Biomimetic Double-Layered Carbon Nanofibers with Optimal Pore Size for Efficient Zinc-Ion Storage

Zinc-ion hybrid capacitors, combining the advantages of zinc-ion batteries and supercapacitors, have amazing potential for large-scale energy storage. However, the construction of carbon cathode suitable for zinc anode kinetics and capacity is still a key challenge, hampering the development of industrialization. Inspired by the structure of the Juncus, carbon nanofibers are fabricated from crop straw via electrospinning and in situ bilayer network structure growth. The size compatibility between nanopores and solvated [Zn (H₂O)₆]²⁺ enhances ultrafast ion and electron transport for the zinc-ion storage. Moreover, interconnected pores and excellent specific surface area ensure highly efficient charge delivery at high mass loadings. The biomimetic carbon nanofibers deliver exceptional capacity (268.3 mAh g^-1), battery-quality energy density (215 Wh kg^-1), and superior cyclic stability (96.15% retention rate after 75 000 cycles at 20 A g^-1), surpassing commercial porous carbon electrodes. Insights into the zinc-ion storage behavior testify that the optimal pore size for zinc-ion storage ranging to be 0.87-3.80 nm, bilayer carbon network structure, and reversible surface physical/chemical interaction enable remarkable energy storage capability. This work provides simple approach for preparing efficient thick electrodes and offers valuable insights into the charge storage mechanism of zinc-ion hybrid capacitors.