An anti-freezing hydrogel electrolyte based on hydroxyethyl urea for dendrite-free Zn ion batteries

Hydroxyethyl urea is a widely used moisturizer in cosmetics, since it can form strong hydrogen bonds with water. It could be introduced into the hydrogel to reduce the freezing point and enhance the performance of electrolyte at low temperature. Additionally, hydroxyethyl urea can change the solvation structure of Zn2+, further prevent dendrite formation and side reactions. We constructed a hydrogel electrolyte made from polyacrylamide crosslinked using hydroxyethyl urea, which can form an antifreeze gel and reduce the HER, corrosion and dendrite growth reactions. This work provides a simple strategy for enhancing low temperature performance of zinc ion batteries. [Display omitted] •The hydroxyethyl urea additive can break the hydrogen bonds of water.•The hydroxyethyl urea additive can optimizes the solvation structure of Zn2+.•At a temperature of -40 ℃, the Zn//Zn symmetry achieves steady cycles over 3000h.•The Zn//NH4V4O10 full battery delivers a capacity of 195.14 mAh g−1 at −40 ℃. Aqueous zinc ion batteries are considered as a promising energy storage resource due to their high security, abundant resources and low price. However, the development of aqueous zinc ion batteries has been severely hindered by compulsive dendrite generation, serious side reactions and poor temperature adaptability. Herein, we used hydroxyethyl urea as a hydrogel electrolyte additive to address above-mentioned challenges. Hydroxyethyl urea can break the hydrogen bonds (HBs) of water and enhancing the freezing-tolerance ability of the electrolyte. Meanwhile, hydroxyethyl urea can prevent the corrosion issue and inhibition of Zn dendrites. Consequently, the Zn//Zn symmetric battery can sustain stable cycling for over 3000 h at 1 mA cm−2, and it achieves a high coulombic efficiency of 99.6 %. Even at −40 ℃ the batteries show excellent cycling stability, the Zn//Zn symmetry battery can achieve steadily cycles over 3000 h. The Zn//NVO battery equipped with the altered electrolyte exhibits enhanced capacity retention compared to the one without additives.It demonstrates not only excellent cycling stability at room temperature but also maintains commendable functionality down to −40 ℃, validating the method’s efficacy. This work provides a simple strategy for enhancing low temperature performance of zinc ion batteries.