In Situ Insights into Anisotropic Lithiation and Superior Electrochemical Stability of Nitridated Mo ₂ N MXene

Layered metal nitrides derived from 2D transition metal carbides or nitrides (MXenes) represent a new class of materials with unique structural features and electrochemical properties. Despite growing interest, the fundamental understanding of their structural evolution and lithiation mechanisms remains limited due to lack of in situ characterization studies. Herein, we synthesize layered Mo₂N via one-step nitridation of Mo₂C MXene, systematically probing its structural evolution using synchrotron spectroscopy and in situ electron microscopy. X-ray absorption fine structure (XAFS) spectroscopy quantitatively revealed the differences in the coordination environment during the nitridation process, with Mo─Mo coordination number decreasing from 6.1 to 4.8. In situ transmission electron microscopy (in situ TEM) provided direct visualization of anisotropic volume evolution during lithiation/delithiation in Mo₂N, showing unidirectional expansion of only 24% along the c-axis. Combined with density functional theory (DFT) calculations, the distinct lithiation/delithiation pathways are elucidated in Mo₂N, revealing a reduced energy barrier of 0.1525 eV compared to 0.1584 eV in Mo₂C. The preserved layered architecture and atomic structure synergistically enabled Mo₂N to achieve 92.48% capacity retention after 1000 cycles. This work establishes a comprehensive methodology combining photon and electron probe techniques for structural analysis of MXene derivatives, providing fundamental insights into structure-property relationships in layered nitrides.