A first-principles study of twist-modulated lithium storage and diffusion in Ti₃C₂O₂ moiré superlattices for Li-ion...

The discovery of moiré superlattices has introduced a new dimension to twist engineering, enabling structure-level modulation beyond conventional compositional design. However, the electrochemical energy-storage properties of MXene moiré superlattices remain largely unexplored. In this work, we systematically investigate structural stability, electronic band structures, mechanical moduli, and some key electrochemical energy storage properties for representative bilayer Ti₃C₂O₃ moiré superlattices with different twist angles (0°, 21.78°, 27.8° and 38.22°) and interlayer stacking structures (AA-, AB- and AC-stackings) using first-principles calculations. All investigated moiré superlattices are predicted to have negative binding energies with respect to the Ti₃C₂O₂ monolayer and also show high mechanical stiffness (690-723 N m^-1 for Young's modulus and 265-286 N m^-1 for shear modulus) with Poisson's ratios about 0.27-0.29. The bilayer superlattices retain metallic electronic band dispersions and the robust mechanical integrity with limited in-plane lattice variation (<1.6%) and moderate interlayer expansion (<0.5 Å) upon Li intercalation, indicating excellent structural stability during charge-discharge cycles. The moiré modulation introduces diverse adsorption sites and enhances Li accommodation, leading to high theoretical capacities (300 mAh g^-1) and favorable average open-circuit voltages (1.7 V). Meanwhile, the relatively low migration barrier (<0.2 eV) is also obtainable for Li ions in Ti₃C₂O₂ moiré superlattices, suggesting promising rate performance. Notably, the adsorption energy landscape of Li species in the interlayer spacing of bilayer Ti₃C₂O₂ superlattices is mainly modulated by the local atomic registries of moiré spots, while the adsorption energies on the surfaces of bilayer structures are determined by the surface O-terminations and the intercalated Li layer in the interlayer spacing. Overall, our current work highlights the tuning of the electrochemical properties of MXenes through twist engineering, probably offering a new theoretical paradigm to further optimize the performance of moiré superlattices as electrode materials in lithium ion batteries.