Effects Of La On The Microstructure And Properties Of Al-Fe Alloy For Lithium-Ion Battery Soft Package

With the continuous expansion of lithium-ion battery applications,packaging materials,which are important components of lithium-ion batteries,are bound to usher in a golden age of development.Due to low strength and poor formability,traditional soft packaging aluminum foil cannot satisfy the future requirement of light weight and high capacity of lithium ion batteries.In this study,we developed several Al-Fe alloys for lithium-ion battery soft packaging materials,and improved the mechanical properties and corrosion performance of the alloys by adding rare earth La.The effects of annealing temperature and rare earth La on the microstructure,mechanical properties and corrosion resistance of the Al-Fe alloys were investigated by microstructure analysis,tensile test and electrochemical corrosion test.With the increase of Fe addition,Fe-rich phase gradually changed from fine particles and short rods to flakes and needle-like shape.New phase of AlFeLa formed with the addition of La.AlFeLa phase tended to form at the surface of Fe-rich particles,resulting in the refinement of Fe-rich phase.With the increase of La addition,the needle-like Fe-rich phase transformed to short rods and particles.Compared to AA8021 alloy,the tensile strength and elongation of La microalloying Al-Fe alloy were improved obviously.Compared to the Al-1.2 wt.% Fe alloy,La microalloying had a more significant effect on the mechanical properties of the Al-1.5 wt.% Fe alloy.Rare earth La microalloying could improve the corrosion performance of the Al-Fe alloy,while Fe element could deteriorate the corrosion resistance of the alloy.With the increase of La addition,the corrosion potential of the alloys was shifted positively,the corrosion current density decreased,and the corrosion resistance increased.The corrosion of the alloys in NaCl solution was dominated by pitting corrosion.The corrosion surface morphology of the alloys was similar,showing only the difference in corrosion degree.Compared to the Al-1.2 wt.% Fe alloy,La microalloying had a more significant effect on the improvement of corrosion performance of the Al-1.5 wt.% Fe alloy.The grains still presented with a slender fibrous shape after annealing at 200 °C,indicating only recovery rather than recrystallization occured.For the alloys annealed at 250 °C,the new equiaxed grains replaced the elongated grains due to recrystallization.When the annealing temperature increased to 380 °C,triple junctions were observed and the finer equiaxed grains grew into coarse grains.Compared to the Al-1.5 wt.% Fe alloy,the Al-1.2 wt.% Fe alloy had a higher degree of recrystallization at the same annealing temperature.The alloy annealed at 250 °C had the optimal corrosion performance with the most positive corrosion potential,minimum corrosion current density and maximum corrosion resistance.After annealing at 380 °C,the grain size of the alloy was coarsened,the ratio of the large-angle grain boundary increased,and the intergranular corrosion tendency of the alloy was enhanced.