Binary Solvent Induced Stable Interphase Layer for Ultra-Long Life Sodium Metal Batteries

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Sodium metal batteries (SMBs) offer high energy density but suffer from poor reversibility due to reactive sodium metal and unstable solid electrolyte interphase (SEI) layers.
• Developing stable and efficient SMBs is crucial for next-generation energy storage solutions.

Purpose of the Study:

• To enhance the stability and performance of sodium metal batteries by optimizing electrolyte solvation structure.
• To investigate the effect of co-solvent addition on SEI layer formation and battery cycling performance.

Main Methods:

• Tuning electrolyte solvation structure by adding 2-methyl tetrahydrofuran (MTHF) as a co-solvent to diglyme (Dig).
• Utilizing time-of-flight mass spectroscopy to analyze solvation structure and SEI layer composition.
• Conducting electrochemical cycling tests on Cu||Na and Na||Na symmetric cells, and full cells with Na0.44MnO2 cathode.

Main Results:

• The MTHF co-solvent promotes an anion-dominated solvation structure, leading to a thin and uniform SEI layer.
• A Dig:MTHF (50% v/v) electrolyte achieved an average Coulombic efficiency of 99.72% over 300 cycles in Cu||Na cells.
• Na||Na symmetric cells demonstrated over 7000 hours of stability, and full cells retained 80% capacity after 500 cycles.

Conclusions:

• Optimizing electrolyte solvation structure with MTHF-based binary solvents is key to achieving high-performance and long-term stable SMBs.
• The study highlights the potential of environmentally sustainable co-solvents for advancing sodium metal battery technology.