Electronic and structural insights into K@C24–Li2S/Na2S systems: The role of solvent and potassium-induced charge redistribution

The interaction between C 24 and Li 2 S/Na 2 S systems was investigated through NBO and DOS analyses to elucidate their charge transfer and electronic behavior. For C 24 –Li 2 S, the charge transfer is predominantly localized, limiting adsorption as the number of Li 2 S units increases. The introduction of the DOL:DME solvent mixture enhances medium polarization, redistributing charge over the C 24 surface and reducing the binding energy from −5.06 to −2.85 eV. Conversely, in the C 24 –Na 2 S system, stronger C–S interactions (−5.6 eV) lead to reversibility issues during the adsorption–desorption process, although solvent effects attenuate the interaction to −3.12 eV. Hybridization between C 24 and Li 2 S/Na 2 S significantly modifies the electronic structure, decreasing the E gap eff and inducing a transition from semi-insulating to semiconducting behavior. Moreover, endohedral K doping promotes a more homogeneous charge distribution over the C 24 surface. The combination with the DOL:DME solvent, known for its high polysulfide solvation capability, enhances the system’s reversibility and conductivity. This allows M 2 S ⇌ 2M + +S+2 e − (M = Li, Na) reactions to proceed with a significantly reduced overpotential. The synergistic interaction between K doping and solvent polarization stabilizes Li 2 S/Na 2 S species, preserving their high electrochemical capacity and facilitating sulfur dissociation, thereby improving the reversibility and overall efficiency of the system.