In situ-grown tungsten carbide nanoparticles on nanocarbon as an electrocatalyst to promote the redox reaction kinetics of high-mass loading sulfur cathode for high volumetric performance

The volumetric energy density of lithium-sulfur (Li-S) batteries is particularly important to accommodate the ever-shrinking space of practical devices. A feasible path for improving the volumetric energy density of the cathode is to increase the utilization of active materials within a limited volume. However, the sluggish conversion kinetics and severe migration of polysulfides hinder its development. Herein, different from simple additives with large aggregation, we propose in situ growth of ultra-small tungsten carbide nanoparticles on highly conductive nanocarbon in a relatively low-temperature process. As evidenced by the comprehensive density functional theory (DFT) calculations, X-ray photoelectron spectroscopy (XPS) and electrochemical kinetic analyses, the in situ formed WC nanoparticles could strongly enhance the absorption ability of the sulfur species and reduce the reaction energy barriers, boosting the whole interconversion kinetics. Benefiting from these advantages, the as-synthesized hybrid cathode delivered a high rate capability of 6C (627 mA h g(-1)) and enabled a long-term cycling lifespan of 500 cycles with a low decay rate of 0.039% at 5C. Moreover, a high volumetric capacity up to 625 mA h cm(-3) (volumetric energy density of 1312 W h L-1) was reached at the cathode-level with a high sulfur loading of 5.9 mg cm(-2) at 1C, suggesting a great promise in the development of Li-S batteries with high volumetric energy density.