Hofmeister Effects in Supramolecular Chemistry for Anion-Modulation to Stabilize Zn Anode

Aqueous Zn-ion batteries (AZIBs) are considered as promising candidates for the next-generation large-scale energy storage, which, however, is facing the challenge of instable Zn anodes. The anion is pivotal in the stability of anodes, which are not being paid enough attention to. Herein, the modulation of anions is reported using the Hofmeister series in supramolecular chemistry to boost the stability of Zn anodes. It is found that the right-side anions in the Hofmeister series (e.g., OTf^-) can enhance the Zn²⁺ transference number, increase the Coulombic efficiency, facilitate uniform Zn deposition, reduce the freezing point of electrolytes, and thereby stabilize the Zn anodes. More importantly, the right-side anions can form strong interaction with β-cyclodextrin (β-CD) compared to the left-side anions, and hence the addition of β-CD can further enhance the stability of Zn anodes in OTf^--based electrolytes, showing enhancement of cycling lifespan in the Zn//Zn symmetric cells more than 45.5 times with β-CD compared with those without β-CD. On the contrary, the left-side anions show worse rate performance after the addition of β-CD. These results provide an effective and novel approach for choosing anions and matching additives to stabilize the anodes and achieve high-performance AZIBs through the Hofmeister effect.