A Five Micron Thick Aramid Nanofiber Separator Enables Highly Reversible Zn Anode for Energy‐Dense Aqueous Zinc‐Ion Batteries

Abstract The rampant dendrites growth caused by uncontrolled deposition of Zn 2+ ions at Zn metal anode poses a significant obstacle to the practical applications of aqueous zinc‐ion batteries (ZIBs). Herein, an ultrathin (5 µm) aramid nanofiber (ANF) separator is reported to enhance the Zn anode stability and the ZIB energy density. Through systematic experimental studies and DFT simulations, it is demonstrated that the ANF separator with unique surface polarity can modify the solvation configuration, facilitate desolvation, and regulate the deposition orientation of Zn 2+ ions. Consequently, the Zn anode with the ANF separator demonstrates an 85‐fold increase in running time beyond 850 h compared with the conventional glass fiber separator at 5 mA cm −2 /2.5 mAh cm −2 . Even under the harsh depth of discharge conditions of 50% and 80%, the Zn anodes still sustain extended cycling periods of over 475 and 200 h, respectively. As pairing this ANF separator with thin Zn anode and high‐areal‐capacity Mn 2.5 V 10 O 24 ∙5.9H 2 O cathode in a low negative capacity/positive capacity ratio (2.64) full cell, superior gravimetric/volumetric energy density (129.2 Wh kg −1 /142.5 Wh L −1 ) is achieved, far surpassing majority of the ZIB counterparts reported in the literature. This work offers a promising ultrathin separator for promoting the utilization of energy‐dense aqueous ZIBs.