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Revealing key structures for reversible sulfur redox in amorphous polymeric sulfur

Nature Materials volume 25, pages 791–798 (2026) Cite this article

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Abstract

Amorphous polymeric sulfur cathodes, such as sulfurized polyacrylonitrile (SPAN), enable high-energy lithium–sulfur batteries without cobalt or nickel, leveraging abundant sulfur. However, the limited in situ understanding of their synthesis and electrochemistry has impeded targeted optimization. Here we integrate operando high-energy total scattering with sulfur K-edge X-ray absorption spectroscopy to monitor SPAN’s formation and cycling in real time. Our results show that S–C bond formation halts further fusion of cyclized polyacrylonitrile, fostering π–π stacking and a transition from long-chain to short-chain sulfur—critical for reversible sulfur redox. These features synergistically minimize polysulfide dissolution and charge-transfer resistance, enabling optimized SPAN to achieve high capacity retention over 1,000 cycles. Operando X-ray absorption spectroscopy reveals that residual protons drive thiol–thione tautomerism, with lithium replacement during the first discharge causing ~20% irreversible capacity loss. To enhance performance, minimizing –NH groups and expanding pyridine networks are key. These findings transform SPAN optimization from empirical tuning to mechanism‑guided engineering and point the way towards sulfur loadings and energy densities competitive with state‑of‑the‑art Li‑ion cathodes.

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Fig. 1: Exemplary R-space and Q-space data for structural analysis and operando total scattering experiment setup.
The alternative text for this image may have been generated using AI.
Fig. 2: Operando total scattering of SPAN synthesis.
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Fig. 3: Sequential stages of SPAN synthesis and structural evolution.
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Fig. 4: Impact of π–π stacking and sulfur-chain length on the reversibility and stability of organosulfur electrochemistry.
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Fig. 5: First‑cycle irreversibility in SPAN.
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Data availability

Data generated or analysed during this study are provided in the Article or the Supplementary Information. Further data are available from the corresponding authors upon request. Source data are provided with this paper.

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Acknowledgements

N.W., S.L., S.T., D.Y. and E.H. were supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office (VTO), of the US Department of Energy (DOE) through the Advanced Battery Materials Research (BMR) Program including the Battery500 Consortium under contract number DE-SC0012704. Y.Z., D.K. and P.B. were supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, VTO, of the US DOE, through the BMR Program (Battery500 Consortium phase 2) under DOE contract number DE-AC05-76RL01830 from the Pacific Northwest National Laboratory (PNNL). S.W. and P.L. were supported by the VTO of the US DOE through the BMR Program (Battery500 Consortium) under contract numbers DE-EE0007764 and PNNL-595241 from PNNL. This research used beamlines 28-ID-2, 23-ID-2 and 8-BM of NSLS-II, a US DOE Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory, under contract number DE-SC0012704.

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Authors and Affiliations

  1. Chemistry Division, Brookhaven National Laboratory, Upton, NY, USA

    Nan Wang, Seungmin Lee, Sha Tan, Dean Yen & Enyuan Hu

  2. Department of Nanoengineering, University of California, San Diego, La Jolla, CA, USA

    Shen Wang & Ping Liu

  3. Department of Chemical Engineering, Texas A&M University, College Station, TX, USA

    Yu Zheng, Dacheng Kuai & Perla Balbuena

  4. National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY, USA

    Hui Zhong, Sanjit Ghose & Yonghua Du

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Contributions

N.W. and E.H. conceived the idea and designed the experiments. S.W. and P.L. helped carry out the electrochemical measurements. Y.Z., D.K. and P.B. performed the calculations. S.G., H.Z. and Y.D. helped carry out the synchrotron experiments. S.L. assisted with the DRT analysis. S.T. and D.Y. contributed to the PDF analysis results. N.W. and E.H. wrote the paper with input from all authors.

Corresponding author

Correspondence to Enyuan Hu.

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Nature Materials thanks Hong-Gang Liao and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information (download PDF )

Supplementary Figs. 1–25, Table 1 and Note.

Supplementary Data 1 (download TXT )

Atomic coordinates of SPAN with long-chain sulfur and π–π stacking.

Supplementary Data 2 (download TXT )

Atomic coordinates of SPAN with short-chain sulfur and π–π stacking.

Supplementary Data 3 (download TXT )

Atomic coordinates of SPAN with short-chain sulfur but without π–π stacking.

Source data

Source Data Fig. 1 (download XLSX )

PDF data for c-PAN and S8 (Fig. 1a). X-ray scattering data for hard carbon (Fig. 1b).

Source Data Fig. 2 (download XLSX )

Operando PDF (Fig. 2a,b) and X-ray scattering data (Fig. 2c) during SPAN synthesis.

Source Data Fig. 4 (download XLSX )

Charge–discharge data for SPAN and 4,4-dipyridyl disulfide (Fig. 4a,b). Impedance (Fig. 4c,d) and cycle performance data (Fig. 4e) of SPAN synthesized at different temperatures.

Source Data Fig. 5 (download XLSX )

Spectroscopy data of SPAN (Fig. 5a) and reference standards (Fig. 5b). Operando spectroscopy of SPAN during charge–discharge in the first cycle (Fig. 5d). PDF data and first-cycle charge–discharge profile of SPAN (Fig. 5f).

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Wang, N., Wang, S., Zheng, Y. et al. Revealing key structures for reversible sulfur redox in amorphous polymeric sulfur. Nat. Mater. 25, 791–798 (2026). https://doi.org/10.1038/s41563-026-02484-y

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