Charge-Complementary Hydrogen-Bonded Complex Separator for Realizing Dendrite-Free Aqueous Zinc-Ion Batteries

With the merits of high reliability, cost-effectiveness, and ecofriendliness, aqueous zinc-ion batteries (AZIBs) are promising for grid-scale energy storage. However, zinc dendrites and associated side reactions are encountered in AZIBs, leading to a reduced lifespan. This work presents a novel separator design strategy to tackle these problems through a synergistic combination of chitosan and sodium alginate, which contain cationic and anionic functional groups, respectively. The complementary polarity of these two polymer matrices and the strong hydrogen bonding between them can establish a unique electrostatic environment that offers isolated transport paths for cations and anions and can construct a robust and stable complex structure. Besides, both biopolymers have a strong affinity with H₂O molecules and the Zn(002) crystal facet. Hence, the complex separator can effectively promote Zn²⁺ ion transport, uniformize Zn²⁺ ion distributions, restrain interfacial planar diffusion of Zn²⁺ ions, facilitate the desolvation process, and boost the interfacial dynamics. It is demonstrated through systematic experiments that the complex separator can effectively suppress adverse phenomena at the zinc metal/electrolyte interface, resulting in significantly stabilized zinc chemistry. With the use of such a separator, extraordinary cycling stability is achieved for Zn//Zn cells and full batteries even under remarkable areal capacities. This research presents a new design concept for battery separators.