Self-Limiting Covalent Ligation Mechanism Enabling Anomalously High Interfacial Compatibility in Organic-in-Sulfide All-Solid-State Lithium Batteries

Polymer-in-sulfide composite electrolytes have emerged as highly promising candidates for all-solid-state lithium batteries (ASSLBs) due to their on-demand shaping and rapid ion diffusivity. However, a striking paradox arises in the case of ethylene oxide-tethered polyacrylates (EO-PAs): their high polarity/strong nucleophilic tendencies constitute a major threat to sulfide stability yet exhibit anomalously high polymer/sulfide compatibility in practice. The underlying mechanism remains a matter of uncertainty. Herein, we first reveal a self-limiting covalent ligation mechanism that accounts for this compatibility paradox. Central to this principle is the identification of intimate interactions between terminal −CH₃ in EO-PAs and PS₄³⁻ units in Li₆PS₅Cl, not only suppressing parasitic nucleophilic reactions by EO ligands but also enhancing air stability. The self-limiting interface was rigorously validated by density functional theory calculations, ³¹P solid-state nuclear magnetic resonance, x-ray computed tomography, and time of flight secondary ion mass spectrometry. The robust polymer-in-sulfide electrolyte achieves dendrite-free Li plating/stripping for over 1200 h at 3 mA cm⁻² and delivers approximately 100% capacity retention over 1000 cycles in NCM811-based ASSLBs. These findings elucidate the core mechanism of interface regulation and provide pivotal guidance for the development of high-performance ASSLBs.