Heterostructured and Mesoporous Nb 2 O 5 @TiO 2 Core-Shell Spheres as the Negative Electrode in Li-Ion Batteries.

Niobium pentoxides have received considerable attention and are promising anode materials for lithium-ion batteries (LIBs), due to their fast Li storage kinetics and high capacity. However, their cycling stability and rate performance are still limited owing to their intrinsic insulating properties and structural degradation during charging and discharging. Herein, a series of mesoporous Nb 2 O 5 @TiO 2 core-shell spherical heterostructures have been prepared for the first time by a sol-gel method and investigated as anode materials in LIBs. Mesoporosity can provide numerous open and short pathways for Li + diffusion; meanwhile, heterostructures can simultaneously enhance the electronic conductivity and thus improve the rate capability. The TiO 2 coating layer shows robust crystalline skeletons during repeated lithium insertion and extraction processes, retaining high structural integrity and, thereby, enhancing cycling stability. The electrochemical behavior is strongly dependent on the thickness of the TiO 2 layer. After optimization, a mesoporous Nb 2 O 5 @TiO 2 core-shell structure with a ∼13 nm thick TiO 2 layer delivers a high specific capacity of 136 mA h g -1 at 5 A g -1 and exceptional cycling stability (88.3% retention over 1000 cycles at 0.5 A g -1 ). This work provides a facile strategy to obtain mesoporous Nb 2 O 5 @TiO 2 core-shell spherical structures and underlines the importance of structural engineering for improving the performance of battery materials.