Elucidating sodium ion storage mechanisms in hard carbon anodes at the electronic level

Sodium‐ion batteries (SIBs) are a promising technology for advanced energy storage systems. Hard carbon (HC) is a commonly used SIB anode material; however, the Na ion storage mechanism in HC remains poorly understood and highly debated. Here, the paramagnetic species in HC during Na ion storage are systematically studied to elucidate the underlying mechanism at an electronic level using high‐resolution electron paramagnetic resonance (EPR) spectroscopy, complemented by in situ Raman spectroscopy, in situ synchrotron X‐ray diffraction, and density functional theory calculations. This investigation identifies and characterizes the coexistence of two distinct intercalation processes in HC: Na ion intercalation and Na+‐solvent co‐intercalation, which are active across both the sloping and plateau voltage regions. Additionally, in the sloping region, Na ions are also stored at in‐plane Stone‐Wales defect sites, which transition into a quasi‐metallic state and subsequently to metallic Na as Na ion intercalation progresses. This transformation is driven by charge redistribution within the graphene layers. These insights establish a direct paramagnetic‐electronic structure‐electrochemical property relationship in HC, providing new insights into the Na ion storage mechanism. Furthermore, this study highlights the unique capability of EPR spectroscopy in elucidating the charge storage mechanism in electrode materials. © 2025 The Author(s). Advanced Functional Materials published by Wiley-VCH GmbH. This is an open access article under the terms of th eCreative Commons Attribution-NonCommercial-NoDerivs License,which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modiﬁcations or adaptations are made

Keywords

Lithium ion batteries, Energy storage systems, Energy storage, Sodium, Carbon, Raman spectroscopy, High energy physics, Adsorption

Citation

Xia, Q., Ko, C.-L., Cooper, E. R., Gu, Q., Knibbe, R., & Harmer, J. R. (2025). Elucidating sodium ion storage mechanisms in hard carbon anodes at the electronic level. Advanced Functional Materials, (Early view), 2421976. doi:10.1002/adfm.202421976

URI

https://doi.org/10.1002/adfm.202421976
https://apo.ansto.gov.au/handle/10238/16239

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