Structural optimization of carbonized polymer dots for modulation of electrochemical performance of aqueous electrolytes

Aqueous zinc ion batteries (AZIBs) are considered to be one of the most promising energy storage devices due to the advantages of high cost-effectiveness, safety, and environmental friendliness, however, they suffer from problems such as Zn dendrites growth and by-product generation. Carbonized polymer dots (CPDs) with polar groups as additive have been introduced to modulate the solvated structure of Zn²⁺ and reduce the water activity, promoting the uniform deposition of Zn and inhibiting the occurrence of side reactions. However, CPDs with different functional group contents from different precursor molar ratios variably affect the electrochemical performance of aqueous electrolytes. Therefore, in this work, we designed and synthesized CPDs with different molar ratios of the precursors (citric acid and urea) as electrolyte additives for AZIBs and explore the optimal molar ratios of the precursors. The Zn//Zn symmetrical cells using electrolytes with optimal ratios CPDs achieve an extended cycle life over 615 h at 2 mA cm^-2 and 1 mAh cm^-2. This work offers great potential for future practical applications of CPDs.