Nitroxyl radical triggered the construction of a molecular protective layer for achieving durable Zn metal anodes

The issues of dendrite growth, hydrogen evolution reaction, and zinc anode corrosion have significantly hindered the widespread implementation of aqueous zinc-ion batteries (AZIBs). Herein, trace amounts of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) additive is introduced into AZIBs to protect the zinc metal anode. Trace amounts of the TEMPO additive with nitroxyl radical can provide fast Zn²⁺ transport and anode protection ability by forming an adsorbed molecular layer via Zn-O bond. This interface not only provides strong interfacial compatibility and promotes dynamic transport of Zn²⁺, but also induces deposition of Zn²⁺ along Zn (002) plane. Additionally, the molecular protective layer significantly inhibits hydrogen evolution reaction (HER) and corrosion. The Zn anodes achieve high Coulombic efficiency of up to 99.75 % and long-term plating/stripping of more than 1400 h at 1 mA cm^-2 and 0.5 mAh cm^-2. The Zn//Zn symmetric cell can operate continuously for 2500 h at a current density of 1 mA cm^-2 and 1 mAh cm^-2, and it can still last for nearly 1400 h even when the current density is increased to 5 mA cm^-2. Furthermore, the Zn//V₂O₅ full cell using TEMPO/ZnSO₄ electrolyte effectively maintains a maximum capacity retention rate of 53.4 % even after 1500 cycles at 5 A/g. This innovative strategy introduces trace additive with free radicals into the electrolyte, which may help to achieve large-scale, ultra-long-life, and low-cost AZIBs.