Thermodynamic descriptor-guided ligand screening enables dendrite-free zinc deposition in alkaline flow batteries.

Abstract

Alkaline zinc-based flow batteries suffer from poor zinc reversibility due to dendrite growth and parasitic reactions, which significantly shorten their cycling lifespan. A key challenge lies in the rational design of ligands to eliminate concentration polarization caused by mismatched diffusion and interfacial reaction rates, thereby inducing and regulating uniform zinc deposition. In this study, we propose a thermodynamic descriptor-guided ligand screening strategy, using the metal-ligand stability constant (log K) as a quantitative criterion to simultaneously optimize deposition morphology and interfacial ion kinetics. Guided by this principle, nitrilotriacetic acid (NTA, log K = 11.98) is identified as a robust chelating agent under strongly alkaline conditions (pH > 14). Its moderate coordination strength enables the disruption of the native Zn²⁺-H₂O network, effectively suppressing hydrogen evolution while maintaining near-theoretical Zn²⁺ desolvation kinetics. In situ microscopy and electrochemical analyses reveal that NTA directs preferential Zn(002) growth, yielding dendrite-free deposition at ultrahigh current densities (80 mA cm^-2) and high areal capacities (40 mAh cm^-2). Furthermore, NTA facilitates efficient Zn²⁺ diffusion (5.77 × 10^-7 cm²/s), outperforming strong chelators such as ethylenediaminetetraacetic acid. As a result, Zn//Zn symmetric cells exhibit stable cycling over 400 h, while NTA-enabled ZnFe flow batteries achieve 700 cycles with 99 % coulombic efficiency and minimal capacity decay. This work establishes log K as a practical screening descriptor for multi-objective electrolyte optimization and provides a scalable pathway for the development of high-performance alkaline zinc flow batteries.