Tailoring Electrolyte Toward Low-Temperature Aqueous Sodium-Ion Batteries

Aqueous sodium-ion batteries (ASIBs) offer important advantages in terms of safety, ionic conductivity, environmental friendliness, and cost-effectiveness. However, their industrial development has been hindered by a narrow electrochemical stability window (ESW) and suboptimal energy density. In this work, a cost-effective high-entropy electrolyte formulation was developed, consisting of 6 M sodium acetate (NaAc) and 2 M zinc acetate [Zn(Ac)₂]. The introduced Zn(Ac)₂ not only effectively disrupted the hydrogen bonds between water molecules but also dramatically reduced the bound water in the first solvation of Na. It demonstrated that such an entropy-driving structure could efficiently expand the ESW up to 2.68 V and substantially lower the freezing point of the electrolyte to −79 ℃. As a result, the optimized electrolyte enabled the full cell to achieve a high energy density of 190 Wh/kg and maintained 60.3% of its capacity at −40 ℃ compared to room temperature. This work provides scientific insights for designing high-entropy electrolytes for sodium storage over a wide temperature range.