Redox-active, self-polymerized dopamine shows promise as organic cathode materials for Li- and Na-ion batteries.

The Li-binding thermodynamics and redox potentials of seven different quinone derivatives are investigated to determine their suitability as positive electrode materials for lithium-ion batteries. First, using density functional theory (DFT) calculations on the interactions between the quinone derivatives and Li atoms, we find that the Li atoms primarily bind with the carbonyl groups in the test molecules. Next, we observed that the redox properties of the quinone derivatives can be tuned in the desired direction by systematically modifying their chemical structures using electron-withdrawing functional groups. Further, DFT-based investigations of the redox potentials of the Li-bound quinone derivatives provide insights regarding the changes induced in their redox properties during the discharging process. The redox potential decreases as the number of bound Li atoms is increased. However, we found that the functionalization of the quinone derivatives with carboxylic acids can improve their redox potential as well as their charge capacity. Through this study, we also determined that the cathodic activity of quinone derivatives during the discharging process relies strongly on the solvation effect as well as on the number of carbonyl groups available for further Li binding.

Reduced graphene oxides are active as positive electrodes for lithium-ion energy storage based on the surface redox reactions between oxygen functional groups and Li ions. For effective Li-ion energy storage within a confined mass and volume, free-standing, high-packing density, and redox-active graphene films were fabricated by a simple two-step compression and vacuum-drying process from a hydrothermally reduced graphene hydrogel. The assembled graphene films showed a folded microstructure with high packing densities up to ∼0.64 g/cm3. Redox-active oxygen functional groups on the graphene oxide were activated and controlled by the hydrothermal reduction temperature. Density functional theory (DFT) calculations revealed that the carbonyl and epoxide groups among various oxygen functional groups on graphene were the main contributors for the high potential redox reactions with Li ions. The folded graphene film electrodes delivered both a high gravimetric energy of ∼419 Wh/kg and a high volumetric energy of ∼239 Wh/L. In addition, the folded graphene film electrodes exhibited an exceptional cycling stability, retaining a gravimetric capacity of ∼160 mAh/g after 50 000 cycles. These results provide significant insights on the effective utilization of surface redox reactions to design graphene-based electrodes for high-performance Li-ion energy storage devices.