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.