Alleviating Zn Dendrites by Growth of Ultrafine ZnO Nanowire Arrays through Horizontal Anodizing for High-Capacity, Long-Life Zn Ion Capacitors

Zn ion capacitors (ZICs) composed of a carbon-based cathode and a Zn anode are one of the most promising energy storage devices due to their inherent safety and high-power output. However, their poor cycling stability originating from the Zn dendrites' formation and low energy density limited by insufficient activated carbon properties remain major challenges for development of high-performance ZICs. Hence, we constructed a facile and effective strategy to alleviate "edge effects" and suppress Zn dendrites by growing ZnO nanowire arrays on Zn foil (ZnO@Zn) using a horizontally potentiostatic anodizing technique. The electrochemical characterizations and in situ optical microscopy observation revealed that the introduction of ZnO nanowire arrays can significantly suppress the growth of Zn dendrites and enhance the cycling stability of the Zn anode. The superfine and interlaced ZnO nanowire arrays provide uniform nucleation sites and high electrical conductivity for the Zn metal anode, reducing the local current density and promoting the rapid diffusion and migration of Zn ions on the Zn anode surface. As a result, the ZnO@Zn electrode has a very low nucleation overpotential and excellent cycle stability, far superior to the bare Zn anode. Furthermore, a ZnO@Zn//NPHC ZIC assembled with an N, P-codoped hard carbon (NPHC) cathode delivers a high specific capacity of 110.3 mAh g-1 at 0.1 A g-1 and achieves outstanding cycling stability with 90% capacity retention together with ∼100% Coulombic efficiency after 20000 cycles.