Effect Of Potential On Corrosion And Fatigue Of Copper Foam Collector In Lithium Ion Battery Electrolyte

The current collector,as an important part of the lithium ion battery,plays the role of carrying active materials,collecting and outputting current,maintaining the stability of the battery and increasing the battery voltage.In recent years,with the widespread application of lithium ions,social demands have also put forward higher requirements for the performance of lithium ion batteries.The negative electrode current collector of lithium ion batteries has also gradually developed from a single structure copper foil to a complex three-dimensional porous structure.The change of the structure of the negative electrode current collector effectively increases the capacity of the lithium ion battery and makes the battery more efficiency.On the other hand,the larger specific surface area of the three-dimensional porous structure makes it more susceptible to corrosion by the electrolyte.At the same time,due to the volume change of the electrode material during the charge and discharge process of the battery,it also brings the effect of cyclic stress on the negative electrode current collector.In order to obtain the failure information of the open-cell foam copper used as the negative electrode current collector of lithium ion batteries,this paper studies the influence of the potential on the corrosion and fatigue of the copper foam current collector in the electrolyte of the lithium ion battery.The main conclusions are as follows:(1)Open-cell foam copper is subject to corrosion at different potentials in the electrolyte of a lithium-ion battery,and the corrosion characteristics are different depending on the potential.At the negative electrode potential(-0.5V,-1.0V,-1.5V),the corrosion method of open-cell foam copper is mainly pitting,and the degree of corrosion increases with the increase of the potential.Analysis of the impedance spectrum of the sample shows that under three negative potentials,the solution resistance of the sample did not change much,indicating that the change in negative potential has little effect on the electrolyte.At the positive potential(+0.5V,+1.0V,+1.5V),the corrosion mode of the sample is mainly grain boundary corrosion,accompanied by pitting corrosion.According to the results of electrochemical impedance spectroscopy,the lower the positive potential is,the higher the corrosion resistance of the sample is.Unlike the negative potential,when the potential is+1.5V,the Rs value of the electrolyte resistance will be significantly smaller than the Rs value at other potentials,and the R1 value of the sample at the positive potential is significantly smaller than the Rt value of the sample at the negative potential,indicating that the sample has better corrosion resistance at a negative potential.(2)According to the quasi-static compression experiment,the yield limit of the sample is 0.64 MPa.Based on this,fatigue testing of the open-cell foamed copper under different stress levels was performed.The results shown that at low stress levels(|σ|max/σs≤0.9),the fatigue deformation phase of the sample can be divided into three distinct parts,namely the damage accumulation area,the strain surge area,and the continuous damage area.At high stress levels(|σ|max/σs≥1.0),the sample was in continuous damage,and there was no obvious area of strain surge.It can be obtained from the tracking observation of the sample during the fatigue process that the main way of deformation of the sample is that an inclined squeeze band is first formed in the middle region of the sample.With the progress of the cycle,the squeeze band was continuously deformed by force.Finally,a more obvious crushing zone was formed in the middle horizontal area,and the sample was destroyed.After that,the sample would continue to deform to both sides of the crush zone,causing layer-by-layer damage.According to the analysis of the micro-morphology of the sample after the failure,the sample failure is mainly caused by the bending and fracture of the hole prism,and the buckling and deformation of the hole node.(3)The corrosion fatigue lifc of open-cell foam copper is different at different potentials Under negative potential(-0.5V,-1.0V,-1.5V),the relationship curve between the strain accumulation of corrosion fatigue and the number of cycles in the lithium ion battery electrolyte was similar to the relationship curve of the sample in the air environment,which can be divided into obvious three areas.At the positive potential(+0.5V,+1.0V,+1.5V),the relationship diagram of the sample shown a large difference.The sample was in the stage of continuous damage during the cycle,and the strain on the specimen did not vary much within the strain surge zone.The fatigue life of the samples at all three positive potentials is less than that of the samples at negative potentials.