High-Reaction Kinetics SexS1–x Cathodes for All-Solid-State Lithium–Sulfur Batteries

All-solid-state lithium–sulfur batteries are considered one of the most promising candidates for energy storage devices due to their high energy density and safety. However, the poor electron transport of sulfur-based cathodes significantly reduces their reaction kinetics, resulting in low utilization efficiency and subpar rate performance. Herein, leveraging the similar chemical properties of sulfur and selenium, we uniformly deposit SexS1−x (x = 0–0.3) solid solutions with different selenium content on the surface of active carbon via a facile melt-diffusion method to achieve SexS1−x@AC (x = 0–0.3) composite materials. The introduction of selenium effectively enhances the lithium-ion diffusion coefficient of the SexS1−x@AC (x = 0–0.3) cathodes, and improves the stability of the cathode/solid electrolyte interface. With the increase in selenium content, the reaction kinetics of the SexS1−x@AC (x = 0–0.3) cathodes are altered. Specifically, the average lithium-ion diffusion coefficients for the S@AC and Se0.2S0.8@AC cathodes are 6.11 × 10−14 and 1.65 × 10−13 cm2 s−1, respectively, showing a twofold increase. Concurrently, the Se0.2S0.8@AC cathode exhibits higher discharge capacity (698.8 mA h g−1) than that of the S@AC cathode (501.3 mA h g−1) at 1 A g−1. Surprisingly, even when the mass loading increases to 8.85 mg cm−2, the Se0.2S0.8@AC cathode still shows superior cycling stability, which is attributed to the fast ionic/electronic transport pathways within the cathode. Moreover, the Se0.2S0.8@AC cathode maintains good physical contact at the cathode/SE interface after cycling. In all-solid-state lithium–sulfur batteries, the introduction of selenium in the sulfur cathode enhances reaction kinetics (1.65 × 10−13 cm2 s−1), provides additional reactive sites, and significantly improves the electrochemical performance of Se0.2S0.8@AC even with high mass loading (8.85 mg cm−2).