Lithium Thiostannate Molecular Mediator Enables Interfacial Electronic Reconstruction for Low‐Barrier Li 2 S Chemistry

The practical implementation of Li 2 S cathodes in all‐solid‐state lithium‐sulfur batteries is severely hindered by sluggish ionic/electronic transport and a high activation barrier, particularly under high‐mass‐loading conditions. Herein, lithium thiostannate (Li 4 SnS 4 ) is introduced as a molecular mediator to activate Li 2 S redox chemistry. In situ growth of Li 4 SnS 4 on Li 2 S constructs a continuous Li + ‐transport network, increasing the ionic conductivity from 2.25 × 10 −5 to 3.99 × 10 −5 S cm −1 . More importantly, the hybridization between unsaturated Sn p orbitals and interfacial sulfur atoms induces the formation of Sn─S bonds, leading to local electron‐density redistribution around sulfur. This interfacial electronic reconstruction weakens Li + confinement within the sulfur lattice, softens the Li─S bond, and lowers the oxidation barrier, thereby reducing the initial charge potential from 2.94 to 2.41 V. Consequently, the Li 2 S@Li 4 SnS 4 cathode delivers stable cycling over 100 cycles under demanding conditions of 50 wt.% Li 2 S and areal loading of 5 mg cm −2 . Moreover, a prototype pouch cell retains sufficient capacity to power a light‐emitting diode panel after 100 cycles. This work demonstrates that interfacial electronic‐structure engineering offers an effective strategy for activating Li 2 S cathodes toward high‐energy all‐solid‐state Li‐S batteries.