Ion-sieving separators modified by sulfonate-functionalized carbon nitride towards highly stable zinc metal anodes

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, we developed an economical and eco-friendly sulfonated carbon nitride (SCN) to functionalize a commercial glass fiber separator (SCN@GF). Carbon nitride (CN) serves as an eco-friendly, low-cost, and zincophilic material and 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 SO₄²⁻, 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 mA h g⁻¹ and initial capacity remaining at 82.7% after 1000 cycles at a high current density of 5 A g⁻¹. Parallel evaluations in a 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 AZIB systems.