An anti-freezing flexible polymer electrolyte for high-performance zinc-ion batteries

Aqueous rechargeable zinc-ion batteries (ZIBs) encounter several challenges that hinder long-term performance and stability due to the water-induced side reactions, dendrite growth, and limited low-temperature operation, which are mostly associated with water freezing. In this study, the anti-freezing properties of a novel polymer electrolyte composed of a PAES-g-PEG and H₂O/EG based eutectic solution are examined for ZIB application. The optimized polymer electrolyte (1.0 M Zn–eutectic–SPE) demonstrates excellent performance, achieving an ionic conductivity of 2.46 mS cm⁻¹ and a zinc transference number of 0.69 at room temperature (RT). Notably, it maintains a high ionic conductivity of 0.19 mS cm⁻¹ even at −20 °C. Moreover, the 1.0 M Zn–eutectic–SPE not only possesses a high tensile strength (4.18 MPa) with excellent flexibility, but also provides a high oxidative stability window (up to 2.5 V). Apart from its application as an electrolyte component, the synthesized PAES-g-PEG (without H₂O/ EG) is also utilized as a binder material for electrode preparation. The anti-freezing ZnjV₁₀O₂₄$nH₂O@rGO battery fabricated with 1.0 M Zn–eutectic–SPE demonstrates exceptional electrochemical performance. At RT, it delivers high reversible capacities of 306.4 mA h g⁻¹ at 1.0 A g⁻¹ and 101.5 mA h g⁻¹ at 20 A g⁻¹. Notably, even at −20 °C, the ZIB maintained impressive capacities of 277.7 mA h g⁻¹ at 0.05 A g⁻¹ and 63.2 mA h g⁻¹ at 2.0 A g⁻¹. Remarkably, the ZnjV₁₀O₂₄$nH₂O@rGO cells exhibit excellent cycling stability. After 300 cycles at a current density of 1.0 A g⁻¹, they retain 87% of their initial capacity at RT and 91% at −20 °C. Furthermore, at RT, the ZnjV₁₀O₂₄$nH₂O@rGO cell demonstrates outstanding long-term cycling performance, maintaining 83% capacity retention even at a high current density of 10 A g⁻¹. These results confirm that the developed SPE enables stable ZIB operation over a wide temperature range, ensuring reliable performance in diverse environmental conditions.