A Uniform Solid Electrolyte Interface Enabling Long Cycling in Sodium-Metal Batteries with Fast Charging

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Sodium-metal batteries (SMBs) face safety challenges due to high sodium reactivity and unstable solid electrolyte interphase (SEI) formation.
• Commercialization of SMBs is hindered by safety concerns and limited cycle life, necessitating advanced electrolyte solutions.

Purpose of the Study:

• To develop a novel deep eutectic electrolyte (DEE) for SMBs that enhances safety and electrochemical performance.
• To investigate the effect of N-methylacetamide on electrolyte nonflammability and SEI composition.
• To evaluate the cycling stability and rate capability of SMBs utilizing the developed DEE.

Main Methods:

• Formulation of a deep eutectic electrolyte (DEE) incorporating N-methylacetamide.
• Characterization of the electrolyte's ionic conductivity, electrochemical stability window, and nonflammability.
• Analysis of the solid electrolyte interphase (SEI) composition on the sodium anode using electrochemical techniques.
• Fabrication and electrochemical testing of Na3V2(PO4)3||Na cells with the DEE.

Main Results:

• The DEE demonstrated high ionic conductivity and an extended electrochemical stability window up to 4.8 V.
• Stable, uniform, and inorganic-rich SEI formation (Na2S, NaF) on the sodium anode was observed.
• Na3V2(PO4)3||Na cells exhibited excellent capacity retention (96% after 1,500 cycles at 5 C) and fast-charging capabilities.

Conclusions:

• The developed DEE effectively addresses safety concerns and improves the performance of sodium-metal batteries.
• The electrolyte promotes stable SEI formation and enhances interfacial kinetics, paving the way for commercial SMBs.
• This research provides critical insights for designing advanced electrolytes for safe and high-performance sodium-metal energy storage systems.