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• Jr, Andrew Pastusic; Skurtveit, Amalie & Koposov, Alexey Y. (2026). Comparative Study of Bi2S3 and Sb2S3 as Conversion/Alloying Anodes for Na-Ion Batteries. ACS Applied Energy Materials. doi: 10.1021/acsaem.6c02364. Full text in Research Archive Show summary

  Bi- and Sb-based materials have gained a significant interest as anode materials for Na-ion batteries. Bi2S3 and Sb2S3 are isostructural and isovalent chalcogenides that should undergo similar conversion/alloying reaction with the Na-ion when placed in a battery. However, the effect of cation (Bi vs Sb), particle morphology, and electrolyte environment on (de)sodiation mechanisms and cycling stability remains poorly understood. Herein, a systematic study of several morphologies of Bi2S3 and Sb2S3 in two electrolyte systems for Na-ion batteries is presented. Bi2S3 exhibited distinct electrochemical plateaus associated with crystalline-crystalline phase transitions, clearly resolved by operando and ex situ X-ray diffraction, following a conventional Bi-based conversion/alloying pathway via Na3Bi and Na2S during sodiation and a back-conversion reaction culminating in NaBiS2 at the end of desodiation. In contrast, Sb2S3 rapidly lost long-range order and cycled predominantly in the amorphous regime. Ex situ total X-ray scattering and X-ray absorption spectroscopy revealed that the (de)sodiation involved the formation and rearrangements of amorphous Na–Sb–S networks approximated by NaSbS0.5, Na2S4, and ternary Na5–xSbS. In both systems, ether-based electrolytes improved the cyclability relative to carbonate-based electrolytes regardless of particle morphology and size, revealing that electrolyte choice plays a decisive role in controlling the performance of conversion/alloying anodes.

• Brennhagen, Anders; Saha, Dipankar; Berdiell, Izar Capel; Jr, Andrew Pastusic; Koposova, Marta & Wragg, David S. [Show all 10 contributors for this article] (2025). Mechanical deformations in battery current collectors observed by operando X-ray diffraction on Si/graphite anodes. Chemical Communications. ISSN 1359-7345. 61(98), p. 19485–19488. doi: 10.1039/d5cc04995d. Full text in Research Archive Show summary

  Current collectors in Li-ion batteries are often considered passive components with minimal influence on performance. However, materials with large expansion during lithiation may influence the current collector. Herein, we demonstrate mechanical deformations of the Cu current collector in Si/graphite electrodes using operando X-ray diffraction.

• Skurtveit, Amalie; Jr, Andrew Pastusic; Brennhagen, Anders; Maddar, Faduma M.; Mohn, Chris Erik & Karmakar, Abhoy [Show all 13 contributors for this article] (2025). Unique Na5−xSbSe Phase Enables High-Rate Performance of Sb2Se3 Anodes in Na-Ion Batteries. Advanced Energy Materials. ISSN 1614-6832. 15(31), p. 1–16. doi: 10.1002/aenm.202501433. Full text in Research Archive Show summary

  Na-ion batteries (NIBs) need new anode materials to improve energy density. Metal chalcogenides, such as Sb2Se3, represent a promising alternative to commonly used hard carbon materials, demonstrating high-rate performance up to 5 A g−1 with minimal capacity losses. However, Sb2Se3 is believed to operate under the conversion/alloying mechanism, typically linked with large structural transformations and volumetric changes—quite contrary to its performance. Herein, by combining multiple operando techniques and atomistic simulations, a new fully sodiated phase, Na5−xSbSe, is unambiguously revealed as the origin of the high-rate performance of Sb2Se3. Na5−xSbSe is stable within 0.01–0.80 V versus Na/Na+ and crystallizes in I4/mmm. The remarkable structural flexibility of Na5SbSe to changes in Na-content allows the anode to be (de)sodiated with minimal volumetric changes (≈3.4%). This unique “breathing effect” is intimately linked to high inherent vacancy concentration, disordered, and structurally flexible anion sublattice, providing a stable framework for fast Na diffusion, contributing to the fast-charging properties of Sb2Se3. The study showcases the power of operando methods for discovering new phases that are hidden in the mechanistic paths of well-studied reactions and underlines the intertwined nature of various characterization methods assisted by atomistic insights for a comprehensive understanding of complex (de)sodiation mechanisms.

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• Skurtveit, Amalie; Jr, Andrew Pastusic; Brennhagen, Anders; Maddar, Faduma M.; Mohn, Chris Erik & Karmakar, Abhoy [Show all 13 contributors for this article] (2026). Hidden Na5SbSe Unlocks Sb2Se3 Anodes for Na-Ion Batteries. Full text in Research Archive Show summary

  Antimony selenide (Sb2Se3) is a promising alternative to commonly used NIB anodes, storing 12 Na+ per formula unit, to achieve a capacity of 670 mAh g-1. The (de)sodiation mechanism is very complex: the material progresses through multiple phases when interacting with Na+, including intercalation, con-version, and alloying reactions. These multiple chemical transformations may kinetically limit the material at high rates, however, Sb2Se3 can deliver almost 150 mAh g-1 at 5000 mA g-1. Understanding this unusual behavior is important not only to rationalize the electrochemical performance, but also for the design of other materials capable of working at high (dis)charge rates. Meanwhile, subtle phase transitions or transformations of active battery materials can be traced in operando X-ray diffraction (XRD), which enables the extraction of real-time information about potentially hidden mechanistic pathways, including the discovery of new materials. In this study, Na5SbSe was discovered as the main sodiated product of Sb2Se3 anodes. Na5SbSe is predominantly composed of Na-ions and has a highly flexible composition (breathing effect) that unlocks the exceptional high rate performance of Sb2Se3 anodes

• Skurtveit, Amalie; Jr, Andrew Pastusic; Brennhagen, Anders; Maddar, Faduma M.; Mohn, Chris Erik & Karmakar, Abhoy [Show all 13 contributors for this article] (2026). Material's Discovery via Synchrotron Operando XRD and XAS: the Case of Sb2Se3 Anodes for Na-Ion Batteries. Full text in Research Archive Show summary

  Antimony selenide (Sb2Se3) is a promising alternative to commonly used NIB anodes, storing 12 Na+ per formula unit, to achieve a capacity of 670 mAh g-1. The (de)sodiation mechanism is very complex: the material progresses through multiple phases when interacting with Na+, including intercalation, con-version, and alloying reactions. These multiple chemical transformations may kinetically limit the material at high rates, however, Sb2Se3 can deliver almost 150 mAh g-1 at 5000 mA g-1. Understanding this unusual behavior is important not only to rationalize the electrochemical performance, but also for the design of other materials capable of working at high (dis)charge rates. Meanwhile, subtle phase transitions or transformations of active battery materials can be traced in operando X-ray diffraction (XRD), which enables the extraction of real-time information about potentially hidden mechanistic pathways, including the discovery of new materials. In this study, operando XRD and X-ray absorption spectroscopy (XAS) were employed to unravel the mysteries of the (de)sodiation mechanism of Sb2Se3 anodes. Complete elucidation of the reaction pathway was further enabled by solid-state NMR, ex situ work, and ab initio simulations.

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