Waterborne polyurethane dispersions as mechanically adaptive polymer binders: Molecular design, colloidal film formation, and applications in silicon-based anodes

Silicon-based anodes are promising for high-energy lithium-ion batteries, but their practical application is limited by severe volume expansion, particle fracture, loss of electronic contact, current collector delamination, and unstable solid-electrolyte interphase formation. Waterborne polyurethane dispersions offer a versatile aqueous binder platform with tunable colloidal film-forming behavior. Unlike solution-type binders, WPU binders are introduced as latex particles that form continuous polymer networks through particle packing, coalescence, and chain interdiffusion during drying. This review systematically discusses WPU-based binders from molecular design to electrode-level electrochemical performance. Emphasis is placed on the roles of soft/hard segment chemistry, microphase separation, hydrogen bonding, polar functional groups, particle size, zeta potential, film-forming temperature, drying conditions, and calendering in regulating slurry rheology, binder distribution, adhesion, mechanical integrity, transport properties, and SEI stability. Particular attention is given to silicon, silicon oxide, silicon–carbon, and silicon-rich composite anodes, where WPU networks must balance stress relaxation, pore preservation, and conductive pathway continuity. Finally, standardized reporting protocols are proposed to correlate polymer structure, electrode processing, mechanical behavior, interfacial chemistry, electrochemical performance, and manufacturing scalability.