Interweaving Elastic and Hydrogen Bond-Forming Polymers into Highly Tough and Stress-Relaxable Binders for High-Performance Silicon Anode in Lithium-Ion Batteries

Abstract

A central challenge in practically using high-capacity silicon (Si) as anode materials for lithium-ion batteries is alleviating significant volume change of Si during cycling. One key to resolving the failure issues of Si is exploiting carefully designed polymer binders exhibiting mechanical robustness to retain the structural integrity of Si electrodes, while concurrently displaying elasticity and toughness to effectively dissipate external stresses exerted by the volume changes of Si. Herein, a highly elastic and tough polymer binder is proposed by interweaving polyacrylic acid (PAA) with poly(urea-urethane) (PUU) elastomer for Si anodes. By systematically tuning molecular parameters, including molecular weights of hard/soft segments and structures of hard segment components, it is demonstrated that the mechanical properties of polymer binders, such as elasticity, toughness, and stress relaxation ability, strongly affect the cycling performance of Si electrodes. This study provides new insight into the rational design of polymer binders capable of accommodating the volume changes of Si, primarily by judicious modulation of the mechanical properties of polymer binders. To address the volume change issues of Si anodes for lithium-ion batteries, highly tough polymer binders exhibiting mechanical robustness, elasticity, and stress-relaxing ability are developed by interweaving poly(acrylic acid) (PAA) and poly(urea-urethane) (PUU) elastomer. Systematic modulation of various molecular parameters of PUU elastomer enables accessing optimized mechanical properties of binders, thereby achieving long-lasting Si anodes.image