Heterostructured NiS/TiO2 Nanosheets Assembled into Microflowers with Enhanced Cycling Stability for Sodium-Ion Storage

Transition metal sulfides are characterized by their low price and strong capacity performance and show a great potential for development as materials for anodes in sodium-ion batteries (SIBs). However, the structure instability and inherently poor conductivity limit their practical application. In this work, heterostructured NiS/TiO2 microflower composite materials assembled by nanosheets are synthesized through a hydrothermally assisted postsulfidation method. Meanwhile, the nanosheets are further coated by N, S double-doped carbon using pyrolytic dopamine to increase their electrical conductivity. It is demonstrated that the unique heterostructure not only narrows the band gap of composite materials but also generates an electron-concentrated region on the heterointerface, which significantly enhances the rate of charge transfer, Na+ diffusion ability, and reaction kinetic properties. As a consequence, the composites reveal superior electrochemical properties for Na+ storage; the specific capacity is 632.1 mA h g–1 after 100 cycles at 0.1 A g–1 and even up to 1.0 A g–1, while a capacity of 514.2 mA h g–1 is maintained after 250 cycles. The full battery is assembled by NiS/TiO2, and Na4Fe3(PO4)2P2O7 also displays a good capacity and stability performance. These results provide a direction for the exploration of anode materials for SIBs.