Encapsulating nickel sulfide nanoparticles within porous carbon nanocages for sodium-ion batteries†

Abstract

Nickel sulfide has been widely studied as an anode material for sodium-ion batteries (SIBs) owing to its relatively high theoretical capacity and cost-effective features, while it suffers from significant volume expansion, low ionic conductivity during the insertion and extraction of Na ions, leading to poor sodium storage electrochemical performance. To solve this issue, a kind of NiS@C anode material, in which NiS nanoparticles with a diameter of about 13 nm were encapsulated within porous carbon nanocages, was strategically synthesized using a nickel-based metal–organic framework as a precursor. The crystalline structures, specific surface areas, pore structures, surface chemical states and morphologies of this kind of material were analyzed using XRD, N₂ sorption curves, XPS, SEM and TEM techniques, respectively. During the charge and discharge process, porous carbon nanocages can act as a buffer to restrict volume expansion and enhance the conductivity of NiS hybrid materials, thus improving the stability of electrode materials. The NiS@C composite with an appropriate amount of NiS nanoparticles encapsulated in carbon nanocages showed an ideal rate performance, good long-cycling stability, and outstanding specific capacity with a high capacity of 385 mA h g⁻¹ at 0.05 A g⁻¹ for SIBs, which were much superior to those of NiS@C–NiS having many NiS nanoparticles on the outer surface of carbon nanocages. This work provides an innovative approach to synthesize core-shelled NiS-C composites for high-performance SIBs.