Agar/polyacrylamide-based hydrogel polymer electrolyte for ultra-stable flexible aqueous lithium-zinc hybrid ion batteries

The burgeoning demand for wearable and implantable electronic devices has spurred the necessity for the development of flexible and safe energy storage systems. Rechargeable aqueous hybrid-ion batteries (RAHBs) are considered promising alternatives, thanks to their high operating voltage, high power density, and enhanced safety. In this study, we introduce a hydrogel polymer electrolyte designed for flexible quasi-solid-state aqueous lithium-zinc (Li-Zn) hybrid ion batteries. The hydrogel polymer electrolyte (HGPE) is fabricated from a blend of agar and polyacrylamide, gelled with a 1M ZnSO₄/2M Li₂SO₄ aqueous electrolyte solution. The resultant hydrogel polymer electrolyte (AP-HGPE) exhibits exceptional characteristics, including outstanding ionic conductivity, a broad electrochemical stability window, and a notable ion migration number. Additionally, the Zn/AP-HGPE/Zn symmetric cells have demonstrated stable cycling for 350 h at 1 mA cm^-2, verifying the consistent deposition and stripping behavior of ions. Leveraging these properties, the full battery (Zn/AP-HGPE/LiMn₂O₄) presents remarkable cycle performance, retaining 80.5 % of its initial capacity after 500 cycles at 1 C, accompanied by exemplary rate performance. Furthermore, RAHB maintains its stable electrochemical performance even under torsion and bending, highlighting its viability for integration into flexible devices. This research represents a significant stride forward in the development of RAHBs that are stable, flexible and long-lasting.