Solid state reaction-enabled in situ construction of ultrafine CoS nanoparticles encapsulated within heteroatom-doped carbon scaffold for high performance sodium-ion batteries

Abstract

Developing an efficient and reliable method for achieving high-yield and high-quality synthesis of transition metal sulfides combined with carbonaceous materials is highly desirable but still challenging. Herein, a very simple and cost-effective solid state reaction method for the fabrication of ultrafine CoS nanoparticles encapsulated within heteroatom-doped carbon scaffold is presented. By directly grinding cobalt acetate tetrahydrate, o-vanillin and o-phenylenediamine together with a molar ratio of 1:2:1 at ambient temperature in the presence of sulfur powder, a self-assembly solid state reaction took place to give rise to a bis-Schiff base complex with cobalt (II), which was evenly distributed in the sulfur powder surroundings. After subsequent annealing at elevated temperature, simultaneous carbonization and sulfidization occurred, resulting to the in-situ formation of ultrafine CoS nanoparticles (∼3.8 nm) encapsulated within an irregular N, S-codoped carbon scaffold (denoted as CoS⊂NSC). When evaluated as an anode material for sodium-ion batteries (SIBs), the CoS⊂NSC hybrid exhibits good cycling stability (305.6 mA h g−1 after 400 cycles at 100 mA g−1) and excellent rate capability (412.3 and 263.3 mA h g−1 at current densities of 200 and 5000 mA g−1, respectively), demonstrating exceptional electrochemical sodium storage performances. The findings in this work pave a novel way to synthesize the promising anode materials for high performance SIBs.