Nitrogen‐Doped and Sulfonated Carbon Dots as a Multifunctional Additive to Realize Highly Reversible Aqueous Zinc‐Ion Batteries

Aqueous zinc-ion batteries (ZIBs) using the Zn metal anode have been considered as one of the next-generation commercial batteries with high security, robust capacity, and low price. However, parasitic reactions, notorious dendrites and limited lifespan still hamper their practical applications. Herein, an eco-friendly nitrogen-doped and sulfonated carbon dots (NSCDs) is designed as a multifunctional additive for the cheap aqueous ZnSO₄ electrolyte, which can overcome the above difficulties effectively. The abundant polar groups (-COOH, -OH, -NH₂ , and -SO₃ H) on the CDs surfaces can regulate the solvation structure of Zn²⁺ through decreasing the coordinated active H₂ O molecules, and thus redistribute Zn²⁺ deposition to avoid side reactions. Some of the negatively charged NSCDs are adsorbed on Zn anode surface to isolate the H₂ O/SO₄ ^2- corrosion through the electrostatic shielding effect. The synergistic effect of the doped nitrogen species and the surface sulfonic groups can induce a uniform electrolyte flux and a homogeneous Zn plating with a (002) texture. As a result, the excellent cycle life (4000 h) and Coulombic efficiency (99.5%) of the optimized ZIBs are realized in typical ZnSO₄ electrolytes with only 0.1 mg mL^-1 of NSCDs additive.