Ultrafine 3D Nanoporous Carbon Coated Multicomponent Sulfide Heterojunction for Enhanced Na Ion Storage

Abstract Transition metal sulfides are promising sodium‐ion battery anodes. Herein, a multicomponent MnNiFe‐based sulfide heterojunction with ultrafine nanoporous structure and inherent 3D carbon coating is synthesized using commercially available MnNiFeCO ₃ as the precursor. It is found that the multicomponent metal interaction greatly inhibits the surface diffusion during carbonate decomposition process, resulting in ultrafine nanoporous MnNi(Fe)O ₃ (≤ 10 nm) with a much larger surface area when compared with a single metal‐based counterpart. To enhance the conductivity and structure stability of the heterojunction, a thin layer of N, S‐doped 3D porous carbon is inherently coated on the nanoporous MnNiFeS _x (NS‐C@MnNiFeS) by first forming a 3D polyaniline layer on the nanoporous MnNi(Fe)O ₃ , which is then transformed into doped carbon during the vulcanization process. Owing to the multicomponent heterojunction design (which may provide more active sites for effective Na ⁺ adsorption), much increased specific surface area, and 3D inherent carbon coating, the NS‐C@MnNiFeS exhibits significantly enhanced performance for Na ⁺ storage. After 90 cycles at 0.1 A g ⁻¹ , a record‐high reversible capacity of 859.2 mAh g ⁻¹ is achieved, and it can be stably cycled for 1500 cycles at a current density of 10.0 A g ⁻¹ . DFT calculation reveals the modified electronic structure and enhanced Na ⁺ adsorption by constructing the heterojunction.