A Fumed SiO2-based Composite Hydrogel Polymer Electrolyte for Near-Neutral Zinc-Air Batteries

Near-neutral zinc-air batteries show great promise for long-cycle applications in ambient air owing to their impressive deposition/stripping compatibility with zinc anodes and greater chemical stability towards CO 2 in ambient air compared to batteries with traditional alkaline electrolytes . However, the inherent water volatilization of liquid electrolytes and the flexibility of electrolytes required for wearable devices severely limit the practical application of this system. In this study, a fumed SiO 2 -based composite hydrogel polymer electrolyte (SiO 2 -HPE) was prepared for application in near-neutral zinc-air batteries. The design of the SiO 2 -HPE was carried out considering the following three aspects. Firstly, it is widely acknowledged that the polyacrylamide polymer skeleton is beneficial to excellent ionic conductivity and the mechanical strength of the SiO 2 -HPE. Secondly, fumed SiO 2 bearing multiple silicon hydroxyl groups is a suitable option as a water-retaining additive. Thirdly, the near-neutral liquid electrolyte (1 mol·kg −1 Zn(OTf) 2 ) absorbed in the SiO 2 -HPE is stable towards CO 2 in ambient air. In conclusion, these three aspects of the electrolyte design contribute to the practical application of the SiO 2 -HPE. Raman spectroscopy and scanning electron microscopy revealed that the synthesized SiO 2 -HPE exhibited a high degree of polymerization, plentiful surface pores, and a uniform distribution of elements. According to the infrared and Raman spectra, the abundant hydroxyl groups located on the surface of the SiO 2 particles enhanced water molecule binding by altering the hydrogen bond network within the SiO 2 -HPE. This conclusion was further confirmed by thermogravimetry and differential scanning calorimetry . After exposure to ambient air (30% relative humidity) for 96 h, the SiO 2 -HPE exhibited a water retention capacity of 49.52%, which is 6.23% and 1.73% higher than those for 1 mol·kg −1 Zn(OTf) 2 and the HPE (hydrogel polymer electrolyte without SiO 2 ). Moreover, owing to the dynamic recombination of the hydrogen bonds between the silicon hydroxyl groups and the gel skeleton, SiO 2 -HPE exhibited a higher mechanical strength and modulus than HPE under tensile and compressive conditions, respectively. This further rendered it an ideal electrolyte for flexible zinc-air batteries. The near-neutral zinc-air battery assembled with the SiO 2 -HPE exhibited a cycle life of up to 200 h under 30% relative humidity, far exceeding those of 1 mol·kg −1 Zn(OTf) 2 and the HPE. Based on such remarkable performance, the flexible near-neutral zinc-air battery device assembled by the SiO 2 -HPE has shown a satisfactory performance under special conditions, such as bending and cutting, and can be used as a power supply for different electronic devices, making it a promising next-generation electrochemical energy storage device. Overall, this work provides new insight into the development of flexible zinc-air battery devices with long-term stability in ambient air. Download: Download high-res image (83KB) Download: Download full-size image