Thiol–Ene Functionalization of a PS-b-PI-b-PS Binder for Enhanced Interfacial Adhesion and Rate performance in Sulfide-Based All-Solid-State Batteries.

All-solid-state batteries (ASSBs) employing sulfide solid electrolytes are promising energy-storage systems owing to their high ionic conductivity and enhanced safety. Solution-based electrode fabrication is attractive because it is compatible with established lithium-ion battery manufacturing and enables scalable production through roll-to-roll coating. However, sulfide electrolytes are incompatible with polar solvents, whereas binders soluble in weakly polar solvents often exhibit insufficient adhesion.  Herein, polystyrene-block-polyisoprene-block-polystyrene (PS-b-PI-b-PS, SIS) was partially functionalized via thiol–ene chemistry using 3-mercaptopropionic acid (3-MPA), 1-thioglycerol (1-TG), and 2-mercaptoethanol (2-ME). The degree of grafting was controlled at approximately 10%.  Small-angle neutron scattering (SANS) revealed comparable radii of gyration for pristine and functionalized SIS, suggesting that its solution-state chain dimensions and effective solvation behavior were largely preserved despite the introduction of polar functionalities.  Among the modified binders, 3-MPA-functionalized SIS showed the highest adhesion strength, exceeding that of pristine SIS by more than 20-fold. Cells containing the 3-MPA-functionalized binder also exhibited improved capacity retention under stepwise C-rate variation.  These results demonstrate that controlled thiol–ene functionalization enhances interfacial adhesion and electrochemical performance while retaining the solution processability required for sulfide-based ASSBs.