A Hybrid Phosphate–Ether Electrolyte for High-Temperature and High-Safety 18650 Cylindrical Sodium-Ion Batteries

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Abstract
Sodium-ion batteries (SIBs) for grid-scale energy storage require electrolytes with high-temperature durability and intrinsic safety. Here, we report a nonflammable triethyl phosphate/tetrahydrofuran (TEP/THF) hybrid electrolyte for high-temperature SIBs. Weakly coordinating THF increases anion participation in the Na+ solvation structure, promoting robust inorganic-rich interphases on both electrodes, while its low viscosity accelerates Na+ transport, enabling fast ion kinetics and stable interfacial chemistry. As a result, Prussian blue||hard carbon full cells exhibit good rate capability and retain 76.0% capacity after 500 cycles at 80 °C, and 18650 cylindrical cells maintain 80.6% capacity after 300 cycles at 80 °C. Nail-penetration tests show no combustion or smoke, with a peak temperature of only 88.9 °C. Moreover, the electrolyte also supports stable cycling of layered oxide cathodes at 80 °C. This work provides a viable electrolyte design strategy for high-temperature and high-safety SIBs.
Funding Information
  • Ministry of Science and Technology (2025ZY01041)
  • Wenzhou Municipal Science and Technology Bureau (GK20250158)
  • High-end Foreign Experts Recruitment Plan of China (G2023016009L)
  • Science and Technology Plan Project of Wenzhou Municipality (ZG2022032)
  • Key Research and Development Program of Zhejiang Province (2023C01232)
  • Key Research and Development Program of Zhejiang Province (2024C01057)
  • Ministry of Finance (2025ZY01041)
  • National Natural Science Foundation of China (52250710680)

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