Organic additives with high dipole moments transform aqueous zinc-ion battery interfaces

The advent of organic aqueous electrolytes represents an advancement in battery technology over the past decade. These additives have proven to be remarkably efficacious in modulating the solvation structure and establishing interfacial layers.

The efficacy of aqueous zinc-ion batteries (AZIBs) can be optimized through the enhancement of safety, electrochemical reversibility, and ion mobility. A delicate equilibrium must be maintained between performance and operational stability, as certain organic additives may precipitate undesirable side reactions or intricate phase behavior, thereby nullifying their advantageous effects.

In a study published in the Journal of Colloid and Interface Science, a group led by Prof. Zhang Yining from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences has reported a novel approach to enhancing the performance of AZIBs through the introduction of triethyl 2-phosphonopropionate (Tp), a high-dipole-moment electrolyte additive, and found that Tp effectively replaces free water in the electrolyte, thereby suppressing hydrogen evolution and zinc corrosion while promoting reversible zinc deposition and mitigating dendrite growth.

Researchers prepared Tp electrolyte solutions with varying volume ratios to ascertain the optimal concentration ratio. Tp effectively replaced the free water in the electrolyte through strong ion-dipole interactions to alter the solvated structure, combating the free water-induced side reactions and the disordered growth of zinc dendrites.

The high binding energy between Tp and zinc foil ensured that Tp was firmly attached to the zinc anode surface and inhibited dendrite growth. The addition of Tp was shown to significantly change the hydrogen bonding network structure in the electrolyte.

Furthermore, researchers compared performance differences between Tp electrolytes with different volume ratios and the initial electrolyte in practical electrochemical tests. The Zn//Na₂V₆O₁₆ with the optimal concentration of Tp electrolyte exhibited 92% capacity retention after 4,000 cycles at a current density of 3 A g^-1.

In contrast, Zn//Na₂V₆O₁₆ with the initial electrolyte exhibited only 70% capacity retention after 600 cycles and a significant decrease in Coulombic efficiency. These findings suggest that the electrolyte incorporating Tp has superior cycling stability and multiplicity performance compared with the initial electrolyte.

Moreover, researchers estimated the practical application potential of the Tp electrolyte. They prepared a Zn//Na₂V₆O₁₆ flexible pack battery with Tp electrolyte and successfully illuminated an LED light.

This study emphasizes the importance of high dipole moments in additive strategies that contribute to the practical application of AZIBs.