One-step preparation of an anti-freezing and flame-retardant eutectic gel electrolyte for assembling a flexible and high-performance zinc-ion battery

Abstract

Flexible zinc-ion batteries have attracted considerable attention owing to their intrinsic safety, high specific capacity, low cost, and environmental benefits. However, the choice of electrolyte plays a critical role in battery performance. A eutectic gel electrolyte with good properties has recently attracted much attention. However, high viscosity of the deep eutectic solvent (DES) poses the challenge of impairing the ionic conductivity of the gel. To achieve a stable electrolyte with high ionic conductivity, herein, a zinc deep eutectic solvent (ZDES) was combined with a small amount of water to directly dissolve polyvinyl alcohol (PVA) to develop a highly stable eutectic gel electrolyte (PVA-ZDES) via a one-step process. This gel electrolyte possessed a robust physical crosslinked network and offered good mechanical properties (maximum tensile strength of 0.74 MPa), exceptional ionic conductivity (4.55 × 10⁻³ S cm⁻¹), a stable electrochemical window (∼2.1 V), and anti-freezing and flame-retardant abilities. The assembled Zn‖PANI button battery based on the eutectic gel electrolyte exhibited remarkable cycling stability (79% capacity retention after 2000 cycles at 1 A g⁻¹) and excellent low-temperature performance (down to −35 °C). Additionally, the in situ assembly of a flexible soft-package battery was achieved depending on the rapid gelation, which could simplify the manufacturing process and optimize the electrode–electrolyte interface. This study proposes a novel approach for the design and industrial production of flexible and safe zinc-ion battery electrolytes under extreme environments.