Sulphur-doped graphene quantum dot electrolyte additives for enhanced cycling stability of aqueous zinc-ion batteries

Abstract

Aqueous zinc-ion batteries (AZIBs) represent a promising alternative to conventional monovalent metal-ion technologies due to their high energy density, low cost, environmental friendliness, and improved safety. Nonetheless, their practical applications still face significant challenges due to vigorous dendrite formation and side reactions on the zinc anode, as well as weakly solvated structures at the electrode/electrolyte interface. Herein, sulphur-doped graphene quantum dots (GQDs) are designed as additives for high-concentration electrolytes, characterized by their exceptional chemical stability, design flexibility, and favorable electrochemical activity. The high electronegativity of their polar functional groups (–OH, –COOH, –NH₂, and –SCN) on the GQD surfaces facilitates strong Zn²⁺ affinity, rapid ionic mobility, homogeneous Zn deposition, and tunable Zn plating/stripping. Consequently, the incorporation of these GQDs successfully mitigates interfacial corrosion of the Zn anode by water molecules and disrupts the conventional solvated structure. Compared to the 2 mol L⁻¹ ZnSO₄ (ZS) electrolyte system, batteries assembled with the ZS/Q2-0.7 electrolyte demonstrated better electrochemical performance. The Zn||Zn symmetric cell short-circuited after 2000 cycles at 0.1 mA cm⁻², while the Zn||Cu asymmetric cell achieved an average coulombic efficiency of 99.05% after 1500 cycles. The Zn||activated carbon (AC) zinc-ion capacitor maintained 85.48% capacity retention after 25 000 cycles, and the Zn||Na₂V₆O₁₆ (NVO) zinc-ion battery retained 52.4% of its capacity after 4000 cycles.