Fluorinated solvent coupled anions-derived hybrid interphase enabled highly reversible and cryogenic silicon anode

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Silicon (Si) anodes offer high theoretical capacity for next-generation batteries.
• Poor low-temperature performance of Si anodes is due to slow ion transport and diffusion.
• Developing electrolytes for cryogenic conditions is crucial for advanced energy storage.

Purpose of the Study:

• To develop a weakly solvating electrolyte for improved silicon anode performance at subzero temperatures.
• To investigate the formation and composition of a hybrid solid electrolyte interphase (SEI) on silicon anodes.
• To demonstrate the electrochemical viability of silicon anodes in cryogenic environments.

Main Methods:

• Formulation of a novel electrolyte using 1 M lithium bis(fluorosulfonyl)imide (LiFSI) in fluoroethylene carbonate (FEC) / methyl trifluoroacetate (MTFA).
• Electrochemical characterization of silicon anodes with the developed electrolyte at subzero temperatures.
• Molecular dynamics (MD) calculations and comprehensive material characterizations to analyze SEI composition and ion transport.

Main Results:

• The novel electrolyte facilitates ion desolvation and forms a hybrid SEI on Si anodes.
• The hybrid SEI comprises an organic outer layer and an inner layer rich in lithium fluoride (LiF) and sulfurized species.
• Silicon anodes exhibit high capacities (3100-2600 mAh g⁻¹) from 0 °C to -20 °C and 2100 mAh g⁻¹ at -30 °C.

Conclusions:

• The developed weakly solvating electrolyte significantly enhances silicon anode performance at cryogenic temperatures.
• The unique hybrid SEI structure promotes rapid Li⁺ diffusion and maintains electrode integrity in subzero conditions.
• This research paves the way for reliable high-energy batteries operating in extreme cold environments.