Defects introducing and heterostructures engineering synergistically constructing active sites for achieving stable and fast ion transport in sodium-ion batteries

Bronze phase TiO ₂ (TiO ₂ (B)) has attracted significant interest as potential anode materials for sodium-ion batteries (SIBs) due to its distinctive open tunnel structure, offering abundant insertion sites for Na ⁺ -ions. However, the practical application has been hindered by its poor electrical conductivity and insufficient Na ⁺ diffusion kinetics. Herein, we propose a novel strategy that integrates defect introducing and heterostructures engineering to enhance the performance of TiO ₂ (B) anode. Specifically, we aim to induce oxygen vacancies (OVs) into TiO ₂(B) through N-doping and in-situ growth on MXenes nanosheets, thereby fabricating N-doped TiO ₂(B)/MXenes (N-TiO-MX) heterostructures. This strategy leverages the synergistic effects of OVs and N-atoms, along with the formation of heterointerfaces, to effectively reduce the bandgap, increase the number of Na ⁺-ion storage sites, and shorten ion diffusion distances. The robust coupling between TiO ₂(B) and MXenes ensures the structural integrity of N-TiO-MX heterostructures. Consequently, the N-TiO-MX exhibits a high specific capacity of 211.3 mAh g ⁻¹ at 0.1 A g ⁻¹ after 400 cycles and superior cycling stability with 163.1 mAh g ⁻¹ after 1000 cycles at 1.0 A g ⁻¹ . The study provides unique insights for designing heterostructure materials to achieve high capacity and excellent fast-charging capability.