Fluorinated Weakly Coordinating Solvent Enables High-Areal-Capacity Low-Temperature Sodium Batteries

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Abstract
High areal capacity and stable low-temperature operation are critical for the practical implementation of sodium-ion batteries, yet their development is hindered by sluggish charge/mass transfer kinetics at low temperatures and interfacial instability during cycling. Herein, we incorporate the weakly coordinating solvent ethoxy(pentafluoro)cyclotriphosphazene (PFPN) into the conventional NaPF6-PC/DEC electrolyte. PFPN competitively binds to Na+ with PC/DEC through its steric hindrance effect, weakening solvent-ion interactions to enhance Na+ migration kinetics at low temperatures. Concurrently, it coordinates with highly electronegative PF6- anions, facilitating their redistribution and the formation of a stable anion-derived electrode-electrolyte interphase. At a high areal capacity of 2.0 mAh cm-2 (N/P = 1.29) and -40 °C, the NaNi1/3Fe1/3Mn1/3O2∥hard carbon batteries utilizing the PFPN-modified electrolyte exhibit stable cycling with 89.9% capacity retention over 200 cycles, while the pouch cell delivers a high energy density of 112.5 Wh kg-1. This work offers valuable insights for the design of high-areal-capacity sodium batteries tailored for cold regions.
Funding Information
  • Fundamental Research Funds for the Central Universities (HIT.OCEF.2023039)
  • National Natural Science Foundation of China (21975100)
  • National Natural Science Foundation of China (22075063)
  • National Natural Science Foundation of China (22409042)
  • National Natural Science Foundation of China (92372110)
  • Guizhou Province (018)
  • Guizhou Province (ZZSG[2024]00)
  • FAW Group Co., Ltd., China (20220301018GX)
  • FAW Group Co., Ltd., China (20220301019GX)

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