Probing the interaction mechanism of heterostructured VOxNy nanoparticles supported in nitrogen-doped reduced graphene oxide aerogel as an efficient polysulfide electrocatalyst for stable sulfur cathodes

Abstract

Reversible redox of sulfur to lithium sulfide through a series of lithium polysulfides (LiPS) still pose a key challenge to appreciate high-performance sulfur cathodes mainly because of shuttling phenomenon and sluggish kinetics. Herein, a simple novel synthetic approach has been presented to realize porous vanadium nitride oxide (VOxNy) nanoparticles spatially decorated within nitrogen doped reduced graphene aerogel (VONNG) via concurrent in-situ nitridation and carbonization processes. Nitrogen-doped reduced graphene aerogel enhances the physical retention and polar interaction of LiPS and contributes toward the overall conductivity of the matrix. Whereas, vanadium nitride oxide has exhibited a redox potential window intermediate to its oxides’ counterparts around which LiPS can form polythionate complexes to enhance the kinetics and LiPS retention by exploiting the V–N and V–O interfaces at cathode. The interaction mechanism has been probed through in-operando Raman spectroscopy, XPS and electroanalytical methods. The assembled cells from VONNG/S cathodes exhibit the initial discharge capacity of 1400 mAh g−1 at 0.05 C, 1250 mAh g−1 at 0.1 C and maintained reversible capacity about 700 mA h g−1 at 0.2 C after 200 cycles. The loss in capacity is less than 0.05% per cycle for 850 cycles with Coulombic efficiency close to 99% even at 5C.