Nitrogen/Fluorine Co-Doped Carbon Dots as an Electrolyte Additive to Stabilize the Zinc Anode

The inherent limitations of zinc anodes constrain the performance of zinc-ion batteries (ZIBs). Viable electrolyte additives offer a practical approach for stabilizing the zinc anode interfaces. This work systematically investigates the role of nitrogen/fluorine co-doped carbon dots (NF-CDs) as an electrolyte additive. Theoretical investigations indicate that the nitrogen and fluorine atoms on NF-CDs have stronger binding energies with Zn²⁺ than water molecules and Zn²⁺, enabling NF-CDs to partially replace coordinated water within the Zn²⁺ solvation sheath and reconstruct the Zn²⁺ solvation structure. This mechanism is corroborated by nuclear magnetic resonance and Fourier transform infrared spectroscopy. The reconfigured solvation structure weakens the coordination between the bound water and Zn²⁺, inhibiting water-induced side reactions and enhancing the electrode's electrochemical stability. Concurrently, NF-CDs' steric hindrance contributes to interfacial stabilization, facilitates the diffusion of solvated Zn²⁺, and mitigates zinc aggregation. Consequently, the zinc-symmetric cells incorporating NF-CDs achieve stable cycling for 1600 h at 1 mA cm^-2, while the zinc-copper cells maintain a 99.67% average coulombic efficiency over 900 cycles. The Zn||NVO (NaV₃O₈·1.5H₂O) full cell retains a specific capacity of 140 mAh g^-1 after 1000 cycles at 5 A g^-1. The results demonstrate the NF-CDs' potential as additives for enhancing the stability of ZIBs.