Stabilizing Sodium-Ion Batteries in Harsh Environments via a Versatile Additive Strategy

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Sodium-ion batteries (SIBs) face stability issues at elevated temperatures and pressures.
• The NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) cathode exhibits poor performance under harsh conditions.
• Developing robust electrolytes is critical for SIB commercialization.

Purpose of the Study:

• To design a novel electrolyte additive for stabilizing NFM cathodes in SIBs.
• To investigate the mechanism by which the additive enhances electrochemical performance.
• To evaluate the long-term cycling stability and practical applicability of the modified electrolyte.

Main Methods:

• Synthesis and characterization of Ethoxy(pentafluoro)cyclotriphosphazene (PFPN) as an electrolyte additive.
• Electrochemical testing of NFM cathodes in SIBs with and without PFPN under elevated temperatures.
• Analysis of the cathode electrolyte interphase (CEI) formation and properties using advanced techniques.
• Coin cell and pouch cell performance evaluation.

Main Results:

• PFPN effectively modulates Na⁺ solvation, reducing desolvation energy barriers.
• A stable, ionically conductive CEI layer enriched with NaF, NaCl, and Na₃N is formed.
• Capacity retention for NFM//Na coin cells improved from 43.34% to 78.07% after 300 cycles at 45 °C.
• PFPN enhanced electrode wettability and suppressed undesirable side reactions.
• NFM//HC full coin cells demonstrated excellent cycling stability over 1000 cycles (≈0.02% weekly attenuation).
• Ah-grade pouch cells achieved 83.79% capacity retention after 500 cycles.

Conclusions:

• PFPN is a highly effective additive for enhancing the high-temperature performance and cycling stability of NFM-based SIBs.
• The additive promotes superior CEI formation and electrolyte stability, addressing key challenges in SIB operation.
• The findings suggest PFPN's potential for practical application in high-performance, long-lasting SIBs.