Dense T-Nb₂O₅/Carbon Microspheres for Ultrafast-(Dis)charge and High-Loading Lithium-Ion Batteries

Orthorhombic niobium pentoxide (T-Nb₂O₅) is regarded as a potential anode material for lithium-ion batteries (LIBs) due to ultrafast charge/discharge and high safety. However, the poor electronic conductivity and low mass loading of nanostructured T-Nb₂O₅ limit its practical application in LIBs. Herein, we design and construct dense microspheres consisting of nanostructured T-Nb₂O₅ embedded in amorphous N-doped carbon (Nb₂O₅@NC) via a facile method to achieve fast ionic and electronic transport as well as a high mass loading. The dense micro-sized particles with an interconnected carbon network avoid the low mass loading and volumetric energy density of conventional nanostructures. Interconnected pores in the range of a few nanometers are also formed in the Nb₂O₅@NC microspheres. Notably, at a high mass loading of 12.8 mg cm^-2, Nb₂O₅@NC can achieve a high specific capacity of 171.5 mAh g^-1 and an areal capacity of 2.05 mAh cm^-2, showing its high lithium storage capacity. The intercalation reaction mechanism with a small volume change during cycling at both crystal lattice and microsphere levels is confirmed by in situ X-ray diffraction and in situ high-resolution transmission electron microscopy. The elegant structure and the electrochemical reaction mechanism disclosed in the work is important for designing ultrafast-(dis)charge electrode materials.