Engineering low-temperature aqueous Zn metal batteries via coupled regulation of water H-bonding, facet-selective deposition, and hydrophobic SEI formation

Low-temperature performance is crucial for aqueous zinc metal batteries (AZMBs). Subzero temperatures modify the chemical interactions between solvents, anions, and Zn 2+ ions, which in turn affect the hydrogen-bond structures, molecular adsorption, and solid electrolyte interphase (SEI) formation. However, few studies have investigated how these factors collectively enhance electrochemical performance. In this study, 2-picolinamide (PA), an organic compound with an aromatic heterocyclic ring and amide groups, is introduced into the electrolyte. PA molecules substantially disrupt the original hydrogen bonds between water molecules, enabling the operation at extremely low temperatures. The breakdown of adsorbed PA forms a robust, hydrophobic SEI composed of soft organic materials and inorganic frameworks, which helps reduce cracking and dendrite formation during plating and stripping at subzero temperatures. It also expels free water from the electric double layer, minimizing side reactions. Additionally, PA adsorption on the electrode surface and the presence of the SEI layer promote the preferential growth of the (101) facet, thereby alleviating slow mass transport and sluggish reaction kinetics and consequently maintaining a stable electrode morphology under low-temperature conditions. Accordingly, at −20 °C, the Zn/Zn symmetric cell achieves stable cycling for over 8000 h at 1 mA cm −2 and 1 mAh cm −2 . Even at −40 °C, the cell can maintain stable operation for up to 2200 h at 0.5 mA cm −2 and 0.5 mAh cm −2 . At room temperature, the Zn//Zn x V 2 O 5 ⋅H 2 O pouch cell delivers a promising specific capacity of 500 mAh g −1 , and it can still reach 370 mAh g −1 even at −20 °C. This study improves the low-temperature performance of advanced AZMBs by modifying solvation structures, constructing interfacial molecular layers, and forming an SEI layer in situ on the Zn anode.