Doped hexa-peri-hexabenzocoronene as anode materials for lithium- and magnesium-ion batteries

The adsorption processes of Li⁺, Li, Mg²⁺, and Mg on twelve adsorbents (pristine and N/BN/Si-doped hexa-peri-hexabenzocoronene (HBC) molecules) were studied using density functional theory. The molecular electrostatic potential (MESP) analyses show that the replacement of C atoms of HBC by N/BN/Si units can provide a more electron-rich system than the parent HBC molecule. Li⁺ and Mg²⁺ exhibit strong adsorption on pristine and doped HBC molecules. The adsorption energy of cations on these nanoflakes (E_ads-1) was in the range of -247.44 (Mg²⁺/m-C₄₀H₁₈N₂ system) to -47.65 kcal mol^-1 (Li⁺/B₂₁H₁₈N₂₁ system). Importantly, our results suggest the weaker interactions of Li⁺ and Mg²⁺ with the nanoflakes as the MESP minimum values of the nanoflakes became less negative. In all studied systems, we observed electron donation from the nanoflakes to Li⁺ and Mg²⁺. For the metal/nanoflake systems, the adsorption energy of metals on the nanoflakes (E_ads-2) was in the range of -33.94 (Li/C₃₈H₁₈B₂N₂ system) to -2.14 kcal mol^-1 (Mg/B₂₁H₁₈N₂₁ system). Among the studied anode materials for lithium-ion batteries (LIBs), the highest cell voltage (V_cell) of 1.90 V was obtained for B₂₁H₁₈N₂₁. Among the studied anode materials for magnesium-ion batteries (MIBs), the highest V_cell value of 5.29 V was obtained for m-C₄₀H₁₈N₂. E_ads-2 has a significant effect on the variation of V_cell of LIBs, while E_ads-1 has a significant effect on the variation of V_cell of MIBs.