Tailoring Pure Inorganic Electrolyte for Aqueous Sodium-Ion Batteries Operating at −60 °C

Aqueous sodium-ion batteries (ASIBs) have attracted increasing attention for next-generation energy storage technologies due to their abundant resources and environmentally-safe, while their application scenarios are severely limited by the high freezing point of conventional aqueous electrolytes. To overcome the aforementioned issues of ASIBs, a novel hybrid 3.5 m Mg(ClO₄)₂+0.5 m NaClO₄ electrolyte (m: mol kg⁻¹) with an ultra-low freezing point (<−80 °C) is proposed. The exceptional anti-freezing feature is mainly attributed to the higher ionic potential of Mg²⁺, greatly affecting the chemical environment of water molecules and inhibiting ice formation under subzero conditions. Benefiting from the superiority of ionic conductivity (4.86 mS cm⁻¹) for the hybrid electrolyte at −60 °C, the full cell of active carbon||NaTi₂(PO₄)₃@C delivers an ultra-long lifespan of 10000 cycles under 8 C (1 C=133 mA g⁻¹) at −60 °C. More importantly, some representative devices in daily life including smartphone and motor can be powered by ASIBs at −60 °C. Therefore, this work provides a rational and effective strategy for design and application of ASIBs with excellent electrochemical performance that can work in extremely cold environments.