Cationic Complex Polymer Separator Confined Anionic [Zn(OH)₄]^2‒ Reduction for Stable Alkaline Batteries

Unlike neutral aqueous batteries with cationic Zn²⁺ as the charge carrier, alkaline batteries with anionic [Zn(OH)₄]^2‒ and OH^‒ are actually commercially feasible and thermodynamically stable thanks to their ability to suppress hydrogen evolution. Whereas commercial separators in alkaline batteries, without ion regulation capability, fail to suppress severe dendrite and passivation of anionic [Zn(OH)₄]^2‒ and accelerate ion transport of anionic OH^‒. Herein, we tailor the coordination structures of alkali-stable cationic complexes in polymer separators (CCPS) to construct anionic OH^‒ selective transfer channels. Synchrotron spectroscopic characterizations and theoretical calculations reveal that the low-coordination cationic complexes expose more positive charge density, electrostatically attracting more negative charge from [Zn(OH)₄]^2‒. In situ electrochemical digital holography technology and time-of-flight secondary ion mass spectrometry analyses further confirm the homogeneous [Zn(OH)₄]^2‒ distribution at the CCPS-electrode interface, oriented Zn deposition, and impeded passivation. As a result, CCPS enables alkaline Zn||Cu cells to operate over 5500 cycles at 1 mA cm^‒2 with a high coulombic efficiency of 99.99%. Alkaline Ni-Zn batteries exhibit ultrastable cycling over 1000 cycles at 6 C and maintain 86.17% of their maximum capacity at 10 C. Our work may provide practical and effective separator strategies to accelerate the commercialization of alkaline batteries.