Designing Self-Sustained Hydrogel Electrolytes for Aqueous, Transparent, and Flexible Batteries

The arrival of aqueous sodium-ion batteries has been an essential sustainable advancement in energy storage devices. The use of electrolytes based on polymeric hydrogel is emerging due to the facility in which they can be obtained as film, flexibility, and high ionic conductivity. Additionally, these electrolytes have a dual purpose by acting also as separators. This work deals with the preparation and characterization of hydrogels based on polyvinyl alcohol (PVA), sodium chloride (NaCl), and boric acid (H₃BO₃) to be used as electrolytes in transparent and flexible aqueous sodium-ion batteries. It was observed that lower amounts of NaCl yielded transparent and conductive gels, while increasing the amount of NaCl yielded translucent samples, due to the non-dissolved NaCl. The preparation, gelation step and electrode deposition were optimized to achieve the maximum transparency and conductivity. Subsequently, the selected electrolyte was applied in symmetric devices based on transparent nanocomposite films as electrodes. These devices demonstrated both high transparency and grand current rates. Furthermore, the performance of the electrolyte was verified in a flexible and symmetrical device, revealing an increased current, indicating improved electrode/electrolyte contact. This observation underscores the efficacy of hydrogels in enhancing device performance, particularly in flexible configurations.

Keywords:
hydrogel; flexibility; transparency; electrolytes; polyvinyl alcohol