High-Efficiency Lithium Sulfur Cells With Suppressed Polysulfide Solubility Using a Cost-Effective Ammonium-Based...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Lithium-sulfur (Li-S) batteries face challenges with polysulfide shuttle (PS) and unstable lithium metal anodes.
• Existing electrolytes often struggle to simultaneously address these critical issues, limiting battery performance and lifespan.
• Developing advanced electrolytes is crucial for unlocking the high theoretical energy density of Li-S battery technology.

Purpose of the Study:

• To engineer a mixed-anion ionic liquid (IL) electrolyte for stable lithium metal passivation and effective polysulfide suppression in Li-S batteries.
• To investigate the impact of the novel electrolyte on electrochemical performance, including capacity retention and cycling stability.
• To elucidate the mechanism of solid-electrolyte interphase (SEI) formation and its correlation with battery performance.

Main Methods:

• Synthesis and characterization of a mixed-anion ionic liquid electrolyte (N1113FSI with LiFSI and LiTFSI).
• Electrochemical testing (specific capacity, retention, cycling) and electrochemical impedance spectroscopy (EIS).
• Spectroscopic analysis (Raman, depth-resolved XPS) to study polysulfide suppression and SEI composition.

Main Results:

• Achieved a specific capacity of 900 mAh g⁻¹ with 70% retention after 300 cycles, demonstrating excellent stability.
• Electrolyte showed insensitivity to electrolyte-to-sulfur ratio, unlike conventional electrolytes.
• XPS analysis revealed formation of a dense, inorganic-rich SEI layer (rich in LiF) by N1113FSI, suppressing polysulfide dissolution to sub-mM levels.

Conclusions:

• The designed mixed-anion IL electrolyte effectively suppresses polysulfide shuttle and enables stable lithium metal anode operation.
• The cation-dependent SEI chemistry, particularly the abundant LiF formation with N1113FSI, is key to superior Li-S battery performance.
• This tailored IL approach offers a promising strategy for developing high-performance, long-lasting lithium-sulfur batteries.