Factors That Influence Formation of AlF[sub 3] Passive Film on Aluminum in Li-Ion Battery Electrolytes with LiPF[sub 6]

The effects of ( i ) potential, ( ii ) the electrolyte's concentrations of and , ( iii ) the aluminum's air-formed oxide, ( iv ) an anodized layer of , and ( v ) the purity of aluminum, on the formation of a protective layer of during anodic polarization of aluminum were investigated. Most tests were conducted in lithium-ion battery electrolytes with . At potentials above a critical value, a film of forms on top of the air-formed oxide, creating a duplex, or two-layered film. The thickness of the increases with applied potential. The critical value of potential for formation of is independent of the composition of the aluminum alloys investigated, and increases with the thickness of pre-existing surface films, such as the native air-formed oxide. There is a threshold value of concentration of ( ) for the formation of a protective layer of . Protective films of are formed in electrolytes with concentrations of in the range of . LiTFSI causes severe pitting corrosion of aluminum that is covered by only its air-formed oxide. A thin film of significantly improves the resistance of aluminum to pitting corrosion in 1:1 ethylene carbonate with LiTFSI.