Fluorinated Artificial Solid-Electrolyte-Interphase Layer for Long-Life Sodium Metal Batteries.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Sodium metal batteries offer high capacity and cost-effectiveness but suffer from safety issues due to dendritic sodium formation and unstable solid-electrolyte interphase (SEI) layers.
• Uncontrolled SEI formation leads to increased cell impedance and premature battery failure, limiting the practical application of sodium metal batteries.

Purpose of the Study:

• To develop a stable, artificial SEI layer on sodium metal surfaces to mitigate safety concerns and improve battery performance.
• To investigate the efficacy of a fluorinated protective layer formed using tin fluoride in enhancing the cycling stability of sodium metal batteries.

Main Methods:

• A cost-effective, single-step method was employed to create a fluorinated artificial SEI layer using various weight percentages of tin fluoride in a dimethyl carbonate solution.
• The performance of sodium metal symmetric cells with the engineered artificial SEI was evaluated through cycling tests at a current density of 0.25 mA/cm².

Main Results:

• The developed fluoride-rich artificial SEI layer effectively stabilized the sodium metal surface, suppressing dendrite formation and reducing undesired SEI growth.
• Sodium metal symmetric cells with the engineered artificial SEI exhibited an enhanced lifetime of over 3.5 times (exceeding 700 hours) compared to untreated sodium.
• The improved cycling performance is attributed to the suppression of dendrite formation and the reduction of parasitic reactions during high-current cycling.

Conclusions:

• A stable, fluorinated artificial SEI layer can be successfully fabricated using a simple and cost-effective method, significantly enhancing the safety and longevity of sodium metal batteries.
• The engineered SEI layer effectively addresses the critical challenges of dendrite formation and unstable SEI growth, paving the way for practical sodium metal battery applications.