Surprising Relationship between Silicon Anode Calendar Aging and Electrolyte Components in a Localized...

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Silicon anodes offer high capacity for next-generation batteries but suffer from poor calendar lifetime.
• Localized high-concentration electrolytes (LHCEs) have shown promise in extending silicon anode lifespan.
• The specific roles of individual electrolyte components in silicon anode calendar aging are not fully understood.

Purpose of the Study:

• To investigate the influence of electrolyte constituent ratios on silicon anode calendar aging.
• To elucidate the formation mechanisms of the solid electrolyte interphase (SEI) under different LHCE conditions.
• To determine the relationship between SEI composition and silicon anode passivity.

Main Methods:

• Utilized a voltage hold (V-hold) protocol to assess calendar aging.
• Employed LHCEs with varied molar ratios of lithium bis(fluorosulfonyl)imide (LiFSI), tetramethylene sulfone (TMS), and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE).
• Analyzed SEI composition using X-ray photoelectron spectroscopy (XPS) and measured parasitic current.

Main Results:

• Calendar lifetime and irreversible lithium loss were independent of the tested LHCE formulations.
• SEI composition varied significantly with electrolyte formulation.
• TMS-coordinated species decomposed into alkanes and LiOH; LiF originated from anion complexes.
• SEI composition did not correlate with silicon anode passivity, indicating SEI-electrolyte interactions are dominant.

Conclusions:

• Electrolyte formulation in LHCEs does not directly influence silicon anode calendar lifetime.
• The solid electrolyte interphase (SEI) composition is dependent on electrolyte constituents but not the primary factor in silicon anode passivity.
• SEI-electrolyte interactions are identified as the critical mechanism governing silicon anode calendar aging in LHCEs.