First-Principles Study on Desolvation and Capacitive Performance of Bispyrrolidinium Cations in Pristine/Oxygen-Functionalized Bilayer Graphene Flat Pores

Supercapacitors are limited by electrolyte cation desolvation, which directly impacts ion storage efficiency and capacitance. This study uses density functional tight-binding (DFTB+) first-principles calculations to investigate the desolvation of bispyrrolidinium cation complexes ([SBP(AN)]+, acetonitrile as solvent) in pristine (FP) and oxygen-functionalized (OFP: hydroxyl-HFP, carbonyl-CFP, aldehyde-AFP) bilayer graphene flat pores with AA/AB stacking. Critical desolvation diameters were determined: 5.0 Å (FP), 5.2 Å (HFP), 5.0 Å (AFP), and 4.6 Å (CFP). Hydroxyl functionalization expanded the critical diameter, reduced SBP+ intercalation energy, and increased relative capacitance by 1.02~1.03 times; carbonyl groups had the opposite effect, while aldehyde groups showed no significant impact. Density of States (DOS) analysis revealed enhanced conductivity for HFP and AFP after SBP+ embedding, but reduced conductivity for CFP. Charge density difference and Bader charge analysis confirmed electron transfer primarily between SBP+ (electron donor) and oxygen atoms in functional groups (electron acceptor), with SBP+ interacting mainly with functional groups rather than the carbon basal plane. This work provides theoretical guidance for optimizing graphene-based supercapacitor electrodes via pore structure and surface functionalization.