Hierarchical Porous Nanosheets Constructed by Graphene-Coated, Interconnected TiO2 Nanoparticles for Ultrafast Sodium Storage

Sodium-ion batteries (SIBs) are considered promising next-generation energy storage devices. However, a lack of appropriate high-performance anode materials has prevented further improvements. Here, a hierarchical porous hybrid nanosheet composed of interconnected uniform TiO2 nanoparticles and nitrogen-doped graphene layer networks (TiO2@NFG HPHNSs) that are synthesized using dual-functional C3N4 nanosheets as both the self-sacrificing template and hybrid carbon source is reported. These HPHNSs deliver high reversible capacities of 146 mA h g(-1) at 5 C for 8000 cycles, 129 mA h g(-1) at 10 C for 20 000 cycles, and 116 mA h g(-1) at 20 C for 10 000 cycles, as well as an ultrahigh rate capability up to 60 C with a capacity of 101 mA h g(-1). These results demonstrate the longest cyclabilities and best rate capability ever reported for TiO2-based anode materials for SIBs. The unprecedented sodium storage performance of the TiO2@NFG HPHNSs is due to their unique composition and hierarchical porous 2D structure.