Dendrite-free Zn anode induced by Zn-Cu alloy NP@NC yolk-shell nanostructure for ultralong cycle stability alkaline Zn batteries

Abstract

This paper discusses the dendrite-free Zn anode for long-term cycle stability of Alkaline Zn batteries. A unique Zn-Cu alloy NP@NC is synthesized through solution synthesis and heat treatment. The Cu precursor was inserted in ZIF-8 by simple drop-casting. Heat treatment allowed for ZIF-8 and Zn, Cu species to transform into N-doped carbon (NC) and Zn-Cu solid solution respectively, enhancing overall electrochemical performance. The as-prepared Zn-Cu alloy NP@NC is characterized by Powder X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Brunauer-Emmett-Teller (BET), and X-ray Photoelectron Spectroscopy (XPS). Then the symmetric cell was assembled to verify plating/stripping behavior. Electrode evaluation was performed by cycle test in high-pH environment. The Zn-Cu alloy NP@NC exhibited remarkable electrochemical performance compared with that of the bare Zn foil. It stably operated over 500 h, while short circuit occurred only after 25 h for bare Zn foil. In order to demonstrate the excellent cycle stability of Zn-Cu alloy NP@NC, characterization of electrode was conducted after cycle test. Furthermore, DFT calculation supports the fundamental principle of excellent cycle performance for Zn-Cu alloy NP@NC. The outstanding electrochemical behavior is ascribed to mainly two points. First one is that well-distributed sub-nano size Zn-Cu alloy nanoparticles (NPs) derived low-energy barrier Zn nucleation sites. Second one is the abundant micro-, mesoporous N-doped carbon structure acted as an ion-sieving mesh and enabled redox ions to diffuse easily. As a result, our electrode, Zn-Cu alloy NP@NC lead to stable and smooth Zn plating in high-pH electrolyte. This paper shows the promising methodology for designing anode material to realize long-term cycle stability of rechargeable Alkaline Zn batteries.