Interlayer Spacing Expansion and Active Site Engineering of MXene@TiO₂ Heterostructures as Robust Cathodes for Rechargeable Aluminum-Ion Batteries

Aluminum-ion batteries (AIBs) have become a highly promising energy storage technology due to their high theoretical capacity, cost-effectiveness, and excellent safety. However, there is still a lack of stable and efficient cathode materials capable of reversibly inserting/extracting aluminum complex ions, which constitutes a key challenge in the field. Herein, we propose a facile and controllable hydrothermal strategy to in situ construct Ti₃C₂T_X MXene@TiO₂ heterostructures, and systematically elaborate the regulatory mechanism of hydrothermal temperature and reaction duration on the morphology, interlayer structure, surface chemistry, and electrochemical behaviors of the composites. The results demonstrate that uniformly dispersed anatase TiO₂ nanoparticles are anchored on MXene nanosheets, which effectively suppresses layer stacking, expands interlayer spacing from 1.040 nm to 1.344 nm, and synchronously regulates surface terminal groups of MXene. Benefiting from the synergistic effect of expanded ion diffusion channels, abundant pseudocapacitive active sites, and robust heterointerfaces, the optimized Ti₃C₂T_x@TiO₂ electrode delivers a high initial reversible capacity of 243.8 mAh g⁻¹ and maintains a stable capacity of 80 mAh g⁻¹ after 200 consecutive cycles with negligible capacity decay. The proposed structural engineering strategy provides universal guidance for the rational design of high-performance MXene-based electrode materials for next-generation aluminum-ion batteries and other advanced energy storage systems.