Enhanced Lithium Storage of an Organic Cathode via the Bipolar Mechanism

Electrochemically polymerized anthraquinone derivatives on conductive carbon nanotubes are redox-active as organic cathode materials for lithium-ion batteries. Density functional theory calculations and electrochemical measurements reveal that the polymerized anthraquinone cathodes exhibit the multiple redox reactions with electrolyte ions through a bipolar charge storage mechanism: (1) the n-type doping/dedoping mechanism associated with Li+ binding in a potential window of 1.5-3.0 V versus Li and (2) the PF6- -invoIved p-type doping/dedoping mechanism in a potential window of 3.0-4.5 V versus Li. Polymerized 1- aminoanthraquinone (AAQ) shows progressive deactivation upon cycling because of the charge trapping effect. On the other hand, the polymerized 1,5-diaminoanthraquinone (DAAQ) delivers extraordinarily high charge capacities up to 311 mA h/g while effectively avoiding undesirable charge trapping behaviors. We establish the relationship between the structure and charge storage performance of the polymerized quinone derivatives, suggesting a high-performance organic cathode material for rechargeable battery applications.