Solubility Activation of Recessive Solvent Mitigates Interphase Dissolution for High-Performance Sodium-Ion Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Solid electrolyte interphase (SEI) dissolution in sodium-ion batteries (NIBs) leads to electrolyte decomposition, gas evolution, capacity fade, and safety concerns.
• Reducing electrolyte solvation power can mitigate SEI dissolution but often compromises ionic conductivity.

Purpose of the Study:

• To develop a weakly solvating electrolyte (WSE) that maintains high ionic conductivity while preventing SEI dissolution in NIBs.
• To design a stable and robust inorganic-rich SEI layer for improved NIB performance and safety.

Main Methods:

• A recessive solvent activation strategy using 1,2-epoxy-3,3,3-trifluoropropane (TFPO) and diethylene glycol diethyl ether (DEE).
• Formulation of a WSE with a low DEE content (24 vol%) and a high anion-to-DEE ratio.
• Electrochemical testing of full cells (hard carbon || NaMn0.33Fe0.33Ni0.33O2) and 1.0 Ah pouch cells.

Main Results:

• The DEE-TFPO system demonstrated tunable solvation behavior, enabling the design of a WSE.
• The optimized WSE mitigated solvent-induced SEI dissolution and promoted an inorganic-rich SEI layer.
• Full cells retained 80.0% capacity after 500 cycles; 1.0 Ah pouch cells retained 99.5% capacity after 230 cycles with suppressed gas release.

Conclusions:

• The recessive solvent activation strategy effectively balances solvation power and ionic conductivity in NIB electrolytes.
• The developed WSE significantly enhances the cycle life and safety of sodium-ion batteries.
• This approach offers a promising pathway for developing high-performance and stable sodium-ion energy storage systems.