Selenium-Doped Sulfurized Poly(acrylonitrile) Composites as Ultrastable and High-Volumetric-Capacity Cathodes for Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries, despite their superior gravimetric energy density, are inferior to lithium-ion (Li-ion) batteries in terms of volumetric energy density because of the intrinsic low density of sulfur and the lightweight carbon host. Here, a new strategy is proposed to improve the volumetric capacity of sulfur cathode with selenium-doped sulfurized poly(acrylonitrile) (SPAN) as the electrode material. The introduction of Se not only accelerates the redox kinetics of sulfur conversion but also leads to dramatically enhanced active materials content and higher tap density of the electrode material. Consequently, the Se0.4SPAN composite delivers an impressive volumetric capacity of 1185 mAh cm–3 at 0.1 C, a high rate capability of 850 mAh cm–3 at 4 C, and excellent long-term stability over 500 cycles at 1 C. Self-discharge behavior and the shuttle effect are completely avoided due to the absence of soluble intermediates. Moreover, a remarkable volumetric energy density of 1537 Wh Lcathode–1 is achieved based on the densification effect with a high cathode density (1.51 g cm–3), which is comparable to the metal oxide cathode of Li-ion batteries. This study demonstrates a promising way to overcome the bottlenecks of current Li–S technologies for high volumetric-energy-density rechargeable batteries.