Molecular Engineering of Coacervate Network Binders for Stable Silicon-Based Anodes in Lithium-Ion Batteries

Abstract

The growing demand for high-energy-density lithium-ion batteries (LIBs) has spurred interest in silicon (Si)-based anodes, but their practical use is hindered by volumetric expansion during cycling, leading to electrode degradation and uncontrolled solid electrolyte interphase (SEI) growth. Here, a molecularly engineered approach is presented to regulate Coulomb interactions in coacervate charged polymer binders for stabilizing Si anodes. By systematically tuning effective charge density through different functional groups, electrostatic interactions within the binder network are modulated to optimize adhesion, mechanical integrity, and electrochemical performance. Four charged polymers with varying functional groups: amine (A), guanidine (G), sulfonate (S), and carboxylate (C) are synthesized and studied. The G-C binder, exhibiting the strongest Coulomb interaction, demonstrated superior adhesion, mechanical stability, and cycling performance. This binder enabled the fabrication of ultra-high areal capacity Si-based electrodes (12.2 mAh cm(-2)), outperforming previously reported binder systems. Moreover, full-cell evaluations of Si-based anodes with G-C binders and Ni-rich layered cathodes demonstrated stable cycling at high areal capacities (4.7 mAh cm(-2)), underscoring the practical viability of this approach. These findings establish Coulomb interactions as a key design parameter for next-generation polymer binders, offering a promising strategy to address the long-standing challenges of Si-based anodes in LIBs.