Enhancing MXene electrochemistry through spatial control of O and F termination distributions

Abstract

MXenes have attracted considerable attention as potential electrode materials due to their adjustable chemical properties while retaining excellent metallic conductivity. Mixed surface functionalization, exemplified by O and F terminations on Ti${}_3$C${}_2$O${}_{2(1-x)}$F${}_{2x}$ MXenes, dictates electrochemical performance, yet the specific role of their spatial arrangement is poorly understood. This study utilizes a synergistic combination of density functional theory (DFT), kinetic Monte Carlo (KMC), and ab initio molecular dynamics (AIMD) to investigate how the nanoscale distribution of surface terminations governs Li transport and storage. DFT calculations identify distinct local neighbourhood environments characterized by unique Li diffusion barriers, challenging the simplification inherent in weighted-average compositional models. KMC simulations over 100 random O/F configurations show a 147-fold variation in Li diffusivity at room temperature, despite identical compositions. Furthermore, a composition-dependent analysis indicates that F-rich mixed-terminated surfaces facilitate faster Li diffusion compared to O-rich counterparts. The accuracy of the KMC model itself is validated by AIMD results, ensuring reliable dynamic predictions. Additionally, we show that the theoretical Li storage capacity is sensitive to these local termination environments. These findings reveal that, even at constant composition, the spatial configuration of surface terminations critically impacts electrochemical behaviour. This underscores the limitations of averaging approaches and highlights local termination structure as a key design parameter. Nanoscale control of termination patterns can significantly enhance MXene performance, enabling a new approach to modelling and optimizing 2D materials.