Ti₃C₂ MXene as a High Capacity Electrode Material for Metal (Li, Na, K, Ca) Ion Batteries

TLDR

Two‑dimensional materials can accommodate high charge rates because ions need not diffuse through a 3‑D lattice, yet the most studied 2‑D material, graphene, lacks lithium capacity. The study predicts Li, Na, K, and Ca adsorption on Ti₃C₂ MXene using first‑principles density‑functional calculations. The model shows that larger effective ionic radii enhance alkali‑atom interactions, leading to lower surface coverage. The calculations reveal that Li, Na, K, and Ca adsorb with capacities of 447.8, 351.8, 191.8, and 319.8 mAh g⁻¹, respectively, with Na, K, and Ca adsorption energies decreasing with coverage while Li remains largely unaffected, indicating MXene’s potential to improve high‑rate Li and Na‑ion battery performance.

Abstract

Two-dimensional (2-D) materials are capable of handling high rates of charge in batteries since metal ions do not need to diffuse in a 3-D lattice structure. However, graphene, which is the most well-studied 2-D material, is known to have no Li capacity. Here, adsorption of Li, as well as Na, K, and Ca, on Ti3C2, one representative MXene, is predicted by first-principles density functional calculations. In our study, we observed that these alkali atoms exhibit different adsorption energies depending on the coverage. The adsorption energies of Na, K, and Ca decrease as coverage increases, while Li shows little sensitivity to variance in coverage. This observed relationship between adsorption energies and coverage of alkali ions on Ti3C2 can be explained by their effective ionic radii. A larger effective ionic radius increases interaction between alkali atoms, thus lower coverage is obtained. Our calculated capacities for Li, Na, K, and Ca on Ti3C2 are 447.8, 351.8, 191.8, and 319.8 mAh/g, respectively. Compared to materials currently used in high-rate Li and Na ion battery anodes, MXene shows promise in increasing overall battery performance.