Activating Redox Kinetics of Li ₂ S via Cu ⁺ , I ⁻ Co‐Doping Toward High‐Performance All‐Solid‐State Lithium Sulfide‐Based Batteries

All-solid-state lithium sulfide-based batteries (ASSLSBs) have drawn much attention due to their intrinsic safety and excellent performance in overcoming the polysulfide shuttle effect. However, the sluggish kinetics of Li₂S cathode severely impede commercial utilization. Here, a Cu⁺, I^- co-doping strategy is employed to activate the kinetics of Li₂S to construct high-performance ASSLSBs. The electronic conductivity and Li-ion diffusion coefficient of the co-doped Li₂S are increased by five and two orders of magnitude, respectively. Cu⁺ as a redox medium greatly improves the reaction kinetics, which is supported by ex situ X-ray photoelectron spectroscopy. Density functional theory calculation (DFT) shows that Cu⁺, I^- co-doping reduces the Li-ions diffusion energy barrier. The co-doped Li₂S exhibits a remarkable improvement in capacity (1165.23 mAh g^-1 (6.65 times that of pristine Li₂S) at 0.02 C and 592.75 mAh g^-1 at 2 C), and excellent cycling stability (84.58% capacity retention after 6200 cycles at 2 C) at room temperature. Moreover, an ASSLSB, fabricated with a lithium-free (Si─C) anode, obtains a high specific capacity of 1082.7 mAh g^-1 at 0.05 C and 97% capacity retention after 400 cycles at 0.5 C. This work provides a broad prospect for the development of ASSLSBs with practical energy density exceeding that of traditional lithium-ion batteries.