Ion-Sieving Separator Modified by Sulfonate Functionalized Carbon Nitride towards Highly Stable Zinc Metal Anode

Abstract

Aqueous zinc ion batteries (AZIBs) show promise for next-generation energy storage due to their safety, cost-effectiveness, and high specific capacity, but face challenges like dendritic growth and unwanted reactions at the Zn anode. To mitigate these issues, sulfonated carbon nitride (SCN) is proposed to functionalize the commercial glass fiber separator (SCN@GF) via vacuum filtration method. Carbon nitride (CN), as a highly stable and zincophilic substance with high N content, can induce the uniform dispersion of Zn²⁺ flux and even deposition. The introduction of sulfonate groups, known for their strong electronegativity, serves multiple functions: enhancing Zn²⁺ affinity, creating electrostatic barriers against SO₄^2-, and promoting the de-solvation of hydrated Zn²⁺ complexes. These synergistic effects lead to improved Zn²⁺ deposition uniformity and suppress parasitic reactions. Electrochemical characterization reveals that the Zn//Zn symmetric cell equipped with the SCN200@GF separator demonstrated superior performance metrics, including an elevated Zn²⁺ transference number (0.65), enhanced cycling durability, and significantly prolonged operational lifetime. In addition, when implemented in a Zn//NHVO full cell system, the SCN200@GF separator exhibited stable performance, with its specific capacity remaining at 297.3 mAh g^-1 and initial capacity remaining at 82.7% after 1000 cycles at a high current density 5 A g^-1. Parallel evaluations in pouch cell showed 90.1% capacity preservation over 125 cycles at 1 A g^-1. This study shows an innovative strategy for separator design in AZIBs systems.