Hybrid Zn Battery with Coordination-Polymer-Derived, Oxygen-Vacancy-Rich Co3O4 as a Cathode Material

To achieve high power/energy density and capacitance/voltage in a safe and cost-effective battery system, a hybrid aqueous Zn battery is assembled by kneading Zn-air and Zn-Co3O4 batteries at the cell level. A new coordination-polymer-derived, oxygen-vacancy-rich Co3O4-based composite is chosen as a cathode material for this hybrid battery. The pseudocapacitance property of this composite is attractive with a specific capacitance of 213.7 mAh.g(-1) at 1 A-g(-1). Its rate capability is promising with 62.6% capacitance retained when the current density increases to 20 A.g(-1). The composite follows a typical four-electron mechanism during the oxygen reduction reaction (ORR). In the oxygen evolution reaction (OER), its overpotential and Tafel slope are 347 mV and 79.4 mV.dec(-1), respectively. For the hybrid aqueous Zn battery, the discharge process is divided into two stages, namely, a Zn-Co3O4 battery and a Zn-air part. With the current density at 1 mA.cm(-2), two discharge plateaus locate at 1.72 and 1.02 V. In this case, the specific capacitance of the hybrid battery reaches 788 mAh.g(-1) with an energy density of 921 Wh.kg(-1). Its peak power density reaches 48.9 mW.cm(-2) at 34.8 mA.cm(-2). The charge-discharge platforms and specific capacitance remain stable after continuous experiments for 300 cycles. This work introduces a referable example for the design and fabrication of a high-performance hybrid aqueous Zn battery.