Identification of the Solid Electrolyte Interface on the Si/C Composite Anode with FEC as the Additive

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Silicon anodes offer high lithium storage capacity for next-generation lithium-ion batteries.
• Challenges include large volume changes and unstable solid electrolyte interface (SEI) formation during cycling.
• The exact mechanism of fluoroethylene carbonate (FEC) additive's benefit remains unclear.

Purpose of the Study:

• To elucidate the role of FEC in improving the electrochemical performance of silicon-based anodes.
• To characterize the composition, structure, and inhomogeneity of the SEI layer with and without FEC.
• To understand how FEC influences SEI formation and its impact on silicon anode stability.

Main Methods:

• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.
• X-ray photoelectron spectroscopy (XPS).
• X-ray photoemission electron microscopy (XPEEM).

Main Results:

• A denser SEI layer is formed on Si/C anodes when using FEC as an electrolyte additive.
• The denser SEI with FEC suppresses the penetration of small molecules like LiPF₆, P-O, and Li-O species.
• FEC-containing SEI mitigates the hydrolysis of LiPF₆ and promotes the formation of protective LiF, reducing silicon particle cracking.

Conclusions:

• FEC additive significantly enhances SEI properties on silicon anodes.
• The improved SEI layer contributes to better electrochemical performance and stability of silicon anodes.
• This work provides insights for optimizing silicon-based anodes for advanced lithium-ion batteries.