Tailoring of a reinforcing and artificial self-assembled alkyl sulfonic acid layer electrolyte interphase on silicon as an anode for high-energy-density lithium-ion batteries

Making anodes from silicon results in various longstanding challenges, including drastic volume expansion, formation of a thick and high-impedance solid electrolyte interphase (SEI), rapid capacity decay, and poor rate performance. The use of these anodes in high-energy-density lithium-ion batteries is thus limited. Herein, an artificial SEI with a self-assembled alkyl sulfonic acid (SAASA) reinforcement structure is deposited onto the surface of Si through an organosilane approach (to obtain a Si-SAASA electrode). A coupling agent, 3-mercaptopropyl trimethoxysilane (MPTMS), was tailored on the surface of Si to produce strong siloxane (Si–O–Si) bonds. The thiol group (-SH) in the MPTMS molecule consequently oxidized into sulfonic acid (-SO 3 H), resulting in sulfonated artificial SEI reinforcement on the Si surface. With sulfonated MPTMS, the Si anode was improved through the formation of -SO 3 Li, which enhanced Li + -ion diffusion and ionic mobility. The Si-SAASA electrode has the highest discharge capacity of 1507.1 mAh g −1 at 0.5 C after 400 cycles with a retention capacity of 74.3%, high rate capability, and a high lithium-ion diffusion coefficient (2.88 × 10 −12 cm 2 s −1 ). This study demonstrated that the SAASA reinforcement, acting as an artificial SEI, gives the electrode mechanical integrity, meaning that during cycling, expansion of the Si's volume can be accommodated and the fragmentation of Si particles can be prevented through the strong siloxane bonds. Additionally, the SAASA serves as a protection against parasitic reactions between the electrolyte and active interface, thus preventing the repeated growth of a thick and high-impedance SEI layer. The developed approach will be exceedingly effective and minimize the cost of developing high-performance Si anodes for next-generation lithium-ion batteries.