Distinctive Formation of Bifunctional ZnCoS-rGO 3D Hollow Microsphere Flowers with Excellent Energy Storage Performances

Distinctive formation of ZnCoS-reduced graphene oxide (rGO) hollow microsphere flowers (HMFs) undergoes three stages with aggregation–dissolution–incubation, aiming to achieve excellent electrochemical performance for Li-ion batteries (LIBs) and supercapacitors (SCs). The interconnected petals composed on the hollow microsphere surface of ZnCoS HMFs are observed with a rich and hierarchical porous structure. This unique structure can not only provide much more space exposed to electrolytes but also promote rapid ion diffusion and electron transmission, thereby contributing to reversible electrochemical reactions. The bifunctional electrochemical activity is also evaluated through a density functional theory (DFT) study in terms of the electronic properties of ZnCoO and ZnCoS, as well as the interaction between ions and these metal compounds. After the decoration with rGO, ZnCoS HMFs can effectively improve the electrical conductivity and further absorb the stress generated during repeated electrochemical reactions. As an LIB electrode, ZnCoS-rGO HMFs can deliver an initial discharge capacity of 2084.2 mAh g–1 at 100 mA g–1 and even a considerable reversible capacity after 2000 cycles at 5000 mA g–1, while as an SC electrode, they have a capacity of 1225.1 F g–1 at 1 A g–1 and a capacity retention rate of 81.9% after the current density is increased to 20 A g–1. The dual-domain application as LIBs and SCs shows that ZnCoS-rGO HMFs with unique structures have excellent competitiveness in energy storage devices.