Super Hydrous Solvated Structure of Chaotropic Ca2+ Contributes Superior Anti-Freezing Aqueous Electrolytes and Stabilizes the Zn anode.

Abstract

The further development of aqueous zinc (Zn)-ion batteries (AZIBs) is constrained by the high freezing points and the instability on Zn anodes. Current improvement strategies mainly focus on regulating hydrogen bond (HB) donors (H) of solvent water to disrupt HBs, while neglecting the environment of HB-acceptors (O). Herein, we propose a mechanism of chaotropic cation-regulated HB-acceptor via a "super hydrous solvated" structure. Chaotropic Ca2+ can form a solvated structure via competitively binding O atoms in H2O, effectively breaking the HBs among H2O molecules, thereby reducing the freezing point of hybrid 1 mol L-1 (M) ZnCl2 + 4 M CaCl2 electrolyte (-113.2 °C). Meanwhile, the high hydratability of Ca2+ contributes to the water-poor solvated structure of Zn2+, suppressing side reactions and uneven Zn deposition. Benefiting from the anti-freezing electrolyte and high reversible Zn anode, the Zn||Pyrene-4,5,9,10-tetraone (PTO) batteries deliver an ultrahigh capacity of 183.9 mAh g-1 at 1.0 A g-1 over 1600-time stable cycling at -60 °C. This work presents a cheap and efficient aqueous electrolyte to simultaneously improve low-temperature performances and Zn stability, broadening the design concepts for antifreeze electrolytes.