Hollow heterostructured Cu1.96S/NiS microspheres coupled with nitrogen/sulfur dual-doped carbon realizing superior reaction kinetics and sodium storage

Abstract

Metal sulfides have received increasing attention recently as anodes for sodium-ion batteries (SIBs) due to their large capacity, high electrical conductivity, and excellent redox potentials. However, the application of metal sulfides is hindered by the vast volume effect, leading to electrode structure deterioration and degrading cycling and rate properties. Herein, hierarchical hollow double-shelled Cu_1.96S/NiS@nitrogen/sulfur dual-doped carbon (Cu_1.96S/NiS@DC) microspheres are fabricated via a template-free method, followed by sulfidation, poly-dopamine coating, and carbonization procedures. The synergistic function of heterostructured sulfide components and core–shell structures mitigates the volume variation, alleviates the agglomeration of nanoparticles, and further improves the electrochemical activity. The most remarkable feature of Cu_1.96S/NiS@DC is the ultra-stability at a high current density while maintaining a large capacity. The resultant Cu_1.96S/NiS@DC microspheres deliver a high reversible capacity of 565 mA h g⁻¹ at 0.1 A g⁻¹. They can steadily operate for up to 1000 cycles at 1.0 A g⁻¹, with a reversible capacity of 396.2 mA h g⁻¹ at the 1000th cycle, corresponding to a high capacity retention of 89.1%. Systematic kinetics analysis further reveals that the enhanced sodium storage of Cu_1.96S/NiS@DC is attributed to its low charge-transfer resistance, large capacitive contribution, and high Na⁺ diffusion coefficients. The research findings presented in this work may provide a revelation to future material structure design strategies and accelerate developments and applications of SIBs.