Cooperative Multisite Adsorption-Enabled Interface-Adaptive Binder for Stabilizing High-Capacity Si/C Composite...

Silicon-graphite (Si/C) composite anodes are promising for next-generation lithium-ion batteries because of their high capacity and industrial compatibility; however, their practical application is hindered by unstable interfacial chemistry and electrode degradation associated with the large volume changes of silicon during cycling. Herein, an interface-adaptive polymer binder, poly(2-acrylamido-2-methylpropanesulfonic acid-co-2-ethylhexyl acrylate-co-acrylic acid) [P(AMPS-co-2-EHA-co-AA), PAEA], is developed to stabilize the heterogeneous Si/C interface through synergistic molecular interactions. PAEA integrates amide, lithium sulfonate, and lithium carboxylate moieties within a single polymer network, enabling reversible hydrogen bonding, ionic interactions, Li+ affinity, and adhesion to hydroxylated Si surfaces. These functional groups establish a multisite adsorption network across Si-rich and carbon domains, thereby enhancing interparticle cohesion and maintaining interfacial contact during cycling. Meanwhile, the lithium sulfonate and carboxylate moieties regulate the local Li+ distribution and facilitate interfacial ion transport, which helps reduce polarization and homogenize interfacial reactions. The enhanced interfacial affinity between PAEA and Si, together with the regulated Li+ flux, reduces direct electrolyte attack and parasitic side reactions, leading to the formation of a thin (4.65 nm), inorganic-rich SEI containing ROCO2Li, Li2CO3, Li2O, LiF, and LiPOxFy, with a Li+ diffusion coefficient of 16.3 × 10-6 cm2 s-1. This interfacial layer contributes to the stabilization of the electrode/electrolyte interface and suppresses continuous SEI growth and structural degradation during cycling. The PAEA-based electrode delivers a capacity of 633.3 mAh g-1 with 82.6% retention after 400 cycles at 0.5 C and maintains a capacity of 633.8 mAh g-1 at 1 C. Furthermore, high-loading pouch-type full cells paired with LiNi0.8Co0.1Mn0.1O2 cathodes retain 79.7% of their initial capacity after 200 cycles, demonstrating the potential of PAEA as a binder for Si/C-based lithium-ion batteries.