Sulfur‐Doped Carbon Matrix‐Coated Co _{1‐ <i>x</i>} S/Ni _0.96 S@NC Rhombic Cubes Significantly Enhanced the Storage Performance and Kinetics of Lithium/Sodium‐Ion Batteries

ABSTRACT Metal sulfide, as a type of lithium/sodium‐ion battery material, possesses merits such as high capacity and low cost. Nevertheless, it is prone to structural changes during the cycling process, leading to volume changes and affecting electrochemical performance. Here, we employ a gas‐phase deposition method to subject the Co‐Ni‐NH 2 precursor to high‐temperature carbonization/sulfidation, which produces defective nitrogen‐ and sulfur‐co‐doped carbon‐encapsulated bimetallic sulfides (Co 1‐ x S/Ni 0.96 S@NC). Incorporating S into the carbon lattice facilitates the expansion of interlayer spacing, creating an environment conducive to Li + /Na + insertion/extraction. Furthermore, leveraging the synergistic effect of bimetallic sulfides accelerates the reaction kinetics for storing alkaline metal ions and exhibits higher capacity. The X‐ray photoelectron spectroscopy (XPS) depth profiling analysis of the cycled Co 1‐ x S/Ni 0.96 S@NC reveals the stable formation of a solid electrolyte interphase (SEI) film on the sample surface, and ex situ X‐ray diffraction (XRD) indicates that the storage mechanism of Co 1‐ x S/Ni 0.96 S@NC involves a highly reversible conversion reaction. As a result, Co 1‐ x S/Ni 0.96 S@NC as the anode for lithium‐ion batteries (LIBs) exhibits an outstanding capacity and demonstrates remarkable stability with a capacity retention of 381.12 mAh g −1 after 800 cycles at 10 A g −1 . Furthermore, the full battery LiCoO 2 //Co 1‐ x S/Ni 0.96 S@NC is capable of attaining a discharge‐specific capacity at 3 A g −1 for 154.92 mAh g −1 . Besides, in sodium‐ion batteries (SIBs), Co 1‐ x S/Ni 0.96 S@NC maintains a specific capacity of 336.10 mAh g −1 over 1000 cycles at 5 A g −1 . In summary, Co 1‐ x S/Ni 0.96 S@NC, characterized by high stability and high specific capacity, emerges as a highly promising candidate material for high‐performance lithium/sodium‐ion batteries.