Long-life and low-polarization Zn metal anodes enabled by a covalent triazine framework coating

The development of aqueous zinc-ion batteries is greatly hindered by the intrinsic defects of Zn metal anodes, such as uncontrollable dendrite growth and complicated side reactions. Herein, a covalent triazine framework (CTF), with abundant zinc ion transfer channels and strong chemical stability, is fabricated as a coating layer of zinc anodes to address these problems. The CTF layer not only regulates uniform Zn2+ transport path but also effectively separates zinc anodes from bulk electrolytes, thereby preventing the occurrence of side reactions. Moreover, the triazine ring can serve as zincophilic sites to enhance Zn deposition kinetics. Thus, the CTF-protected Zn anode enables a Zn//Zn symmetric cell to achieve a long cycle lifespan of over 7000 h, about 40 times larger than that of bare Zn anodes. This symmetric cell also has a low and stable voltage polarization of 36 mV even after 3000 h. Meanwhile, the full cell coupled with calcium-doped V2O5 exhibits capacity retention of 66.7 % after 300 cycles at a current density of 1 A g−1, while the cell with bare Zn anode could only retain 24.3 % of capacity under the same condition. This work provides a promising method to address the anode problems in metal-ion batteries.