Synergistic interfacial-mechanical binder design for high-areal-capacity and long-lifespan Si-based negative electrodes in practical pouch cells.

The pursuit of high-energy-density lithium-ion batteries demands high-silicon silicon-graphite composite negative electrodes, yet their commercialization remains hindered by interfacial incompatibility and mechanical instability. While an ideal binder must simultaneously achieve robust adhesion to both silicon and graphite, accommodate substantial silicon volume changes, and maintain high binder bulk stability, existing systems fail to harmonize these requirements. Here, we present a molecularly engineered binder that resolves this trilemma through interfacial-mechanical synergy. By integrating a hydrophobic-soft copolymer and hydrophilic-hard copolymer, our design enables amphiphilic interfacial adhesion and provides mechanical properties specifically tailored to accommodate silicon volume changes. A supramolecular crosslinker further reinforces interchain cohesion, ensuring binder bulk stability during long cycling life. This design enables a 2 Ah-level pouch cell to sustain 500 cycles at 0.3 C with 99.83% average Coulombic efficiency. At a commercial binder loading of 5 wt%, 1 Ah cells deliver over 2000 cycles at 1 C with an average Coulombic efficiency of 99.93%. Our work has the potential to not only resolve the long-standing trade-off between interfacial and mechanical stability in silicon-based negative electrodes but also provide a practical framework for designing next-generation binders targeting energy-dense, durable batteries.