Influence of the SEI Formation on the Stability and Lithium Diffusion in Si Electrodes

Silicon (Si) is an attractive anode material for Li-ion batteries (LIBs) due to its high theoretical specific capacity. However, the solid-electrolyte interphase (SEI) formation, caused by liquid electrolyte decomposition, often befalls Si electrodes. The SEI layer is less Li-ion conductive, which would significantly inhibit Li-ion transport and delay the reaction kinetics. Understanding the interaction between the SEI components and Li-ion diffusion is crucial for further improving the cycling performance of Si. Herein, different liquid electrolytes are applied to investigate the induced SEI components, structures, and their role in Li-ion transport. It is found that Si electrodes exhibit higher discharge capacities in LiClO₄-based electrolytes than in LiPF₆-based electrolytes. This behavior suggests that a denser and more conductive SEI layer is formed in LiClO₄-based electrolytes. In addition, a coating of a Li₃PO₄ artificial SEI layer on Si suppresses the formation of natural SEI formation, leading to higher capacity retentions. Furthermore, galvanostatic intermittent titration technique (GITT) measurements are applied to calculate Li-ion diffusion coefficients, which are found in the range of 10^-23-10^-19 m²/s.