Flexible waterproof rechargeable hybrid zinc batteries initiated by multifunctional oxygen vacancies-rich cobalt oxide

Abstract

Although both are based on Zn, Zn-air batteries and Zn-ion batteries are good at energy density and power density, respectively. Here, we adopted Ar-plasma to engrave a cobalt oxide with abundant oxygen vacancies (denoted as Co<inf>3</inf>O<inf>4-x</inf>). The introduction of oxygen vacancies to cobalt oxide not only promotes its reversible Co-O → Co-O-OH redox reaction but also leads to good oxygen reduction reaction and oxygen evolution (ORR/OER) performance (a half-wave potential of 0.84 V, four-electron transfer process for ORR, and 330 mV overpotential, 58 mV·dec^-1 Tafel slope for OER). We then constructed a battery system based on both Zn-Co<inf>3</inf>O<inf>4-x</inf> and Zn-air electrochemical reactions. The hybrid battery reveals both a high-power density of 3200 W·kg^-1 and high-energy density of 1060 Wh·kg^-1. Furthermore, the developed flexible solid-state hybrid batterydemonstrates good waterproof and washable ability (99.2% capacity retention of after 20 h water soaking test and 93.2% capacity retention after 1 h washing test). Interestingly, the fabricated flexible battery can work under water, and after the power is exhausted, the battery can automatically recover electricity output as long as it is exposed to air. The developed device is suitable for wearable applications considering its electrochemical performances, great environmental adaptation, and "air recoverability". In addition, this study underscores the approach to develop hybrid energy-storage technologies through modification of electrode materials.