Stage-Controlled Synthesis of MXene/MAX Heterostructures With Local Atomic Disorder for Enhanced Lithium-Ion Storage

Molten-salt etching has emerged as an effective and environmentally friendly strategy for converting MAX phases into MXene, while also offering opportunities to access novel intermediate heterostructures through precise process control. However, previous studies have mainly focused on the complete transformation from MAX phases to MXene, whereas the controllable synthesis and structural elucidation of intermediate products remain largely unexplored. Here, by tuning the etching time in a CuCl₂-based molten-salt system, controllable structural evolution from Nb₂GaC to Nb₂CT_x is achieved. A series of intermediate products, denoted as Nb₂GaC-n, are successfully isolated. With increasing etching time, the interlayer Cu and Ga contents gradually decrease, enabling precise tuning of the interlayer atomic configuration. Synchrotron x-ray absorption fine structure spectroscopy reveals that the controlled etching process induces electronic-structure modulation and short-range structural disorder. Benefiting from the optimized local atomic environment, the intermediate heterostructure delivers enhanced lithium-storage performance, including a high reversible capacity of 281 mAh g^-1 at 0.1 A g^-1 and remarkable cycling stability, with 177 mAh g^-1 retained after 2000 cycles at 1.0 A g^-1. This work establishes a viable strategy for engineering MXene-based heterostructures with tailored local atomic configurations.