Research On Corrosion Properties Of Negative Copper Current Collectors Of High Capacity Lithium Ion Batteries

As a highly efficient secondary battery,lithium ion battery has been widely used in portable electronic devices.However,with the extension of application fields such as electric vehicles,aerospace and large-scale energy storage,the storage performance,energy density,and safety performance of batteries have become one of the major research topics.The corrosion of the negative current collector of the lithium-ion battery affects the storage performance and safe of the battery.The thesis studies the corrosion behavior of copper cathode collectors of lithium-ion batteries at different temperatures.Polypyrrole coatings are prepared by electrodeposition method on the surface of copper foil and copper foam to improve the corrosion resistance of copper current collector.The main results obtained in the thesis are as follows:(1)In the lithium-ion battery electrolyte,the effects of temperature on the corrosion behavior of the negative copper foil current collector of lithium-ion batteries were studied.Potentiodynamic polarization curves show that the corrosion rate of copper foil increases with the increase of temperature.After immersion in the electrolyte at-20? and 25 ? for 720h,HF stemming from the spontaneous decomposition of electrolyte adsorbed on the surface of the copper foil and caused pitting corrosion;At 50?,a loose corrosion products layer which is composed of LiF formed on the surface of the copper foil.Nevertheless,no pitting hole was observed.With the extension of immersion time,the solution resistance Rs increased indicating that the decomposition of the electrolyte contribute to the variation of composition.Thus,the conductivity of the solution decreased.At the same time,the solvent decomposed and HCO3-was formed,which inhibited the corrosion of HF.Therefore pitting corrosion of the copper foil doesnot occurr.(2)After corrosion in electrolyte at-20?for 240 h,a lot of pitting holes with smaller sizes appeared on the surface of copper foam.After corrosion in the electrolyte at 25 ? for the same time,pitting corrosion occurred on the surface of the copper foam and there was a partial loss of the corrosion product layer.At 50?,intergranular corrosion of copper foam occurred and the decomposition of the electrolyte was more severe.The decomposition products adhere to the surface of the copper foam The corrosion rate of copper foam in the electrolyte increases with the temperature increases.(3)Polypyrrole coating was electrochemically prepared on the copper foil current collector surface with sodium lauryl sulfate and oxalic acid,respectively.Obvious pores could be observed in the polypyrrole coating on the surface of copper foil with sodium dodecyl sulfate as the dopant.However,the polypyrrole coating doped with oxalic acid is dense and uniform.EIS results showed that the former lost the protective effectiveness for the substrate after immersion in the electrolyte for 72h.However,the charge transfer resistance Rt of polypyrrole doped with oxalic acid is 3.5 times than the copper foil after immersion in the electrolyte for 240h showing an increased corrosion resistance.(4)The polypyrrole coating prepared on the surface of foam copper current collector with oxalic acid is dense.The coating partly peeled off after corrosion in the electrolyte for 240 h.However,the charge transfer resistance(Rt)of polypyrrole coated copper foam is significantly higher than that of the substrate after etching for 240h.This is due to the fact that the conductive polymer coating has a catalytic oxidation effect on the matrix metal,which render it in passivated state and improve the corrosion resistance of the substrate.