Growing Sodiophilic ZnO Nanorod Arrays on Al Substrate for High-Energy-Density Anode-Free Na Batteries.

Anode-free Na batteries maximize energy density but suffer from poor cycling performance originating from the uncontrolled Na growth and large volume change. Herein, we report dense ZnO nanorod arrays on Al foil (D-ZnO NRAs/Al) synthesized by electrodeposition and low-temperature heat treatment methods as a lightweight current collector for selective nucleation and homogeneous plating of Na. The nanorod arrays not only offer abundant interspace to reduce structural stress and enable high Na plating but also promote uniform Na deposition by manipulating Na+ ion flux and reducing local current density. In addition, the sufficient sodiophilic active sites minimize nucleation barriers and serve as preferred nucleation sites, thereby homogenizing Na nucleation and growth. As expected, the D-ZnO NRAs/Al host presents a highly reversible Na plating/stripping with low nucleation overpotential and dendrite-free Na morphology. When coupled with a 4.3 V-class cathode, the assembled anode-free pouch cell achieves stable cycling performance with a capacity retention of 86% for 105 cycles and a high energy density of 441.7 Wh kg-1 based on the active materials of both anode and cathode.