Porosity and Conductivity Dual-Gradient Design on Ultrathin 3D Nanofibrous Anode for Flexible Zn-Ion Batteries

Flexible Zn-ion batteries (ZIBs) have been regarded as a promising energy storage solution for flexible electronics. However, the challenges of dendrite growth due to uneven current density distribution and limited anode flexibility have impeded their practical application. Herein, a flexible 3D zinc anode with a dual gradient in porosity and conductivity is presented. This dual-gradient nanofibrous anode exhibits exceptional flexibility and durability, showing less than a 10% change in resistance after 15 000 bending cycles. The vertical gradient distribution in conductivity promotes preferential zinc deposition at the bottom section, while the gradient in porosity facilitates Zn 2 ⁺ ion migration and ensures timely replenishment of the inner space of the membrane. The combination of the 3D structure and dual-gradient design fosters bottom-up zinc deposition, effectively preventing dendrite formation. Symmetric cells with this dual-gradient anode demonstrate outstanding cycling stability, maintaining more than 410 h of operation at a current density of 1 mA cm −2 for 1 mA h cm −2 , surpassing reference samples and most previously reported 3D zinc anodes. The quasi-solid-state ZIBs assembled with this dual-gradient anode exhibit excellent stability under various mechanical deformations. These 3D nanofibrous anodes with dual-gradient designs hold great promise for advancing the practical application of flexible Zn-ion batteries.