Designing Adaptive Binders for Microenvironment Settings of Silicon Anode Particles.

This study reports the concept of an "adaptive binder" to address the silicon anode challenge in Li-ion batteries. Binders exhibit adaptable capabilities upon gradual changes in the microenvironments surrounding silicon particles during anodic expansion-shrinkage cycles. Long, flexible binder chains are repositioned and reoriented upon the gradual formation of Si-micro-environments (Si-μ-env) during the early battery cycles. At this stage, the chemical interactions between the polymeric binders are reversible hydrogen bonds. As the Si-μ-env become stably set by repeated battery cycles, the chemical interactions exhibit reversible-to-irreversible transitions by the formation of covalent linkages between the binder polymers at the later stage of cycles. The binder polymer showing the aforementioned adaptive properties is hyaluronic acid, which has never been explored as a silicon-anode binder material, onto which the plant-inspired adhesive phenolic moiety, gallol (1,2,3-trihydroxybenzene), is conjugated (HA-GA) for stable adhesion to the surfaces of silicon particles. It is confirmed that the HA-GA binder can maintain a charge capacity that is approximately 3.3 times higher (1153 mAh g-1 ) than that of the nonconjugated HA binder (347 mAh g-1 ) after 600 cycles even at a rapid charge/discharge rate of 1 C (3500 mA g-1 ), indicating that adaptive properties are an important factor to consider in designing silicon-anode binders.