Strategy of Electrolyte Design: Triethanolamine as a Polydentate Ligand to Improve Solvation of Zinc in Zinc-Air Batteries

The zinc-air batteries (ZABs) are regarded as the most potential energy storage device for the next generation. However, the zinc anode passivation and hydrogen evolution reaction (HER) in alkaline electrolyte situations inhibit the zinc plate working efficiency, which needs to improve zinc solvation and better electrolyte strategy. In this work, we propose a design of new electrolyte by using a polydentate ligand to stabilize the zinc ion divorced from the zinc anode. The formation of the passivation film is suppressed greatly, compared to the traditional electrolyte. The characterization result presents that the quantity of the passivation film is reduced to nearly 33% of pure KOH result. Besides, triethanolamine (TEA) as an anionic surfactant inhibits the HER effect to improve the efficiency of the zinc anode. The discharging and recycling test indicates that the specific capacity of the battery with the effect of TEA is improved to nearly 85 mA h/cm2 compared to 0.21 mA h/cm2 in 0.5 mol/L KOH, which is 350 times the result of the blank group. The electrochemical analysis results also indicate that zinc anode self-corrosion is palliated. With density function theory, calculation results prove the new complex existence and structure in electrolytes by the data of the molecular orbital (highest occupied molecular orbital-lowest unoccupied molecular orbital). A new theory of multi-dentate ligand inhibiting passivation is elicited and provides a new direction for ZABs' electrolyte design.

Automated summary

In this work, a new electrolyte design using a polydentate ligand to stabilize the zinc ion and triethanolamine (TEA) as an anionic surfactant is proposed, which greatly suppresses the passivation film formation and improves the efficiency of the zinc anode. The experimental results show that the specific capacity of the battery with the effect of TEA is significantly improved compared to the traditional electrolyte, and the zinc anode self-corrosion is mitigated. The density functional theory calculations confirm the existence and structure of the new complex in electrolytes.