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

We employ density functional theory (DFT) to examine the vibrational, electronic, and ion transport properties of Nb 2 C and Nb 2 CO 2 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 Nb 2 C, as well as Nb 2 CO 2 , to evaluate structural response and its correlation with charge transfer. The predicted Raman modes reproduce known experimental peaks in Nb 2 C, 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 Nb 2 CO 2 exhibiting stronger binding due to surface oxygen terminations. Diffusion barrier analysis reveals enhanced ion mobility in Nb 2 C, particularly for Na ions, while Nb 2 CO 2 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 Nb 2 C for fast-charging applications and Nb 2 CO 2 for high-energy-density systems. • First-principles simulations predict Raman-active E 1 g and A 1 g modes in Nb 2 C and Nb 2 CO 2 , consistent with experimental spectra. • Li/Na intercalation modifies Raman intensities without shifting peak positions, indicating preserved structural integrity in Nb 2 C. • Charge transfer from Li/Na affects polarizability and electron–phonon interactions, explaining Raman intensity variations. • Nb 2 C exhibits lower ion diffusion barriers, supporting faster ion transport, particularly for Na ions. • Oxygen-functionalized Nb 2 CO 2 offers stronger ion adsorption and higher open-circuit voltage, enhancing energy storage capability.