Revealing Structural Change of Amorphous Polymeric Sulfur During Synthesis

Amorphous materials, characterized by their disordered atomic structure, are indispensable in advanced technologies like catalysis ^[1], electronics ^[2], optics^[3], and energy storage^[4,5]. Unlike crystalline materials, they offer unique properties beneficial in mechanical, optical, and electrical applications ^[6]. In energy storage, amorphous materials play crucial roles: solid-state electrolytes exhibit enhanced ionic conductivity compared to crystalline counterparts, while amorphous separators in batteries improve functionality ^[7-9]. Despite their significance, synthesizing and understanding amorphous materials remain challenging due to characterization complexities. Polymeric sulfur cathodes, for instance, are promising for advancing Li-S battery technology, which provides high energy density using abundant, low-cost sulfur without relying on precious metals ^[10-13]. Understanding the synthesis of amorphous materials, including their structures and reaction mechanisms, is essential but challenging ^{[10, 12]}.<br/>In this work, we developed and applied operando Pair Distribution Function (PDF) analysis to study the chemical synthesis process of polymeric sulfur. PDF is a total scattering technique that transcends the limitations of crystallinity and symmetry ^[14-16], making it a powerful tool for studying amorphous materials. The high energy X-ray is highly penetrating, making it capable of comprehensively probing the condensed phases (solids and liquids), with minimal interference from gases. Moreover, conducting the experiments under ambient pressure conditions ensures that the intrinsic properties of the materials are accurately represented during synthesis or battery operation. This is crucial for accurately characterizing the chemical synthesis processes of battery materials such as polymeric sulfur. Our experimental setup, developed at a synchrotron beamline, replicates the chemical synthesis conditions of polymeric sulfur conducive to total scattering data collection. This setup has allowed us to observe the interactions between polyacrylonitrile (<i>l</i>-PAN where l stands for linear) and sulfur, detailing how S-C bonds form and the subsequent arrangement of <i>c</i>-PAN (where c stands for cyclic) blocks. This study highlights the complex interplay of chemical and structural changes in amorphous materials that underpin the performance enhancements in Li-S batteries.<br/><br/><br/><b>References:</b><br/>[1] Smith, R. D. L.<i> et al.</i> <i>Science</i> <b>340</b>, 60-63 (2013).<br/>[2] Kamiya, T. & Hosono, H. <i>NPG Asia Mater.</i> <b>2</b>, 15-22 (2010).<br/>[3] Salleo, A.<i> et al.</i> <i>Nat. Mater.</i> <b>2</b>, 796-800 (2003).<br/>[4] Irisarri, E., Ponrouch, A. & Palacin, M. R. <i>J Electrochem. Soc.</i> <b>162</b>, A2476-A2482 (2015).<br/>[5] Tan, S.<i> et al.</i> <i>ACS Energy Lett.</i> <b>8</b>, 2496-2504 (2023).<br/>[6] Berthier, L. & Biroli, G. <i>Rev. Mod. Phys.</i> <b>83</b>, 587-645 (2011).<br/>[7] Kamaya, N.<i> et al.</i> <i>Nat. Mater.</i> <b>10</b>, 682-686 (2011).<br/>[8] Zhang, Z. Z.<i> et al.</i> <i>Energ. Environ. Sci.</i> <b>11</b>, 1945-1976 (2018).<br/>[9] Kudu, Ö. U.<i> et al.</i> <i>Energy Storage Mater.</i> <b>44</b>, 168-179 (2022).<br/>[10] Wang, J. L., Yang, J., Xie, J. Y. & Xu, N. X. <i>Adv. Mater.</i> <b>14</b>, 963-+ (2002).<br/>[11] Huang, C. J.<i> et al.</i> <i>J Power Sources</i> <b>49</b><b>2, </b>229508 (2021).<br/>[12] Liu, H.<i> et al.</i> <i>Mater. Today</i> <b>42</b>, 17-28 (2021).<br/>[13] Wang, S.<i> et al.</i> <i>J Am. Chem. Soc.</i> <b>145</b>, 9624-9633 (2023).<br/>[14] Wang, X. L., Tan, S., Yang, X. Q. & Hu, E. Y. <i>Chinese Phys B</i> <b>29</b> (2020).<br/>[15] Billinge, S. J. L. & Levin, I. <i>Science</i> <b>316</b>, 561-565 (2007).<br/>[16] Wiaderek, K. M.<i> et al.</i> <i>J Am. Chem. Soc.</i> <b>135</b>, 4070-4078 (2013).