Directional Anchoring Cross-Linked Binder for High-Performance Silicon–Carbon Anodes in Li-Ion Batteries

Silicon-based materials have garnered significant attention as anodes for Li-ion batteries due to their high theoretical capacity. However, the substantial volume expansion of silicon during cycling poses challenges such as particle pulverization and unstable solid electrolyte interface (SEI) formation. This study developed an in situ thermally cross-linked poly(acrylic acid)-tannic acid (PLT) binder with directional anchoring mechanisms to address the problems caused by volumetric expansion of silicon–carbon (Si/C) anodes. By incorporating tannic acid (TA) into the lithiated poly(acrylic acid) (PAALi) matrix, a directionally anchored cross-linked network with dual-interaction mechanisms was constructed: the aromatic moieties of TA establish robust π–π stacking interactions with graphitic carbon layers, while the carboxyl groups of PAALi form covalent esterification bonds, hydrogen bonds, and ionic dipole interactions with surface hydroxyl groups of silicon. This molecular-scale directional anchoring strategy significantly enhanced interfacial binding strength (180° peeling force of 2.6 N) and endowed the electrode with exceptional mechanical stability (elastic modulus of 6.03 GPa). Electrochemical tests demonstrated that the Si/C@PLT electrode delivered superior initial discharge capacity (1137.7 mAh/g) and capacity retention (90.02% after 100 cycles). The work provides a novel molecular engineering strategy for binder design in silicon-based composites, highlighting the critical role of interfacial directional anchoring in enhancing cycling stability for high-capacity electrodes.