Here we propose a chemical SEI reinforcement strategy via introducing multiple functional components as SEI components, which have strong interactions with Li-alloy material surface and effectively improve the SEI stability, including its tolerance to volume changes and surface passivation during cycling. Using a modular synthetic approach, we realized a one-step fabrication of diverse components with designed structure and anchoring amount, allowing the facile construction and optimization of the SEI. Si nanoparticle (SiNP) materials were used as the platform for demonstrating this concept. After screening and optimizing the SEI structure using various pre-anchored components, one chemically reinforced SEI (CR-SEI), reinforced by a combination of two functional components with moderate anchoring amount shows significantly improved stability compared to the SEI derived from electrolyte with FEC additives. During cycling, the CR-SEI presents unique and stable chemical composition, resulted form the addtion of pre-designed functional components, which differs from the composition of conventioal SEI. Meanwhile, the CR-SEI also maintains good and durable morphology during cycling. After many cycles, only very limited “SEI accumulation” was observed in the TEM images of SiNP with CR-SEI and the CR-SEI remains thin and uniform. This is in contrast with the poor stability of conventional SEI. Large amount of SEI accumulation and SiNPs decrease in size were observed. Finally, owing to the improved SEI stability, SiNP electrode with CR-SEI presents significantly increased electrochemical performance, including increased 1st cycle Coulombic efficiency (CE), improved cycling CE and capacity retention, and limited increase in electrochemical impedance. Particularly, the SiNP electrode with CR-SEI present much better cycle life in the full-cell system than one containing electrolyte additive improved SEI. Moreover, this strategy has also been applied to GeNP SEI reinforcement with dramatic enhancement of the SEI stability, suggesting its viability for other Li-alloy materials. Owing to the facility and modularity of the synthetic approach, we are also able to further examine more functional components potentially suitable for SEI reinforcement.