Nitrogen and Sulfur Vacancies in Carbon Shell to Tune Charge Distribution of Co₆Ni₃S₈ Core and Boost Sodium Storage

Abstract

Abstract Recently, the metal sulfide‐carbon nanocomposites have been suggested as a low‐cost alternative to lithium ion batteries, but commercial application is seriously hindered by their relatively inferior cyclic performance. Herein, N and S vacancies in an N,S co‐doped carbon (NSC) shell for anchoring a new bimetallic sulfide core of Co 6 Ni 3 S 8 using Co‐Ni‐alginate biomass are introduced. The obtained Co 6 Ni 3 S 8 /carbon aerogels (Co 6 Ni 3 S 8 /NSCA) exhibit excellent sodium‐ion storage properties, high reversible capacity (568.1 mAh g −1 at 1 A g −1 ), and an excellent cycle stability (94.4% after 300 cycles). Density functional theory calculation results disclose that nitrogen and sulfur vacancies in the carbon shell can enhance the binding between the Co 6 Ni 3 S 8 core and NSC shell, ensuring an improved structural and electrochemical stability. In addition, an increased adsorption energy of Na + (−1.88 eV) and a decreased barrier energy for Na + diffusion (0.46 eV) are observed indicating a fast Na + diffusion process. The powder X‐ray diffraction refinement confirms that the lattice parameters of Co 6 Ni 3 S 8 extend to 0.9972 nm compared with Co 9 S 8 (0.9928 nm), suppressing the volume expansion in Na + diffusion processes.