Solvent oligomerization pathways facilitated by electrolyte additives during solid-electrolyte interphase formation.

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• The solid-electrolyte interphase (SEI) layer is critical for lithium-ion battery longevity.
• Optimal SEI formation depends on factors and mechanisms not fully understood.
• Electrolyte additives, such as fluoroethylene carbonate (FEC) and vinylene carbonate (VC), are crucial for enhancing SEI characteristics.

Purpose of the Study:

• To investigate how FEC and VC electrolyte additives influence SEI formation.
• To elucidate the reaction networks and oligomerization pathways involved in SEI layer development.

Main Methods:

• Employed molecular dynamics (MD) simulations to study reaction networks.
• Utilized density functional theory (DFT) to investigate oligomerization pathways.
• Simulated three systems: ethylene carbonate (EC) with lithium ion, plus FEC or VC.

Main Results:

• MD simulations indicated radical oligomerization pathways via SN1 mechanisms.
• DFT analysis of both SN1 and SN2 mechanisms revealed lower free energy barriers and more stable adducts for FEC and VC compared to EC.
• FEC and VC act as branching and termination points, respectively, in the EC oligomerization process.

Conclusions:

• Electrolyte additives FEC and VC significantly alter the oligomerization of EC.
• These additives contribute to the formation of more stable SEI layers, enhancing battery performance and lifespan.
• Understanding these mechanisms is key to designing advanced lithium-ion batteries.