Inhibiting the shuttle effect in sodium-sulfur batteries using Mo2CT2 (T = S, O) MXenes: A DFT investigation

The rising demand for electrification has highlighted sodium–sulfur (Na–S) batteries as a promising energy-storage technology due to their high theoretical capacity, abundant materials, and low cost. However, their performance is limited by polysulfide dissolution, or the shuttle effect, which slows redox kinetics and accelerates capacity fading. This study employs the DFT method to investigate Mo₂CT₂ (T = S, O) MXenes in 1T and 2H phases as potential anchoring materials for sulfur cathodes. All Mo₂CT₂ structures effectively adsorb sodium polysulfides (Na₂S_n), demonstrating higher adsorption strength than commercial electrolytes and effectively suppressing the shuttle effect. Structural phase notably affects Na₂S_n adsorption on Mo2CS2, while its influence is minor for Mo₂CO₂. Higher Na₂S_n-Mo₂CO₂interaction arises from greater charge transfer from Na to O atom driven by higher electronegativity difference. Among the candidates, 2H-Mo2CS2 and 1T-Mo₂CO₂ exhibit higher binding energies than its counterpart and maintain metallic conductivity after Na₂S_n adsorption, benefiting electron transport. Gibbs free energy calculations indicate more favorable sulfur reduction pathways on Mo₂CT₂ surfaces, along with reduced energy barriers for Na₂S oxidation. Overall, Mo₂CT₂ MXenes exhibit strong anchoring capability and catalytic activity, making them promising materials for mitigating the shuttle effect and enhancing electrochemical performance in Na–S batteries.