Study On Dimethyl Sulfoxide As A Low-Temperature Additive For Aqueous Batteries Electrolytes And Its Mechanism

With the widespread application of renewable energy such as solar energy and wind energy,electrochemical energy storage has entered a stage of large-scale development.Lithium-ion batteries based on organic electrolytes are expensive,flammable,explosive and environmentally unfriendly,which limit their application in large-scale energy storage.Compared with organic electrolytes,aqueous electrolytes have the advantages of economy,high safety,environmentally friendly,and high ionic conductivity.Therefore,aqueous batteries have greater application prospects in future large-scale energy storage systems.The electrolyte is one of the most important components of battery.However,an obvious problem faced by aqueous batteries is that the electrolytes freeze at low temperatures.The ionic conductivity of the frozen electrolyte is insufficient,which will cause the battery to lose most of its capacity and power.Therefore,the problem of electrolyte freezing at low temperatures needs to be solved urgently.At present,using appropriate electrolyte additives is one of the effective ways to improve the performance of aqueous batteries at low temperatures.In this paper,low-temperature electrolyte additives are studied.The specific research is as follows:1.With dimethyl sulfoxide?DMSO?as an additive,the effects of DMSO with different molar fractions on the low temperature performance of aqueous sodium-ion batteries were explored.Using 2M Na Cl O₄ as the electrolyte,the results of differential scanning calorimetry?DSC?,thermal polarization microscope?TPM?and electrochemical alternating current impedance?EIS?tests showed that the addition of DMSO can significantly reduce the freezing point of the electrolyte,whereas the degree of freezing point reduction of the electrolyte is not directly proportional to the amount of DMSO.After optimization,it was found that the low temperature performance of the electrolyte was improved most significantly when the mole fraction of DMSO was0.3(?_DMSO=0.3),which could lower the freezing point of the electrolyte to below-130?.The ionic conductivity test results showed that the ionic conductivity of the2M Na Cl O₄ solution with DMSO molar fraction of 0.3?2 M-0.3?was still as high as0.11m S cm^-1 at the ultra-low temperature of-50?.Applying the 2M-0.3 electrolyte to AC/Na Ti₂?PO₄?₃battery,electrochemical test results showed that the battery exhibits a capacity of 68 m Ah g^-1 at a rate of 0.5C(1 C=133 m A g^-1)at-50?,corresponding to a 61%capacity retention of that at 25?.In contrast,the battery without DMSO could not work normally at-50?.The results of Fourier transform infrared spectroscopy?FTIR?,Raman spectroscopy,Nuclear magnetic resonance?NMR?,X-ray photoelectron spectroscopy?XPS?,Scanning electron microscopy?SEM?,and molecular dynamics simulations?MD?showed that the mechanism of freezing point reduction is the formation of hydrogen bonds?HBs?between DMSO and water molecules,which destroys the formation of HBs among water molecules and prevents the formation of ice crystal grids.2.The universality of DMSO as a low temperature additive was explored.The optimized amount of DMSO with a mole fraction of 0.3 was selected and used in aqueous lithium and potassium ion batteries.DMSO with?_DMSO=0.3 was added to 0.5M Li₂SO₄ as the electrolyte to assemble AC/LiTi₂?PO₄?₃ battery.Electrochemical test results showed that the LTP||0.5 M-Li₂SO₄-0.3||AC battery displays a capacity of 65m Ah g^-1 at a rate of 0.5 C(1 C=130 m A g^-1)at-50?,corresponding to a 62%capacity retention of that at 25?.The AC/polyimide battery was assembled using 1 M KCl as electrolyte with DMSO added with?_DMSO=0.3.The electrochemical test results showed that the PI||1 M-KCl-0.3||AC battery system displays a capacity of 58 m Ah g^-1 at a rate of 0.5 C(1 C=183 m A g^-1)at-50?,corresponding to a 62%capacity retention of that at 25?.By contrast,the battery systems without DMSO additions could not work properly at-50?.All these results demonstrate that the DMSO is universal as a low-temperature additive.