A facile route to unlock the high capacity of molecular organic cathode for aqueous zinc-ion battery

The small-molecule organic materials have become promising candidates for aqueous zinc-ion batteries (AZIBs). However, the capacity output of these molecular organic cathodes still remains far from their theoretical values. Herein, we present a facile route by integrating a small amount of porous carbon (ketjen black, KB) into phenazine (PNZ) organic cathode by a facile route, which significantly improves the specific capacity for aqueous zinc-ion storage. Specifically, the PNZ/KB based battery delivers a high specific capacity of 179 mAh g−1 at 50 mA g−1 and still remains a high-rate capacity of 81 mAh g−1 at 1000 mA g−1. Additionally, the battery demonstrates stable cycling performance, retaining 70.6% of the initial capacity after 1000 charge-discharge cycles at 500 mA g−1. The spectroscopic analyses show that the zinc-ion coordination process of PNZ/KB cathode is highly reversible. The good performance of PNZ/KB cathode is ascribed to the unique branched chain shape of KB, which can give full access to active material of PNZ and generate more conductive paths for zinc-ion. The theoretical computation demonstrates that the intermolecular coordination between zinc-ion and PNZ molecule is more stable than that through the intramolecular interaction. This work provides a facile and effective strategy to boost the high capacity of organic cathode materials for aqueous zinc-ion batteries. •A phenazine/Ketjen black composite cathode has been facilely prepared via a hydrothermal route.•KB additive enlarges the interfacial area between PNZ cathode and the electrolyte.•DFT computations disclose the intermolecular binding model of Zn2+ ion with PNZ.