Preparation And Properties Of Low-Temperature Flexible Zinc-Ion Batteries

Aqueous rechargeable batteries are considered promising electrochemical energy storage systems for grid-scale applications due to their low cost,high safety,environmental benignity.With the demand for a wide range of application scenarios,batteries are required to work in various harsh conditions,especially the cold weather.Nevertheless,electrolytes would freeze at extremely low temperatures,resulting in dramatically sluggish kinetics and severe performance degradation.TThis study mainly focuses on the freezing of electrolytes in aqueous zinc-ion batteries at low temperatures.Inspired by the Hofmeister series,TFSI^-anions with large surface charges were selected to disrupt the internal order of water molecules,and then the content of free water molecules in the electrolyte at low temperature was regulated by adding organic solvents to the electrolyte.Therefore,firstly,four organic solvents with potential as low-temperature additives were screened from a large number of solvents,namely acetonitrile,dimethyl sulfoxide,dimethylformamide,ethyl acetate,and their performance at low temperature was tested.It was found that the batrreriess showed the best low temperature performance when ethyl acetate was added.At-20°C,with 60%ethyl acetate addition,it has the lowest freezing point of-36.79°C and the highest ionic conductivity of 6.66 m S cm^-1.Raman and infrared spectroscopy revealed the fundamental reason for the additive’s antifreeze ability at low temperatures:the interaction between ethyl acetate,H₂O and Zn（TFSI）₂,forming different solvated structures.This structure makes it easier for water molecules to combine with solvent molecules or salts,reducing the number of free water molecules in the solution and lowering the solution’s freezing point.The Zn//PBAs assembled with this electrolyte showed no capacity fading even after 4000 cycles at-20°C,the capacity retention rate was 100%,and the Coulombic efficiency of almost 100%was maintained during these4000 cycles.Using Zn（TFSI）₂as a supporting salt and EA as a low-temperature additive,a low-temperature-resistant flexible electrolyte was prepared,and the electrolyte remained soft at-65°C.And the added EA interacts with groups on the polymer network,weakening the van der Waals forces between the polymer molecules,making its ionic conductivity higher than that of the additive-free electrolyte at all temperatures.Infrared spectroscopy shows that EA,and PAM immobilize free water in different ways,which greatly reduces the freezing point of the gel.The Zn//PBAs assembled using this flexible electrolyte showed a specific capacity of 105 m Ah g^-1at 0°C,with an 80%capacity retention rate after 500 cycles.The successful preparation of low-temperature-resistant zinc-ion aqueous batteries and flexible batteries demonstrates that EA can be used as an excellent low-temperature additive.