N-Doped Porous Graphitic Carbon Hybridized with CrN Nanocrystals: Electrocatalysis-Induced Li2S Three-Dimensional Growth and Enhanced Cathode Kinetics

Abstract

Lithium-sulfur (Li-S) batteries hold potential for use as next-generation rechargeable devices due to their high theoretical energy density (2600 W h kg(-1)) as well as the high abundance and environmental friendliness of sulfur. However, the commercial use of such devices is hindered by sluggish cathode reaction kinetics and the polysulfide shuttle effect. Herein, we report the synthesis of an N-doped porous graphitic carbon that is hybridized with CrN nanocrystals (CrN@N-PGC) and show that Li-S batteries that contain such a composite may overcome the existing challenges. The CrN@N-PGC composite is synthesized by calcinating a porous, dry gel derived from a brine solution containing glucose, (NH4)(2)CrO4, and urea. Although NH3 is commonly used as a nitrogen source to form transition-metal nitrides, the reagent is a gas and toxic. The synthetic procedure described herein employs urea as a safe and efficient replacement. When used in Li-S batteries, the CrN nanocrystals (1) electrocatalytically promote polysulfide conversion reactions, (2) suppress the polysulfide shuttle effect, and (3) facilitate the deposition of Li2S in a 3D fashion, which ultimately increases sulfur utilization. Li-S cells containing the CrN@N-PGC composite show outstanding electrochemical performance, including a high specific capacity (1591 mA h g(-1) at 0.1 C), a high rate capability (548 mA h g(-1) at 6 C), and a low decay rate (0.066% per cycle over 600 cycles at 2 C).