Binder-induced interphase regulation in electric double layer for enhanced stability of silicon anode

The significant volume expansion (over 300%) of silicon (Si) leads to rupture and erratic regeneration of the solid electrolyte interphase (SEI), resulting in parasitic reactions and capacity degradation. While polymer binders assist in the formation of stable SEI, the impact of binders on the electric double layer (EDL) structure and the mechanism underlying SEI formation at the molecular scale remains inadequately understood. In this study, we present a binder for Si anode that can modulate the initial adsorption properties and the solvent coordination behavior in EDL to achieve superior SEI. The strong affinity of the functional group for Li⁺ competes with the solvent to reduce the desolvation energy. This results in a redistribution of Li⁺ and the electrolyte solvent, decreasing free solvent content while inhibiting organic solvent reduction. The findings demonstrated that ultra-thin SEI (11 nm) consists of the inorganic inner layer and organic outer layer with high modulus and exceptional ionic conductivity, contributing to impressive capacity retention and exemplary rate performance. This work substantiates the role of binders in interfacial conditioning while providing novel insights into their practical application in silicon anode.