Carbon-based materials, commonly used as commercial anodes in lithium/sodium ion batteries, nevertheless suffer from sluggish kinetic properties. Constructing electrode materials with one-dimensional nanostructures that offer convenient ion/electron transport pathways can improve Li⁺/Na⁺ storage behavior. Recently, metalsingle-atomdoping has also emerged as an effective strategy to enhance storage kinetics. However, it remains challenging to construct one-dimensional carbon materials doped with metal single atoms using simple methods to achieve outstanding Li⁺/Na⁺ storage performance. Herein, three-dimensional intertwined short carbon nanofibers (SCNFs) coupled with single atomic iron dopants were tailored through a hydrothermal strategy followed byhigh-temperaturecarbonization free from strong acids etching metals. In the SCNFs, only a trace amount of Fe(0.37 at.%)was introduced; the nitrogen-coordinated Fe single atoms and the nanofibers-intertwined structure promoted Li-ion adsorption, improved diffusion kinetics, and enhanced conductivity, thereby facilitatingLi⁺/Na⁺storage capacity. Acting as an anode in lithium/sodium batteries, SCNFs demonstrated an outstanding electrochemical performance. After assembling lithium ion batteries, the optimal Fe-N-C-2 exhibited a high reversible capacity of 903.4 mAh g^-1 at 50 mA g^-1 with retention of 518.7 mAh g^-1 at 1.0 A g^-1. For sodium-ion storage, Fe-N-C-2 preserved excellent high-rate cyclic stability, maintaining 152.6 mAh g^-1 after 500 cycles at0.5 A g^-1.Moreover, the hydrothermal method is simple and convenient for large-scale preparation. Our strategy offers a heuristic perspective on the controllable design of nitrogen-coordinated atomic metals for energy storage applications.

Aqueous zinc-ion batteries (ZIBs) hold great promise for energy storage applications. Nevertheless, the realization of high-capacity ZIBs with extended cycle durability remains a significant scientific challenge, predominantly attributed to two inherent limitations: the uncontrollable dendritic growth and concomitant side reactions. In this study, we present a polymer electrolyte membrane denoted as TAC, which addresses these challenges by enhancing the uniform distribution of zinc ions. By incorporating phenolic hydroxyl groups from tannic acid (TA) onto the surface of cellulose fibers, TAC is synthesized, which not only effectively shields both the front and back surfaces of the zinc anode from corrosive effects of the liquid electrolyte, but also exhibits a high liquid-retention capacity under pressures up to 5 MPa. Combining density functional theory simulations with experimental investigations, we demonstrate that the phenolic hydroxyl groups from TA actively engage with zinc ions, thereby significantly reducing the desolvation energy during the plating/stripping processes of the zinc anode. The assembled battery utilizing 1% TAC achieves remarkable performance, retaining 83.1% of its discharge capacity after 1,000 cycles at a current density of 5 C. Moreover, it exhibits high reversibility, high coulombic efficiency of 99.9%, and an impressive lifespan exceeding 2,300 h at 0.5 mA cm^-2. Furthermore, 1% TAC demonstrates excellent cycling stability across four different electrolyte systems [ZnSO₄, Zn(CF₃SO₃)₂, Zn(OAc)₂, and ZnCl₂], highlighting its outstanding compatibility across diverse electrolyte compositions. The exceptional performance of the assembled batteries underscores the efficacy of our design, offering a novel strategy for the development and fabrication of polymer electrolyte membranes tailored for aqueous ZIBs.