A Dilute Hybrid Electrolyte With Trimethylolpropane Additive for High‐Voltage Aqueous Sodium‐Ion Batteries Operated at Low Temperature

Aqueous sodium-ion batteries (ASIBs) have attracted significant attention due to the advantages of high safety and low cost for energy storage devices. However, the narrow electrochemical stability window (ESW) of aqueous electrolytes and freezing at low temperatures limit practical applications. Herein, we broaden the ESW to 2.85 V and reduce the freezing point (below -80 °C) by using trimethylolpropane (TMP) additive to 1 M NaNO₃ aqueous solution. Based on this hybrid electrolyte and equipped with a bimetallic Prussian blue analogue (NaCuHCF) cathode and 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) anode, the full cells display a specific capacity of 56.6 mAh g^-1, 88% capacity retention after 800 cycles. Even at low temperatures of -20 °C, a specific capacity of 50.1 mAh g^-1 after 500 cycles is also achieved. A series of spectral tests illustrate the interaction between TMP and water molecules, which realizes the excellent electrochemical performances, especially at low temperatures. This work provides a new strategy for the application of ASIBs in extreme weather and expands the practical application of aqueous batteries.