High Temperature Corrosion Behaviour Of Metallic Collectors Of Sodium-Sulfur Battery

Sodium-sulfur battery is a promising energy storage technology,it has the advantages of high energy density,high safety,high efficiency,long service life,convenient operation and maintenance.However,the high temperature corrosion of the collector caused by molten sodium polysulfide produced in the battery greatly affects the lifetime and safety of the battery.At present,the high temperature corrosion behavior and mechanism in molten salt of metallic current collector materials for sodium sulfur battery still need to be further clarified.Electrochemical impedance spectroscopy(EIS)is an effective method to study the corrosion mechanism and kinetic process,and more information of corrosion process can be obtained by EIS measurement.In this paper,combined with the microstructure analysis,EIS was used to study the high temperature corrosion behavior and explore the high temperature corrosion mechanism of pure aluminum,aluminum alloy and stainless steel,which are commonly used in sodium sulfur battery as collector.The main results are as follows:The electrochemical impedance spectrum of 304 stainless steel in 350 molten sodium polysulfide is composed of capacitive arc in high frequency and straight line in low frequency,showing Warburg impedance characteristics,indicating that the corrosion reaction is mainly controlled by charge diffusion;the corrosion resistance Rt value is small(0.857-1.828 Ω·cm2),indicating that the corrosion rate of stainless steel in molten sodium polysulfide is fast.It is found that stainless steel 304 will form two layers of corrosion product film in the corrosion environment of sodium sulfur battery.The outer layer of corrosion product film is mainly composed of FeS2 with FeNiS2 on the surface,and the inner layer is mainly composed of Cr2S3.The outer layer of corrosion product film is loose and porous,and the process of growth,dissolution,breaking off and regrowth of it is repeated in the molten salt of sodium polysulfide,which makes the corrosion reaction rate fluctuate up and down.Aluminum and aluminum alloy show dual capacitive reactance in molten sodium polysulfide.Dense Al2S3 corrosion product film was formed on the surface of pure aluminum and 6061 aluminum alloy.However,due to the existence of impurity phase in 6061 aluminum alloy,corrosion micro couple is formed in alloy,so its corrosion product film resistance Rox and charge transfer resistance Rt are smaller than those of pure aluminum.The annual corrosion depth values of pure aluminum and 6061 aluminum alloy measured by weight loss method in molten sodium polysulfide are similar,and compared with stainless steel,the annual corrosion depth values of pure aluminum and aluminum alloy 6061 are one or two orders of magnitude smaller than stainless steel 304.This shows that the corrosion resistance of pure aluminum and aluminum alloy is better than that of stainless steel 304 in the corrosion environment of sodium sulfur battery,and the corrosion resistance of pure aluminum is slightly better than that of aluminum alloy.