Secondary Bonding Channel Design Induces Intercalation Pseudocapacitance toward Ultrahigh-Capacity and High-Rate Organic Electrodes.

Abstract

Organic electrode materials have shown extraordinary promise for green and sustainable electrochemical energy storage devices, but usually suffer from low specific capacity and poor rate capability, which is largely caused by inactive components and diffusion-controlled Li+ intercalation. Herein, high-rate Li+ intercalation pseudocapacitance in organic molecular crystals is achieved through introducing weak secondary bonding channels, far exceeding their theoretical capacity based on redox chemistry at functional groups. The authors' combined experimentally electrochemical characterization with first-principles calculations show that the heterocyclic organic molecule 2,2'-bipyridine-4,4'-dicarboxylic acid (BPDCA) crystal permits a four-electron redox reaction at conventional CO and CN groups and a six-electron intercalation pseudocapacitance along conjugated alkene hydrogen bonding channels (H2 NC5 H⋯OC(OH)) and heterocyclic aromatic stacking channels (C5 H3 N⋯NH3 C5 ). The BPDCA electrode delivers an ultrahigh reversible capacity of 1206mAhg-1 at 0.5Ag-1 and an exceptional rate capability. A 4.8V high-energy/power-density BPDCA anode-based hybrid Li-ion capacitor is thus realized. This work opens a new avenue for developing organic intercalation pseudocapacitive materials via secondary bonding structure design.