Dual‐Conductivity Optimization Toward High‐Rate and Ultralong Life All‐Solid‐State Lithium‐Sulfur Batteries

All-solid-state lithium-sulfur batteries (ASSLSBs) hold great promise as next-generation energy storage systems due to their high energy density. However, the practical application of sulfur-based cathodes are largely hampered by their sluggish reaction kinetics, especially under high current densities and long-term cycling. Herein, by employing electronic structure modulation via same-group element doping, we successfully engineer lithium sulfide to concurrently facilitate ionic diffusion and electronic conduction, thereby significantly boosting its reaction kinetics. The formation of Se─S bonds, achieved by partial Se substitution, reorganizes the electronic structure of Li₂S. This effect concurrently weakens sulfur's electronegativity to facilitate Li⁺ diffusion and narrows the bandgap to boost electronic conduction. As a result, the Li₂Se_0.2S_0.8 cathode exhibits remarkable high-rate capability, retaining 97.5% of its capacity after 1000 cycles at 1 A g^-1. Moreover, a full cell combining Li₂Se_0.2S_0.8 with a Si anode delivers a high energy density of 1324 Wh kg^-1, highlighting the feasibility of high-specific-energy and high safety ASSLSBs. This work provides an effective strategy toward high-energy and high-power solid-state batteries.