Polyvinyl Alcohol-Based Gel Electrolytes with High Water Content for Flexible Zinc-Air Batteries with High Rate Capability

Abstract

Due to the fast development of consumer electronics and wearable devices, demand for safe and light batteries is soaring. Flexible zinc-air batteries using quasi-solid gel electrolytes are considered a potential candidate because of their high energy density, long-term durability and safety. In this work, spinel NiCo2O4 is employed as the bifunctional catalyst for fabricating flexible zinc-air batteries. Electrochemical measurements in both the three-electrode and full-cell configurations indicate a good bifunctionality for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The flexible zinc-air batteries are assembled using a gel electrolyte consisting of polyvinyl alcohol (PVA) and 6 M KOH. A simple method for preparing the gel electrolyte is reported to maintain a high water content within the gel, which is the key factor facilitating the high discharge rate of flexible zinc-air batteries. The optimal flexible battery can be discharged at a large current density of 50 mA cm−2 for 5 min and reaches a capacity of 37 mAh cm−2 and a maximum power density of 64 mW cm−2. The origin of the decayed charge/discharge behavior and cell failure is investigated by the three-electrode chronopotentiometry and post-mortem X-ray diffraction (XRD) analysis. ZnO precipitation is considered the main reason for the decay of both zinc and air electrodes. The good flexibility during cycling is also demonstrated by a continuous bending test, revealing its potential for practical applications.