Mechanically Robust Bilayer Solid Electrolyte Interphase Enabled by Sequential Decomposition Mechanism for...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Micron-sized silicon (Si)-based materials offer high capacity and low cost for battery anodes.
• Severe volume expansion during lithiation causes mechanical stress on the solid electrolyte interphase (SEI), leading to premature capacity decay.
• Existing SEI regulation strategies often compromise manufacturability and cost.

Purpose of the Study:

• To develop a novel, low-cost electrolyte additive for Si-based anodes.
• To engineer a robust bilayer SEI with high Li+ conductivity to mitigate volume expansion and enhance cycle life.
• To improve the stability and performance of Si-based anodes in energy storage applications.

Main Methods:

• A novel electrolyte additive, BE-TF, composed of 3 wt% trimethyl phosphate (TMP) and 5 wt% fluoroethylene carbonate (FEC) in a carbonate electrolyte, was employed.
• A sequential decomposition mechanism was utilized to generate a bilayer SEI architecture.
• Electrochemical performance was evaluated using micron-sized SiOₓ anodes and industrial-grade pouch cells.

Main Results:

• The BE-TF electrolyte successfully generated a bilayer SEI with a LiF-rich inner layer and a Li₃PO₄-rich outer layer.
• The engineered SEI effectively suppressed volume expansion and shielded particles from detrimental side reactions.
• A micron-sized SiOₓ anode using BE-TF electrolyte demonstrated 88% capacity retention after 200 cycles at 1 A g⁻¹.
• A 3.5 Ah NCM||Gr-micron-sized SiOₓ pouch cell maintained >81% capacity retention after 1000 cycles at a 3 C charging rate.

Conclusions:

• The novel BE-TF electrolyte additive provides a cost-effective strategy for constructing a robust bilayer SEI for Si-based anodes.
• This approach significantly enhances the cycle life and capacity retention of Si-based anodes, addressing key challenges in their application.
• The developed electrolyte shows promise for long-term stability in industrial-grade battery cells, paving the way for advanced energy storage solutions.