Supporting Information. Multistep Lithiation of Tin Sulfide: An Investigation Using in Situ Electron

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1 Supporting Information Multistep Lithiation of Tin Sulfide: An Investigation Using in Situ Electron Microscopy Sooyeon Hwang, Zhenpeng Yao, Lei Zhang, Maosen Fu,, Kai He, Liqiang Mai, Chris Wolverton, Dong Su*, Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11953, United States Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan , P. R. China Shanxi Materials Analysis and Research Center, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an , P. R. China

2 Figure S1. (a) X-ray diffraction pattern acquired from pristine SnS 2 sample used in this work and reference diffraction pattern of SnS 2 (JCPDS ). (b) STEM-EELS elemental mappings of pristine SnS 2. S-2

3 Figure S2. Discharge-charge profiles of SnS 2. These profiles were acquired from commercial SnS 2 particles. Flower-like SnS 2 sample, which we used for this work, was loaded into TEM grid and we assembled 2032 type of coin cells with TEM grids. S-3

4 Figure S3. Detailed procedure for obtaining electron diffraction intensity profile. Figure 2(a) is produced from in situ diffraction video (Movie S1). Movie S1 was recorded every 0.5 s. Each frame is a standard diffraction pattern, such as (a). Integration the intensity across the full 2π range (yellow dotted circle) along r direction (white solid line) results in a radially averaged intensity profile shown in (b). We set and subtract the background using power-law model embedded in Digital Micrograph (c), then, final intensity profile is acquired shown in (d). To process a number of frames efficiently, we employ customized functions in Matlab. S-4

5 Figure S4. Raw selected area electron diffraction (SAED) patterns during lithiation from Movie 1. SAEDs with false colors were presented in Figure 2c in the manuscript. S-5

6 Figure S5. (a) In situ selected diffraction patterns from a single SnS 2 sheet. Zone axis is close to [101] direction and 121 diffraction spots are highlighted. Magnified 121 diffraction spots are shown as insets at each frame. (b) Simulated diffraction patterns of SnS 2, LiSnS 2 along [101] zone axis. Among LiSnS 2 polymorphs, LiSnS 2 adopting P3 m1 space group was considered as a product of Li intercalation. Peak splitting is experimentally observed as a result of lithium insertion, indicating that intercalation process has two-phase reaction nature as suggested in previous report. 1 S-6

7 Figure S6. Voigt fitting for diffraction peak of 102 plane in order for precise determination of d- spacing. S-7

8 Figure S7. Determination of second lithiated phase of Li y SnS 2 at 604 s. In order to figure out the Li y SnS 2 phase, we considered three different structures (P3 m1, R3 m, and Fm3 m). (a) P3 m1 structure is the same structure of original SnS 2, having Li ions between S-S layer. (b) In R3 m structure, the sequence of Sn-S layer is shifted from A-A to A-B-C while Li ions are introduced between S-S layer. (c) Fm3 m, rocksalt structure, have sulfur framework with A-B-C stacking while cations (Sn and Li) are disordered. Based on DFT calculations in the manuscript and Materials Project ( metastable LiSnS 2 phase can have either P 3 m1or R 3 m structures while having R 3 m structure is energetically more favorable. Interestingly, one of Li-Sn-S compound, Li 2 SnS 3, has similar atomic arrangement of rock-salt structure. 2 In addition, R3 m and Fm3 m have same sulfur framework with/ without cation order. We could guess that lithiated SnS2 phase can have all three structures. Thus, we simulated diffraction patterns from P3 m1, R3 m, and Fm3 m structures. Diffraction pattern of rocksalt structure is the clostest to the experimental result; therefore, we determine Li y SnS 2 as disordered rocksalt structure. S-8

9 Figure S8. Electron beam effect (1). (a)~(c) present time series high-resolution (HR) images at [021] zone-axis of SnS 2 and corresponding fast Fourier transformation (FFT) results during lithiation. Even though the crystal structure is well maintained until s, the morphology of SnS 2 sample becomes porous, indicating that electron beam may damage the sample. (d) Brightfield (BF) image acquired at lower magnification shows that the area of interest was damaged after obtaining a video at high-resolution mode. For high-resolution imaging, the electron dose rate (often in C/cm 2 ) is much higher than conventional imaging or diffraction. High dose rate (beam intensity) and accumulation of electron dose during in situ experiments strongly affect the irradiation damage on sample. 3 The current density for high-resolution TEM imaging (Figure S8) was measured as 14.3 pa/cm 2 on the fluorescent screen, while that of in-situ STEM imaging at lower magnification (Figure 3) was 0.3 pa/cm 2. In order to minimize radiation effect, we controlled both electron dose rate and total dose as low as possible to observe full lithiation events without noticeable radiation effects. S-9

10 Figure S9. Electron beam effect (2). Electron beam can produce wrinkles in sheet-like SnS 2 samples. (a)~(c) shows a time series high angle annular dark field (HAADF) and BF images during lithiation. During taking a video, evolution of wrinkles was observed. After taking video, these wrinkles were found at other areas, shown at (d), and (e). These morphological changes also take place without biasing. Even though SnS 2 sheet sample was flat after lithiation (f), post TEM observation developed creases in the sample (g). These wrinkles remained after lithium extraction (h). The generation of crinkles can happen under electron beam with or without biasing; therefore, extra care should be required not to provoke unwanted morphological change during in situ and ex situ experiments. S-10

11 Figure S10. Time-sequence raw dark field images from Movie 2. Figure 3a in the manuscript is presented these images with false colors. S-11

12 Figure S11. HAADF and HRTEM images after in situ lithiation experiments. S-12

13 Figure S12. Calculated Li-Sn-S ternary phase diagram at 0 K at equilibrium states. Red dotted line indicates the reaction path under equilibrium states. A table presents possible reactions along equilibrium reaction path, calculated capacity and potential at each reaction. S-13

14 Figure S13. Possible Li intercalation sites in SnS 2 S-14

15 Figure S14. A concept of special quasi-random structure (SQS) method for considering cation mixing at DFT calculation. S-15

16 Figure S15. Raw time sequence SAEDs during delithiation from Movie 3. Figure 6b in the manuscript presented them with false colors. S-16

17 References (1) Gao, P.; Wang, L.; Zhang, Y.-Y.; Huang, Y.; Liao, L.; Sutter, P.; Liu, K.; Yu, D.; Wang, E.-G. High-Resolution Tracking Asymmetric Lithium Insertion and Extraction and Local Structure Ordering in SnS 2. Nano Lett. 2016, 16, (2) Brant, J. A.; Massi, D. M.; Holzwarth, N. A. W.; MacNeil, J. H.; Douvalis, A. P.; Bakas, T.; Martin, S. W.; Gross, M. D.; Aitken, J. A. Fast Lithium Ion Conduction in Li 2 SnS 3 : Synthesis, Physicochemical Characterization, and Electronic Structure. Chem. Mater. 2015, 27, (3) Egerton, R. F.; Li, P.; Malac, M. Radiation Damage in the TEM and SEM. Micron 2004, 35, S-17