Assessing (Mo2/3Sc1/3)(2)C and (Mo2/3Sc1/3)(2)CT2 (T = -O, -OH, and -F) i-MXenes as High-Performance Electrode Materials for Lithium and Non-Lithium Ion Batteries

Employing first-principles calculations, the energy storage properties and ion diffusion dynamics of Li+, Na+, K+, Mg2+, Ca2+, Zn2+, and Al3+ on bare (Mo2/3Sc1/3)(2)C and surface-functionalized (Mo2/3Sc1/3)(2)CT2 (T = -O, -OH, and -F) i-MXenes are predicted. The investigated i-MXenes show weak adsorption ability to the Zn2+ ion regardless of the surface terminations, excluding their use as anodes for Zn ion batteries. The first-principles molecular dynamics simulations indicate that the adsorption of alkaline (earth) metal ions and Al3+ on (Mo2/3Sc1/3)(2)C(OH)(2) and (Mo2/3Sc1/3)(2)CF2 causes the surface reaction between metal ions and surface terminations, leading to the formation of metal hydride or fluorite overlayers covering the underneath remaining i-MXenes. We find that the bare (Mo2/3Sc1/3)(2)C and (Mo2/3Sc1/3)(2)CO2 are suitable candidates for use as anodes for alkaline (earth) metal and Al ion batteries. Specifically, both (Mo2/3Sc1/3)(2)C and (Mo2/3Sc1/3)(2)CO2 i-MXenes show good ion storage capacities, ideal open circuit voltages, and fast ion diffusion dynamics for alkaline (earth) metal ions. Notably, the predicted theoretical capacities of (Mo2/3Sc1/3)(2) C ((Mo2/3Sc1/3)(2) CO2) for Li+, Mg2+, and Al3+ are 291 mAh g(-1) (254 mAh g(-1)), 490 mAh g(-1 )(436 mAh g(-1)), and 886 mAh g(-1) (640 mAh g(-1)), respectively. In addition, the calculated open circuit voltage profiles of Li+, Mg2+, and Al3+ exhibit the small on-set voltage and the board plateau region. The climbing image-nudged elastic band predicts that the diffusion energies of Li+, Na+, K+, and Ca2+ ions on bare (Mo2/3Sc1/3)(2)C are extremely small (<0.05 eV), and the O-terminated surface show higher diffusion energies for various metal ions. Overall, (Mo2/3Sc1/3)(2)C and (Mo2/3Sc1/3)(2)CO2 are good electrode materials for fast charging alkaline (earth) metal ion batteries and supercapacitors.