Dual-atom pairs with electron buffering enable ultrastable-cycling all-solid-state lithium-sulfur batteries

All-solid-state lithium-sulfur batteries (ASSLSBs) show promise in balancing high energy density and safety, but face the bottleneck of sluggish sulfur conversion kinetics. Single-atom catalysts (SACs) could alleviate this by maximizing active-site utilization and intimate contact with sulfur. However, the metal centers often undergo irreversible electronic reconstruction, causing fast degradation and capacity fading. Here, we report an atomic-scale electron buffering strategy with electronegativity-matched dual-metal atom sites, which strengthen interfacial bonding with sulfur species while maintaining stability. The dual-metal Cu and Ni atoms are anchored on the polymeric carbon nitride (Cu₁Ni₁-PCN) to form spatial proximity (∼3.4 Å) single-atom pairs with similar electronegativity. This pair mediates electron buffering between the metals, enabling dynamic valence modulation that suppresses deactivation and enhances interfacial d-p orbital hybridization with sulfur. Consequently, the catalyst enables consistently low activation energy during long cycling, retaining a high capacity of 948 mAh g^-1 after 2500 cycles at 1 mA cm^-2 and exhibiting almost no capacity decay over 7000 cycles at 2 mA cm^-2. This work establishes electron buffering as a robust approach to stabilize atomic-scale catalysts and offers a general design framework for high-performance sulfur electrocatalysis in ASSLSBs.