Optimizing the Energy Storage Performance of Titanium Carbonitride MXenes for Potassium-Ion Batteries by Modulating Nitrogen Content

Abstract

Precise control over the synthesis and properties of MXenes has attracted significant attention due to their broad applicability in energy storage and various other fields. Recently, Gogotsi et al. synthesized titanium carbonitride MXenes with tunable carbon-to-nitrogen (C/N) ratios, greatly expanding the compositional diversity of MXenes and offering new strategies for property optimization (J. Am. Chem. Soc. 2023, 145, 22374). Building on this foundation, we explore the ordered structural models of Ti₃(C_1−yN_y)₂ MXenes solid solutions with varying N ratios (y = 0.125, 0.25, 0.375 and 0.5) using first-principles calculations. The predicted variations in lattice parameters and stability with increasing nitrogen content align well with experimental observations. Notably, the increasing nitrogen content enhances the structural toughness of the MXenes. Ti₃(C_1−yN_y)₂ MXenes demonstrate significantly improved theoretical capacities and reduced potassium-ion migration barriers compared to Ti₃C₂. Among these, the Ti₃(C_0.5N_0.5)₂ MXene exhibits an ultralow potassium-ion migration barrier of 0.001 eV, enabling ultrafast charge-discharge rates. This improvement can be attributed to the differences in valence electron numbers and electronegativity between carbon and nitrogen, which alter the charge distribution and orbital hybridization within the material. These findings offer valuable insights into the rational design of MXene-based anode materials for potassium-ion batteries (KIBs), paving the new pathway for advancing their energy storage performance.