Intertwined nature of electrochemical reactions and mechanical instability in sulfide-based all-solid-state batteries

All-solid-state batteries (ASSBs) employing sulfide solid electrolytes (SEs) are widely recognized as promising candidates for future energy storage owing to their excellent ionic conductivity, facile processability, and compatibility with high-energy electrodes. When integrated with Ni-rich layered oxides and Li metal, sulfide SEs enable energy densities and safety margins beyond those of conventional lithium-ion batteries. Yet their practical application is hindered by complex electrochemo-mechanical degradation that originates from intertwined electrochemical reactions and mechanical instability. Electrochemical reactions such as SE oxidation and interfacial decomposition can both induce and be exacerbated by mechanical degradation, e.g., active material cracking and interfacial contact loss. These coupled processes highlight that sustainable interfacial stability is not simply a matter of chemical passivation or mechanical reinforcement, but requires strategies that address both issues simultaneously. In this Feature Article, we review the origins and evolution of electrochemo-mechanical degradation in sulfide-based ASSBs, elucidate its detrimental impact on cell performance, and propose potential strategies for its mitigation. By providing a unified view of electrochemo-mechanical challenges, this work outlines a roadmap toward practical and reliable sulfide-based ASSBs.