Controllable Synthesis of Sub-10 nm ZnS Nanograins Confined in Micro-Size Carbon Skeleton for Aqueous Zn-S Batteries

Aqueous zinc-sulfur battery (AZSB) is a promising technology for energy storage, but its practical application is severely limited by the sluggish redox kinetics and large volume expansion of the sulfur cathode. Herein, the controllable synthesis of sub-10 nm ZnS nanograins confined in micro-size carbon skeleton (MN-ZnS/C & horbar;H) and its application as the cathode for AZSB is reported. It is revealed that the carbon source, polyvinylpyrrolidone (PVP), can weakly coordinate with Zn2+ and provide a physical confinement for inhibiting the agglomeration of ZnS nanograins during the calcination process. Moreover, the particle size of ZnS (from sub-10 to 350 nm) and the shape of ZnS/carbon composite (from bulk to sphere) can be well controlled by tuning the chain length of PVP. In the unique hierarchical structure, the ZnS nanograins can provide an optimized ion transmission path, and the micro-size carbon network not only ensures high electronic conductivity but also maintains structure integrity upon volume variation, endowing the MN-ZnS/C & horbar;H electrode with a high reversible capacity of 370 mA h g-1 at 0.2 A g-1, high rate capability of 209 mA h g-1 at 4 A g-1, and a long lifespan of 210 cycles with 93.2% capacity retention at 2 A g-1. A large-scalable strategy for constructing micro-nano structured ZnS/carbon composite is developed. Based on the weak coordination and physical confinement of polyvinylpyrrolidone in active component trapping and agglomeration suppressing, the engineered cathode with sub-10 nm ZnS nanograins embedded in carbon microsphere shows fast redox kinetics and excellent structural stability, providing new insights into the cathode design for aqueous Zn-S batteries. image