An autotransferable alloy overlayer toward stable sodium metal anodes

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Sodium metal anodes offer high energy density but suffer from reactivity and surface instability.
• Achieving uniform sodium deposition on anodes is critical for reliable battery performance, especially without inert environments.
• Existing methods struggle with the challenges posed by sodium foil's reactivity and volumetric expansion.

Purpose of the Study:

• To develop a method for fabricating stable and uniform sodium metal anodes.
• To overcome the limitations of traditional sodium anodes, focusing on reactivity and deposition uniformity.
• To enhance the performance and reliability of sodium-based batteries.

Main Methods:

• Fabrication of a tin nanoparticle-assembled film conforming to separator pores.
• Development of a separator-assisted technique for transferring a sodium-tin alloy overlayer onto sodium foil.
• Evaluation of the sodium-tin alloy overlayer's properties, including sodiophilicity, ion conductivity, and nucleation behavior.
• Testing of half and full battery cells to assess Coulombic efficiency, polarization, and capacity retention.

Main Results:

• The fabricated tin nanoparticle film facilitated the formation of a seamless, autotransferable sodium-tin alloy overlayer.
• This alloy overlayer acted as uniform nucleation sites, reducing deposition barriers and promoting compact sodium plating.
• Sodium metal anodes with the alloy overlayer achieved a high average Coulombic efficiency of 99.9% at 3.0 mA cm⁻² for 1200 hours.
• Full cells demonstrated excellent capacity retention of 97.5% after 200 cycles at high mass loading.

Conclusions:

• The developed separator-assisted technique and sodium-tin alloy overlayer effectively stabilize sodium metal anodes.
• This approach significantly enhances the Coulombic efficiency, cycling stability, and overall performance of sodium-based batteries.
• The findings offer a promising strategy for practical applications of high-energy sodium metal batteries.