Nanoemulsion-directed assembly of hierarchical ZnS@C nanospheres with penetrating pores for sodium storage

To follow up on the performance of lithium-ion batteries (LIBs), transition metal sulfides (TMSs) have been developed as promising carbon alternatives for sodium-ion batteries (SIBs). Although attractive, it is still a great challenge to fulfill their capacity utilization with high cycling performance. Herein, a nanoemulsion-directed method has been developed to control the spherical arrangement of ZnS@C units with both penetrating macropores from the center to the surface and inner mesopores distributed among the bulks. With respect to ion diffusion, the penetrating macropores could serve as the built-in ion-buffer reservoirs to keep a steady flow of electrolyte, while the inner mesopores facilitate the ion diffusion across the whole bulks. In terms of stability, the radical porous structure could work as self-supported vertical bones to accommodate the volume change from both lateral and vertical sides. Besides, the localized carbon distributed among the ZnS nanoparticles not only acts as binding agents to join the numerous ZnS nanoparticles but also endows the radical bones with effective electron transmission capability. As a proof of concept, such hydrangea-like ZnS@C nanospheres deliver sodium storage performance with high-rate and long-cycling capability. This nanoemulsion-directed approach is anticipated for other TMSs with penetrating pores for post-lithium-ion batteries applications.