Constructing LiF-Dominated Interphases with Polymer Interwoven Outer Layer Enables Long-Term Cycling of Si Anodes

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Developing high-energy-density silicon (Si)-based lithium-ion batteries is crucial.
• Constructing a robust solid electrolyte interphase (SEI) is a key challenge.
• Accurate manipulation of SEI chemical composition and structure remains elusive.

Purpose of the Study:

• To achieve a LiF-dominated SEI film intertwined with a highly elastic polymer.
• To regulate the defluorination mechanism of fluorinated carbonate additives on Si electrode surfaces.
• To enhance the performance and stability of Si-based lithium-ion batteries.

Main Methods:

• Experimental and computational analysis of additive effects on SEI formation.
• Utilizing trans-difluoroethylene carbonate (DFEC) and lithium difluoro(oxalato)borate (LiDFOB) additives.
• Investigating the defluorination mechanism and polymerization of DFEC.

Main Results:

• LiDFOB additive alters DFEC decomposition, inducing direct defluorination and exclusive LiF-SEI formation.
• Defluorinated DFEC polymerizes to poly(vinylene carbonate), enhancing SEI elasticity.
• The LiF-dominated SEI with a polymer outer layer improves ionic conductivity and mechanical stability.
• Si electrodes with the designed dual-additive show superior cycling stability and rate performance (1487.3 mAh g⁻¹ after 1000 cycles at 2 A g⁻¹).

Conclusions:

• Regulating the defluorination mechanism of DFEC with LiDFOB is critical for SEI construction.
• The resulting SEI film enhances electrode reaction kinetics and structural integrity.
• This strategy significantly improves the electrochemical performance of Si-based lithium-ion batteries.