Ion‐Electron Convergent Interphases Enable Ultrahigh Sulfur Utilization for All‐Solid‐State Li–S Batteries

ABSTRACT All‐solid‐state batteries offer a safer route toward electrochemical energy storage with high energy density, but the active‐material utilization is commonly limited by unbalanced carrier transport dynamics through spatially decoupled delivery pathways, which overlap only at restricted reaction fronts. Such an issue is particularly severe for electronically and ionically insulating sulfur/Li 2 S, making efficient sulfur conversion the key bottleneck for practical all‐solid‐state lithium–sulfur batteries (ASSLSBs). Here, we propose surface‐bound ion‐electron convergent interphases on the Li 2 S surface that reconstruct localized triple‐phase contacts into an integrated active surface. Using the effective magnetic moment, originating from spin asymmetry, as a screening criterion for interfacial affinity, Li 2 FeS 2 is identified to form a robust surface‐bound interphase with Li 2 S, which bridges separated ion and electron pathways at the reaction areas, decreasing the transport tortuosity and lowering the activation barriers for both Li 2 S oxidation and reduction. Consequently, ASSLSBs stably work over 10 000 cycles at 1 mg cm −2 while delivering a loading‐insensitive sulfur utilization of 97.8% and 95.8% at 1 and 8 mg cm −2 , respectively. Moreover, a record areal capacity of 38.69 mAh cm −2 is achieved, highlighting the spatially surface‐bound mixed conductors as an effective design principle for synchronizing coupled ion‐electron transfer (CIET) in all‐solid‐state batteries.