High-sulfur coal-based carbon dots as an electrolyte additive to enhance the performance of aqueous zinc-ion batteries

Abstract

Aqueous zinc-ion batteries (AZIBs) are promising for large-scale energy storage but suffer from zinc anode issues like dendrite growth and side reactions. This study synthesized sulfur-containing carbon dots (S-CDs) from high-sulfur coal via hydrodynamic cavitation. These quasi-spherical S-CDs have abundant surface groups (O–H, CC, C–S) and good aqueous compatibility. As a 0.5 mg mL⁻¹ additive in 2 mol per L ZnSO₄ electrolyte, S-CDs weakened Zn²⁺–water interaction, bound Zn²⁺ via negative groups, inhibited hydrogen/oxygen evolution and corrosion (corrosion current down to 0.168 mA from 2.3 mA), restricted Zn²⁺ diffusion, and induced dense (002) plane zinc deposition to suppress dendrites. Electrochemical tests showed Zn‖Zn symmetric batteries with S-CDs had R_ct reduced to 200 Ω (from 610 Ω), cycling stably over 1120 h (1 mA cm⁻²) and 2000 h (5 mA cm⁻²). Zn‖NH₄V₄O₁₀ full cells delivered 310.1 mAh g⁻¹ at 3 A g⁻¹ (vs. 250.5 mAh g⁻¹ for pristine electrolyte) and retained 90.3% capacity after 500 cycles (vs. 72.1%). This work enables high-value use of high-sulfur coal and provides a scalable additive to boost AZIBs' practicality in large-scale energy storage.