Stabilizing nickel sulfide nanoparticles with an ultrathin carbon layer for improved cycling performance in sodium ion batteries

Nanostructured metal sulfides are potential electrode materials for sodium-ion batteries; however, they typically suffer from very poor cycling stability due to large volume changes and dissolution of discharge products. Herein we propose a rational material design strategy for sulfide-based materials to address these problems. Taking nickel sulfide (NiS_x) as an example, we demonstrated that its electrochemical performance can be dramatically improved by confining the NiS_x nanoparticles in a percolating conductive carbon nanotube network, and stabilizing them with an ultrathin carbon coating layer. The carbon layer serves as a physical barrier to alleviate the effects of both the volume change and dissolution of active materials. The hybrid material exhibited a large reversible specific capacity of > 500 mAh/g and excellent cycling stability over 200 cycles. Given the traditionally problematic nature of NiS_x as a battery anode material, we believe that the observed high performance reported here reflects the effectiveness of our material design strategy.