Ostwald ripening and sulfur escaping enabled chrysanthemum-like architectures composed of NiS₂/NiS@C heterostructured petals with enhanced charge storage capacity and rate capability

Transition metal sulfides are considered as a type of promising materials for battery-supercapacitor hybrid (BSH) devices because of their high theoretical capacity, yet suffer from low output performance and poor rate capability due to the sluggish charge transport. Herein, sacrificial template strategy is proposed to design the chrysanthemum-like carbon-coated nickel sulfide heterostructures (NiS₂@C, NiS₂/NiS@C, and NiS@C) using nickel-based metal-organic frameworks as the precursors. Through balancing Ostwald ripening and sulfur escaping, the particle size and composition of the products are finely tuned. The abundant hetero-interfaces facilitate ion migration and charge transfer, thereby enhancing the redox activity of nickel sulfides significantly. Compared to NiS₂@C and NiS@C, NiS₂/NiS@C heterostructures exhibit superior performances in specific capacity and rapid charge/discharge, delivering 754 and 570 C g⁻¹ respectively at 2 and 20 A/g. The BSH energy storage device assembled with NiS₂/NiS@C cathode and Fe₂O₃ anode provides 244 C g⁻¹ at 1 A/g and 49 Wh kg⁻¹ at 725 W kg⁻¹.