Fast reaction kinetics of amine group spatially confined in pillared graphene interlayers for high-rate lithium-ion capacitors

Grafting p-type amine-containing monomers onto carbonaceous materials (CMs) holds great potential for achieving high capacity cathodes with high redox potentials. Herein, the p-phenylenediamine (pPD) covalently pillared reduced graphene oxide (rGO-pPD) is synthesized and used as cathode for lithium-ion capacitors (LICs). Various ex- and in-situ results demonstrate that the pseudocapacitance of rGO-pPD mainly arises from the faradaic adsorption/desorption reactions between amine groups and PF₆^-. Surprisingly, it is solvated Li⁺ rather than PF₆^- intercalates/deintercalates within the graphene interlayers, serving as the main charge carrier for charge exchange with electrolyte. The expanded interlayers pillared by pPD reduce the desolvation degree of the intercalated/deintercalated Li⁺, significantly minimizing the energy barrier from the solvation sheath stripping and reorganization and accelerating Li⁺ transport within the rGO-pPD interlayers during cycling. Such improved kinetics endows rGO-pPD a high rate capability of 116mAh g⁻¹ at 10 A g⁻¹. The covalent bonding between active amine groups and graphene guarantees high capacity retention for rGO-pPD cathode in 10,000 cycles at 2 A g⁻¹. This work not only presents a competitive amine-functionalized CM cathode for high-rate electrochemical energy storage devices, but also proposes leveraging the d-spacing of CMs to control intercalation compounds is a way to yield favorable electrode kinetics.