Effect of Double Substitutional Doping (2C → 2N/2S) in Graphene on the Interfacial Adhesion of CMC and LCmA: A DFT Study Aimed at Sustainable Lithium-Ion Battery Electrodes

Density functional theory (DFT) was used to investigate how bisubstitution doping in graphene alters its electronic structure and interfacial stability with two model lignocellulosic binders, carboxymethylcellulose (CMC), and a representative aromatic fragment (LCmA). The properties were evaluated at the ωB97X-D/LANL2DZ level for pristine graphene and its bisubstitution-doped variants with nitrogen (graphene-2N) and sulfur (graphene-2S), integrating frontier orbitals, electrostatic potential (ESP) maps, electronic localization functions (ELF/LOL), and QTAIM topology. Doping with 2N markedly reduces the HOMO–LUMO gap from 0.16052 eV (graphene) to 0.10560 eV (−34.2%), while 2S reduces it to 0.14222 eV (−11.4%), evidencing different electronic activation mechanisms. The interaction energies show doping-controlled selectivity: In pristine graphene, adsorption strongly favors LCmA (ΔEint = −99.3 kcal·mol−1) over CMC (−23.7 kcal·mol−1); in graphene-2N, CMC coupling intensifies (−93.7 kcal·mol−1) while maintaining a high interaction with LCmA (−74.3 kcal·mol−1); and in graphene-2S, CMC remains favorable (−71.9 kcal·mol−1) while LCmA falls to a practically marginal regime (−4.1 kcal·mol−1). QTAIM the presence of confirms closed-layer interactions in all complexes (∇2Pc > 0, H > 0, |V|/G < 1), with |V|/G close to unity for graphene–LCmA (0.994) and less compaction when doped with 2N (0.760 for 2N–LCmA). The bisubstitution modulates the electronic heterogeneity of the basal plane and redefines the binder–surface compatibility, favoring the multipoint anchoring of polar ligands in 2N and penalizing efficient aromatic stacking in 2S.