Size‐Dependent Trade‐off between Sulfur Catalysis and Sulfide Electrolyte Decomposition for Room‐Temperature Ultrahigh‐Rate All‐Solid‐State Li–S Batteries

All‐solid‐state lithium‐sulfur batteries (ASSLSBs) hold immense promise for next‐generation safe and high‐energy storage, yet their power capability is fundamentally limited by sluggish solid‐state sulfur redox kinetics. While catalysis is effective in accelerating these reactions, we reveal for the first time that under overlapping potentials, such catalytic acceleration inevitably triggers severe parasitic decomposition of sulfide solid‐state electrolytes (SSEs), a critical yet overlooked bottleneck that disrupts Li + transport and limits high‐rate performance. To decouple efficient sulfur conversion from interfacial degradation, we devise a spatially selective catalyst architecture. Precisely sized cobalt clusters are confined within an ultra‐microporous carbon host. This design ensures intimate sulfur‐catalyst contact for rapid conversion while physically isolating the catalytic surfaces from the bulk SSE, thereby suppressing its catalytic decomposition. Consequently, the continuous Li + transport network is preserved. The resulting ASSLSB achieves an unprecedented room‐temperature rate capability, stably cycling at an ultrahigh current density of 25.0 mA cm −2 (15 C) for over 15,000 cycles. This work provides a general design principle for reconciling catalysis with interfacial stability in high‐power solid‐state batteries.