Prediction of Raman signatures, electronic structure, and ion transport mechanisms in Nb2C and Nb2CO2 MXenes for Li/Na-ion batteries: An Ab Initio study

Abstract

We employ density functional theory (DFT) to examine the vibrational, electronic, and ion transport properties of Nb₂C and Nb₂CO₂ MXenes as potential anode materials for lithium-ion and sodium-ion batteries. For the first time, we simulate the Raman spectra of pristine and Li/Na-intercalated Nb₂C, as well as Nb₂CO₂, to evaluate structural response and its correlation with charge transfer. The predicted Raman modes reproduce known experimental peaks in Nb₂C, persistent upon intercalation. Raman peak positions remain unchanged with ion insertion indicating minimal structural distortion. We observed variations in peak intensities indicating modifications in polarizability due to charge transfer and altered electron phonon coupling.

Our analysis confirms that both MXenes retain metallic conductivity after intercalation, ensuring efficient electron transport. Adsorption energy calculations identify the T4 and H3 sites as favorable for Li/Na, with Nb₂CO₂ exhibiting stronger binding due to surface oxygen terminations. Diffusion barrier analysis reveals enhanced ion mobility in Nb₂C, particularly for Na ions, while Nb₂CO₂ delivers higher open-circuit voltage and stronger ion retention.

This study demonstrates the utility of Raman spectroscopy, coupled with first-principles simulations, as a predictive tool for probing structural and electronic behavior in energy materials. Our findings position Nb₂C for fast-charging applications and Nb₂CO₂ for high-energy-density systems.