Yingjie Gao,Gaofeng Li,Feng Wang,Jun Chu,Pu Yu,Baoshan Wang,Hui Zhan,Zhiping Song
In spite of the recent rapid progress of organic cathode materials for aqueous rechargeable zinc batteries (ARZBs), there are still many challenges such as unaffordable synthesis, unsatisfactory electrochemical performance, and unclear mechanisms in this field. Herein, we report 5,7,12,14-tetraaza-6,13-pentacenequinone (TAPQ) as an easily-synthesized organic cathode material with a novel quinone/pyrazine hybrid structure. Benefitting from the multiple electroactive C=O and C=N bonds, TAPQ possessed a theoretical capacity of 515 mAh g –1 (based on a six-electron reaction) and a practically reversible capacity of 443 mAh g –1 within 0.1–1.6 V vs. Zn 2+ /Zn, both of which set new records for organic cathodes in ARZBs. The H + /Zn 2+ co-insertion mechanism involving H + as the predominant participant was confirmed by detailed investigations including various ex-situ characterizations, electrochemical tests, and DFT calculations. Based on the clear mechanism understanding, a modified voltage range of 0.5–1.6 V was adopted to simultaneously achieve high energy density (270 mAh g –1 × 0.84 V = 227 Wh kg –1 ) and excellent cycling stability (capacity retention of 92% after 250 cycles under 50 mA g –1 , with an average Coulombic efficiency of 99.96%). Furthermore, the evolution mechanism of TAPQ electrode structure during cycling was also carefully studied to reveal the origin of capacity decline. The novel molecular structure, easy synthesis, superior electrochemical performance, and deeper mechanism understanding provide researchers important insights into the further development of organic cathode materials for ARZBs toward practical applications.
Improving electrical conductivity and increasing the active site are important directions for improving the technology of manganese-based cathode materials for zinc ion batteries (ZIBs). In this paper, cobalt-doped and oxygen-vacancy coupled MnO2 nanorods (Vo-CMO) were prepared by defect engineering and an ion doping strategy as cathode materials for rechargeable ZIBs. Oxygen vacancies can increase the defect density of the material and provide more migration paths for zinc ions, thereby increasing the electrochemical activity and improving the specific capacity. The introduction of cobalt can adjust the electronic structure of manganese oxide, change the Fermi level of the material, and promote the generation and transmission of charge carriers, thereby increasing the charge transfer rate and increasing the conductivity of the material. The synergistic effect among them can improve the diffusion kinetics of zinc ions, thereby increasing the capacity and cycle stability of the material. The Vo-CMO has better Zn2+ storage capacity of 295.6 mAh·g–1 at 0.1 A·g–1. The reaction mechanism of Vo-CMO material was H+/Zn2+ coinsertion through galvanostatic current intermittent titration (GITT) and ex situ experiments. In addition, the Vo-CMO material assembled the flexible quasi-solid ZIB. The synergistic effect of cobalt doping and oxygen vacancy can provide a new way to develop water-based ZIBs.
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