Engineering the architecture and oxygen deficiency of T-Nb₂O₅-carbon-graphene composite for high-rate lithium-ion batteries

Developing advanced architectures using a cost-effective synthesis strategy is still a challenge for wide-spread commercial application of Nb₂O₅ in high-power rechargeable lithium-ion batteries (LIBs). Here we report a new two-dimensional (2D) architecture composed of oxygen-vacancy-rich T-Nb₂O₅ on reduced graphene oxide nanosheet and carbon (2D Nb₂O₅-C-rGO), which is synthesized via a one-pot hydrolysis route followed by a heat-treatment. As an anode for LIBs, the 2D Nb₂O₅-C-rGO architecture shows excellent rate capability (achieving a capacity of 114 mAh g⁻¹ at 100 C or 20 A g⁻¹) and cycling stability (maintaining a capacity of 147 mAh g⁻¹ at 5 C for 1,500 cycles and 107 mAh g⁻¹ at 50 C for 5,000 cycles). Experimental investigations and density functional theory (DFT)-based calculations reveal that the outstanding Li⁺ storage performance of the 2D Nb₂O₅-C-rGO electrode is attributed to the enhanced electronic conductivity facilitated by the C-rGO electronic network and fast Li⁺ migration within small Nb₂O₅ grains enhanced by in-situ formed lattice oxygen vacancies, which alter the Nb d band structure and Li⁺ interaction. This work results in an anode with advanced architecture for fast Li⁺ storage and provides more insight into the energy storage mechanism in the Nb₂O₅-based carbonaceous composite electrodes.