Lithium metal has been considered an ideal anode for high-energy rechargeable Li batteries, although its nucleation and growth process remains mysterious, especially at the nanoscale. Here, cryogenic transmission electron microscopy was used to reveal the evolving nanostructure of Li metal deposits at various transient states in the nucleation and growth process, in which a disorder–order phase transition was observed as a function of current density and deposition time. The atomic interaction over wide spatial and temporal scales was depicted by reactive molecular dynamics simulations to assist in understanding the kinetics. Compared to crystalline Li, glassy Li outperforms in electrochemical reversibility, and it has a desired structure for high-energy rechargeable Li batteries. Our findings correlate the crystallinity of the nuclei with the subsequent growth of the nanostructure and morphology, and provide strategies to control and shape the mesostructure of Li metal to achieve high performance in rechargeable Li batteries.
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The data that support the findings of this study are available from the corresponding authors upon reasonable request. Source data are provided with this paper.
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We thank the UC Irvine Materials Research Institute (IMRI) for the use of the Cryo-Electron Microscopy Facility and Kratos XPS, funded in part by the National Science Foundation Major Research Instrumentation Program under grant no. CHE-1338173. We thank X. Pan, T. Aoki, L. Xing and J.-G. Zheng for their assistance with the microscopy. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231. The SEM was performed in part at the San Diego Nanotechnology Infrastructure (SDNI), a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation (grant ECCS-1542148). We also thank A. van Duin of the Pennsylvania State University for providing the ReaxFF parameters used in this work. We thank W. Xu and M. Olguin for discussing the results. This work is supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the US Department of Energy in the Advanced Battery Materials Research (BMR) Program (Battery500 Consortium). Idaho National Laboratory (INL) is operated by Battelle Energy Alliance under contract no. DE-DE-AC07-05ID14517 for the US Department of Energy.
The authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Co-first authors: Xuefeng Wang, Gorakh Pawar.
Extended Data Fig. 1 Influence of local mass transport, energy transfer and current density (as represented by packing density) on the nucleation and phase transition of Li metal deposits by using ensembles of 600 Li atoms as the basis for the simulation.
The packing density in a-d is 0.0534, 0.13, 0.27 and 0.47 g cm−3 respectively. The crystal structure (that is the bcc lattice) is represented in blue, whereas the amorphous fractions or phases in white or grey.
Cryo-TEM images (a-d) and their FFT patterns (e-h) of Li deposits at 0.5 mA cm-2 for 2h. Besides (110) plane of Li metal, lattice fringes or FFT spots with lattice spacing of ~0.174 and ~0.142 nm was also observed, which belongs to the (200) and (211) planes of Li metal, respectively. Specially in d and h, both (200) and (110) planes of Li metal are present, which helps to determine the zone axis of  and confirm the phase of Li metal.
Cryogenic STEM image (a), EELS Mapping (b) and spectra (c) of EDLi obtained at 0.5 mA cm-2 for 2h. The EELS mapping (b) is based on the intensity EELS spectra ranging from 53.5 eV to 58.5 eV (highlighted by the blue square in c), which contains the characteristic metallic/elemental Li K-edge threshold at about 55 eV. c presents the EELS spectra taken from Area 1 and Area 2 (labeled in b) representing the feature of highly crystalline Li and glassy Li respectively. Due to the presumed same SEI on the surface of Area 1 and Area 2, they show similar extended fine structure of Li K-edge after 60 eV. Both of them have the obvious characteristic metallic/elemental Li K-edge threshold at about 55 eV while the highly crystalline Li Area 1 shows a peak with slightly higher intensity than the glassy Li Area 2. This is reasonable due to the different degree of order/disorder structure in these two areas. It is worth to noting that it is difficult to obtain the higher-resolution STEM mapping due to the radiation damage caused by the high-energy beam used for STEM scanning even at cryogenic temperature. Source data
Extended Data Fig. 4 Nanostructure evolution of Na, K, Mg and Zn deposits as a function of current density.
TEM images (a-d and i-l) and the corresponding FFT patterns (e-h and m-p) of Na at 0.1 mA cm−2 (a and e) and 0.5 mA cm−2 (i and m), K at 0.1 mA cm−2 (b and f) and 0.5 mA cm−2 (j and n), Mg at 0.05 mA cm−2 (c and g) and 0.1 mA cm−2 (k and o) and Zn at 0.1 mA cm−2 (d and h) and 0.5 mA cm−2 (l and p). The crystalline portion of the Na, K, Mg, and Zn deposits are labeled by the white dash lines.
Supplementary Figs. 1–21, discussion and Tables 1–2.
The heating stage during the simulated annealing approach. The kinetics of the Li nucleation are intriguing. Several nucleation sites rapidly formed and continued to evolve, showing substantial variability in the nucleation kinetics.
The quenching stage during the simulated annealing approach. The coarsening and condensation of intermediate Li nucleation sites (nuclei) resulted in crystalline clusters with sizes in the range of 2–5 nm. This crystalline cluster size range is critical in determining the material’s reactivity in practical applications.
The equilibration stage during the simulated annealing approach. The cluster that evolved through maturation either remained in an amorphous state at lower current densities or transformed into a ‘crystalline’ state at higher current densities.
The condensation process at a relatively lower current density (for example, an ensemble with 500 Li atoms). The Li aggregate remained amorphous even after 5.3 ns in simulation. Irrespective of the timescale, the nanostructure is the key that could substantially impact the underlying material’s properties and have profound implications in a variety of applications such as in electrodeposition, catalysis, semiconductor fabrication and so on.
The condensation process at a relatively moderate current density (for example, an ensemble with 700 Li atoms). The condensed Li aggregate remained in an amorphous state with a long incubation time (>2 ns) and eventually transformed into a nucleus structure.
The condensation process at a relatively higher current density (for example, an ensemble with 900 Li atoms). The initial amorphous Li cluster rapidly transformed into a crystalline structure with a substantially short incubation time (<0.7 ns). Accessing such information at the nanosecond and/or picosecond timescales could be challenging with the experimental methods.
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Wang, X., Pawar, G., Li, Y. et al. Glassy Li metal anode for high-performance rechargeable Li batteries. Nat. Mater. (2020). https://doi.org/10.1038/s41563-020-0729-1