Hollow TiNb₂O₇Nanospheres with a Carbon Coating as High-Efficiency Anode Materials for Lithium-Ion Batteries

TiNb2O7 (TNO) has been extensively investigated as a promising energy storage material due to its superior structural stability, excellent electrochemical properties, and environmental benignancy. However, poor electrical/ionic conductivity restricts the practical application of TNO. Herein, phenolic resin spheres (PRs) are used as sacrificial templates to fabricate hollow-structured TNO nanospheres assembled from secondary nanoparticles, which are further coated with polydopamine to fabricate N-doped carbon-coated hollow TNO (HTNO@N-C) nanospheres. The HTNO@N-C nanospheres with an average diameter of ∼600 nm consisted of an inner cavity and a functional shell. The unique inner cavity provides a buffer space to relieve the volume expansion upon the lithiation process, thus ensuring excellent cycle performance. The porous TNO shell assembled by secondary interconnected nanoparticles provides extra channels to accelerate the diffusion of Li+ into the inner active sites. The coated N-doped carbon layer can increase the electronic conductivity, which is beneficial to enhance Li+ ions/electrons transfer to improve rate performance. Consequently, as an anode for lithium-ion batteries (LIBs), HTNO@N-C exhibits a high reversible capacity of 278.3 mAh/g at 1C, with a capacity retention of 78.0% (217.1 mAh/g) after 1000 cycles. Even when cycled at 10C and 20C, high reversible capacities of 138.0 and 100.9 mAh/g can be obtained. Moreover, HTNO@N-C electrode demonstrates excellent long-term cycling stability, delivering a reversible capacity of 116.2 mAh/g after 5000 cycles at 5C, which endows HTNO@N-C with great potential as a candidate anode for high-efficiency LIBs. More importantly, this strategy can be generally applied for the fabrication of various unique hollow structures for energy-related applications.