Enhanced Li+ ion adsorption on pristine and defected graphene via organic radical interaction – A DFT study

Highlights: • Defected graphene with organic radicals enhanced the adsorption of Li+ ion. • Charge transfer occurs from Li+ ion to graphene-radical complexes. • Fermi energy level is upshifted on adsorption of Li+ ion. • High energy density were observed for the Li+ ion adsorbed on divacancy defected graphene - TEMPO radicals. Recently, organic radical compounds have attracted much attention for their utility as electrodes in rechargeable Lithium-ion batteries due to their cost-effective, ecofriendly, and fast transport of Li⁺ ion. In the present study, the interaction of organic radicals such as 2,5,5, -Tetramethylpyrrolidin-N-oxyl, 2,2,6,6-Tetramethyl-4-piperidinyl-N-oxyl and Nitronylnitroxyl radicals with pristine and defective graphene sheet and their electronic and thermodynamic properties upon the adsorption of Li⁺ ion are studied using density functional theory (DFT) calculations. Organic radical containing 2,2,6,6-Tetramethyl-4-piperidinyl-N-oxyl radical with the pristine and defected graphene can enhance the adsorption of Li⁺ ion. The natural population and Bader's charge analysis are used to understand the charge transfer between the Li⁺ ion and graphene–radical complexes and calculate the theoretical specific capacity of the anode. Our results suggest that the adsorption of Li⁺ ion on divacancy defected graphene sheet with 2,2,6,6-Tetramethyl-4-piperidinyl-N-oxyl radical exhibits as promising electrode materials containing the highest energy density of about 297.80 Wh Kg⁻¹ with redox potential of 2.25 V. The theoretical study demonstrates that the adsorption of Li⁺ ion on graphene–radical complexes acts as an promising electrode material for next-generation Lithium-ion batteries.