Stereoisomeric engineering for critical balance of solvation and adsorption capability

Aqueous zinc-ion batteries (AZIBs) demonstrate remarkable advantages in high safety, abundant reserves, and cost-effectiveness. Nevertheless, the zinc metal anode fails to deliver optimal performance during repeated plating/stripping processes, where water molecules serve as critical instigators of corrosion and heterogeneous deposition.

To strategically regulate aqueous species in both bulk electrolyte and interfacial regions, electrolyte additives have been extensively employed to modulate electrolyte properties. These additives primarily function through two mechanisms: 1) interfacial adsorption to eliminate free water molecules, or 2) solvation structure modification through hydrogen-bond network disruption to immobilize reactive water in bulk electrolyte.

Consequently, the solvation-modulating capability and adsorption potential of additives constitute crucial metrics for evaluating their effectiveness. Notably, organic additives containing multiple functional groups frequently exhibit structural isomerism – compounds sharing identical molecular formulas but distinct configurations. Such structural divergences often translate to substantially different electrochemical behaviors, highlighting the importance of molecular engineering in additive design.

In a new study published in the KeAi journal Advanced Powder Materials, sorbitol (Sor) and mannitol (Man), a pair of polyhydroxy stereoisomerisms, were chosen as electrolyte additives for designing two electrolyte systems to identify the equilibrium between solvation and adsorption.

“Both Sor and Man have six hydroxyl groups, with only the spatial position of the hydroxyl group on the second carbon being different,” explains the study’s first author Wen Liu. “It’s the structure-activity relationship between these two compounds that accounts for the observed differences in battery performance.”

Surprisingly, the trihydroxy group on the same side of Sor exhibits a stronger adsorption capacity than the dihydroxyl groups on the same side of Man, and it generates a coplanar templating effect.

“This effect promotes the uniform distribution of charges, increases nucleation sites, and induces (002) preferred growth. Compared to base ZnSO₄ electrolyte, Sor and Man molecules present stronger binding energy with Zn²⁺ ions and they can participate in solvation structure of Zn²⁺ ions,” says Liu.

Due to the weaker interaction force between Sor molecular and Zn²⁺ ions compared to Man, it ensures a faster de-solvation process and accelerates the deposition kinetics. These unique advantages make Zn anode in Sor added electrolyte demonstrate more exceptional performance for more than 3470 h at 2 mA cm^-2 and 1 mAh cm^-2.

“Moreover, Zn//AC full cell with Sor additive can steadily operate for 50000 cycles at 3 A g^-1. In order to test the practical application, Zn//I₂ full cell under low N/P ratio of 4.37 can also steadily run for 710 cycles at 1 A g^-1, exhibiting four-times lifespan than bare ZnSO₄ electrolyte,” adds Liu.

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Contact the author: Yuejiao Chen (cyj.strive@csu.edu.cn); Libao Chen (lbchen@csu.edu.cn) , State Key Laboratory of Powder Metallurgy, Central South University, Changsha, 410083, P. R. China.

The publisher KeAi was established by Elsevier and China Science Publishing & Media Ltd to unfold quality research globally. In 2013, our focus shifted to open access publishing. We now proudly publish more than 200 world-class, open access, English language journals, spanning all scientific disciplines. Many of these are titles we publish in partnership with prestigious societies and academic institutions, such as the National Natural Science Foundation of China (NSFC).