Synergic Coordination Effect in Nonflammable Deep Eutectic Electrolyte for High-Performance Sodium-Ion Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Deep eutectic electrolytes (DEEs) are crucial for advancing safe sodium-ion batteries (SIBs).
• A key challenge is developing DEEs that balance conductivity, interfacial compatibility, and safety.
• Existing DEEs often struggle to meet these demanding requirements for high-performance SIBs.

Purpose of the Study:

• To engineer a novel DEE for SIBs by combining N-methylacetamide (NMA) and sodium-difluoro(oxalato)borate (NaDFOB).
• To investigate the synergistic interactions (Na-bonds and hydrogen bonds) within the DEE and their impact on battery performance.
• To evaluate the electrochemical properties, interfacial compatibility, and cycling stability of the developed DEE in SIBs.

Main Methods:

• Synthesis of a DEE by mixing N-methylacetamide (NMA) and sodium-difluoro(oxalato)borate (NaDFOB).
• Characterization of the DEE's ionic conductivity, oxidation voltage, and nonflammability.
• Electrochemical testing of NVP||Na cells and full cells using the developed DEE, including cycling performance, rate capability, and elevated temperature stability.

Main Results:

• The engineered DEE exhibits high ionic conductivity (4.03 mS cm⁻¹ at 25 °C) and a high oxidation voltage (4.63 V vs. Na⁺/Na).
• The DEE demonstrates nonflammability and enhanced electrode-electrolyte interfacial compatibility.
• NVP||Na cells show excellent cycling performance (86.8% retention after 7000 cycles at 5 C) and rate capability, with robust performance at elevated temperatures.
• Full cells achieve significant improvements in cycle stability (90.7% retention after 300 cycles) and rate performance.

Conclusions:

• The synergistic interplay between Na-bonds and hydrogen bonds in the NMA-NaDFOB DEE is key to its superior performance.
• This amide-based DEE offers a promising avenue for designing advanced electrolytes for high-performance and safe sodium-ion batteries.
• The developed DEE significantly advances the potential of SIB technology for future energy storage applications.