Balancing Tetrahedral and Cation Entropies for Long-lifespan Low-temperature Zn-ion Batteries

Aqueous Zn-ion batteries (AZIBs) are promising candidates for next-generation energy storage. However, their application is hindered by Zn anode instability and reduced ionic conductivity at low temperatures. Here, we identified two decisive factors for low-temperature performance and anode stability of batteries: tetrahedral entropy and cation entropy. The former is closely related to antifreezing ability of electrolyte, while the latter is associated with the desolvation kinetics of Zn²⁺. We propose an effective strategy to balance the above two thermodynamic quantities by precisely tuning the molar fraction of the 1,3-butanediol (BDO) cosolvent with notable glass-forming ability. BDO enhances the tetrahedral entropy due to the disruption of the hydrogen-bond networks among water molecules, decreasing the solid-liquid transition temperature from -16.4 to -101 °C. Additionally, BDO modifies the solvated structure of Zn²⁺ to limit the active water content, thus suppressing by-reactions at the electrode/electrolyte interface. The optimized electrolyte enables long-term cycling of Zn||Zn symmetric cells for over 4000 h at -40 °C under 0.1 mA cm^-2/0.1 mAh cm^-2, and renders PANI||Zn full cells capable of working across a broad temperature range (-40 °C to 60 °C). This work offers a guideline to design stable and low-temperature AZIBs, expanding the application scope for aqueous electrolytes.