A Janus separator towards dendrite-free and stable zinc anodes for long-duration aqueous zinc ion batteries

Critical issues of Zn anodes including undesirable dendrites formation and parasitic reactions severely limit the reversibility and cyclability of Zn anodes. To address these issues, a functional Janus separator with the structure of a mechanically strong sulfonated poly(arylene ether sulfone) (SPAES) dense layer composited on a porous glass fiber (GF) substrate is designed. The SPAES dense layer that faces the Zn anode containing abundant sulfonic acid groups effectively promotes the desolvation process of hydrated Zn ions, guides uniform Zn ion transfer, and blocks anions and water, contributing to dendrite-free and highly reversible Zn plating/stripping cycles, while the porous GF substrate retains high electrolyte uptake. As a result, the Zn symmetric cell with the Janus separator demonstrates an ultralong cycling lifespan of over 2000 h at the areal capacity of 1 mA h cm⁻², which is 23-fold superior to that with a pristine glass fiber separator (<90 h). More impressively, the as-prepared Janus separator enables outstanding rate performance and excellent cycling stability of full Zn ion batteries with diverse cathode materials. For instance, when paired with the V₂O₅ cathode, the full battery with a Janus separator attains an ultrahigh initial specific capacity of 416.3 mA h g⁻¹ and capacity retention of 60% over 450 cycles at 1 A g⁻¹, exceeding that with a glass fiber separator. Hence, this work provides a facile yet effective approach to mitigating the dendrites formation and ameliorating the parasitic reactions of Zn metal anodes for high-performance Zn ion batteries.