3D Carbon Fiber Skeleton Film Modified with Gradient Cu Nanoparticles as Auxiliary Anode Regulates Dendrite-Free, Bottom-Up Zinc Deposition

Achieving stable Zn plating/stripping under high current density and large area capacity remains a major challenge for metal Zn anodes. To address this issue, common filter paper is utilized to construct 3D carbon fiber skeleton film modified with gradient Cu nanoparticles (CFF@Cu). The original zincophobic hydrophilic CFF is transformed into gradient zincophilic and reversed gradient hydrophilic composite, due to the gradient distribution of Cu nanoparticles. When CFF@Cu is placed above Zn foil as an auxiliary anode, Zn foil anode exhibits stable, reversible, and dendrite-free Zn plating/stripping for 1200 h at 10 mA cm^-2 and 2 mAh cm^-2, 2000 h at 2 mA cm^-2 and 2 mAh cm^-2, 340 h at 10 mA cm^-2 and 10 mAh cm^-2. Additionally, nucleation barrier of Zn, Zn²⁺ transport and deposition kinetics are improved. The deposits on the Zn foil anode become homogeneous, dense, and fine. Side reactions and by-products are effectively inhibited. The excellent performance is mainly attributed to the gradient zincophilic field in 3D CFF. A portion of Zn²⁺ is captured by Cu and deposited within CFF@Cu from bottom to top, which reduces and homogenizes Zn²⁺ flux on Zn foil, as well as weakens and homogenizes electric field on Zn foil.