Sulfide-based all-solid-state lithium batteries (ASSLBs) have garnered considerable attention owing to their high energy density and enhanced safety. In such systems, composite cathodes are commonly fabricated via either a solvent-free dry process or a slurry-based wet process, typically employing polytetrafluoroethylene (PTFE) and acrylonitrile–butadiene rubber (NBR) as binders, respectively. However, a comprehensive understanding of how these binders influence electrochemical performance and degradation mechanisms remains limited. In this study, the effects of PTFE and NBR binders on interfacial degradation are systematically elucidated through electrochemical analyses, morphological characterizations, and digital-twin computational modeling. The results reveal that PTFE effectively mitigates interfacial deterioration by maintaining intimate contact and minimizing void formation, whereas NBR suffers from accelerated interfacial degradation and void growth during prolonged cycling. These findings highlight the critical role of binder-induced interfacial phenomena in determining cell performance and offer valuable insights for optimizing cathode fabrication strategies tailored to each processing route, while guiding the rational design of advanced binders for composite cathodes in ASSLBs.