The efficient redox electron transfer and powered polysulfide confinement of carbon doped tungsten nitride with multi-active sites towards high-performance lithium-polysulfide batteries

Abstract

Functional oxide materials have been widely used as promising building blocks in lithium-sulfur/polysulfide batteries, however, their poor conductivity is an extreme challenge to further improve the device performance in practical applications. Herein, we develop a facile synthesis strategy to convert oxide into nitride materials - which represent high conductivity - by using nontoxic urea instead of hazard ammonia as nitric source. In particular, we have successfully synthesized carbon doped tungsten nitride (C-WN) materials through tungsten oxide, which introduces carbon-doping and lacunar surface to WN but with the conserved overall nanostructures of tungsten oxide. Their potential applications as the polysulfide host for lithium-polysulfide batteries are also investigated, as featured by the elevated electronic conductivity of WN materials with multi-active sites of tungsten, nitrogen and carbon. Attributable to the tailored material of synergetic effects, the enhanced electronic conductivity of the C-WN material not only accelerates the redox electrochemical reaction of polysulfides via the efficient redox electron transfer, but also reveals effectively immobilize polysulfides on the multi-active sites. As a result, C-WN-based lithium-polysulfide cell achieves initial 909 mAh/g at 3.2 mA/cm2, and retains 638 mAh/g after 500 cycles. This work offers a facile nitride synthesis strategy with carbon doping and rough surface, and further towards developing high efficiency lithium-polysulfide batteries and enlightening the material design in the energy storage technologies.