[Paper Review] Influence of stacking, coordination, and surface chemistry on Al intercalation in V$_2$CT$_2$ and Ti$_3$C$_2$T$_2$ MXenes for Al-ion batteries

Amal raj Veluthedath nair, Nuala M. Caffrey|arXiv (Cornell University)|Mar 3, 2026

MXene and MAX Phase Materials0 citations

TL;DR

The study uses density functional theory to show that MXene stacking, surface terminations, and intercalant coordination govern Al intercalation energetics, diffusion barriers, and capacity in Ti3C2T2 and V2CT2 for Al-ion batteries.

ABSTRACT

As the energy storage ecosystem evolves beyond lithium, MXenes, a versatile family of 2D materials derived from MAX phases, have emerged as promising candidates for next-generation energy storage electrodes due to their tunable surface chemistry, large interlayer spacing, and excellent electronic conductivity. In this work, we use density functional theory to investigate Ti$_3$C$_2$ and V$_2$C MXenes as cathodes in Al-ion batteries. Four stacking configurations of the two-dimensional sheets and two different ion coordination sites are evaluated to understand their influence on ion intercalation and mobility. We find that the stacking configuration and surface chemistry critically impact interlayer spacing and electrochemical performance. O-terminated layers in an octahedral stacking exhibit remarkable structural stability with minimal interlayer expansion upon ion intercalation, particularly for Al intercalation in V$_2$C which exhibits an interlayer expansion of 0.1 angstrom, consistent with experimental findings. While octahedral stacking is observed to be energetically more favourable, it reduces ion mobility compared to prismatic stacking. Furthermore, O-terminated MXenes exhibit high theoretical specific capacities, reaching more than 270 mAh/g. F-terminated MXenes are considerably more unstable after intercalation and as a result exhibit much lower Al capacities. These findings highlight the importance of stacking configurations, termination and intercalant chemistry in MXenes for battery applications.

Motivation & Objective

• Assess how MXene stacking configurations (octahedral vs prismatic) influence interlayer spacing and Al intercalation energetics.
• Evaluate the impact of surface terminations (O vs F) on thermodynamics and capacity for Al intercalation.
• Examine Al diffusion barriers in different stackings to infer ion mobility and cycle stability.
• Determine maximum Al concentrations and voltage profiles for Ti3C2T2 and V2CT2 under realistic intercalation conditions.

Proposed method

• Perform density functional theory calculations with PAW, PBE-GGA, and D3 dispersion corrections to model Ti3C2T2 and V2CT2 MXenes.
• Explore four stacking configurations (WS-oct, ZZ-oct, ZZ-pris, WS-pris) with uniform O and F terminations.
• Model dilute and concentrated Al, Na, and Mg intercalation using 3x3x1 supercells with appropriate k-point sampling.
• Compute open-circuit voltage from formation energy via V(x) = -ΔG/(zF) with ΔG approximated by E(AlxMXene) - E(MXene) - xE(Al).
• Use NEB to estimate Al migration barriers in ZZ-oct and ZZ-pris Ti3C2O2 and V2CO2.

Fig. 1: (a) WS–oct Ti 3 C 2 T 2 , (b) WS–pris Ti 3 C 2 T 2 , (c) ZZ–oct Ti 3 C 2 T 2 , and (d) WS–pris Ti 3 C 2 T 2 . (e), (f), (g), and (h) present the corresponding V 2 CT 2 structures.

Experimental results

Research questions

• RQ1 How do MXene stacking (octahedral vs prismatic) affect interlayer spacing and Al intercalation energetics?
• RQ2 What is the influence of surface terminations (O vs F) on Al intercalation thermodynamics and capacity?
• RQ3 How do Al diffusion barriers vary with stacking and termination, and what does this imply for cycle stability?
• RQ4 What are the maximum achievable Al concentrations and corresponding voltages/capacities for Ti3C2T2 and V2CT2 MXenes?
• RQ5 How do these factors compare for Al with other intercalants (Na, Mg) in the same hosts?

Key findings

• Octahedral stacking is energetically favored over prismatic stacking for unintercalated MXenes, with oct vs pris differences up to 90 meV/f.u. for Ti3C2T2 and 63 meV/f.u. for V2CT2.
• Upon Al intercalation, ZZ-oct stacking remains more stable than ZZ-pris, and Al intercalation is thermodynamically favorable mainly for O terminations, especially in ZZ-oct stacking.
• O-terminated MXenes can sustain higher Al concentrations (up to 0.55–0.77 Al/f.u. depending on material) with positive OCVs, while F-terminated MXenes show much lower stability and capacities (e.g., V2CO2 up to 277.63 mAh/g; V2CF2 around 166.51 mAh/g; Ti3C2F2 unfavourable).
• Al diffusion barriers are higher in ZZ-oct (Ti3C2O2: 1.32 eV; V2CO2: 1.44 eV) than in ZZ-pris (Ti3C2O2: 0.59 eV; V2CO2: 0.50 eV), indicating slower diffusion in octahedral stacking.
• Interlayer expansion is modest for Al intercalation in O-terminated ZZ-oct structures (Δd ≈ 0.1 Å in V2CO2; up to 0.12–0.43 Å in various pris/oct configurations), consistent with experimental observations of minimal layer breathing.
• Total charge transfer indicates TM and termination atoms dominate the Al-derived charge redistribution, with more TM-sink participation at higher Al loadings, especially in O-terminated MXenes.

Fig. 2: (a) Energy difference between ZZ–oct and ZZ–pris stacking ( $\Delta E_{\mathrm{oct-pris}}$ ) for Ti 3 C 2 T 2 (b) Energy difference between ZZ–oct and ZZ–pris stacking for V 2 CT 2 , where T = –O and T = –F terminations are denoted as solid blue and dashed orange lines. Units are meV per for