Grafting functional groups in polymeric binder towards enhancing structural integrity of LixSiO2 anode during electrochemical cycling

Abstract: The development of a novel polymeric binder material is necessary for improving 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 LixSiO2 using molecular dynamics simulations. A pulling test reveals that the binder with a polar group shows better adhesion properties with LixSiO2 than those 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 LixSiO2 from lithiation. The current study reveals detailed mechanisms on how polar and nonpolar polymeric binders work differently with glasses of varying degree of lithiation and can guide the design of future generations of Si-based anodes.