a decrease in current density. The corresponding pores also decreased in number and increased in size. Large pores facilitated the free growth of Li particles in all Research Digest 1. Outline of Research2. Research ActivitiesYueying PENGFig. 2. (a) Mean volumes of Li particles as functions of height, (b) Numbers per area as functions of the height.References1) Lin, D., Liu, Y., and Cui, Y. Nat. Nanotechnol. 12, 20172) Bruce, P.G., Freunberger, S.A., Hardwick, L.J., and Tarascon, J.M. Nat. Mater. 11, 20143) Y. Peng, and K. Nishikawa. Cell Rep. Phys. Sci., 6(2), 202Fig. 1. (a) Stacks of cross-sectional SEM images of the electrodeposited Li acquired via the automatic procedure comprising Xe PFIB milling and SEM imaging, (b) Image segmentation of the metallic Li and Li grains, magnified image shows metallic Li (black), the pores (white), and each Li particle covered by the SEI layer (thin white lines), (c) 3D reconstruction of the Li metal (blue), separated Li particles, and inner pores (green).the three-dimensional directions, which results in Li particles with highly spherical morphologies and smooth surfaces. Further analyze the Li growth mechanism in Figure 2, a distinct difference at 0.2 mA cm–² are revealed: the particle number density is almost constant, in contrast to the significant increases observed under other conditions. This suggests that electrochemical growth dominates when the obtained overpotential (ηp) is low (≤20 mV at 0.2 mA cm–2), which results in large-sized Li particles with less particle numbers. However, both growth and new nucleation occur simultaneously when the obtained overpotential is higher, thereby leading to small-sized Li particles with increased particle numbers. 20Three-Dimensional Characterization forUnravelling Lithium Metal Anodes Mechanism