Crystallinity engineering of carbon nitride protective coating for ultra-stable Zn metal anodes

Ineffective control of dendrite growth and side reactions on Zn anodes significantly retards commercialization of aqueous Zn-ion batteries. Unlike conventional interfacial modification strategies that are primarily focused on component optimization or microstructural tuning, herein, we propose a crystallinity engineering strategy by developing highly crystalline carbon nitride protective layers for Zn anodes through molten salt treatment. Interestingly, the highly ordered structure along with sufficient functional polar groups and pre-intercalated K⁺ endows the coating with high ionic conductivity, strong hydrophilicity, and accelerated ion diffusion kinetics. Theoretical calculations also confirm its enhanced Zn adsorption capability compared to commonly reported carbon nitride with amorphous or semi-crystalline structure and bare Zn. Benefiting from the aforementioned features, the as-synthesized protective layer enables a calendar lifespan of symmetric cells for 1100 h and outstanding stability of full cells with capacity retention of 91.5% after 1500 cycles. This work proposes a new conceptual strategy for Zn anode protection.