Enhanced Lithium Storage of an Organic Cathode via the Bipolar Mechanism
Tianyuan Liu, Ki Chul Kim, Byeongyong Lee, Shikai Jin, Michael J. Lee, Mochen Li, Suguru Noda, Seung Soon Jang, Seung Woo Lee
Abstract
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–-involved 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.