Grafting Functional Groups in Polymeric Binder toward Enhancing Structural Integrity of Li_xSiO₂ Anode during Electrochemical Cycling

Development of a novel polymeric binder material is necessary for improving the electrochemical performance of silicon-based anodes for Li-ion batteries, suffering from irreversible capacity loss due to their huge volume change during the electrochemical cycling. However, relevant mechanisms on how adhesion and mechanical properties of the binder are correlated to the stability of Si anode are still lacking. In this study, we investigate the role of functional groups attached in the polymeric binder on the structural stability of Li x SiO 2 using molecular dynamics simulations. A pulling test reveals that the binder with a polar group shows better adhesion properties with Li x SiO 2 than that with a nonpolar group. In addition, cohesive failure dominates the failure mode for the nonpolar group, but an adhesive to cohesive failure transition occurs for the polar group as the amount of lithiation is increased. For mechanical properties, the polar binder exhibits a larger maximum stress, while the nonpolar one can hold a larger strain. Finally, the polar group works more effectively to suppress the volume expansion of Li x SiO 2 from lithiation. The current study reveals detailed mechanisms on how polar and nonpolar polymeric binders work differently with glasses of varying degrees of lithiation and can guide the design of future generations of Si-based anodes.