Symmetric Vs Asymmetric Imide Anion Decomposition Pathways And Their Influence On Solid Electrolyte Interphase...

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• A stable solid electrolyte interphase (SEI) is crucial for the longevity of silicon anodes in lithium-ion batteries (LIBs).
• Conventional carbonate electrolytes yield unstable SEIs, limiting the practical use of Si anodes.
• Fluorinated sulfonylimide (FSI-/TFSI-) based ionic liquid (IL) electrolytes offer a promising alternative for SEI formation and enhanced capacity retention.

Purpose of the Study:

• To investigate the role of symmetric and asymmetric anions in directing SEI formation and evolution in IL-based electrolytes.
• To elucidate the mechanistic interplay between anion decomposition pathways and interfacial chemistry.
• To understand how IL electrolytes impact SEI properties and silicon anode performance.

Main Methods:

• Investigated SEI chemistry and morphology using various imidazolium-based ILs with symmetric and asymmetric anions.
• Analyzed SEI composition (e.g., LiF, LiOH, Li2SO4) and structure using surface analysis techniques.
• Correlated electrochemical performance (capacity retention, cycling stability) with SEI characteristics.

Main Results:

• Symmetrical bis(fluorinated sulfonyl)imide anions synergize with imidazolium cations to form an inorganic-rich inner SEI (LiF/LiOH) and a Li2SO4/polymeric outer layer.
• This conformal SEI coating on 3D Si anodes enhances mechanical integrity and flexibility.
• Achieved a reversible capacity of 2489 mAh/g at 1C over 250 cycles, demonstrating improved battery performance.

Conclusions:

• The synergistic interaction of symmetrical fluorinated sulfonylimide anions and imidazolium cations is key to forming a robust, multi-layered SEI.
• The resulting SEI effectively suppresses Si anode pulverization and enhances cycle life.
• Findings provide critical insights for designing advanced ionic liquid electrolytes for high-performance LIBs.