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

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Sodium-ion batteries require high areal capacity and stable low-temperature operation for practical use.
• Sluggish kinetics and interfacial instability at low temperatures hinder battery development.

Purpose of the Study:

• To improve sodium-ion battery performance at low temperatures.
• To enhance interfacial stability during cycling.

Main Methods:

• Incorporation of ethoxy(pentafluoro)cyclotriphosphazene (PFPN) into NaPF6-PC/DEC electrolyte.
• Investigation of PFPN's effect on Na+ migration kinetics and anion redistribution.
• Electrochemical testing of NaNi1/3Fe1/3Mn1/3O2∥hard carbon batteries at -40 °C.

Main Results:

• PFPN weakens solvent-ion interactions, enhancing Na+ migration at low temperatures.
• PFPN facilitates stable anion-derived interphase formation.
• Batteries achieved 2.0 mAh cm-2 areal capacity and 89.9% retention over 200 cycles at -40 °C.
• Pouch cells delivered 112.5 Wh kg-1 energy density.

Conclusions:

• PFPN-modified electrolytes significantly improve low-temperature sodium-ion battery performance.
• This approach is promising for developing high-areal-capacity batteries for cold regions.