Aqueous zinc-ion batteries (ZIBs) are considered as the promising candidate of flexible energy storage devices due to their high safety, eco-friendliness, and low-cost. However, conventional flexible aqueous ZIBs undergo severe capacity loss at bending and subzero temperature states. Herein, an anti-freezing hydrogel electrolyte based on zinc tetrafluoroborate (Zn(BF₄)₂) and polyacrylamide (PAM) is developed. Owing to the strong electronegativity of F atoms, BF₄⁻ anions interact with water molecules by OH···F to replace the OH···O between water molecules in Zn(BF₄)₂-PAM hydrogel electrolyte, inhibiting the formation of ice crystal lattice in hydrogel electrolyte at low-temperature. Therefore, the Zn(BF₄)₂-PAM hydrogel remains unfrozen state, good flexibility, and high ionic conductivity even at −70 °C, which ensures that they can act as the electrolytes of anti-freezing flexible ZIBs. As a proof of concept, anti-freezing flexible ZIBs with all-in-one integrated configuration are assembled based on Zn(BF₄)₂-PAM hydrogel. They display enhanced electrochemical performance at −70 °C, such as high capacity retention and remarkable cyclic stability. Furthermore, they also maintain stable electrochemical performance under different bending states even at −70 °C. This work broadens the practical application of flexible aqueous ZIBs at ultralow temperature.

中文翻译：

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用于 −70 °C 柔性锌离子电池的防冻水凝胶电解质

水系锌离子电池（ZIBs）由于其高安全性、生态友好性和低成本被认为是柔性储能设备的有前途的候选者。然而，传统的柔性水性 ZIBs 在弯曲和零下温度状态下会发生严重的容量损失。在此，开发了一种基于四氟硼酸锌 (Zn(BF ₄ ) ₂ ) 和聚丙烯酰胺 (PAM)的抗冻水凝胶电解质。由于F原子的强电负性，BF ₄ ⁻阴离子通过O  H···F与水分子相互作用，取代Zn(BF ₄ ) _{2中水分子间的O}  H···O-PAM水凝胶电解质，在低温下抑制水凝胶电解质中冰晶格的形成。因此，Zn(BF ₄ ) ₂ -PAM水凝胶即使在-70 °C下仍保持未冻结状态、良好的柔韧性和高离子电导率，这确保了它们可以作为抗冻柔性ZIBs的电解质。_{作为概念证明，基于 Zn(BF 4} ) ₂组装具有一体式集成配置的抗冻柔性 ZIB-PAM 水凝胶。它们在 −70 °C 时表现出增强的电化学性能，例如高容量保持率和出色的循环稳定性。此外，即使在-70 °C，它们在不同的弯曲状态下也能保持稳定的电化学性能。这项工作拓宽了柔性水性 ZIBs 在超低温下的实际应用。