Mitigate pressure dependence in sulfide-based all-solid-state batteries via structural and interfacial engineering of Ni-rich cathodes

Sulfide-based all-solid-state lithium-ion batteries (ASSLIBs) have emerged as one of the most promising candidates for next-generation energy storage systems owing to their high energy density, wide electrochemical stability window, and intrinsic safety benefits over liquid electrolyte counterparts. Nevertheless, their practical implementation faces a fundamental bottleneck: the strong dependence on high external stack pressure to maintain interfacial contact and suppress mechanical degradation during operation. This requirement not only reduces energy efficiency and packaging flexibility but also severely restricts scalability and commercialization, as maintaining uniform high pressure in large-format cells is technically challenging and economically costly. Addressing the critical challenge of achieving low-pressure or even ambient-pressure operation in sulfide-based ASSLIBs is therefore of both scientific and technological significance. In this review, we systematically analyze the origins of pressure-dependent performance, including particle fracture in Ni-rich layered cathodes, dynamic interfacial instability, and insufficient mechanical compliance of composite electrodes. Building on this mechanistic understanding, we summarize recent advances and design strategies across multiple scales. At the cathode level, particle size regulation, compositional doping, and engineered porosity, combined with conformal interfacial coatings, effectively mitigate stress concentration and suppress degradation. On the electrolyte and electrode interface, optimizing particle size distribution, tailoring interfacial chemistry, and introducing dynamic polymeric binders with balanced adhesion and elasticity significantly enhance ionic transport and maintain robust contact under low pressure. At the system level, strategies such as optimized temperature management, adjustment of the electrochemical window, and controlled isostatic pressure provide additional means to stabilize operation and complement materials-level solutions. Taken together, these advances demonstrate that the key to pressure-independent ASSLIBs lies in a synergistic design framework that integrates intrinsic materials engineering, interfacial stabilization, and system-level control. We further propose a cross-scale design roadmap toward the realization of low-pressure and flexible ASSLIBs, highlighting the need for dynamic adaptation between mechanical properties and electrochemical processes. This perspective underscores that enabling stable performance under minimized external pressure is not only essential for translating laboratory demonstrations into practical large-scale devices but also paves the way for safer, lighter, and more energy-efficient solid-state battery technologies.