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<p>Hard carbon (HC) remains the most commercially viable anode for sodium-ion batteries, yet its low initial Coulombic efficiency and unstable solid electrolyte interphase (SEI) hinder long-term performance. Electrolyte engineering offers a promising strategy to regulate SEI chemistry, enhancing interfacial Na<sup>+</sup> transport and interphase stability. However, the respective roles of solvents and anions in tailoring the SEI on HC remain elusive. Here we propose a “revitalization” strategy to clarify the synergistic influence of solvent and anion chemistry by systematically evaluating three electrolytes: 1.0 M NaPF<sub>6</sub> in EC/DMC, 1.0 M NaPF<sub>6</sub> in diethylene glycol dimethyl ether (NaPF<sub>6</sub>-G2), and 1.0 M sodium trifluoromethanesulfonate in G2 (NaOTF-G2). Combined experimental and theoretical analyses reveal that weak Na<sup>+</sup>-G2 interactions permit more anions to enter the primary solvation shell, facilitating the formation of an inorganic-rich SEI that promotes high ionic conductivity and redox kinetics. Additionally, the preferential decomposition of OTF<sup>−</sup>-anions results in a uniform and robust SEI. As a result, HC anodes cycled in NaOTF-G2 deliver a reversible specific capacity of ~200 mAh g<sup>−1</sup> over 3000 cycles. Furthermore, a Na<sub>3</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>||HC pouch cell incorporating this optimized electrolyte achieves a capacity retention of 81% at −40 °C. This work provides molecular-level insights into electrolyte design principles and highlights the critical role of solvation structure in enabling durable low-temperature sodium storage.</p>

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Insights into targeted effects of salt and solvent on Na+ storage in hard carbon anodes toward ultra-low temperature sodium batteries

  • 期刊论文

  • 发表日期：

    2025年10月16日

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  • Sainan Luo,
  • Zhen Hou,
  • Zixin Qi,
  • Qin Li,
  • Yuepeng Pang,
  • Jiafeng Ruan,
  • Shiyou Zheng

摘要

Hard carbon (HC) remains the most commercially viable anode for sodium-ion batteries, yet its low initial Coulombic efficiency and unstable solid electrolyte interphase (SEI) hinder long-term performance. Electrolyte engineering offers a promising strategy to regulate SEI chemistry, enhancing interfacial Na+ transport and interphase stability. However, the respective roles of solvents and anions in tailoring the SEI on HC remain elusive. Here we propose a “revitalization” strategy to clarify the synergistic influence of solvent and anion chemistry by systematically evaluating three electrolytes: 1.0 M NaPF6 in EC/DMC, 1.0 M NaPF6 in diethylene glycol dimethyl ether (NaPF6-G2), and 1.0 M sodium trifluoromethanesulfonate in G2 (NaOTF-G2). Combined experimental and theoretical analyses reveal that weak Na+-G2 interactions permit more anions to enter the primary solvation shell, facilitating the formation of an inorganic-rich SEI that promotes high ionic conductivity and redox kinetics. Additionally, the preferential decomposition of OTF−-anions results in a uniform and robust SEI. As a result, HC anodes cycled in NaOTF-G2 deliver a reversible specific capacity of ~200 mAh g−1 over 3000 cycles. Furthermore, a Na3V2(PO4)3||HC pouch cell incorporating this optimized electrolyte achieves a capacity retention of 81% at −40 °C. This work provides molecular-level insights into electrolyte design principles and highlights the critical role of solvation structure in enabling durable low-temperature sodium storage.