Anion-rich zinc solvation structure enables low-temperature zinc plating/stripping efficiency

It is generally believed that low-temperature Zn²⁺ plating/stripping efficiency is lower than at room temperature. However, theoretical and experimental results indicate that a reversal where low-temperature efficiency outperforms that at room temperature. Under the 3 mol·kg⁻¹ (3 m), Zn(ClO₄)₂ delivers 99.87% efficiency over 3800 cycles at −40 °C, far outperforming its room−temperature efficiency (94.92% over 110 cycles). Zn(BF₄)₂ achieves 99.76% over 3450 cycles at −40 °C versus 59.23% over 30 cycles at 25 °C. Above reversal phenomenon is closely related to anions (ClO₄^-, BF₄^-) with weak interactions toward H₂O and Zn²⁺, which minimize water aggregation around anions and reduce repulsion between inner−sphere Zn²⁺ and outer−sphere anions, promoting an anion−rich, water−poor outer solvation structure that disrupts the hydrogen−bond network and lowers the freezing point. Conversely, strong anion–water interaction (e.g., ZnCl₂) induces a water-rich structure with inferior low-temperature performance (−40 °C: 90.56% vs. 25 °C: 96.82%). To validate the above principle, Zn(CF₃SO₃)₂ and ZnSO₄ electrolytes were further employed for testing: the former forms anion−rich structure with superior low−temperature efficiency, while the latter forms water−rich structure with inferior efficiency. This work provides a general strategy for designing high−performance anti-freezing aqueous electrolytes.