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

Micron-sized Si-based materials are promising anodes due to their high capacity, low cost, and ease of production, yet in application they suffer from severe volume expansion upon lithiation, which puts mechanical stress on the solid electrolyte interphase (SEI) that leads to premature capacity decay. Constructing a robust SEI with high Li⁺ conductivity is crucial in addressing this challenge, but most SEI regulation strategies for Si-based anodes come at the expense of manufacturability and cost. A novel and low-cost combination of additives comprised of 3 wt% trimethyl phosphate (TMP) and 5 wt% fluoroethylene carbonate (FEC) in carbonate electrolyte (BE-TF) was used to generate a bilayer SEI architecture specifically tailored for Si-based anodes by a sequential decomposition mechanism, where the lithium fluoride (LiF)-rich inner layer suppresses the volume expansion and the Li₃PO₄-rich outer layer forms a barrier that shields inner particles from detrimental side reactions. A high capacity retention of 88% after 200 cycles at 1 A g^-1 can be achieved in a battery with a micron-sized SiO_x (0 < x < 2) anode using BE-TF electrolyte. Additionally, an industrial-grade 3.5 Ah NCM||Gr-micron-sized SiO_x pouch cell using BE-TF electrolyte could maintain long-term stability after 1000 cycles with high-capacity retention of >81% at a high charging rate of 3 C.